GB2442385A

GB2442385A - Sintered sliding member and connecting device

Info

Publication number: GB2442385A
Application number: GB0725290A
Authority: GB
Inventors: Takemori Takayama; Tetsuo Ohnishi; Kazuo Okamura
Original assignee: Komatsu Ltd
Current assignee: Komatsu Ltd
Priority date: 2003-07-31
Filing date: 2004-07-30
Publication date: 2008-04-02
Anticipated expiration: 2024-07-30
Also published as: GB2442385B; GB0725290D0

Abstract

A sintered sliding member comprises a back metal 10(21a) and a ferrous sintered sliding body (20) which is sinter-bonded to the back metal (21a). The ferrous sintered sliding body (20) has martensite phase having a solid soluble carbon concentration of 0.15 to 0.5wt% and contains carbide in a content of 5 to 50% by volume. The sintered sliding member is excellent in abrasion resistance, seizing resistance and heat crack resistance.

Description

1 2442385 SINTERED SLIDING MEMBER 1\ND CONNECTING DEVICE

Field of the Inventi.on

The present invention relates to a double_laYered sintered sliding member used for a connecting device, such as a thrust bearing, of a construction machine.

More parncu]arly, the present invention relates to a sintered sliding member, such as a sintered thrust bearing and a floating seal, which is formed with a ferrous sintered sliding material excellent in abrasion resistance, seizing resistance and heat crack resistance, at sliding surfaces thereof, in which the ferrous sinered sliding material is combined tO a back ineal, and a connecting device using the sintered thrusL bearing.

Background of the Invention

Conventionally, a connecting device of a construction machine is equipped with a thrust bearing to slide under a large thrust load. For such a thrust bearing, a thrust bearing made of a carburiZed steel or an induction hardened steel has been used in order to obtain sufficient seizing resistance and abrasion resistance for withstanding a highbearing stress and low-speed sliding condition and a grease ubriCatiflg condition. And, recently, in view of the demand for easy maintenance, in order to extend a lubricating interval F' 2 of a thrust bearing, a thrust bearing, in which a steel is coated with a superhard thermal splay material excellent in seizing resistance and abrasion resistance comprising WC and 5elf-fluxiflg alloy, is sometimes put in practical use for such a thrust bearing equipped for a connecting device of a construction machine.

On the contrary, a track roller assembly Of a construction machine is equipped with floating seals for the purpose of preventing leakage of a lubricating oil from inside thereof, as well as preventing sand or gravel from entering therein. Thus, in many cases, such a floating seal is made of a hard high_strengt}1 high-carbon and high-Cr cast iron jch has excellent corrosion resistance and improved seizing resistance and abrasion resistance by crystafliziflg hard Cr-?C3-tYPe carbide in a large content of 30% or more by volume.

Summary of Invention

In a case of a connecting device of a construction machine, a thrust bearing operates with sand or gravel being jammed therein. And, a connecting device equipped for a bucket of a hydraulic shovel operates under a large offset load. As a result, seizing and abrasion are likely to occur in such a connecting device and therefore it is necessary to be lubricated at frequent intervals before operating-And, in a case of a thrust bearing lfl which a steel is coated with a superhard thermal splay material, the superhard thermal splay material layer easilY breaks down because of its insufficient seizing resistance and its thin thickness. In addition, the resultant breakage pieces may further damage the layer.

In order to improve seizing resistance and abrasion resistance of a thrust bearing, a thrust bearinci, of which surfaces are made such that S45C is induction hardened, is often used. Such a thrust bearing has improved heat crack resistance, but insu[f1Cient seizIng resistance, causing fouling easily. Further, the thrust bearing has insufficient abrasion resiSta1ce. When various work steels such as a cold-work stee and a high speed steel (SKD, SKH) are used, heat crack resistance thereof is so insufficient that seizing easiJy occurs.

In addition, since such work steels are SO expensive that material costs would increase in view of material yields before a product is finished.

In a floating seal used for sealing a ubriC3t1ng oil in a reduction gear and a tracker roller, seal sliding surfaces thereof are abraded, while being exposed to fine particles of sand or gravel by hulling motion in the sand or gravel, and are lubricated with the lubrication oil sealed therein. PccordinglY, such a floating seal is required to operate under very severe lubrication conditions. In a case of a high hard floating seal made of a high-carbon and high-Cr cast iron, when setting pressure (press force) at assembling is high, considerab1e quenching crack (heat crack), seizing and abnormal abrasion occur on the seal sliding surfaces, resulting in leakage of oil. In addition, sand or gravel clogs around the floating seal, resulting in damaging the floating seal.

Eurtherrnore, in resent years, a construction machine such as a bulldozer is required to be driven at a high speed for improvement in working efficiency, and therefore, the floating seal necessarily rotates at a high speed. This also causes quenching crack, seizing and abnormal abrasion. In order to prevent such problems, a floating seal made of a high-carbon and high-alloy cast iron, in which hard carbide is dispersed in a large content, has been studied. 1-lowever, such floating seal has decreased flexural strength. Thus, a damage-proof floating seal has been required.

In addition, a track roller assembly having longer life operation is demanded for the purpose of cost reduction. But, conventionally-used cast irons for a floating sea]. do not have sufficient abrasion resistance.

In order to solve the above-mentioned problems an object of the present invention is to provide a sintered sliding member, a connecting device and a floating seal excellent in abrasion resistance, seizing resistance and heat crack resistance. s

In order to achieve the aforesaid object, a sintered sliding material according to the present invention comprises a back metal and a ferrous sintered sliding body which is combined to the back metal, wherein the ferrous sintered sliding body comprises martensite phase prepared to have a solid soluble carbon concentration of 0.15 to 0.Swt% and contains carbide lfl a content of 5 to 50% by volume.

In the present invention, the ferrous sintered sliding body may be formed with at least one of closed pores or recesses in an area ratio of 1 to 10% at a sliding surface thereof. nd, the ferrous sintered sliding material may contain one or more elements selected from the group consisting of Cr of 9wt% or more, Mo of 3.5wt% or more, Mo and W in a total amount of 4.5wt% or more and V of 3wt% or more so that the martensite phase may contain one or more carbideS selected from the group consisting of Cr7C3-type carbide, M6C-type carbide and NC-type carbide dispersed therein.

P sintered sliding member according to the present invention comprises a back metal and a ferrous sintered sliding body which is combined to the back metal, wherein the ferrous sintered sliding body contains carbon of 0.9 to 3.8wt%, Cr of 9 to 3Swt%, and V of 0 to 3wt%, in which a content of carbon satisfies the following equation: O.i43xCr(wt%)_l.41+14xMtYPe carbide (volume fraction) Carbon (wt%) 0.156xCr(t6) 0.58414xMC-type carbide (volume fraction), and has martensite phase, in which the martensite phase, forming a solid solution with carbon of 0.2 to 0.45wt% and Cr of 6.5 to l2wt%, contains Cr7C3-type carbide in a content of 5 to 40% by volume and MC-type carbide in a content of 5% or less by volume dispersed therein jith a total content of the carhides being 5 to 40% by volume, and wherein the ferrous sintered sliding body contains one or more elements selected from the group consisting of Si, Mn, NI, P, S, B, N, Mo, W, Ti, Co. Cu and Al.

A sintered sliding member according to the present invention comprises a hack metal arid a ferrous slntered sliding Dody which is combined to the back metat, wherein the ferrous sintered sliding body contains carbon of 1.8 to 4.5wt%, Cr of 12 to 3Owt%, V of 3.5 to lOwt% and either one of Mo of 2 to 6.4wt% or Mo and W in a total amount of 2 to 6.4wt%, and has martensite phase, in which the rnartensite phase, forming a solid solution with carbon of 0.2 to 0.45wt%, Cr of 6.5 to l2wt% and further one or more elements selected from the group consisting of Mo of 1 to 3.5wt%, Mo and W in 3 total amount of 1 to 3.5wt%, and V of 0.4 to 0.6wt%, contains Cr-C3-type carbide in a content of 10 to 35% by volume and MC-type carbide in a content of 5 to 15% by volume dispersed therein with a total content of the carbides being 15 to 40% by volume, and wherein the ferrous sintered sliding body contains one or more elements se'ected from the group onsist1ng of Si, Mn, Ni, P, S, B, N, Mo, W, Co, Cu and Al.

A sintered sliding member according to the present invention comprises a back metal and a ferrous sintered sliding body which s combined to the back metal, wherein the ferrous sintered sliding body containS carbon of 0.6 to j.9wt%, Cr of 1 to 7wt%, V of 0 to 3wt%, Mo of 3.5wt% or more and Mo+0.5XW of 4.5 to 3Owt%, in which O.5xW represents half of a real amount of W, and has martensite phase, in which the martensite phase, having solid so]uhle carbon ccnccntr2tion of 0.2 to 0.45wt%, contains NEC-type carbide n a content of 5% or more by volume arid MC-type carbide in a content of 5 to 40% by volume dispersed therein, and wherein the ferrous sintered sliding body contains one or more e1ements selected from the group consisting of Si, Mn, Ni, I', S, B, N, Ti, Co, Cu and Al.

A sintered sliding member according to the present invention comprises a back metal and a ferrous sintered sliding body which is combined to the back metal, wherein the ferrous sintered sliding body contains carbon of 1.3 to 3wt%, Cr of 1 to Swt%, V of 3 to l2wt%, Mo of lOwt% or more and Mo and W of 10 to 23wt% and has martensite phase, in which the martensite phase, having a solid soluble carbon concentration of 0.2 to 0.45wt%, contains M6C-type carbide in a content of 15 to 35% by volume and MC-type carbide in a content of 5 to 15% by volume dispersed therein, and wherein the ferrous sintered sliding body contains one or more elements selected from the group CQflS)st)ng of Si, Mn, Ni, P, S, B, N, Ti, Co, Cu and Pd.

A sintered sliding member according to the present invention comprises a back metal and a ferrous sintered sliding body which is combined to the back metal, wherein the ferrous sintered sliding body contains carbon of 0.8 to 3.4wt%, Cr of 9 to 28wt%, \i of 0 to 5wt%, Mo of 5wt% or more and, Mo and W, of 5 to lBwt% dnd has martensite phase, in which the martensite phase, having a solid soluble carbon concentration of 0.2 to 0.4Swt%, contains Cr7C3-type carbide in a content of 5 to 25% by volume, M6C-type carbide in a content of 5 to 25% by volume and MC-type carbide in a content of 0 to 5% by volume dispersed therein with a total content of the carbideS being 10 to 40% by volume, and wherein the ferrous sintered sliding body contains one or more elements selected from the group consisting of Si, Mn, Ni, P. S. B, N, Ti, Co, Cu and Al.

A sintered sliding member according to the present invention comprises a back metal and a ferrous sintered sliding body which is combined to th back metal, wherein the ferrous sintered sliding body contalfls carbon of L5 to 3.2wt%, Cr of 7 to 25wt%, Mo of 3.5wt% or more, Mo and W of 5 to lSwt% and also at least either one of V or Ti an a total amount of 3 to Bwt% and has martensite phase, in which the martensite phase, having a solid soluble carbon concentration of 0.2 to 0.45wt%, contains Cr7C3-Lype carbide in a content of 5 to 20% by volume, M6C-type carbide in a content of 5 to 20% by vo:Iume, and MC-type carbide in a content of 5 to 15% by volume dispersed therein with a total content of the carbides being 15 to 50% by volume, and * wherein the ferrous sintered sliding body contains one or more elements selected from the group 0onssiiig of Si, Mn, Ni, P. S. B, N, V, Ti, Ca, Cu and Al.

In the present invention, the sintered sliding member is a thrust bearing, wherein the ferrous sintered sliding body contains CrC3-type carbide, MC-type carbide and MC-type carbide dispersed therein with a total content thereof being 5 to 25% by volume and the back metal has a hardness of Hv170 or more. And, sliding surfaces of the thrust bearing may be formed with at least either one of closed pores or recesses in an area ratio of 1 to 10%.

In the present invention, the sintered sliding member is a floating seal, wherein the ferrous sintered sliding body contains Cr7C3-type carbide, MC-type carbide and MC-type carbide dispersed therein with a total content thereof being 20 to 40% by volume. And, the back metal may have a hardness of Hv170 or more. In addition, sliding surfaces of the floating seal may be formed with at least either one of closed pores or recesses in an area ratio of 1 to 10%.

A connecting device according to the present invention comprises a bearing made of a sintered sliding member having a back metal and a ferrous sintered sliding body which is combined to the back metal, in which the ferrous sintered sliding body has martenSite phase having a solid soluble carbon concentration of 0.15 to 0.5wt% nd contains carbide in a content of 5 to 25% by voiume, and another bearing to slide with respect to the bearing.

Effect of the Invention According to the present invention, a sintered sliding member and a connecting device, which are excellent in abrasion resistance, seizing resistance and heat crack resistance, can be provided.

Brief Description of the Drawings

Figs.1/\ to 1C shows a phase diagram of a Fe-Si-CX ternary alloy.

Fig.2A is a perspective view showing a hydraulic shovel according to a first embodiment of the present I' invention and F'ig.2B is an exploded perspective view showing a bucket-connecting device of the hydraulic shovel.

Fig.3 is a cross secticnal view schematiCallY showing a structure of the cket-CoflneCting device according to the first embodiment of the present invention.

Figs.41\ to 4C show a structure of a thrust bearing.

Fig.51\ is a cross-sectional view showing an example of a thrust hearing in which a ferrous back metal shown in F'ig.4C is formed with a venthole and a groove, Fig.SB is a cross-sectional enlarged view showing a A part of Fig.5a and Fig.5C is a plane v.iew of the thrust bearing of Fig.5A.

Fig.61\ is a plane view showing the ferrous sintered sliding body of Fig.4 in which ventholes and a groove are formed and Fig.613 is a cross-sectional view along B-B line in Fig.6A.

Fig.7 schematically shows a structure of a bucket connecting device according to the second embodiment of the present invention.

Fig.8A is a cross-sectional view showing a thrust bearing and Fig.8B is a plane view showing various oil grooves and recesses formed on a sliding surface of the thrust bearing of Fig.81A.

Fig.9 schematically shows a structure of a bucket-connecting device according to the third embodiment of the present invention.

Fig.1O schematically shows another structure of a bucket-connecting device according to the third embodiment of the present invention.

Fig.l1 shows a principal part of a roller assembly.

Fig.12 is a cross-sectional view showing a structure of a double-layered floating seal.

Fig.13 is a graph showing a relation between concentrations of alloy elements contained in Cr1C3-tYPe carbide and concentrations of alloy elements contained in a parent phase which comes to equilibrium with the Cr7C3-type carbide.

Fig.14 s a graph showing a relation between concentrations of an alloy element contained in M6C-type carbide and concentrations of alloy elements contained in a parent phase which comes to equilibrium with the M6C type carbide.

Fig.15 is a phase diagram of a Fe-C-Cr ternary alloy.

Fig.16 is a phase diagram of a Fe-C-Mo ternary alloy.

Fig.17 is a phase diagram of a Fe-C-W ternary alloy.

Fig.18 is a cross sectional view showing a shape of specimen of a thrust bearing with collar.

Figs.19A and 19B show an oscillating tester.

Fig.2OPi is a photograph showing a sintered structure of the No.25 alloy and Fig.20B is a photograph showing a sintered structure of the No.28 alloy.

F'ig.21 is a photograph showing a santered structure of No.32 alloy and analysis thereof using X-ray micro analyzer.

Figs.221\ and 22B show a structure of a specimen for a sintering-bonding test.

Fig.23 schematically shows a floating seal tester.

Fig.24 shows a test result for abrasion resistance of a floating seal.

F.,ig.25 shows a test result for deflection strength and toughness of a ferrous sintered sliding material.

Detailed Description of Embodiment of the invention (First embodiment) Fig.2A is a perspective view showing a hydraulic shovel according to the first embodiment of the present invention and Fig.2B is an exploded perspective view showing a bucket-connecting device of the hydraulic shovel. Fig.3 is a cross sectional view schematicallY showing a structure of the bucket connecting device according to the first embodiment of the present invention. Figs.4A to 4C show a structure of a thrust bearing.

As shown in Fig.2A, an operating portion 2 of a hydraulic shovel 1, according to this embodiment, is

H

provided with an upper turning body 3 to which a boom 4 is connected by a boom-connecting device 7. The boom 4 is connected to an arm 5 by an arm_connecting device 8, and the arm 5 is connected to a bucket 6 by a bucket connecting device 9. The connecting devices 7, 8 and 9 have the same principal structure. For example, the bucket-connecting device 9, as shown in Fig.2B, is provided with connecting pins 10 and bushingS 11.

Hereinafter, the bucket connecting device 9A arranged at a connecting portion of the arm 5 and the bucket 6 will be described in detail with reference to Fig.3.

Ps shown in Fig.3, the bucket connecting device 9A is provided with two thrust bearingS 12 which connect a bucket (one component) 6 to an arm (the other component) 5 in a rotatable manner and receive a thrust load applied between the bucket 6 and the arm 5. The arm 5 is arranged via a connecting pin (a support shaft) 10 supported by brackets 6a formed on the buckets 6 and bushings (bearing bushings) 11 fitted onto the connecting pins 10. The bushings 11 are forced into a distal end of the arm 5. The connecting pin 10 is fixedly mounted to the bracket 6a by a bolt 13. P seal member 14 and a lubricating oil supply port 15, a lubricating oil supply passage 16 are shown in the figure.

The thrust bearing 12 rotatably oscillates while being applied with a thrust load on sliding surfaces thereof (an upper surface in the figure) as shown in Figs.41\, 4B and 4C, and is constructed such that a hard ferrous sintered sliding body 20, excellent in abrasion resistance, seizing resistance and heat crack resistance, is sintering-bonded to each of back metals 21a and 21h. That is, a connecting device (connecting devices 7, 8 and 9) is provided with a bearing, comprising a back metal and a ferrous sintered sliding body which is combined to the back metal, and another bearing to slide with respect to the former bearing.

Tnd, the back metal is preferably made of steel.

The ferrous sintered sliding body 20 is made of a ferrous sintered sliding material in which martenSite phase prepared to have a solid soluble carbon concentration of 0.15 to Cj.5wt% contains carbide, effective for improvement in abrasion resistance and seizing resistance, dispersed therein in a content of 5 to 50% by volume. In order to have a solid soluble carbon concentration within the aforesaid range easily and contain a harder carbide excellent in seizing resistance, the ferrous sintered sliding body 20 preferably contains one or more elements selected from Cr of 9wt% or more, Mo of 3.5wt% or more, Mo and W in a total amount of 4.5wt% or more and V of 3wt% or more, and the martensite phase preferably contains one or more carbides of Cr7C3-type carbide, M6C-type carbide and MC-type carbide dispersed therein. In such a case, a total content of the carhides is preferably set to 5 to 50% by volume (volume fraction; 0.05 to 0.5) Fig.4A shows an example of a thrust bearing made such that a hollow disk-shaped ferrous sintered sliding body 20 is combined to a hollow disk-shaped back metal 21a. When the thrust bearing is supported in a bucket connecting device, as shown in Fig.413, a cylindrical back metal 21b is formed with a collar 21c, which slides under a thrust load, at one end surface thereof. And, the ferrous sintered sliding body 20 05mm or more thick is sintering-bonded to a sliding surface of the collar 21c. The thrust bearing may have a flat-plate shaped structure or a doughnutShaPed structure. However, in which case, the tnrust bearing is necessarilY formed with a supporting structure for supporting itself separately. So, the thrust bearing is preferablY made such that a cylindrical back metal is formed with a collar, which slides under a thrust load, at one end surface thereof and the ferrous sintered sliding body is sintering-bonded and combined to a sliding surface of the collar.

And, as shown in Fig.4C, a thrust bearing in which a bushing 22 is sintering-bonded and combined to an inner surface of the cylindrical back metal 21b may be used-Alternatively, a thrust bearing in which a cylindrical Cu alloy based porous sintered sliding material or a cylindrical Fe alloy based porous sintered slidinq material is sintering-bonded and combined to an inner surface or an outr surface of the cylindrical back metal may be also used. The bushing 22 is made of a Fe alloy based or a Cu alloy based porous sintered compact in which a lubricating oil material, in other words, a lubricating oil or a lubricatifl9 compound of a lubricating oil and a wax, having a dropping point under 60 C, is filled in the pores (air holes) thereof. This makes it possible to increase a pressure with which the thrust bearing is forced into the end of the arm, resulting in preventing the bushing from slipping out because a thrust load is applied to the collar 21C.

In exchange for the bushing made of the Fe alloy based or the Cu alloy based porous sintered compact, the following bushing may be usable. For example, a ferrous si.ntered sliding material, having substantially the same abrasion resistance, seizing resistance and heat crack resistance as the hard ferrous sintered sliding body 20, is formed with oil pockets or lubricating grooves at sliding surfaces thereof. Such a bushing can achieve sufficient abrasion resistance even under an operating condition in which friction resistance is high at a high bearing stress and a slow sliding speed condition.

In a thrust bearing in which a back metal thereof is coated with a superhard thermal splaying film, when the back metal has a hardness of about Hv400 or less, the film is easy to break by sand or gravel jammed therein. So, it is necessary to form the film more thick, resulting in economical disadvantage. On the contrary, when the back metal is made by a hard material, a thermal splaying film can be thinned as 0.5mm or less. However, bonding strength of the film to the back metal weakens, whereby the film is easy to break or peel due to sand or gravel jammed therein and a large offset load. AccordinglY, in the present invention, a thickness of a ferrous sintered s]iding ]0 body is set to 0.5mm or more, more preferably 1mm or more in order to prevent a ferrous sintered sliding body sintering-bonded to a soft back metal having hardness of I]v70 (yield strength of 2okgf/mm2) from breaking or peeling by sand or grave] jammed therein. And, a ferrous sintered sliding body preferably has flexural strengttl of at least 30kgf/cm or more. And, even if the thrust bearing is used in a operating condition with severe abrasion, it is not preferred that the ferrous sintered sliding body has a thickness of 4mm or more because breakage due to bending caused by a offset load would occur easily. In addition, economical efficiency decreases. And, bonding strength of a conventional sintering-bonded surface is higher than bonding strength of a thermal spraying film (5 to lOkgf/Cm2) and has almost the same strength as a share strength of a sintered material.

A thrust bearing with a collar, according to the present invention, is fixedly mounted to a construction machine in such a manner that a cylindrical portion thereof is forced into the construction machine. So, in order to force the cylindrical portion into the construction machine easily and prevent the cylindrical portion from slipping out therefrom after forcing, the back metal is preferably prepared to have a hardness of Hv170 or more, more preferably Hv220 or more.

Particularly, in view of machinability at post-prOCeSS the back metal preferably has a hardness of Hv400 or less.

When the thrust bearng with a collar is forced into a construCtion machine body, it is difficult to adjust a clearance between the collar and the body to 0.2mm or less. And, in view of bending amount of the body applied with an offset load, it is desired for the ferrous sintered sliding body not to break by bending amount of about 0.1mm.

Fig.51\ is a cross-sectional view showing an example of a thrust bearing in which a ferrous back metal shown in Fig.4C is formed with a venthole and a groove, Fig.5B is a cross-sectional enlarged view showing a A part of Fig.5a and Fig.5C is a plane view of the thrust bearing of E'ig.SA.

In this embodiment, as shown in Fig.5B, a bonded surface of a ferrous back metal 21b to a ferrous sintered sliding body 20 is formed with ventholes 23 and a groove 24. The ferrous sintered s1.idincj body 20 preferably has a structure in which martensjte phase, prepared to have a solid so'uble carbon concentration of 0.2 to 0.45wt%, contains carbide in a content of 5 to 25% by volume. When a ferrous sjntered sliding body i-S sintering-bonded to a ferrous back metal, a great deal of gas is usually generated and therefore accumulated gas may cause defect in bonding of the ferrous sintered sliding body and the ferrous back metal. However, in this embodiment, the ventholeS 23 enables the generated gas to be discharged therethrOljgh and the groove 24 enables formation of liquid phase on the ferrous sintered sliding body at 5i-nteincj_b0nnq. cordinglyi the ferrous sintered sliding body 20 can be sinterea so as to have a high density and also bonded to the ferrous back metal with high bonding strength. it i-S not necessary to form both the ventholeS 23 and the groove 24, like this embodiment, but either one of them may be formed.

In this embodiment, the ventoholes and the groove are formed at a bonded surface of the ferrous back metal to which the ferrous sintered sliding body is bonded.

However, when a ferrous sintered sliding body is formed with closed pores or grooves at a sliding surface thereof in an area ratio of 1 to 10%, it i-S not necessary to form the ventholes and recesses on the bonded surface of the ferrous back metal owing to its excellent characteristics for dischargiflcJ the gas generated at sinteringbonding (outgaSSiflg characteristics) -The closed pores and the recesses can work as oil pockets (in which lubricant is retained) on a sliding surface of a ferrous sintered sliding body, causing improvement in heat crack resistance, in addition to the aforesaid effects.

A height of an ingate on which the ventholes are formed is preferably adjusted to be higher than a half thickness of the ferrous sintered sliding body 20 which is placed on the ferrous back metal 21c.

A counterpart sliding body, which s'ide with respect to the thrust bearing of Fig.5, may he a steel thrust bearing to which a hardening heat treatment such as a carburized quenching and an induction quenching is subjected. The same is applicable to other embodiments

and examples.

For a method for combining a back metal to a ferrous sintered sliding body, a ferrous sliding body sintered previously may be combined to a back metal by brazing. However, since such a method hardly ensure dimensional stability at a high-density process in the sintering, it is necessary to machine the sliding body before bonding, resulting in remarkable cost rise.

Accordingly, this embodiment develops a sintered thrust bearing such that a ferrous sjncered sliding body is formed into a doughnut- ShaPed compact (a doughnut_ShaPed plate) and then the compact is placed on a ferrous back metal so that at least a part of an inner surface and an under surface of the compact will be sintering_bonded to an outer surface of a cylindrical portion and an upper surface of a collar of a ferrousback metal. 1\t the same time, in order to prevent occurrence of defects caused by gas generated from the sintered compact at 5jnteriflg-bonding, ventholes (gas-vent holes) and grooves through 0 which the gas is discharged are formed on a part of a bonded surface of at least either one of the outer surface or the upper surface of the ferrous back metal J\t least either one of the ventholes or the groove may be formed on the bonded surface.

Fig.6A is a plane view showing the ferrous sintered sliding body of Fig.4 in which ventholes and a groove are formed and Fig.68 is a cross-sectional view along B-B line in Fig.61\.

In this embodiment, ventoholeS 231\ and a groove 24P are formed on a ferrous sintered sliding body 20. This embodiment can obtain the same effect as that of Fig.5.

The ferrous sintered sliding body 20, according to the present invention, has a structure comprising carbide in a content of at least 5% or more by volume and martensite phase having a solid soluble carbon concentration of 0.15 to 0.5wt%. This structure enables withstanding a high thrust load and improving abrasion resistance, seizing resistance and heat crack resistance under bad lubricating conditions.

In the ferrous sintered sliding body 20, a dispersion amount of the carbide preferablY does not exceed 25% by volume, more preferably 15% by volume, and a solid soluble carbon concentration of the marteflSite phase is preferably set to 0.2 to 0.45wt%, more preferably 0.2 to 0.35wt%. In addition, the ferrous sintered sliding body 20 is preferably tempered at 150 to 600 C for the purpose of improvement in toughness and flexural strength. This structure allows withstanding a large offset load applied to.the thrust bearing.

The carbide includes mainly at least either one of hard and inexpensive CrC3-type carbide or M6C-tyPe carbide excellent in heat-resistance strength. It is preferable to disperse such carbide in a sintered slidi.ng material from an economical viewpoint. Further more, the carbide may include MC-type carbide. In which case, a content of the MC-type carbide is preferablY set to 5% or less by volume from an economical viewpoint.

Especially, it is most preferable to disperse inexpensive Cr7C3-type carbide mainly and M6c-type carbide and MC-type carbide in a content of 5% or less by volume additionally.

1\nd, adding P in the form of FeP alloy in an amount of 0.1 to]..5wt% can increase a sintered density and improve sinterincj bonding ability of the ferrous sintered sliding material 20. In fact, 0entratiflg P in at least either one of martensite phase or M6C-I carbide moves a melti.ncj point of the ferrous sintered sliding body to lower, causing improvement in 5jnteriflg ability and sintering bonding ability. And, precipitating phosphorus compound such as Fe3P, Cr2P, FeM0P, V2P and FeTiP can improve seizing resistance. In a case of a ferrous sintered sliding material in which carbide comprising M6C-type carbide mainly is dispersed, even if P conta]ning therein is concentrated in the M6C-type carbide, P improves bonding stability, whereby P is preferably added in an amount of Q.3wt% or more.

And, it is preferable to add Cu based alloy phase to a ferrous sintered sliding material in granular form in a content of 1 to 10% by volume. In order to improve slidiriçj performance, the Cu-based alloy phase preferably contains one or more elements selected from the group consisting of P, Sn, Al, Fe and Ni. This improves conformability of a sliding surface. And, since the granulated Cu based alloy is particularly abraded at the beginning of sliding, oil pockets are formed Ofl the sliding surface-Such oil pockets can improve seizing resistance and heat crack resistance.

In order to more improve heat crack resistance, a sintered sliding member, according to this embodiment, preferably comprises a ferrous sintered sliding body and a ferrous back metal to which the ferrous sintered sliding body is sintering-bonded, wherein the ferrous sintered sliding body has a structure in which martensite phase, having a solid soluble carbon concentration of 0.15 to 0.5wt%, contains Cr7C3-tYPe, MC-type and M6C-type carbides dispersed therein in a total content of 5 to 50% by volume and closed pores, having an average pore diameter of 0.03 to 1.0mm, scattered therein in a content of 3 to 10% by volume.

Alternatively, the ferrous sintered sliding body is preferably formed with holes at a sliding surface thereof, in which recesses comprising the holes are dispersed in the sliding surface in an area ratio of 3 to 10% and the recess has an average dameter of 3mm or iess.

Furthermore, it is more preferable to add Si02 particles, for example, to a ferrous sintered sliding material from an economical viewpoint. This makes it possible that Si02 is reduced at sintering and remaining Si is diffused in the ferrous sintered sliding material and also forms a solid solution therewith. /-\s a result, closed pores formed at portions where the Si02 particles had existed can be used as oil pockets on a sliding surface, causing improvement in seizing resistance and heat crack resistance.

A ferrous sintereci sliding body is preferably formed with recesses having a depth of 0.1 to 3mm on at least a sliding surface thereof at forming thereof.

Because, by sintering-bonding the ferrous sintered sliding body formed with the recesses to a ferrous back metal, oil pockets are formed on the sliding surface.

And, a thickness of a ferrous sintered sliding body is preferably 0.5mm or more based on the fact that a conventionally used thermal spraying coating film, which is prepared to have a thickness of 0.1 to 0.3mm, causeS peeling arid brakeage of the coating film due to sand or gravel jammed therein and an offset load. EspeCiallY the upper limit of a thickness of the ferrous sintered sliding body is preferably set in view of abrasion life.

From an abrasion resistant vie.ipoint, a ferrous sintered sliding body other than tile closed pores preferably has a Vjckers hardness of Hv500 or more, more preferably Hv700 or more.

(Second Embodiment) Fig. 7 schematically shows a structure of a bucket-connecting device according to the second embodiment of the present invention. Fig.81\ is a cross_Sectional view showing a thrust bearing and Fig.8B is a plane view showing various oil grooves and recesses formed on a sliding surface of the thrust bearing of FiCJ.BA.

In this embodiment, as shown in Fig.l, a thrust bearing 25 forced into the arm 5 and a thrust bearing 26 mounted on the bucket bracket 6a have the form of a thrust bearing with a collar. Since the bucket 6 is sometimes exchanged depending on work and requires easy maintenance, a sliding surface of the thrust bearing 26 equipped for the bucket bracket 6a is not necessarily made of a ferrous sintered sliding material-So, the sliding surface of the bearing IS preferably made of an induction quenched carbon steel or low-alloy steel and a carburized material from an economical viewpoint-s shown in Fig.8B, a sliding surface (an induCtiofl quenching hardened sliding surface) 27 is preferablY formed with suitable grooves (rounded grooves 28a and diamond-shaped grooves 28b) and recesses (dimples or holes 29) -Such grooves and recesses make it easY tO supp'y a uhricating grease and another lubriCatlnc compound to. the sliding surface 27, causing improving seizing resistance and heat crack resistance.

(Third Embodiment) Fig.9 schematically showS a structure of a bucket connecting device according to the third embodiment Of the present invention-In this embodiment, the et_connect1ng device has almost the same principal structure as that of the second embodiment except for the bushing-/ bushing 1]/ according to this embodiment, is made of a porous iron alloy based sintered body ontaifling a lubricating compound filled in the pores-Such porous iron alloy based sintered body allows extending a lubricating interval of the bucket connecting device-In this embodiment, it is preferable to engage the bushing 11 with the thrust bearing according to the first or second embodiment.

Fig.1O schematically shows another structure of a bucket-connecting device according tO the third embodiment of the present invention. This structure is preferred than the third embodiment.

In this embodiment, by coating a connecting pin with a hard thermal spraying coating film 30, having a thickness of 0.1mm or more, made of Mo mainly, a lubricating interval of the connecting pin and thus the bucket connecting device can be extended.

(Fourth Embodiment) Fig.li shows a principal part of a roller assembly.

In this embodiment, the present invention is applied to a floating seai device equipped for the roller assernb]Y.

Fig.12 is a cross-sectional view showing a structure of a double-layered floating seal (a floating seal) As shown in Fig.l1, the roller assembly 36, according to the embodiment, has a roller retainer 49 a roller shaft 50 supported by the retainer 49, a roller bushing (collar bushing) 51 fitted onto the shaft 50 and a roller 52 arranged through the bushing 51, in which the bushing 51 and the roller 52 are rotatablY connected each other. i floating seal device 53 is provided with one pair of seal rings 54 with seal surfaces thereof being contacted each other and an 0-ring 55 fitted onto each of the seal rings 54. In the roller assembly 36, * 29 the floating seal device 53 is arranged such that the contacted sea]. surfaces of the seal rings 54 are pressed toward the shaft 50 by elastic force of the compressed 0-rings 55. The seal surfaces are relatively slidable while being pressed each other at an adequate pressure so as to prevent entering water, sand or gravel from outside, as well as preventing leakage of lubricati-fl9 oil from inside. To the seal surfaces of the seal rings 54, a ferrous sintered sliding body is 5tering_h0ed in which the ferrous sintered sliding body comprlSes carbide in a content of at least 5 to 50% by volume and martensite phase prepared to have a solid soluble carbon concentration of 0.15 to 0.5wt%. In order to have a solid soluble carbon concentration in the aforesaid range easily and contain a harder carbide excellent in seizing resistance, the ferrous sintered sliding body preferably contains one or more elements selected from the group of Cr of 9wt% or more, Mo of 3.5wt% or more, Mo and W in a total content of 4.5wt% or more and V of 3wt% or more, and the martensite phase preferably contains one or more carbide of Cr7C3-tyPe carbide, M6C-type carbide and MC-type carbide dispersed therein. PLS shown in E'ig.12, this embodiment has the same sintering bonding method and the same structure, in which ventholes 23 and grooves 24 are formed, as those of the thrust bearings shown in Fig.5 and Fig.6. In Fig.ll, a high-speed roller shaft 50 is subjected to a heat treatment for improving sliding performance at the surface G thereof, such as a chemical treatment using zinc phosphate or magnesium phosphate, a chrome plating and a Mo thermal spraying coating treatment.

1ccording to this embodiment, a floating seal device excellent in seizing resistance and heat crack resistance can be provided. In order to improve abrasion resistance further, a floating seal device is preferablY made of a sintered sliding member, in which a ferrous sintered sliding body, having a structure in Wh]Ch martenSite phase, prepared to have a solid soluble carbon concentration of 0.2 to 0.45wt%, contains CrC3-type carbide, M6C-type carbide and Mc-type carbide dispersed therein in a total content of 20 to 40% by volume, is sintering-bonded to a ferrous back meta' having a Vickers hardness of Hv170 or more.

In a large diameter floating seal used for a reduction gear apparatus, a diameter of the seal ring becomes so large that a sliding speed of the seal surface becomes high. ccordingly, a floating seal ring excellent in higher seizing resistance and higher heat crack resistance is required. In order to obtain such a floating seal ring, according to this embodiment, the ferrous sintered sliding material preferably contains at least either one or more groups, in which one group consists of Cu particles and Cu based alloy particles and the other group consistS of Mo particles and closed pores, dispersed therein in a content of 1 to 10% by volume. In such a case, the closed pores are preferablY scattered in a content of 3 to 10% by volume and preferably have an average diameter of 0.03 to 1.0mm. In addition, it is also preferable to form recesses at a sliding surface (a seal surface) of the floating seal in an area ratio of 1 to 30%, more preferablY 1 to 10% or 3 to 10%. And, a size of the closed pore and the recess preferably has about half or less of a width of the seal surface, more preferably 0.5mm or less in the width direction of the seal surface. However, a size of the closed pore and the recess may be 1mm or less in the width direction of the seal surface.

For an inexpensive ferrous sintered sliding material excellent in abrasion resistance, a material an which Cr7C3-type carbide are dispersed and precipitated in martensite, as with a high-carbon and high-Cr based work steel such as SKD1, SKD2 and SKD11, is used. This embodiment pays attention to a phase diagram of a Fe-C-Cr ternary alloy at 900 to iooo c (referring to Fig.15, described below) and an equilibrium relation (a constant carbon activity) in the phase diagram. The phase diagram shows that a solid soluble carbon concentration in martensite phase is 0.2 to 0.45wt% in a two phase region of austenite and Cr7C3-type carbide between Tie Lines A and B. Consequentially in this embodiment, each amount of carbon and Cr to be added to a ferrous sintered sliding body shall satisfy the following equation; O.l43xCr(wt)l.41Catbon(wt%)0.156xCrt0B And, in order to disperse CrC3- tYPe carbide in a content of 5 to 50% by volume, an addition amount of Cr is set to 9 to 35wt%. Since V contributes to improve tempering_softening resistance of martensite phase and disperse Cr7C3-type carbide uniformly, addition amounts of carbon and Cr are determined based on the case that V is added of such amount that MC-type carbide is not precipitated. However, when V is added in an amount such that a slight amount of MC-type carbide (5% or less by volume) is precipitated and di_spersed, the aforesaid performance of V can be demonstrated fully. In which case, V is added in an amount of 0 to 3wt%, and amounts of carbon and Cr added to the ferrous sintered sliding material shall satisfy the following equation; O.I43XCf(Wt%)_1.41+14xMCtYpe carbide(VOlUme fraction) Carbon(wt%)0.l56xCr(wt%)_0584XMCt carbide(V0lU fraction) Specifically1 a ferrous sintered sliding body preferably contains carbon of 0.9 to 3.8wt%, Cr of 9 to 35wt% and V of 0 to 3wt% so that a content of carbon satisfies the following equation; O.l43xCr(wt%)_i.41+14xMtYPe carbide(VOlUme fraction) Carbon(wt%)0.l56xCr(wt%)_0.584xMCt carbide(VOlUme fraction), and has a structure in which martensite phase, which forms a solid solution with carbon of 0.2 to 0.l5wt% and Cr of 6.5 to l2wt%, contains Cr7C3-tyPe carbide in a content of 5 to 40% by volume and Mc-type carbide in a content of 5% or less by volume dispersed therein with a tota1 content of the carbide being 5 to 40% by volume, wherein the ferrous sintered sliding body further contains one or more ejements selected from the group consisting of Si, Mn, Ni, I', S, B, N, Mo, W, Ti, Co, Cu and A].. In view of Si, a content of carbon contained in the ferrous sintered sl3diflg material preferablY satisfies the following ecuatiOn 0.i43xCr(wt%)_1.41+0.1SxSi (.jt%)+14xMC-type. carbide (volume fraction) Carbon(Wt%) 0.l56xCr(Wt%) O.58+O.lSxSi(wt%)-F14XMC-type carbide(VOlUflle fraction).

And, the ferrous sintered sliding body preferably has martensite phase which forms a solid solution with carbon of 0.2 to O.45wt%, Cr of 6.5 to l2wt% and at least either one of Si. of 1 to 5wt% or Al of 0.5 to 4wt% -In the ferrous sintered sliding material in which Cr7C3-type carbide and MC-type carbide are precipitated and dispersed, concentrations of carbon and alloy elements, such as Cr, V and W, and an amount of carbide in the martensite phase of the ferrous sintered sliding material are important factors for determining seizing resistance, heat crack resistance and abrasion resistance of the ferrous sintered sliding material. SO, hereinafter, such concentrations and amount will be examined correctly. In a ferrous sintered sliding material according to this embodiment, a carbon amount (Cwt%) and an element (X) amount (Xwt%) added thereto are expressed by the following equations using volume fractions (fCr7C3, fMC) of Cr7C3-type carbide and Mc-tYP carbide dispersed therein, concentrations (CMar, XMar) of carbon and alloy element in the martenSite, concentrations (C73, X73) of carbon and alloy element in the Cr7C3-type carbide and concentrations (CMC, XMC) of carbon and alloy element in the MG-type carbide, Cwt%CMarX (l-fC7C3) C73xfCr,C3+CMCxfMC Xwt%=XMarx (l-fCr7C3) +X7 3xfCr7C3 XMC;fMC =XMarx{ (l_fCrCJ) KX7xflMCMC} in the aforesaid range according to this embodiment, C73 can approximate 8.7wt% and CMC can approximate l4wt%. By using those values, a suitable range of a carbon concentration is expressed by the following equation; O.2x(l_fCr7C3)+8.7XfCr7C3+14MC Carbofl(Wt%) fCr7C3) +8. 7xfCrC3+l4XfMC.

And, a suitable range of an alloy element concentration is expressed by the following equation; Xwt%=XMar (l_fCr7C3fMC)+KX77C3+1MC<fMC1 Here, KX7 and KXMC (distribution coefficients) are a ratio of a concentration of an alloy element X in CrC3-type carbide and MC-type carbide, respectiVeJY to

S * 35

a concentration of an alloy element X in rnarteflSite phase (that is, KX7=X73/XMar, KXP4C=XMC/XMar) -In this embodiment, suitable amounts of carbon, Cr, Mo, W, V, Si, Al, Ni and Co added to the ferrous sintered sliding material can be calculated using measured distribution coefficients of such alloy elements (KXMC is described as KXM/C, later) In this embodiment, each distributiofl coefficient is measured as follows: KCr78, KMo7 and KW7=7, KV7=13, KSI7 and KA17=0, KNI7=0.1, KCo7=0.23, KCrM/C=3-8, KMoM/C=3, kMWM/C=8.2, KVM/C=119, KSiMIC and KA1M/C=O, KNiM/C and KCQM/C=0.05. In this embodiment, a concetratiOfl of Cr in rnartensite phase is set to 6.5 to l2wt%. However, as described later, each concentration of Mo, W and V is adjusted as following: Mo; 0 to 4wt%, W; 0 to Bwt%, Mo+0. 5xW; 0 to 4wt%, in whiCh 0. 5xW represents half of a real amount of W, and V; 0 to 0.6wt%, for the purpose of obtaifliflY sufficient sintering ability of the martensite phase and adjusting tempering-softening resistance of the martenSite phase.

Since a distribution coefficient KCr7 of Cr covers Cr concentrations in a wide range, KCr7 in this embodiment is preferably set to the following using Cr concentration (CrMar(wt%)) in martensite, KCr7=_0.48XCrMar(Wt%)+hl8-When a sliding surface is heated under a boundary lubricating condition generated under severe lubricat3flg conditions and therefore martenSite phase in the sliding surface is suddenly softened, seizing resistance and abrasion resistance thereof are deteriorated. In this embodiment, in order to improve tempering_soften9 resistance, a double layered sintered sliding member (a sintered sliding member) improved in resistance is developed, in which the double layered sintered sliding member contains at least either one of inexpensive Si of I to 3.5wt% or Al of 0.5 to 2wt% so that at least either one of Si or Al are concentrated in the martensite phase to be I to 5wt% and 0.5 to lwt%, respect3 vei y.

When Mo coexists with the rnartensite phases as described in Japanese Patent No.2003-3BO20 proposed by the inventors, Si will decrease the maximum concentration of Mo, monstrating resistance effectively. AccordinglY, in this embodiment, from an economical viewpoint, a concentration of Mo or Mo and W in the martensite phase is adjusted to 0 to 4.0_0.5x(Si(Wt%H1\1(tU). ConsequentlY, Mo in an amount of 0 to 5.5wt% or Mo and W in an amount of 0 to 5.5wt% is added to the ferrous sintered sliding material. In order to ensure quench_hardening ability by gas cooling after sintering_bonding, Mo is preferably added in an amount of 1 to 5.5wt%. And, an effective concentration of Mo in martensite phase for improving temperiflg softening resistance of the martensite is 0 to 2.5wt%.

Accordingly, in this embodiment, from an economical viewpoint, addition amounts of Si and Mo are preferablY 1 to 2.Swt% and 1 to 2.Bwt%, respeCti-Y more preferably 1.5 to 2.5wt% and 1 to 2wt%, respeCti\7elY.

Si forms a solid solution with rnartensite phase in a large amount and therefore improves temperlnq softening resistance of the rnartensite phase remarkablY-And, Si is inexpensive-So, Si is positivelY added to hot-tool steels such as SKD6, SKD61 and SKD62 which are used without dispersing carbide. In a ferrous sintered sliding material, Si increases a jnteriflg abilitY remarkably, and also increases carbon activitY in austenite phase at sintering and qench1ng so that a solid soluble carbon concentrat1ol in rnartenslte decreases in a relationshiP of 0.15xSi(1t Accordingly, in this embodiment, an adequate concentration of carbon in the aforesaid ferrous sintered sliding material is preferablY adjusted to higher in a relationship of 0.l5xSi(Wt%)-And, since Si stabilizes a Fe phase remarkably and addition of Si moves A3 transformation temperature to higher, Si is expected to work for increasing heat track resistance of a sliding surface. In addition, A3 transformation temperature changes per unit weight of various alloy elements (LA3 C/Wt%, Si:+40, Al:1O, Mo:-f20, V:-f40, W:-i-12, Mn:-30, Ni:-15 *and C:-220) shows that Al, Mo, V and W, in addition to Si, can improve heat crack resistance. However, when a large amount of Si and such elements coexist, ferrite phase is more stabilized and therefore it becomes impossible to perform an adequate quenching treatment. AccordiflCi3-Yi the upper limit of addition amount of Si is set tO 3.5wt% based on phase diagrams of a Fe-SiCX quaternary alloy (as shown in Figs.1A, lB and 1C) thermodyflamCa]!Y calculated. The phase diagrams show that Si can be added in an amount of 3.5wt% in view of a composition of martensite (0.2wt%CarbOfl-6.S to]2wt%Cr) in which Ct;C3 type carbide is dispersed mainly. And, in another embodiment (0.45wt%C3rbOfl3wt%M0-Swt%V) in which M6C type carbide is dispersed mainly, described later, the upper limit of addition amount of Si is preferablY set to 2..Swt% (as shown in Figs.1A, lB nd 1C).

As for Al, Al stabilizes a Fe phase more than Si.

So, an addition amount of Al is set to an about half of an addition amount of Si. And, a ferrous sintered sliding material, to which Si. and Al are added in a high density, preferably contains one or more elements of Ni of 1 to Swt%, Mn of 0.5 to 2wt% and Cu of 1 to lOwt%, which stabilize austenite phase (as shown in Figs.lA, lB and 1C) When a temperature of a sliding surface under a boundary lubricating condition exceeds 500 C, it iS required to increase tempering_s0fteng resistance of martensite phase of the sliding surface. ccordiflglY, this embodiment takes advantage of Mo, W and V, which demonstrate tempering_softening resistance at 500 C or higher more effectively than Si. So, in order to keep a Rockwell hardness of HRCSO or more, more preferablY HRC55 or more, by a quenching treatment (1 hour) at 600 C, a ferrous sintered sliding material preferablY contains at least either one of Mo of 1.6 (preferably 2) to 6.5wt% or Mo and W of 1.6 (preferably 2) to 6.5wt% so that martensite phase thereof contains one or more elements selected from the group consisting of Mo of 1.5 to lwt%, Mo and W of 1.5 to 4wt% and V of 0 to 0.6wt%.

-In vie' of a solid solubility of n6C-type carbide at quenching temperatures within 900 to 1000 C, Mo and W can form a solid solution with martensite up to about 4wt%.

The lower limat of each concentration of Mo and in the martensite phase is not limited. However, in view of a tempering_softening curve of the SKD tool steel and the hot-work tool steel, in order to obtain temperiflg softening resistance higher than that of such tool steels, the lower limit thereof is set to l.Swt% or more, more preferably 2wt% or more.

Mo and W, which are added to the ferrous sintered sliding material, concentrates in Cr7C3-tYPe carbide dispersed in the material. So, addition amounts of Mo and W will be obtained from a relation between the lower and upper limits of dispersion amount of the Cr-7C3tYPe carbide and the lower and upper limits of a concentration of at least one of Mo and W in the martensite phase by means of distributiOn coefficients KMo7 and KW7 of Mo and W between the Cr7C3-tYPe carbide and the martensite phase, obtained in a later embodiment. i\s a result, an addition amount of MO iS preferably set to 1.6 to 6.4wt% and an addition amount of Mo and W is preferablY set to 1.6 to 6.4wt%. 1\nd, when at least one of Mo and IA in the martensite is set to 2 to 4wt%, in a suitable case for the thrust bearing containing Cr7C3-tyPe carbide in a content of 10 to 25% by volume, an addition amount of Mo is preferably set to 2.3 to 5.5w1%, and i-n a suitable case for the floating seal containing Cr7C-tyPe carbide in a content of 20 to 10% by volume, an addition amount of Mo is preferablY set to 2.6 to 6.4wt%. More preferablY when Cr-iC3-tYPe carbide is contained in a content of 25 to 40% by volume, an addition amount of Mo is set to 3.5 tO 6.4wt%.

V is examined as with Mo and IA. V in martenSite phase increases tempering_Softening resistance than MO and IA. 1 concentration of V in rnartensite, which forms a solid solution with carbon of 0.2 to 0.45wt%, is 0.2 to 0.6wt% within a temperature range of 900 to 1100 C because MC-type carbide is remarkably suitable carbide.

In view of a concentration of V concentrated in Cr7C3 type carbide, in this embodiment, V can be added to the ferrous sintered sliding material, ontaifling Cr-iCrtYPe carbide precipitated therein in a content of 50% by volume, up to an amount of about 3.5wt% without MC-tYPe carbide being precipitated. And, as described later, the strength of the material decreases as a larger amount of carbide is dispersed. So, in viewpoint of such fact and an economical efficiency, in a case of a ferrous sintered sliding material containing CrC3-tYPe carbide dispersed therein in a content of 5 to 40% by volume, V is preferably added in an amount of 0.5 to 3.0 (more properly, 2.9) wt% in proportion to a content of the Cr7C3-type carbide. In order to take full advantage of V for increasing empering_soften1P9 resistance of martensite phase effectivelY, MC-tyPe carbide IS preferaily precipitated and dispersed in an economicallY allowable small amount. ccordiflgiy, in this embodiment, MC-type carbide is preferably dispersed in a content of 5% or less by volume. And, since a concentration f V in the MC-type carbide is about 45wt% according to this embodiment, an addition amount of V is set. to 5wt% or less, more preferably 4wt% or less.

And, for a ferrous sintered sliding material used for a thrust bearing which requires an adequate abrasion resistance and toughness, it is preferable to disperse Cr,C3-type carbide and MC-type carbide in a total content of 10 to 20% by volume therein. So, an addition amount of each element is preferably set to the followiflgs C; 1.1 to 2..4wt%, Cr; 10 to 29wt%, Mo; 1.8 to 5wt% and V; 1.1 to 3.5wt%. Furthermore, in order to impt0 seizing resistance, it is preferable to disperse nc-tyPe carbide in a small content of 0.5 to 5% by volume therein and therefore disperse Cr,C3-type carbide and MC-t'P carbide in a total content of 20 to 40% by volume therein.

T\ccordingly, an addition amount ot each element is set to the followings: C; 1.9 to 4wt%, Cr; 15 to 35wt%, Mo; 2 to 6.4wt% and V; 2 to Swt%.

In a case of a ferrous sintered sliding material used for a floating seal which requires higher abrasion resistance than the thrust bearing, it is necessary to further improve abrasion resistance and seizing resistance of the ferrous sintered sliding material.

ConsequentiallYi in the present invention, a sintered sliding member using a ferrous sincered sliding material is developed, fl which theferrous sintered sliding material contains at least carbon of 1.8 to 4.5wt%, Cr of 12 to 3Owt%, V of 3.5 to lOwt%, either one of Mo of 2 to 6.4wt% or Mo and W in a total amount of 2 to 6.4wt% and has martensite phase, wherein the martensite phase, having a solid soluble carbon concentration of 0.2 to 0.45wt%, contains MC-type carbide, harder than Cr7C3tYPe carbide, dispersed and precipitated therein ifl a content of 5 to 15% by volume. And, the rnartenSite phase preferably forms a solid solution with carbon of 0.2 to 0.45wt% and Cr of 6.5 to i2wt% and further one or more elements selected from the group consjstifl9 of Mo of I to 3.Swt%, Mo and W in a total amount of 1 to 3.5wt% and V of 0.4 to 0.6wt%. In view of toughness of the ferrous sintered sliding material, the martensite phase preferably contains Cr7C3-type carbide in a content of 10 to 35% by volume and MC-type carbide in a content of 5 to 15% by volume precipitated and dispersed therein with a total amount of the carbides bencj 15 to 40% by volume. In addition, the ferrous sintered sliding material preferably contains one or more elements in Si, Mn, Ni, P, S, B, N, Co, Cu and IU. In order to improve toughness of the ferrous sintered sliding material, a total amount of the carbides is preferably set to 15 to 30% by volume.

1\nd, when V and Ti are added so as to disperse MC-type carbide, the lower limit of dispersion amount of the MC-type carbide is set to 5% by volume which is an average content of MC-type carbide dispersed in a high-speed steel, described later, and the upper limit thereof is set to 15% by volume from an economical viewpoint. Especially, when MC-type carbide is dispersed while coexisting with Cr7C3-type carbide, v concentrates in the Cr7C3-type carbide in a high density. So, from an economical viewpoint, a content of Cr7C3-type carbide is preferably limited to 10 to 25% by volume. Pnd, in order to ensure toughness of the ferrous sintered sliding material, at least carbon of 1.8 to 3.7wt%, V of 3.7 to 9wt%, Mo of 2.5 to 5.5wt% and Mo and W of 2.5 to 5.5wt% S. 44 is preferably contained so that a total content of the carbides is regulated to 15 to 30% by volume.

Alloy elements such as Ti, Zr, Nb and Hf, producing MC-type carbide remarkably, hardly forms a solid solution with martensite phase and almost all amounts thereof seem to be dispersed as MC-type carbide. And, since such elements are very expensive1 adding such elements in a large amount is not desirable from an economical viewpoint. Accordingly, an addition amount of each of the elements is set to 3wt% or more, and also carbon is added in an amount (wt%) calculated stoichiometrical compositions of TiC, ZrC and NbC SO as to regulata suitable addition amount of carbon.

1\ ferrous sintered sliding material is sinterifl9-bonded to a ferrous back metal at about 1150 to 1220 C.

Tn such a case, even if the ferrous sintered sliding material is continuously quenched by gas cooling from temperatures near the 5jntering_bondil'lg temperatures, no trouble may occur as long as a solid soluble carbon concentration in martensite phase thereof is regulated to 0.2 to 0.45wt%. The higher the quenching temperaturei the larger the concentrations of V, Mo and W in the martensite phase. This fact is preferable for temperiflg softening resistance.

Tempering_softening resistance of martenSite phase at. 600 C is improved in relation tO the following equation using a tempering parameter iHRC represented by Rockwell hardness HRC and concentrati0 of alloy elements in the martensite phase. AccordinglY, On basis of tempering hardness (about)-1RC43) of SKD1 (carbon of 2.O2wt%, Si of 0.34wt%, Cr of l3.O3wt% and V of 0.O4wt%) at 600 C, concentrations of each element in martefl5]te phase are preferably controlled so that iFIRC is 7 or more, more preferably 12 or more.

HRC0. 5x (llxMoMar+7. 5xWMar+25. 7xVmar+5. BxSiMar+S. BxSiMar For example, in order to satisfy a condition of }IRC 12, when each of Mo, W and V is added independently, it is necessary to add Mo of 2.2wt% or more, W of 3.2wt% or more and V of 0.93wt% or more to the martensite phase. And, since a maximum solid soluble V concentration is about 0.6wt%, when V is added by itself without adding Mo and W, temperin950ftY resistance cannot be improved sufficientlY. ccordiflgY, it becomes necessary to add Mo therewith so that the martensite phase contains Mo in an amount of lwt% or more.

As described above, when a ferrous sintered sliding material contains MC-type carbide together with Cr7C3-type carbide dispersed therein, an adequate amount of carbon to be added to the ferrous sintered sliding material is modified. In addition, Cr, Mo and W added thereto concentrate in MC-type carbide remarkablY.

Accordingly, using distribution coefficients of each elements between the MC-type carbide and marteflsi.te makes it possible to calculate suitable additiOn amountS of Cr, Mo and W to be added to the ferrous sintered sliding material for adjusting concentrations of each elements in the martenSite phase adequately. However, since Mo, W, V and Cr concentrate in MG-type carbide fl a significant high density, using plain distribution coefficients cannot provide suffiCient exact values. So, assuming that MC-type carbide is precipitated as Mo4C3, w4C3 or Cr4C3-type composite carbide and the carbide comprises V+Mo+W+Cr of 8Owt%, carbon of 15wt%, Fe+Mn of 5wt% and the like, cacti concentration of V, Mo, W and Cr in the MG-type carbide is modif.ied such that a total amount of the element is 8Owt% with a concentration ratio of each of the element, in whiCh the concentration ratio is determined by dIStribUt1Ofl coefficients of each element between MC-type carbide of each element and martensite (the distribution coefficient of each element is the f0ilOWings KVM/C=119, KMoM/C3, KWM/C=8.2 and KCrM/C3.8) For example, an amount (VMC(Wt%)) of MG-type carbide of V is modified as the following: VMC(wt%)=(VMarXKVMC/ ( (VMarxKVMC+CrMarCtMM0Ma1M0M MarxKWMC)/0.B) (here, KXM/C is represented by KXMC for short). For example, from a composition (MO of 2.Owt%, W of 2.Owt%, Cr of 4.5wto and V of 0.45wt%) of martensite of No.32 MC-type carbide shown in Fig.2l described later, a composition of MC-type carbide dispersed n the martensite phase is calculated as follows; V of 46.OWt%, Mo of 5.2wt%, W of 14.lwt% and Cr of 14.7wt%-The rsu1ts are well agreed with analysis shown in Fig.21 described later, whereby the modification is proved to be preferred.

A high-hard high speed steel such as SKH2(T), SKII1O(T15), SKH54(M4, M6) and SKH57, containinci a large amount of W and Mo, is quenched from quenching io temperatures higher than 1200 C and tempered (at about 550 to 580 C) twice or more so as to decompose retained austenite almost entirely. As a result, the highsPeed steel is prepared to have a so1id soluble carbons concentration of 0.5 to 0.6wt% so as to have a RockJell hardness of HRC65 or more. The high speed steel is a material in which a high alloy martenSite phase, whiCh forms a solid solution with M04-W+V of 5 to iOwt% and Cr of 3.5 to 4/Swt%, contains M6C-type carbide, having a basic crystal structure of Fe3MOC or Fe3W3C, in a content of 5 to 12% by volume and MC-tYPe carbide, having a basic crystal structure of V4C3, in a content of 1 to 9% by volume dispersed therein with a total content of the carbide being 7 to 12% by volume so to demonstrate remarkable mpering_softefhn resistance (referring to J. Japan Inst. Metals, 2 (1963), Sato, Nishizawa, P.564) . So, the high-speed steel does not have sufficient heat crack resistance as with the high-Cr based work steels. 1\nd, when the high-speed steel is used for the floating seal, sufficient seizing resistance and abrasion resistance are not obtained because of a small amount of carbide. ccord1flglY in the present invention, adequate addition amounts of carbon and alloy elements in the case of dispersing a large amount of M6C-type carbide are necessarilY set in the same manner for setting adequate addition amounts of carbon and alloy elements in the case of dispersing the Cr-C3-type carbide and the MC-type carbide in a martensite phase-Therefore, in the present invention, referring.to a phase diagram of a Fe-C-MO ternary alloy at 900 to iooo c (shown in Fig.16 described below), a ferrous sintered sliding material is developed, in which the ferrous sintered sliding material has martenSite phase, having a solid soluble carbon concentration of 0.2 to 0.lSwt%, contains M6C-type carbide dispersed therein. For this purpose, a suitable addition amount of carbon to an addition amount of Mo is approximatelY represented so as to satisfy the following equation; O.O43xMo(wt%)Carbon(wt%)0.038xM0t)O3 1\nd, in view of a phase diagram of a Fe-C4J ternary alloy (shown in Fig.17 described below), as with the Fe-C-Mo ternary alloy, gradients of Tie Line 7 and Tie Line B constructing a two-phase regiOn of austenite (y) and M6C-type carbide are about 1/2 of gradient of Tie Line of the phase diagram of the Fe-C-Mo ternary alloy (Fig.16) and a solid solubility of M6C-type carbide with austeflite in the phase diagram of a Fe-C-W ternary alloy can be approximately equal to that of the Fe-C-Mo ternary alloy. So, when both Mo and W are added together, ifl order to adjust a solid soluble carbon concentration in martensite phase of the ferrous sintered sliding material to 0.2 to 0.45wt%, a suitable amount Of carbon is required to satisfy the following equatiofl.

O.O43x(MO(Wt%)+O.5(Wt%)) Carbon(wt%) 0.036x(MO(wt%)40.5XW('lt%))O36 In addition, the ferrous sintered sliding material contains M6C-type carbide, dispersed therein in a content of 5 to.10% by volume and Mo-fO.5xW dispersed therein fl a content of 4.5 to 3Owt%. The present invention develops a double layered sintered sliding material in which a ferrous sintered sliding material is jnteriflg bonded to a high strength and high toughness ferrous back metal, in.jhjch the ferrous sintered sliding material contains at least carbon of 0.6 to l.9wt%, Cr of I to 7wt%, V of 0 to 3wt, Mo of 3.5wt% or more and Mo-4-0.5xW of 4.5 to 3Owt% (or Mo and W of 6 to 3Owt%) and has a structure in which martensite phase, having a solid soluble carbon concentration of 0.2 to 0.45wt% (more preferably, a solid soluble Mo concentration of 2 to 4wt%, a solid soluble Mo and W concentration of 2 to 4wt%, a solid soluble Cr concentration of 1 to lwt% and a solid soluble v concentration of 0 to 0.6wt%), contains M6C-type carbide in a content of 5% or more by volume (more preferably, 5 to 40% by volume) and NC-type carbide in a content of 5 to 40% by volume dispersed therein. In addition, the ferrous sintered sliding material further contains one or more alloy elements of Si, Mn, Ni, P1 3, N, B, Ti, Co, Cu and Al if necessary.

Since a modified addition amount of carbon and addition amounts of alloy elements depending on a dispersion amount of NC-type carbide are set according to the aforesaid manner, it is apparent that a ferrous sintered sliclang material, in which martensite phase, having a solid soluble carbon concentration of 0.2 to 0.45wt%, contains M6C-type carbide and MC-type carbide dispersed therein, requires that an adequate addition amount of carbon to addition amounts of Mo and satisfies the following equation; 0.043X(MO(Wt%)+O.5xW(Wt%)) l4XMtYPe carbide (volume fraction) Carbon(wt%) O.038X(MO(Wt%)+O.SXW(Wt%))+O.36 14XMC-type carbide (volume fraction) It is necessary to discuss a ferrous sintered sliding material in which M6Ctype carbide is dispersed in the same manner for accurately discussing a composition of a ferrous sintered sliding material in which the Cr7C3-type carbide and the NC-type carbide are precipitated and dispersed. When a volume fraction fMC of M6C-type carbide and a carbon concentration CM6C(Wt%) of the M6C-type carbide in this embodiment are used, an adequate amount of carbon added to the ferrous sintered sliding material is shown in the following equation using solid soluble carbon concentrations of martensite phase of 0.2wt% and 0.45wt%: O.2x(1_fM6C_fMC)+CM6CXtM6c+14MC Carhon(wt%) 0.45X(1 fM6C-fMC) FCM6CxfM6C+l4XfMC.

Furthermore, when the upper limit of a solid soluble carbon concentration in rnartenSlte phase is set to 0.35wt% in order to improve hart crack resistance, a solid soluble carbon concentration of 0.35Wt% is preferably applied to the aforesaid equatiOl.

While a carbon concentration (cM6c) of M6c-type carbide varies depending Ofl a rate of contents of Mo and W in the M5C-type carbide, since distrlbUtl0fl coefficients of Mo and W between M6c-type carbide and martensite phase can be approximately represented as KMo6KW6 from a result of the later embodiment, a carbon concentration (CM6C) of M6C-type carbide can be approximately expressed by the following equation: CM6C=O.9lx(Mo(wt%/(M0(t%)tU)71l A distribution coefficient of each alloy element between M6C-type carbide and rnartenSite phase is measured as follows: KM0620, KW623, KV65.7, KCt6O.95' KS16=2.3, KA16=2.3, KNi6=0-4,. KCo6=0.5 and KP62. By using these distribution coefficients, an addition amount of each alloy element can be calculated as with a case of the aforesaid ferrous sintered sliding material.

And, concentrations of Mo and W in M6c-type carbide are high, for example, Mo of up to 58wt% forms a solid solution in Fe3M03C, and W of up to 7Owt% forms a solid solution in Fe3W3C. So, as with the case for modifying a concentration of each element in MC-type carbide, when Mo coexists with W, an amount (wt%) of MoM6C and WM6C is preferably calculated depending on a value of M0M6C/ (MoM6C+WM6C) For a ferrous sintered sliding material with a high regard for heat crack resistance and toughness1 the upper limit of a solid soluble carbon concentration fl nartensite is set to 0.35wt% so that the martensite phase contains M6C-type carbide in a content of 5 to 20% by volume and MC-type carbide in a content of 5% or less by volume dispersed therein with a total content of the carbides being 10 to 25% by volume. Such prepared ferrous sintered sliding material is suitable for a double layered thrust bearing (a thrust bearing) . For a suitable ferrous sintered sliding material for use in a floating seal which requires excellent seizing resistance and abrasion resistance, it is preferable to disperse M6C-type carbide in a content of 15 to 40% by volume and MC-type carbide in a content of 5% or less by volume with a total content of the carbides being 20 to 40% by volume larger than that of the high speed steel.

As described above, since a high speed steel contains retained austenite phase in a content of 20% or more by volume in a quenched state, the high speed steel used is tempered at 550 to 580 C twice or more so as to decompose the retained austeflite and also be remarkably hardened to have a hardness of HRC65 or more by secondary hardening. So, when the high speed steel is used in a floating seal, initial conformability Of a sliding surface thereof is insufficient, resulting ifl oil leakage and seizing frequentlY-According'Y, in a 0 ferrous sintered sliding material ccordiflq to the present inventlOfl, in order to improve the conformability so as to ensure seizing resistance and obtain a suitabje sealing width of about 0.3 to 2.0mm, retained austenite is dispersed in the matrix in a content of 5% or more by volume, more preferablY 10 to 40% by volume, after tempering. However, when retained austenite will be dispersed in a content of 40% or more by volume, abrasion resistance of the material is deteriorated. So, the upper limit of the retained austenite to be dispersed is set to 40% by volume.

In order to ensure an adequate amount of retained austenite, in the present invention, one or more elements of Ni of 1 to 5wt%, Mn of 2wt% or less and Cu of lOwt%or less are added to the material, in which such elements are not added to a conventional high speed steel.

Since a floating seal requires a sufficient sealing

I

width even during a hulling motion, it is necessary to select a ferrous sintered sliding material capable of obtaining an adequate sealing width. A too narrow sealing width causes not only an insufficient sealing performance but also an increased 5jding_bearing stress applied to a seal surface, resulting in occurrence of seizing and heat crack at the seal surface frequefltlY On the contrary, a too wide sealing width demonstrates stable sealing performance; ubricatiflq performance of the seal surface becomes harsh, resulting in occurrence of seizing and heat crack at the seal surface. So, in a conventionally used sealing member, a seaifl9 width is selected to he 0.3 to 2mm. . The present invention provides a method for improving lubricating ability of a seal surface.

For a method for adjusting a solid soluble carbon concentration in inartensite phase, according to the present invention, based on data of heat_treated high speed steels having a conventional compositiOn (J. Japan Inst. Metals 2 (1963), Sato, Nishizawa, p.S64) a quenching treatment for quenching at 900 to 1150 C, more preferably 900 to 1000 C, is used-As described above, in a ferrous sintered sliding material, an addition amount of Cr is limited to 1 to 7wt% so that Cr7C3-type carbide may not be dispersed. In which case, a concentration of Cr in martensite is about 1 to 7wt%-The higher the Cr concentration, the more the corrosion resistance of the ferrous sintered sliding material efficiently demonstrates. However, as disclosed in Japanese Patent Application No.2002-380203 proposed by the inventors, when a concentration of Cr in martensite exceeds 3.Swt%, tempering treatment precipitates Cr7C3-type carbide so as to deteriorate tempering-softening resistance by Mo, W and V. So, when high tempering-softening resistance is required as described above, the upper limit of a concentration of Cr in martensite phase is preferably set to 3.5wt% and the lower limit thereof is preferably set to lwt% in view of quenching hardenahility. And, quenching ability can be sufficiently adjusted by contents of Ni Mn and Mo in martensite phase. In addition, corrosion resistance can be sufficiently improved by addition of Mo, Ni, Cu, P. Si. and Al other than Cr even if a concentration of Cr in martensite is lwt%. For example, a Ni-hard cast iron suitably used in a floating seal without troubles in corrosion resistance has martensite having a composition of Ni of about Swt%, Cr of lwt% and Si of 1.Swt%.

A maximum addition amount of V added to a sintered sliding material, in which M6C-type carbide is dispersed in a content of 40% by volume and MC-type carbide (V4C3) is not precipitated, is l.2wt% (more accurately, 1.l5wt%). When such maximum addition amount is compared with a maximum addition amount of V added to a sintered sliding material in which Cr7C3-tyPe carbide iS dispersed in a content of 40% by volume and MC-type carbide (V4C3) is not precipitated, it is shown that a ferrous sintered sliding material according to the present invention iS suitable for a ferrous sintered sliding material in which V increases ternpering_softemng resistance of martensite phase economically.

In view of taking full advantage of v improving tempering_softening resistance, when M6C-tYPe carbide is dispersed in a content of 5, 15, 30 and 40% by volume and MC-type carbide is not dispersed, an addition amount of V is 0.5, 0.7, 1.0 and 1.2 wt%, respectivelY. \nd, when MC-type carbide is dispersed Ifl a content of 5% by volume, an addition amount of V is 2.2 to 4.5Wt% obtained by calculation. jccordiflgly, in the present invention, an addition amount of V is preferably set to 0.5 to 4.5wt%. In a ferrous sintered sliding material, used in a thrust bearing, which contains M6c-type carbide in a content of 5 to 25% by volume and MC-type carbide in a content of 5% or less by volume dispersed therein with a total content of the carbides being 10 to 25% by volume, carbon of 0.6 to 1.6wt%, Cr of 1 to 3wt%, Mo of 7.5wt% or more, Mo and W of 7.5 to l5wt% and V of 0.9 to 4wt% are added thereto. In a ferrous sintered sliding material suitable, used in a floating seal, which contains M6C-type carbide in a content of 20 to 40% by volume and MC-type carbide in a content of 5% or less by volume dispersed therein with a total content of the carbides being 20 to 40% by volume, carbon of 08 to 1.9wt%, Cr of 1 to 3..5wt%, Mo of l3wt% *or more, Mo and W of 13 to 25wt% and V of 1.3 to 4.5wt% are preferablY added thereto-When a concentration of Cr in martensite phase is 3.5wt% or less, a tempering_softening parameter AHRC is shown in the following equation using a concentration (XMar(wt%)) of each alloy element X (referring to Japanese Patent Application No.20023892O3)' AHRC=2.8xCrMar+llXMOMar+7.5Ma25.7xVMa5.8 ar) ifl order to obtain a hardnesS of HRC5O or more, more preferably HRC55 or more, by a tempering treatment (I hour) at 600 C, AHRC27 or more, more preferablY HRC3l or more, is required. Such HRC can be obtained in a range in which MoMar is 2 to 4wt%, MoMar+WMar is 2 to lwt%, CrMar is 1 to 3.5wt%, VMar is 0 to 0.6wt%, SiMar is 0 to 7wt% and AlMar of 0 to 4wt%. As described above, when Si and Al are added in a total amount of l.5wt% or more, effects of Mo, W and V on improvement in tempering-softening resistance are decreased.

Accordingly, in a ferrous sintered sliding material according to the present invention, an amount (wt%) Of Si and Al is preferably adjusted to 0.5 to 1.5wt%. When Ni and Al coexist, in which the elements are added in order to obtain retained austenite phase and improve quenching ability and abrasion resistance, rernarkabie age-hardening is demonstrated and therefore temperiflg softening resistance is improved. ccordingly, Ni is preferably added to a ferrous sintered sliding material to which Al is added.

A ferrous sintered sliding material, in which a large amount of M6C-type carbide is dispersed, requires a large amount of Mo and w. So, an economical method for adding Mo and W will be discussed. An amount of M6C-tYPe carbide precipitated by addition of expensive is about 0.8 times an amount of M6C-type carbide precipitated by addition of Mo. And, a effect; of W on tempering-softening resistance is about 0.7 times that of Mo. In addition, when MC-type carbide is dispersed coexistent therewith, W is precipitated in the MC-tyPe carbide in a larger amount than Mo. From the results, it is economical to add Mo mainly than w. And, in view of sintering ability, in the present invention, it is desirable that W does not add. Furthermore, in view of availability in a market of sintering powder, it is not economical to add W in an amount larger than an amount (7wt%) of W added to a conventional Mo-type high-speed steel.

When a ferrous sintered sliding material is used in a floating seal, in order to improve abrasion resistance and seizing resistance, NC-type carbide is preferably dispersed in a large volume (5 to 15& by volume), and a total content of carbides is preferably increased up to to 50% by volume. ConsequefltiallYi the present invention develops a double layered sintered sliding material to which a high hard ferrous sintered sliding material is sintering-bonded, in which the ferrous sintered sliding material contains at least carbon of 1.3 to 3wt%, Cr of 1 to Swt%, V of 3 to l2wt%, Mo of lOwt% or more and Mo and W of 10 to 23wt% and has a structure in which martensite phase, having a solid soluble carbon concentration of 0.2 to 0.45wt%, contains M6C-type carbide in a content of 15 to 35% by volume and MC-type carbide in a content of 5 to]% by volume (a total content of the carbides i 20 to 40% by volume) dispersed therein. Further, the ferrous sintered sliding material contains alloy elements such as Si, Mn, Ni, P, S, B, N, Ti, Co, Cu and 1.

/s described above, a double layered sintered sliding material to which a ferrous sintered sliding material comprising Mo and W mainly is jntering_b0fld is not more economical than a ferrous sintered sliding material in which Cr-,C3-type carbide is dispersed mainly.

Pccordingly, the present invention develops a double layered sintered sliding material in which a ferrous sintered sliding material is sintering_bondedi to a high hard ferrous back metal, in which the ferrous sintered sliding material contains at least carbon of 0.8 to 3.4wt%, Cr of 9 to 28wt%, Mo of Swt% or more, Mo and W of 5 to l8wt% and V of 5wt% or more and has a structure in which martensite phase, having a solid soluble carbon concentration of 0.2 to 0..45wt%, contains CrC3-tYPe carbide, excellent in abrasion resistance, in a content of S to 25% by volume, MC-type carbide in a content of 5% or less by volume and M6C-type carbide, excellent in seizing resistance, in a content of 5 to 25% by volume dispersed therein with a total content of the carbides being 10 to 40% by volume-Further, the ferrous sintered sliding material contains one or more elements of Si, Mn, Ni, P, S, B, N, Ti, Cu, Co and IA1 if necessarY-In a ferrous sintered sliding material for floating seal, Cr7C3-tyPe carbide in a content of 10 to 25% by volume, MC-type carbide in a content of 0.5 to 5% by volume and M6C-type carbide, excellent fl seizing resistance, in a content of 10 to 20% by volume are dispersed with a total content of the carbideS being 20 to 40% by volume-Such ferrous sintered sliding material preferably contains at least carbon of 1.34 to 3.4wt%, Cr of 11 to 28wt%, Mo of 8wt% or more, Mo and of 8 to l6wt% and V of 1 to 5wt%-In a ferrous sintered sliding material for a thrust bearing, Cr,C3tYPe carbide in a content of 5 to 10% by volume, MC-tYPe carbide in a content of 0.5 to 5% by volume and M6C-tyPe carbide, excellent in seizing resistance, in a content of 5 to 10% by volume are dispersed with a total content of the carbides being 10 to 20% by volume-Such ferrous sintered sliding material preferably contains at least carbon of 0.8 to 2.Owt%, Cr of 9 to 2Owt%, Mo of 4.5wt% or more, Mo and W of 4.5 to l2wt% and V of 1 to 4wt%.

In a ferrous sintered sliding material which contains Cr7C3-type carbide and M6C-tYPe carbide and comprises martensite phase having a solid soluble carbon concentration of 0.2 to 0.45wt%, a suitable concentration (Cwt%) of carbon contained therein preferably approximatelY satisfies the following equation using KCr61: 0.043x(Mo(wt%)40.5XW(Wt%))+285 1t6.S) Carbon (wt%) O.O38X(Mo(Wt%)+O.5XW(Wt%))+0.33+2x085tt)6) More correctly, a suitable concentration range of carbon of a ferrous sntered sliding materiai is shown in the following equation: o. 2x (l-fCriC3-fM6C-fMC)+8. 7xfCr7C3+2. 65xfM6C+14XfMC Carbon(wt%) 0.45x(l_fCr7Cr.fM6 fMC) +8. 7xfCr7C3fCM6CXfM6C+14M An addition amount of each alloy element is preferably obtained by calculation using the aforesaid equations.

In the present invention, each addition amount of Cr, Mo, W and V can be calculated using the aforesaid method by setting an amount of each carbide of adequate fCr7C3, fM6C and fMC within each range of CrMar of 6.5 to l2wt%, MoMar+WMar of 2 to 4wt% and V of 0 to 0.6wt%.

In view of availabilitY of raw powder of a ferrous sintered sliding material and economical efficiency, the raw powders are preferably used mixed at a specified mixing ratio. 1\nd, when Cr, Mo, W and V powder or high alloy powder are added to a base alloy steel powder of a ferrous sintered sliding material for preparation of a composition of the material, Cr7C3-tyPe carbide, M6C-tYPe carbide and MC-type carbide, which are coarsened to an average grain size of 40tm or more, can be easily precipitated. In order to improve abrasion reslStaflce and seizinci resistance, one or more such coarse carhides are preferably precipitated and dispersed in a content of 3% or more by volume.

In order to improve abrasion resistance and toughness of the ferrous sintered sliding material, double layered sintered s'iding material in which a ferrous sintered sliding material is sintering_b0 to a high hard ferrous back metal is developed, in which the ferrous sintered sliding material contains at least carbon of 0.8 to 3.4wt%, Cr of 9 to 28wt%, Mo of 5wt% or more, Mo and w of 5 to l8wt% and V of 0 to 5wt% and has a structure in which martensite phase, having a solid soluble carbon concentration of 0.2 to 0.45wt%, contains Cr,C3-type carbide in a content of 5 to 25% by volume, M6C-type carbide in a content of 5 to 25% by volume and MC-type carbide in a content of 0 to 5% by volume dispersed andprecipitated therein with a total content of the carbides being 10 to 40% by volume. Further, the ferrous sintered sliding material containS one or more elements of Si, Mn, Ni, P, S, B, N, Ti, Cu, Co and Al if necessary.

And, in order to improve abrasion resistance of a ferrous sintered sliding material further so as to be used in a floating seal, the ferrous sintered sliding material preferably contains at least carbon of 1.34 to 3.4wt%, Cr of 11 to 28wt%, Mo of 8Wt% or more, Mo and W of 8 to l6wt% and V of 1 to 5wt% so as to contain Cr7C3- type carbide in a content of 10 to 25% by volume, MC- type carbide in a content of 0.5 to 5% by volume and M6C-type carbide, excellent in seizing resistance, in a content of I0 to 20% by volume dispersed therein with a total content of the carbideS being 20 to 40% by volume.

And, for a ferrous sintered sliding material suitable used for a thrust bearing, the ferrous si.ntered sliding material preferably contains at least carbon of 0.8 to 2wt%, Cr of 9 to 2Owt%, Mo of 4.Swt% or more, Mo and W of 4.5 to l2wt% and V of 1 to 4wt% so as to contain Cr7C3-type carbide in a content of 5 to 10% by volume, MC-type carbide in a content of 0.5 to 5% by volume and M6C-type carbide, excellent in seizing resistance, in a content of 5 to 10% by volume dispersed therein with a total content of the carbideS being 10 to 20% by volume, In order to improve abrasion resistance of the ferrous sintered sliding material further, a double layered sintered sliding material in which a ferrous sintered sliding material is sinteringbonded to a high hard ferrous back metal is developed, in which the ferrous sintered sliding material contains at least carbon of 1.5 to 3.2wt%, Cr of 7 to 25wt%, Mo of 3.5wt% or more, Mo and W of 5 to l5wt% and V of 3 to 8wt% and has a structure in which rnartensite phase, having a solid soluble carbon concentration of 0.2 to O.45wt%, contains Cr7C3-type carbide in a content of S to 20% by volume; M5C-type carbide in a content of 5 to 20% by volume and MC-type carbide in a content of 5 to 15% by volume dispersed and precipitated therein with a total content of the carhides being 15 to 50% by volume.

Further, the ferrous sintered sliding material contains one or more elements of Si, Mn, Ni, P, S, B, N, Ti, Cu, Co and /U f necessary. In addition, in order to improve toughness, a total amount of the carbide is preferablY adjusted to 15 to 35% by volume.

Ni, Mn and Cu contained in the ferrous sintered sliding material are austenite stabilized elements, described above, and therefore effective Ofl lowering quenching temperatures1 and also increases sintering ability. In addition, theses elements form retained austenite phase in a ferrous sintered sliding material and therefore improve conformability of a sliding surface thereof thereby to suppress occurrence of heat crack and to improve seizing resistance. However, excess addition of such elements increases retained austefl3.te, resulting in deterioration in abrasion resistance. So, Ni is added in an amount of 1 to Swt% because it IS expensive. Mn is added in an amount of 1 to 2wt% because it easily blocks sinteriflg ability-And, Cu is added fl an amount of 0 to lOwt% for improving sintering ability.

And, when Ni coexists with Al or Mo, age_hardening ability is demonstrated by tempering. In addition, when Cu is added coexistent with Ni, the age_hardening ability is promoted. So, such elements are positively added, preferably.

And, an addition of Co in an amount of 2 to l2wt% moves magnetic transformation temperatures f martensite parent phase to higher so as to increase tempering softening resistance of the martensite phase-And, an addition of Si in an amount of 0.5 rj 3.5wc% or an addition of Al in an amount of 0.2 to 2.Owt% increases tempering_softening resistance of martensite phase.

However, since Si decreases resistance demonstrated by Mo, W and V, Si is preferably added in an amount of l.5wt% or less.

Specifically a ferrous sintered 5lidi.ng material preferably contains one or more elements selected from the group consisting of Ni of 1 to 5wt%, Mn of 1 to 2wt%, Co of 2 to l2wt% and Al of 0.2 to 1.5wt%.

In a double layered sintered sliding member in which a ferrous sintered sliding material is sinteriflg bonded to a high hard ferrous back metal, the ferrous sintered sliding material is preferably densified to have a relative density of at least 95% or more so as to prevent leakage of gas or oil and also hardened after quenching to have a hardness of HRCS5 or more.

Preferably, the ferrous sintered sliding material is tightly combined to the back metal. So, a double layered sintering sliding member to which a ferrous sintered sliding material is sjntering-bonded is developed, in which the ferrous sintered sliding material contains one or more compounds selected from the group nsisting of Fe3P, Cr2P FeMCP, V2P and FeTiP dispersed therein in a content of 10% or less by volume by adding one or more elements of p of 0.1 to 1.Swt% and B of 0.01 to O.2wt%, in which such elements produce a sufficient amount of liquid phase component at the 5jtering_b0flthng.

1\n addition of P is effective 011 improvement in densificatiOn of the ferrous sintered sliding material and sintering-bondin9 ability. So, the lower limit of addition amount of p is set to 0.lwt% at which improvement in sintering ability is demonstrated clearly. When P is added in an amount of 0.5wt% or more, phosphide such as Cr2P, FeM0P, V2P and FeTiP is precipitated and dispersed thereby to improve seizing resistance. However, excess addition of P embrittles the material. So, the upper limit of addition amount of P is set to l.5wt%.

And, as with P, an addition of B is effective On improvement in densification of the ferrous sintered sliding material and sintering-bonding ability. However, an addition of B in an amount of 0.2wt% or more embrittles the material easily. So, an adequate additiOfl range of B is set to 0.01 to 0.2wt%.

In order to improve 5jntering_bondiflg abilitY and heat crack resistance, a double layered sintered sliding member is developed, in which the ferrous sintered sliding material contains soft Cu based alloy phase dispersed therein in granular form in a content of 1 to 10% by volume so as t increase conformabilitY of a sliding surface thereof and form local oil pockets easily.

In order to improve sliding performaflCe the Cu based alloy preferably contains one or more elements of Sn, Al, Si, F', Fe, Ni and Ti in a total amount of 5 to l5wt%.

And, a double layered sintered sliding material improved in seizing resistance of a ferrous sintered sliding material is developed, in which the ferrous sintered sliding material contains at least one of Mo metal particles, w metal particles and graphite particles dispersed therein a content of 1 to 10% by volume and the dispersed particles are surrounded with the Cu or the Cu alloy phase so as to demonstrate solid lubricating performance inherent in Mo and W. The reason that at least either one of Mo or W coexists with Cu particles or Cu alloy particles is for preventing at least either one of Mo or W from being reacted with a ferrous sintered sliding material at siritering-bonding. In which case, the ferrous sintered sliding material is preferably prepared such that Cu element is adjusted to an approximate saturation-When such element will be partially reacted with a ferrous sintered sliding material, at least one carbide of M6C type carbide, Mo2C-type carbide and MC-type carbide (WC) is selected for improvement in abrasion resistance.

Furthermore, a double layered sintered sliding member to which a ferrous sintered sliding material is tightly sintering-bonded is developed, in which the ferrous sintered siichng material is formed with closed pores having an average diameter of 0.03 to 3riiui scattered in a sliding surface thereof in a content Of 1 to 10% by volume so as to improve lubricating ability of the sliding surface-The lower limit of content of the pores is set to 1% by volume at which the pores begin to work as oil pockets effectively. Since a large content of the pores embrittles the ferrous sintered sliding material, the upper limit of volume of the pores is set to 10% by volume. In view of a content of pores formed on a sliding surface of an oil retaining bearing, a content of pores is preferably adjusted to 3 to 10% by volume. Pn average size of the pores is adjusted * 69 depending Ofl application of the double_laYered sintered sliding member. For example, in the double layered floating seal, an average size of pores are adjusted to about 1/2 of the width of the sealing surface, preferably 1mm or less, more preferably 0.5mm or less.

One method for forming the closed pores having the aforesaid average size is follows: SjO2, Ni oxide particles, Co oxide particles, Cu oxide partiCleS Fe oxide particles1 Mo oxide particles and W oxide io particles (empty particle and granular particle are possible) having an suitable size are mixed to a raw powder of the ferrous sintered sliding material in. an suitable amount and then formed. Then, such oxide particles are carbothermicallY reduced at sinteriflg and residual components forms a solid solution in the ferrous sintered sliding material, resulting in forming pores easily. AlternativelY, SIC, Cu and resin having an average diameter of 0.1 to 1mm are mixed to a raw powder of the ferrous sintered sliding material and formed. And then, such SiC, Cu and resin are allowed to form a solid solution or to disappear fl the ferrous sintered sliding material at sintering, resulting in forming pores. Si02, Cu and resin are material easy to be worked into short fibers. The pores may be formed by using such short fibers. In this case, it is necessary that the pores be perfectly closed.

Dispersing the closed pores causes increasing cost of production. And, it is diffiCult to scatter the pores uniformly owing to segregation, resulting in oweriflg strength of the ferrous sintered sliding material.

consequentially1 a double layered sintered sliding member to which a ferrous sintered sliding material is sintering-boded is developed, in which the ferrous sintered sliding material is formed with concave oil pockets on at least sliding surfaces thereof ifl an area ratio of 3 to 10%. In the double layered f1oati1g seal, the concave oil pocket preferably has a size of about 1/2 or less of a seal width, or 1mm or less in the width direction (a width direction of the seal surface), more preferably.O.Smm or less, for preventing oil leakage.

And, for forming carbide, Zr, Nb, Hf, Ta, Ca, S and N may be added in a necessary amount.

The ferrous sintered sliding material used is gas quenched at a quenching temperature of 1100 C or less, more preferably 900 to 1000 C, lowered down from sintering-bonding temperatures. In order to. recover toughness and fJ.exural strength of martensite phase1 the martensite is preferably tempered at 150 to 600 C to turn tempered martensite phase.

In a case of a floating seal, when the ferrous sintered sliding material is tempered at high temperatures of 550 to 580 C thereby to be hardened by secondary hardening to have a hardness of HRC65 or more, initial conformability of a sliding surface thereof is bad and therefore initial oil leakage is easy to occur.

So, in the present invention, it is preferable to set the upper limit of tempering temperature to 500 C or less. Accordingly, in the present invention, an after mentioned method for producing a ferrous sintered sliding material is preferable from an economical viewpoint. After sintering-bondifl9, the double-layered sintered sliding material is maintained in a furnace at a temperature lowered down to 900 to 1100 C and then gas-cooled so as to form martensite phase. And then, the double-layered sintered sliding material is tempered at to 500 C once.

Asan amount of carbide in the ferrous sintered sliding material increases to 5% or more by volume, abrasion resistance and seizing resistance of the ferrous sintered sliding material are improved. However, increasing the amount of carbide necessarily results in decrease of strength and toughness of the material.

Especially, in a case of a thrust bearing easy to be applied with an offset load, sufficient flexural strength and maximum flexural amount thereof are required. Specifically1 it is required to have flexural strength of 400MPa or more (breaking strength of a bonded surface; 200MPa or more) and maximum flexural amount of 0.4mm or more at the breaking. Accordingly, a total amount of the carbides in the ferrous sintered sliding material is adjusted to 30% or less by volume.

And, the quenched ferrous sintered sliding material is preferably tempered at 100 to 600 C once. In addition, from an economical viewpoint, a total amount of the carbides in the ferrous sintered sliding material is adjusted to 20% or less by volume.

1" quenching treatment of the ferrous sintered sliding material after 5jnteringboflding is performed as below: after lowering temperature down to 1100 C or less, or 900 to iooo c after 5jntering_bondg and mainta1fli9 the temperature, the ferrous sintered sliding material is quenched by gas-cooling to be hardened suffiCiently.

In such a case, the ferrous back metal preferably has a mixed composition ot errite, perlite1 baiflite and martensite phase so as to prevent quenching crack and peeling of the ferrous sintered sliding material which is sintering-bonded to the back metal-And, the ferrous sintered sliding material preferablY contains Cr7C3-typre carbide, M6C-type carbide and Mc-type carbide dispersed therein in a total content of 5 to 25% by volume.

However, when a counterpart to the ferroUS sintered sliding material is made of a carburiZing quenched material or an induction quenching material, in view of damage of the counterpart, t is more preferable to disperse the carbides in a total content of 5 to 15% by volume. And, in a case of a thrust bearing provided with a collar at one end of a cylindrical back metal, the cylindrical back metal is necessarily forced into a body of a working machine and tightly mounted thereto.

Accordingly, the back metal preferably has Vickers hardness of at least Hvl7O or more. And, in order for the back metal to have yield stress withstanding the lower limit of flexural strength of the ferrous sintered sliding material, the back metal is preferably formed by a steel hardened to}-1v240 or more. And, when the ferrous sintered sliding material is formed with at least either one of closed pores or recesses in a sliding surface thereof in an area ratio of 1 to 10%, more preferably 3 to 10%, the closed pores or the recesses work as oil pockets (a portion in which lubricant is pooled) on the sliding surface so as to improve heat crack resistance.

In a case of a thrust bearing provided with a collar at one end of a cylindrical back metal, improving seizing resistance and heat crack resistance of a thrust surface thereof can extend a grease_iubriCatifl interval to 500 hours or more. Accordingly, maintenance work of the thrust bearing is easier than that of conventionally used thrust bearings produced by an induction quenching method or a carburizing quenching method. And, since a cylindrical bushing (a bearing) is combined to an inner surface of the cylindrical back metal, it is necessary to extend a lubricating interval of the cylindrical bushing. So, a double layered sintered sliding material in which a cylindrical bushing is sjntering-bonded and combined to an inner surface of a cylindrical back metal is developed, in which the cylindrical bushing is made of a permeable copper based or ferrous porOuS sintered sliding material which retains lubricating oil or lubricating compbund of lubricating oil and wax filled in the pores. The porous sintered sliding material is not limited thereto and another porouS sintered sliding material other than the copper based or the ferrous material may be used.

1s with a thrust bearing, a buShiflY (a lindrical 0 bearing) equipped for a construction machine is used applied with an offset load. So, tile copper based or the ferrous porous sintered sliding material etaiflirg lubricating oil therein does not show sufficient seizing resistance and abrasion resistance. consequet1t1auiy1 a double layered sintered bushing iS developed, in hich the double layered sintered bushing is formed such that the ferrous sintered sliding material for aforesaid thrust bearing is jering_boflded and combined to an inner surface of a cylindrical ferrous back metal.

For a method for combining the ferrous sintered sliding material to the inner surface of the cylindrical ferrous back metal, a method for forcing and shrinkage fitting the ferrous sintered sliding material or a method for 5jntering-bondiflg simultaneously with being sintered is preferable. In a method for sinteriflg bonding simultaneously with being sintered, the ferrous sintered sliding material preferably contains one or more elements of Al, Cu, Sn, Ti and P. /-\s an amount of carbide in the ferrous sintered sliding material increases up to 5% or more by volume, abrasion resistance and seizing resistance thereof are improved. When the ferrous sintered sliding material is used in a floating seal for an oil seal device equipped for a reduction gear and a tracker roller Of a construction machine, it is necessary to have sufficient abrasion resistance against sand or gravel and sufficiently improved seizing resistance. Accordingly, B total content of the carbides in the ferrous sntered sliding raterial is preferably set to 20 to 40% by volume, more preferably 25 to 40% by volume.

(Example 1)

(Equilibrium Composition of Ferrous Sintered Sliding Material after Sintering) In this example, four kinds of mixed alloy powder (A to D), as shown in Table 1, were prepared in such a manner that Fe-0.

3wt%Mo-l.2wt%V alloy powder and Fe_0.6Wt%carb0 O.3wt%Si_O.35wt%Mn_9wt%Cr_6Wt%M0_4wt%t2wt%\l alloy powder and Fe_O.6wt%carbon0.31t%51_4.5wtt_S1t%M0 Gwt%W-2wt%V alloy powder were used mainly and each powder of Ni, Co. Si, FeA1 and FeP each having a grain size under 350 mesh and graphite powder having an average grain size of 6tm or less were mixed thereto.

Then, each of the prepared mixed alloy powders to which paraffin wax of 3wt% was added was press-formed at a pressure of 1.Oton/cm2 to prepared compacts each having a composition A, B, C and D. Next, the compacts having compositions A and B were vacuum sintered at 1190 C for two hours, the compact having a composition C was vacuum sintered at 1135 C for two hours, and the compact having a composition D was vacuum sintered at 1230 C for two hours. Then, after cooling in the furnace down to 1000 C and maintained for one hour, the compacts were cooling quenched under nitrogen gas atmosphere at a pressure of 400torr, and then abrasive machining was applied to a cut surface of each corpact. The cut surface of each compact was analyzed by using an X-ray micro analyzer (EPMA) so as to obtain each concentration of alloy elements contained in martensite parent phase and contained in carbide precipitated in the martensite parent phase. The analysis is shown in Table 2.

Table 1

C Si Al [Mn Cr Mo V W Ni Co p A 3 0.6 0.7 0.4 15 3 1.3 -2 3 0.25 B 3 0.6 -0.4 15 3 1.5 -4 -0.25 C 3 0.6 -0.2 9 6 2 4 4 -0.3 D 3 0.3 -0.3 4.5 5 2 6 --0.5

Table 2

L No. PHASE, K I C Si Al Cr Mo V W Ni Co J tfARENT PHASE 0.4 0.8 0.9 6.2 2.1 0.27 2.1 4 1 I PM15Cr3MO3COI A M7C3 8.45 0.04 0.02 40 4.9 4.7 0.2 L KM7 0.05 0.02 6.45 2.33 17,41 0.10 O.23J [ARENT PHASE 0.43 0.86 7. 12 2.16 0.34 5.2 PM15Cr3MO4Ni B L M7C3 8.42 0.03 39.9 4.96 4.67 0.36 [ KM7 ____________ 5J 2.30 13.74 0.07 PARENT PHASE 0.44 0.85 4.2L1 1.52 0.37 1.23 5.33 4.96 M7C3 7.61 0.04 277 3.72 6.79 3.61 Q,49 1.2 PM9Cr6MO4W C KM7 0.05 6.49 2.45 18.35 2J 0.09 0.24 I M6C 1.85 2.02 4.08 30.3 2.1 28.4 2.11 2.46 I KM6 2.38 1T 19.93 5.68 23,09 0.40 0.50 PARENT pHASE 0.25 1.34 0.41 1.57 M6C 0.6 1L2J 2.55 36.3 PM4Cr5MO6W2'' D ___ KM6 2.40 0.91 19.93 6.22 23.12 ______ I MC ____ 0.01 14.7 5.02 46.1 14,4 __________ L KMM/C 0.04 5.35.75 112.4 9.17 The sintered a1loy A and B are alloys in which Co of 3wt% and Ni of 2wt% or 4wt%, respectivelYi are added to a l5Cr-3Mo based alloy enriched with Cr so that Cr1C3-type carbide comes to equilibrium with marteflSite phase (parent phase). The sintered alloy C is an alloy in which Cr, Mo and W are contained in an increased amount so that Cr7C3type carbide and M6C-type carbide come to equilibrium with martensite parent phase. The sintered alloy D is an alloy in which M6C-type carbide and a small amount of MC-type carbide come to equilibrium w)th martensite parent phase.

In Table 2, columns of parent phase, M7C3 and ME,C show concent.ratioflS of alloy elements contained in the parent phase and each carbide. And, KM7 shows a distribution coefficient, of an alloy element M between Cr7C3-type carbide and the parent phase (an amount (wt%) of the alloy element in the Cr7C3-tYpe carbide I an amount (wt%) of the alloy element in the parent phase), KM6 shows a distribution coefficient of an alloy element M between M6C-type carbide and the parent phase (an amount (wt%) of the alloy element in the M6C-tyPe carbide I an amount (wt%) of the alloy element in the parent phase), and KMMIC shows a distributiOn coefficient of an alloy element M between MC-type carbide and the parent phase (an amount (wt%) of the alloy element in the MC-type carbide /.an amount (.wt%) of the alloy element ifl the parent phase) . Comparison of such distribUti01 coefficients of each alloy element shows characterjst of each alloy element.

Fig.13 is a graph showing a relation between concentrations of alloy elements contained in cr,C3type carbide and concentrations of alloy elements contained in a parent phase which comes to equilibrium with the Cr7C3-tyPe carbide. And, Fig.l4 is a graph showing a relation between concentrations of an alloy element contained in M6C-type carbide and concentrations of alloy io elements contained in a parent phase which comes to equilibrium with the M6C type carbide. Fig.13 and Fig.14 show that each of the alloy elements is distributed at an almost fixed ratio tIerebetWeefl and distribution coefficients of the alloy elements are invariable regardlesS of composition of the ferrous sintered sliding materials-

Table 3

DISTRIBUTION. I COEFFICIENT Si Cr Mo W V Ni Co P KM7 0 8 2.5 2.5 13 0.1 0.23 0 KM6 2.3 0.95 20 23 5.7 0.4 0.5 2 KMM/C 0 3.8 3 8.2 119 0.05 0.05 0 Table 3 shows distribution coefficients of each alloy element between each of Cr-,C3-type carbide, M6C-type carbide and MC-type carbide, which are used in the present invention, and austenite phase (martenSite phase after quenching). By means of such distribUti l coefficients of the alloy elements, the following facts are shown quantitatively.

(1) Si and /1 does not form a solid solution with M7C3-type carbide; almost all of Si and Pd concentrate in martensite parent phase, enhancing mpering_50ftefh resistance of the martenSite phase.

(2) v concentrates in M-C3-type carbide in a larger amount than Cr, Mo and W and causes Cr,C3-tYPe carbide to have a fine-grained structure. 1\nd, V hardly concentrates in M6C-type carbide. In a steel comprising M6C-type carbide and martensite phase, V is easily precipitated as MC-type carbide and therefore improves tempering.softeniflg resistance of martensite phase.

(3) Mo and W concentrate in M6C-tYP carbide more densely than M7C3-type carbide.

(4) Cr remarkably concentrates in Cr,C3tYPe carbide; it hardly concentrates in M6C-tyP carbide.

(5) Ni. and Co concentrate in a martensite parent phase more than each carbide.

And, using the distribution coefficients allows determining suitable concentrati015 of carbon and each alloy element in martensite phase in the present invention-And, by setting types and amounts of carbicles dispersed therein, a suitable compoSitiofl of a ferrous sintered sliding material can be obtained.

On the basis of distribution coefficients of the alloy elements, a compositiOn of martensite and a content of carbide a typical SKD work steel or SKH work steel quenched from a typical quenching temperature can be analyzed from a compositiOn of the steel. Table 4 shows a composition of the martensite phase of each io quenched steel and a content of carbide dispersed in the steel. As shown in Table 4, the SKD steels (SKO1, SKD2, SKD11, 07 and SKD12, a quenching temperature; 950 tO 1000 C) have martenSite parent phase prepared to contain Cr of 4.5 to 7wt% and carbon of 0.65 to 0.9wt% so as to have a structure in which the martensite parent phase contains Cr7C3-type carbide in a content of 8 to 18% by volume and MC-type carbide in a content of 7% or less by volume dispersed therein. Since a solid soluble carbon concentration of the martensite parent phase iS high, heat crack resistance of the steel is insufficient compared with hot work tool steels (for example, SKD7, SKD6, Si<061 and 5KD62) excellent in heat crack resistance. And also, in SKH steels (SKI-12, SKH9), since a solid soluble carbon concentration of the martenSite phase is high as 0.5 to 0.55wt%, sufficient heat crack resistance cannot be achieved.

TabIe4 ________________________ STEEL I I C I Si Mn I Cr Mo w I CARBIDE (% SY VOLUME) V Co Cr703 M6C MC SKD1 STEEL 2.1 0.35 0.52 12.9 18% ________________ 950 C rPARENT PHASE 0.7 0.43 5.5 I _________ SKD2ISTEEL 208 032 053 12.7 2.7 17% 950 C PARENT PHASE 0.7 0.4 5.5 2.1 _______ SKDllSTEEL 1,46 0.37 0.44 11.8 0.95 0.31 3.48 10% 1000 C[ARENT PHASE 0.65 7 0.8 0.31 3.8 07 ISTEEL 2.25 0.31 0.41 12.4 1.07 4 8% 7% 1000 CRENT PHASE 0.7 0.4 6.3 0.82 0.33 SKDI2 STEEL 0.99 0.29 0.68 4.7 0.89 I 0.39 0% 10000 PARENT PHASE 0.9 0.3 4.5 0.89 0.28 SKD61 STEEL 0.38 1.02 0.36 4.8 1.2 0. 89 0% 1030 C PARENT PHASE 0.38 1 4.8 1.2 0.89 SKD62 STEEL 0.37 1.01 0.36 4.9 1.11 1.09 0.34 0% 1 17% 1030 C PARENT PHASE 0.37 1.01 0.36 4.9 1.11 1.09 0.34 1 SKH2 STEEL 0.73 0.2 0.41 4.21 18.6 1 1260eC PARENT PHASE 0.55 016 43 0 8.4 0.6 SKH9 STEEL 0.89 0.26 4.49 4.73 6.72 2.5 1220 C PARENT PHASE 0.5 0.21 4.5 2.3k 3 1.1 10% 1.30 / NOTE) Cr7C3tYPC Carbide: 8.5wt%C, (Fe. Mo)6CtYPe Carbide2.7It%O (Fe.W)6C,17C MGtyPe Carbde.14Wt%C In high-carbon and high-Cr based work steels such as SKDI, SKD2 and SKD11 quenched in a standard manner, Cr7C3-type carbide is dispersed and precipitated in martensite phase, which forms a solid solution with carbon of 0.5 to 0.7wt%, in a content of 10 to 15% by volume. Therefore, heat crack resistance thereof IS not sufficient because of the martenSite having a high carbon concentration. Thus, in view of a phase diagram of a Fe-C-Cr ternary alloy at 900 to 1000 C (Fig.15' described later), which are adequate quenching temperatures of SKD steels, and an equilibrium relation (constant carbon activity) in the phase diagram, in this embodiment, a sintered sliding member to which a ferrous sintered sliding body is sinteringb0nd is prefetredi in which the ferrous sintered sliding body contains at least carbon of 0.9 to 3.Bwt%, Cr of 9 to 35wt% and V of 0 to 3wt% so that martensite phase, having a solid soluble carbon concentration of 0.2 to 0.45wt%, a solid soluble Cr concentration of 6.5 to l2wt% and a solid soluble V concentration of 0 to 0.6wt%, contains Cr7C3 type carbide in a content of 5 to 40% by volume and MC type carbide in a content of 0 to 5% by volume dispersed therein with a total content of the carbides being 5 to 40% by volume. In addition, amounts of Cr, V and carbofl to added to the sintered sliding body are adlusted SO that the following equation is satisfied: 0.l43xCr(Wt%) 1.41+14XMCtYPe carbide (volume fraction) Carbofl(t%) 0.156xCr(wt%)0.58+14xMC-tYPe carbide (volume fraction) Further, the ferrous sintered sliding body contains one or more elements selected from the group consisting of Si, Mn, Ni, P, s, B, N, Mo, W, Ti, Co, Cu and Al if necessary. Alternatively, an addition amount of carbon may be adjusted so that the following equation is satisfied: O.l43xCr(Wt%)_l.4l+0.151(wt4XMCt1 carbide (volume fraction) Carbon(t%) 0.156xCr(Wt%)- 0.58+O.l5xSi(wt)+14xMC-type carbide (volume fraction), in exchange for adjusting addition amounts of Cr, V and carbon for satisfyingthe following equation: 0.l43xCr(wt%)_1.41+14XMC-tYPe carbide (iolume fractiofl) Carbon(t%)0.l56XCr(Wt%)_0.58 l4)<Mtype carbide (volume fraction) Accordingly, in order to demonstrate abrasion resistance equal to or more than that of SKD work steels, it is preferable tO disperse carbide (for example, Cr7C3-type carbide) in a content of 10% or more by volume. For the purpose, a ferrous sintered sliding material preferably contains carbon of 1.05 to 3.8wt% and Cr of 12 to 35wt%. In order to improve abrasion resistance further, it is preferable to contain carbon of 1.45 to 3.8wt% and Cr of 14 to 35wt% so as to disperse Cr7C3-type carbide in a content of 15% or more by volume. When a ferrous sintered sliding material is used in a floating seal, an adequate wear life is required. So, it is preferable to contain carbon of 1.85 to 3.Bwt% and Cr of 16.5 to 35wt% so as to disperse Cr7C3-type carbide in a content of 20% or more by volume.

The upper limit of an amount of Cr to be added to a ferrous sintered sliding material is determined such that the upper limit of content of Cr-C3-tyPe carbide to be dispersed is preferably 40% by volume in view Of sufficient abrasion resistance and strength and economical efficiency.

In order to produce a ferrous sintered sliding material excellent in heat crack resistance equal to that of hot work steels, at least, rnartefl5]te phase preferably has a solid soluble carbon concentratiohl.0f 0.4Swt% or less, more preferably O.3Swt% or less. So, in order to increase heat crack resistance, the upper limit of solid soluble carbon concentration in martensite phase is preferably adjusted to 0.35wt%. For adjusting a solid soluble carbon concentration to 0.35wt%, the upper limit of addition amount of carbon is shown by the following equation: Carbon(wt%) 0.l56XCr(Wt%)0.684x MC-type carbide (volume fraction) Such fact corresponds to a fact that carbon steel or alloy steel having a solid soluble carbon concentration of 0.Swt% or less is selected for an induction quenching method in which quenching crack may be troubling issue.

In a ferrous sintered sliding material comprising Cr-,C3-type carbide and martensite phase mainly in a case in which quenching temperature after sintering-bofldfl9 is set to 900 to 1000 C, in order to adjust a solid soluble carbon concentration in martensite phase to 0.2 to 0.45wt%, an adequate amount (wt%) of carbon to an amount of Cr in a ferrous sintered sliding rnater3al, which is shown in a range between Tie-Lines A and B in a phase diagram of a Fe-C-Cr ternary alloy at 900 C (Fig.15), is shown by the following equation: O.i43xCr(wt%)_1.41Carb0fl(wt%)056ttOS8 In Fig.15, compositions for dispersflq Cr-C-tYPe carbide in a content of 10, 20, 30 and 40% by volume are represented by broken lines. For dispersing CrC3-tYPe carbide in a content of 10% by volume, Cr(wt%) lOwt%1 and for dispersing Cr7C3-type carbide in a content of 40% or less by volume, Cr(wt%)35Wt%.

As described in Japanese Patent J\ppiicatiohl No.2002-380203 proposed by the inventors, increaSifl9 tempering-softening resistance of inartensite phase remarkably improves seizing resistance and abrasion resistance of a sliding surface exposed to sand or gravel under a lubricating boundary condition. And, it is preferable to maintain hardness of HRC5O or more, more preferably HRC55 or more, even if tempered at 600 C.

In addition, alloy compositions are preferably designed in such a manner that concentration of each alloy element which form a solid solution witn rnartensite phase having a solid soluble carbon concentration Of 0.15 to O.4Swt% are applied to the aforesaid equation for obtaining tempering_softening parameter AIIRC.

In view of Fig.16 (a phase diagram of a Fe-C-Mo S ternary alloy), a maximum Mo solid solubility at which Fe6C or Mo6C-type carbide is hardly dispersed and precipitated is about 4wt% (at 900, 1000 C) . And, fl view of Mo concentrated in Cr,C3-type carbide dispersed in a content of 10 to 40% by volume, a suitable addition amount of Mo is 0.6 to 6.Swt%.

In view of Fig.17 (a phase diagram of a Fe-C--W ternary alloy) , the same discussion as the above descriptipn is applied to W. As a result, an amounL Of eacri of Mo and W added to a ferrous abrasion resist:aflt sliding material is 0.6 to 7wt%. EspeCiaUY from an economical standpoint, a maximum solid soluble amount of each of Mo and W with a matrix phase is set to 2.5wt% or less, in which case ternpering_sOftefl11g resistance is efficiently enhanced, so that each addition amount of Mo and W is preferably maintained as small as 4wt% or less.

This is preferred from an economical viewpoint.

Ts described above, since v concentrates in Cr-7C3 type carbide and therefore an amount of V remained in martensite phase decreases remarkablY, it is not preferred as an element which increases temperiflci softening resistance of the martensite phase. However, V works to turn Cr7C3-type carbide into a fine-grain structure. Accordingly, to a ferrous sintered sli.ding material in which rnartensite phase forms a solid solution with V in a rnaxiTnurn amount of 0.5wt%, V is added in an amount of 1.1 to 3.9wt% (Cr7C3-tyPe carbide in a content of 10 to 40% by volume). And, in a ferrous sintered sliding material in which Cr,C3-tyPe carbide is dispersed mainly, it is preferable from an econOm].cal.

viewpoint to maintain an additiO amount of V to 4wt% or less.

In a SKH based sintered sliding material in which I'IC-type carbide, in addition to M6C-type carbide, are dispersed, a solid soluble carbon concentration of martensite phase of the *sintered sliding material Is reported in "J. Japan Inst. Metals" 2 (1963), P56'l, Fig.3, "Carbon ConcentratiOli in Matrix Changed Accompanied with a Solid solution of Carbide". The report recommends that in order to regulate a solid soluble concentration of carbon in the martensite to be 0.4wt% or less easily, a quenching temperature after sintering-bonding is set to the range within 900 to 1100 C, which is lower than quenching temperatures of a conventional SKU high speed steel of 1200 to 1350 C.

Quenching in such lower temperatures is one of the features of the present invention.

Furthermore, the same discussion as the above description of a phase diagram of a Fe-C-Cr ternary alloy is applied to a phase diagram of a Fe-C-MO ternary alloy as shown in Fig.16 and a phase diagram of a Fe-C- W ternary alloy as shown in Fig. 17. In these figures, Tie-lines A and B, which pass O.l5wt% and O.4wt%, respectively, of a solid soluble carbon concentration of martensite phase equilibrium with M6C-type carbide, are represented as mathematical formulas. Comparison the Tie-line of a Fe-CMo ternary alloy with the Tie-line Of a Fe-C-W ternary alloy shows that a gradient of the Tie-line of a Fe-C-W ternary alloy is about half of a gradient of the Tie-line of a Fe-C-Mo ternary alloy, and an amount (wt%) of Mo in the rnartensite phase of the Fe-C-Mo ternary alloy equilibrium with M6C-type carbide is almost equal to an amount (it%) of W in he martensite phase of the Fe-C-W ternary alloy equilibrium with M5C type carbide. So, when Mo is added coexistent with W1 an equilibrium relation between compositions of M6C-type carbide and martensite phase is shown as 0.5xW(wt%)=Mo(wt%) from the phase diagram of a Fe-C-Mo ternary alloy. And, from the mathematical formulas of the Tie-lines A and B, a suitable concentration (Cwt%) of carbon in a ferrous sintered sliding material is simply shown in the following equation: O.043x(Mo(wt%)+0.5xW(wt%)) Carbon(Wt%) 0.038x(Mo(wt%)+O.5xW (wt%))+0.33.

In view of MC-type carbide, it is possible that a content of carbon in a ferrous sintered sliding material (a ferrous sintered sliding body) is within a range shown in the followi.ng equation: O.043(more preferably O.OS)X(MO(Wt%)4.O.5(wt%))1MC type carbide (volume fraction) Carbon(wt%) 0.038x(Mo(wt%)+O.5xW (Wt%)) O.33+l4xMC-type carbide (volume fraction) -Furthermore, in view of Cr7C3-tYPe carbide, it is possible that a content of carbon n a ferrous sintered sliding material (a ferrous sintereci sliding body) is within a range shown in the following equation: O.043x(Mo(Wt%),0.5xw(wt%))-8.5xCr7C3-tYPe carbide (volume f.raction)+14XMC-type carbide (volume fraction) Carbon(wt%) O.O38x(Mo(wt%)+O.5XW(Wt%))+o.33+B7C3 type carbide (volume fraction)+14xMCtYPe carbide - (volume fraction) In view of theses results, it is preferable from an economical viewpoint to add Mo positively with maintaining an addition amount of W as small as possible. And, for the purpose for enhancing sinterability of a ferrous sintered sliding material and tempering-softening resistance of martensite phase thereof, it is preferable to add Mo mainly and W is not necessarily added.

And, it becomes possible to calculate a suitable composition of a ferrous sintered sliding material by setting concentrations of carbon and alloy elements in martensite phase and also amount of M6C-type carbide to be dispersed by means of distribution coefficients KM6 of alloy elements such as Mo, W and Cr-

(Example 2)

(Sinteri.flg Bonding Test of Ferrous sintered sliding Material and Sliding Property thereof) Fig.l8 is a cross sectional view showing a shape of specimen of a thrust bearing with collar and FIgS.19A and 19B show an oscillating tester.

In this example, a thrust bearing with a collar shown in Figl8 was prepared for an 0scillatiflg test using an oscillating tester shown in Fig.19. The oscillating test was performed in such a manner that one pair of.specimenS were contacted with sliding surfaces thereof being faced each other and a rotatiflci axis of one specimen being kept at an oblique angle of 2 with respect to the other specimen. 1nd, the former speClfllen was oscillated around its rotating axis in both directions with applying a load P) in an 05cillati1q cycle, shown in Fig.19B (an abscissa axis: period1 a longitudinal axis: angle), in which an 0ci1lating angle was 120 and an oscillating speed was 2m/min. In this example, each specimen was kept at a biased ntactiflg state (an oblique state) and oscillated being applied with a load, each of which was incremented by iton every 500tirnes oscillation-The heat crack resistance and the seizing resistance were evaluated by using a load when heat crack or seizing occurred-For comparative specimens, thrust bearings made of conventionallY quenched and tempered su32, SKD6, SKD11 and SKH9, and SCM420H steel which was carburiZiflg_qUeflcIed and tempered at 930 C so as to have a surface carbon concentration of 0.8wt%, were prepared.

Each of ferrous sintered sliding bodies shown in Table 5 and Table 6 was sintering-bonded to a collar of S5OC carbon steel at 1130 to 1280 C and then examined in sintering bonding ability thereof using an ultrasonic flaw detection method. No.20 to No.30 ferrous sintered sliding materials shown in Table 5 comprises No.16 alloy steel powder mainly, to which Cu under 41200 mesh, Cu-lOwt%Sn, Fe25wt%P, Cu8w%P, SiC7 milled powder, Si powder under #300 mesh, Cr powder under #300 mesh, Mo, Ni, Co, Si3N, graphite (KS6, manufactured by RONZ) powder, each having an average grain size of 6pm, and Mo/Cu plated particles and graphite/Cu plated particles, each having n average grain size of 0.03 to 0.5mm, were added in

suitable amounts.

------I. I* ----co ci v,co.4wt II-tNJIaIulci oa t) .4 C) C) I) .4 N) () ) Ilflf) Wt(\I r)ItJ r $1) 4 4 N > 0 W 0) 0) 0) cO U) 0) N 0) 0) 0) 0) w I 0) 0) 0) 0) N 0) 0) 0) 1) 0)0)0)0)0) 0) 0)O)C0 m ci

N

-

UI

0 U)')) (-) LI) 0) -------_--------------

F-------------------

z In U) c N C') Nwji -*4.4*tIflIflfl 10

E (U--

W > flU) N x c CD (3 j U) -IflWoflofloU) 0 cjcsjc'jn N N

C

-a--------------U) Z CJ C') N C') N.4 C') C') c C') N C') (J a) ----------. ------- -c - U r) In ID (0 (0.4 4 I-N N N C') N N CS) N N N N I'-N N 0)

CD

00,0o0000oooO0C

-

( OlC'')c')')* C 6o00oD0000N00000OOQO E -) r 4.") 0) N 0) 0 OOOO00000ci00 ci ci ci 000006660006000

Table 6

Composition of Sintered Sliding Material in Example 2 __________ ________________ Cu RATE INGL.OAD VALUE C Si Mn Ni Cr Mo W V Fe25PISi3N4 Cu 1CuiOSn 8P1 SO2 GrICu MoI 18OND!NG WITHSTAND. PV ______ 99% 20 3.9 No.22 O 023 29 45 5.1 62 2 2 -____ _l ______ -______ ______ 99% -24 4.8 No.33 _ _ _ __ No.34 1.20.23Q_.....L. 10 L_L.._..L----1-___I 31 5.6 No.35 1 025 0.31 -4 12 -2 1 ______ 1 ______ ______ I ______ 97% 26 4.9 No.37_ 0.6 0.21 2 1 ___ ___ ___ 1 - ___ No.36 1.7 -I._.__ ____ _____ ______ _____ _____ 1 2.4 No.36 1.5 0.6 I 0.21 0 9 6 + 4 2 --______ 3 -99% -26 _____ ____ C' No 39 1 5 4 2 --I ____ ____ 99% -27 4.8 No.40 I i. I 0.24 0.35 I 2.5 1 45 48 I 99_. 13 2.9

______________ H

SUJ2 I I I I I__..... __ __ ___ 5 ___ SK06 ( I I ___________________________ _________________________________________ I _I 6 1.6 SKO1I I I I I I 8 2.2 SKH9 I I I 4 I 13 CARBURIZED SCM$20H1 FC15Cr3MO I I I 1.8 FC9Cr6MO I I I i\nd, each material, shown in Table 5 and Table 6, to which wax of 3wt% was added were mixiflggran ated at 100 C for 10 minutes using a high-speed mixer. Then, each granulated material was formed on a doughnut_shaPed plate on an upper surface of the thrust bearing with a collar, shown in Fig.18, at a press pressure Of iton/Ctn' and sinteringbonded thereto at the aforesaid jnteriflg temperature using a vacuum incinerator. 1\fter cooling in the incinerator down to 960 C, each compact was cooling quenched with N2 gas at 500torr and then tempered at 200 C for two hours.

Table 5 and Table 6 show 5jntering_b0ng rate and aoads when heat crack or seizing occurs.

No.1 to No.6 alloys are alloys in which P is contained in a large amount of 0.9 to l.6wt% so as to improve sintering ability of a ferrous sintered sliding material and sintering_bonding ability thereof to a steel back metal, and rnartensite phase has a lowered solid soluble carbon concentration and contains MCtype carbide and Si3N4 dispersed and precipitated therein by addition of V. Comparison of the No.1 alloy (a solid soluble carbon concentration; 0.6wt%) with No.2, No4 and No.5 alloys shows that dispersion of MC-tyPe carbide and Si3N4 improves heat crack resistance remarkablY. And, comparison of the No.2 alloy with No.4 and No.5 alloys shows that increasing concentrations of Mo and Cr in rnartensite phase improves resistance and thus heat crack resistance remarkablY.

Furthermore, comparison of the No.1 and No.2 alloys containing phosphor compound, such as Fe3P and V2P dispersed therein, with S1JJ2, SKD6, SKD11, SHH9 and carburizing_qUenching steel shows that dispersing phosphor compound and NC-type carbide and lowering a solid soluble carbon concentration in martensite improve heat crack resistance remarkablY.

In addition, comparison of No.7 to No.23 alloys sho's that the alloys other than No.8, No.10, No.13 and No.16 alloys each having a solid soluble carbon concentration in martensite of 0.5wt% or more are improved in hear crack resistance. And, No.20 and No.21 alloys having increased amount of Cr-,C3-tYCP carbide are improved in heat crack resistance-COrnPar)son No.17 alloy with No.19 alloy shows that an addition of Si decreases a solid soluble carbon concentration in martensite thereby to improve heat crack resistance.

And, in No.14 and No.15 alloys, lowering a solid soluble carbon concentration in martensite phase and jncreasiflg a content of MC-type carbide to be dispersed improve heat crack resistance. In No.22 alloy, dispersing M6C-type carbide by addition of Mo and W improves heat crack resistance. Further, in No.23 alloy, addition of Ni and Co improves heat crack resistance remarkably.

The No.16 alloy has been used in a standard material excellent in corrosion resistance and abrasion resistance for a sintered sliding material used in a floating seal. No.24 to No.26 a1loys are alloys in which the No.16 alloy (a solid soluble carbon concentration in martensite is O.9wt%) contains Cu particles or Cu alloy particles dispersed therein. 1\ddition of the Cu particles or the Cu alloy particles does not cause disadvantage in sintering ability and sintering bonding ability. Comparison of the No.24 to No.26 alloys with the No.16 alloy shows that the No.24 to No.26 alloyS are improved in heat crack resistance remarkably. Ps shown in Fig.20A showing a structure of the No.25 alloy, Cu particles are dispersed in a granular form. Such configuration is preferred Co improve conformability at sliding. The No.25 alloy to which Cu lOwt% Sn alloy is added is more effective for heat crack resistance. In which case, the Cu particles dispersed therein preferably contain one or more alloy elements of Sn, Ni, Ti and P, which are positively added to a copper based sliding material, in an amount of 5 to l5wt%.

No.27 alloy is an alloy in which Si3N4 is dispersed in addition to carbide, whereby a solid soluble carbon concentration of martensite phase thereof is lowered to 0.4wt% or less and Cr,C3-type carbide coexists therein resulting in improving heat crack resistance remarkably.

Compared with the No.6 and No.9 alloys, such result shows that dispersing Si3N particles is more effective on improvement in heat crack resistance.

As shown in Fig.20B, No.28 alloy is an alloy in which the No.16 alloy to which Sb2 of 2.5wt% is added is sintered so that Si02 is reduced by intensive reduction action of carbon at sintering, resulting in producing pores at portions where the Si02 particles exist. In addition, after sintering, the No.28 alloy is prepared to contain carbon of 2wt% and Si of 1.Tlwt%. The No.28 alloy is improved in heat crack resistance remarkablY because lubricating performance thereof is promoted by the pores produced by the reduction of Si02.

No.29 and No.30 alloys are alloys in which graphit:e and Mo metal phase are dispersed mainly as solid lubricant. The No.29 and No.30 alloys are improved in heat crack resistance remarkably. 5o, W and CaF2 are expected to have the same effect as the graphite and Mo metal phase.

No.31 to No.36 alloys are alloys in which M6C-yPe carbide is dispersed mainly, In these alloys, addition of P improves sintering ability and 5jtering_b0)dih1g ability thereof, and dispersion Of phosphorus compound (FeMoP) improves heat crack resistance. Furthermore, increased amount of M6C-type carbide also improves heat crack resistance.

Fig.21 shows a photograph showing a sintered structure of No.32 alloy and analysis thereof using X-ray micro analyzer. The photograph shows that M6CtYPe carbide and MC-cype carbide, which are produced at sintering, are precipitated at grain boundaries. /\nd, such carbide and phosphorus compound (FeMoP or V2P) are precipitated in the particles at a process lowering a temperature down to a quenching temperature of 960 C. In addition, the X-ray micro analyzer analysis of the M6C-type carbide and the NC-type carbide precipitated at the grain boundaries (shown in Fig.21) shows a feature that Si and P are remarkably discharged from NC-type carbide and Cr7C3-type carbide; concentrated in M6C-type carbide remarkably (distribution coefficients of Si and P are follows: K5i6, I<P6=2, which are obtained by another analysis) . in a conventional high-speed steel in which M6C-type carhide is dispersed, a content of Si contained therein i_s limited to 0.4wt% or less. Because, a large addition amount of Si. moves a melting point of M6C-type carbide to lower and therefore lowers a quenCtliflg temperature, resulting in that a sufficient amount of solid soluble for demonstrating tempering secondary hardening is hardly obtained. In addition, a large addition amount of Si promotes stable precipitating of M6C-type carbide by tempering and therefore decreases effect of Mo and W for improving tempering-softening resistance. On the contrary, in a ferrous sintered sliding material in which M6C-type carbide is dispersed mainly, according to the present invention, addition of Si and P increases sintering ability and sintering-.

bonding ability thereof. So, the upper limit of addition amount of Si is preferably limited to l.5wt% for obtaining necessary tempering_softening resistance, and the upper limit of addition amount of p is preferablY limited to 0.35wt% or less for improving sintering ability and sintering-bondiflg ability. 7\nd, p and B, which does not form a large amount of solid solution with martensite phase, and Cu component promoting age-hardening of Ni-Mo in martensite phase are preferablY added.

No.37 to No.39 alloys are alloys in which Cr,C3tYPe carbide coexists with M6C-type carbide. The No.38 alloy, in which an addition amount of carbon is decreased and therefore an amount of Cr-,C3-type carbide is decreased and also a solid soluble carbon concentration of martensite phase is lowered, and the No.39 alloy, in which Ni is added so as to increase an amount of retained austenite, are improved in heat crack resistance.

(Example 3)

(Floating Seal Property of Ferrous Sintered Sliding Material) Figs.22A and 22B show a structure of a specimen for a sintering-bonding test and Fig.23 schematically shows a floating seal tester.

In this example, each of mixed powder having compositions, shown in Table 5 and Table 6 in Example 2, was formed into a ring-shaped compact, shown in Fig.22Pt, at a forming pressure of iton/cm2, and each compact was placed on a base material machined from SS steel and then sintering-honded thereto at 1100 to 1280 C for two hours using a vacuum furnace SO that a relative density of a sintered layer was 93% or more. fter cooled in the furnace atmosphere down to 960 C and maintained for 30 minutes, each compact was quenched in N2 gas atmosphere at 400torr. Then, each compact was tempered at 200 C for two hours so as to prepare a specimen for 5jnteriflg bonding test.

The specimen for a 51ring_b0nd1h1g test was ground into a shape, shown in Fig.22B showing a partially enlarged sectional view thereof, and then finished by lapping a sealing surface 2mm width on an upper surface thereof. The specimens such finished were evaluated in heat crack resistance and seizing resistance in air by using a floating seal tester (a sliding tester) shown in Fig.23. The floating seal test was performed such that each of the prepared specimens was used as a pair of seal rings with the seal surfaces thereof being contacted each other and rotated with varying a load applied to the seal surface and a rotating speed. Then, the same test was performed in muddy water ontainiflg S102 of about 5Owt% for examination in abrasion resistance.

The heat crack resistance and the seizing resistance were evaluated by using a rotating speed at which sliding resistance rapidly increased under a condition in which a seal load (a line pressurea load/a length in a seal surface) was kept at 2kgf/Cm. The abrasion resistance was evaluated by using a moving distance (mm) of a seal surface contact portion after the seal tester was continuouslY operated at a line pressure of 2kgf/cm and a rotating speed of im/seC for 500 hours. As for an alloy showing abnormal abrasion performance, a line pressure was decreased to lkgf/Cm and then abrasion resistance was evaluated. The results are represented by "pv value" showincJ heat crack resistance in Fig.24 and a right column of the Table 5.

For comparative specimens for abrasion resiStaflCe and seizing resistance, cast iron sealing materials (Fel5Cr3Mo, FC9Cr6M0) each having a composition of Fe- 3.4C_l.5Si-15Cr2.5M0l.S and Fe_3.5C_1.5Si9_6M0 4.5W-2V-2Ni3CO, and SKD11 and SKFI9, shown in Table 6, were prepared. The results are shown in F g.24 and Table 6.

The PV value of each element shown in Table 5 and Table 6 has the same tendency as critical load against heat crack resistance evaluated in Example 2.

A broken line in Fig.24 shows a standard abrasion resistance required for a floating seal of a construction machine. For example, for a floating seal of a construction machine, a sintered alloy such as No.3 and No.17 alloy, in which Cr7C3-type carbide and MC-tYPe carbide are dispersed in a content of about 15% by volume and a solid soluble carbon concefltratl.on ifl martensite phase is adjusted to 0.45wt%, is preferred Ifl view of abrasion resistance. And, since abras)Ofl resistance is improved with increasing an amount of carbide, it is preferable to contain one or more carbide selected from the group consisting of CrC3-tYpe carbide M6C-type carbide and MC-type carbide in a content of 20% or more by volume.

The No.13, No.16 and No.37 alloys and the high-carbon and high-Cr, Mo cast iron, which have a trouble in heat crack resistance as shown in Example 2, show remarkable abnormal abrasion accompanied with fine heat crack from an evaluation in abrasion resistance at a line load of 2kgf/cm; a sintered alloy in which a solid soluble carbon concentration in martensite is limited to 0.5wt% or less does not show heat crack after test.

(Example 4)

(Deflecting Strength and Toughness of Ferrous sintered Sliding Material) In this example, No.16, No.17 and No.32 ferrous sintered sliding materials, shown in Table 5 and Table 6 in Example 2, were examined in deflecting strength and toughness. The results are shown in Fig.25 with respect to a content (% by volume) of carbide. In Fig.25, a material marked with "/Temp" next to "No." (for example, No.16/Temp.) shows that the material is tempered.

Tempering at 200 C after quenching from 960 C improves deflecting strength of the ferrouS sintered sliding materials and increases a maximum def1eCti0h1 amount thereof thereby to improve toughness. EspeciallY such tendency is significantlY demonstrated as a sintered alloy has a higher solid soluble carbon concentration in martensite and contains a larger amount of carbide, such as No.16.

In a sintered sliding material tempered at 200 C, deflection strength decreases with jncreaSiflg an amount of carbide. So, since a thrust bearing applied with a large offset load is often applied with bending stress of abopt 6okgf/mm2, it is preferable to suppress a content of carbide to 25% or less by volume, more preferably 20% or less by volume. As shown in Fg.i1, since a floating seal is equipped [or a sealing mechanism via rubber 0-rings, the bending stress does not exceed lokgf/mrn2. So, a content of carbide dispersed in a ferrous sintered sliding material can increase to about 50% by volume, however, it is preferably 40% or less by volume.

As described below, comparison of distribution coefficients KM, of each alloy element M in an equilibrium state of austenite with Cr7C3-tYPe carbide (the distribution coefficient KM78 concentration of an alloy element M in the Cr7C3-tYPe carbide/a concentration of the alloy element M in the austenite) shows that the elements concentrate the Cr7C3-tyPe carbide more densely in the order of V>Cr>MO>W. So, v makes the Cr7C3-tYPe carbide into fine grains (KV7:17, KCri:6.S, KM07:2.S and KM7:2.9), and Si, Al, Ni and Co ate discharged from Cr,C3-type carbide remarkably and concentrates in austeflite.

And, comparison of distribution coefficients KM6 O each alloy element M in an equilibrium state of austenite with M6c-type carbide shows that the elements io concentrate in M6C-type more densely in the order of W>Mo>V>Si, (KWE.:23, KM06:2O, KV6:5.S and KSi6:2.4) . And, Cr is discharged from M6-type carbide slightly and concentrates in austenite, and Ni and Co are j5charged from M6C-type carbide.

As described later, at an equilibrium state of austenite with Cr7C3-type carbide in a ferrous sintered sliding material, v concentrates jn r7C3-type carbide to have a concentration 17 times a concentration of V in austenite. In order for austenite to contain V in an amount of Q.5wt% or more so as to form NC-type carbide while the austenite coexisting with CrC3tYPe carbide in a content of 10, 20, 30 and 40% volume, V IS necessarily added in an amount of 1.1, 1.7, 2.3 and 3.9wt% or more, respectively1 to the ferrous sintered sliding material.

In a ferrous sintered sliding material in which CrC3 type carbide is mainly dispersed, it is not preferred economically that V is added thereto so as to precipitate Mc-type carbide for the purpose of improvement in abrasion resistance. Instead, V is preferably added in a small amount as0.5 to 4wt% in order to prevent Cr7C3-tyPe carbide from oarsefliflg at sintering.

However, when MC-type carbide, in addition to H6C-type carbide, is dispersed in a ferrous sintered sliding material, V does not significantly concentrate in the M6C-type carbide. So, in order for austeflite to contain V in an amount of 0.5wt% so as to form MC-type carbide while the ausrenite coexisting with M6C-type carbide in a content of 10, 20, 30 and 40% volume, V is necessarily added in an amount of 0.74, 0.97, 1.21 and l.44wt% or more, respectively, to the ferrous sintered sliding material. In a ferrous sintered sliding material i-n which M6C-type carbide is mainly dispersed, it is understood that V is added thereto 50 as to precipitate MC-type carbide resulting in improving abrasion resistance effectively. This fact is corresponded to the fact that in a high speed steel SKH1O (SEAT15) containing M6c-type carbide and MC-tYPe carbide in a total content of about 13% by volume, V is added so as to increase a content of the MC-type carbide to about 10% by volume for improving abrasion resistance. In the present invention, the upper limit of addition amount of V is set to 10% by volume for disperse MC-type carbide in the maximum content of 20% by volume. When Mc-type carbide is dispersed in a large content, it Is necessarY to add an alloy element, such as Ti, Nb and Zr, in addition to v. However, adding such alloy elements in a large amount is not preferred for a ferrous sintered sliding material from an economical viewpoint.

Accordil)gly, in view of MG-type carbide dispersed in a high speed steel other than SKD1O, MG-type carbide is preferably contained in a content of 5% or less by volume.

When alloy elements, such as Ti, Nb and Zr, are added to the ferrous sintered sliding material so as to disperse MG-type carbide, carbon is necessarily added to the ferrous sintered sliding material in a suitable amount containing a stoichiometric amount of carbon used for NC-type carbide. ilu

Various aspects and preferred features of the present invention are set out in the numbered clauses below.

1. A sintered sliding member comprising a back metal and a ferrous sintered sliding body which is combined to the back metal, wherein said ferrous sintered sliding body comprises martensite phase prepared to have a solid soluble carbon concentration of 0.15 to 0.5wt% and contains carbide in a content of 5 to 50% by volume.

2. The sintered sliding member according to clause 1, wherein said ferrous sintered sliding body is formed with at least one of closed pores and recesses at a sliding surface thereof in an area ratio of 1 to 10%.

3. The sintered sliding member according to clause 1, wherein said ferrous sintered sliding material contains one or more elements selected from the group consisting of Cr of 9wt% or more, Mo of 3.5wt% or more, Mo and W in a total amount of 4.Swt% or more, and V of 3wt% or more so that said martensite phase contains one or more carbides selected from the group consisting of Cr7C3-type carbide, M6C-type carbide, and MC-type carbide dispersed therein.

4. A sintered sliding member comprising a back metal and a ferrous sintered sliding body which is combined to the back metal, wherein said ferrous sintered sliding body contains carbon of 0.9 to 3.8wt%, Cr of 9 to 35wt%, and V of 0 to 3wt%, in which a content of carbon satisfies the following equation: 0.l43xCr(wt%)_1.41+14XMCtYPe carbide ill * (volume fraction)Carbon(Wt%)O.l56xCr(wt%)_0S84xMC_ type carbide (volume fraction), and has martensite phase, in which said martensite phase, forming a solid solution with carbon of 0.2 to 0.45wt% and Cr of 6.5 to l2wt%, contains Cr,C3-type carbide in a content of 5 to 40% by volume and MC-type carbide in a content of 5% or less by volume dispersed therein with a total content of said carbides being 5 to 40% by volume, and wherein said ferrous sintered sliding body contains one or more elements selected from the group consisting of Si, Mn, Ni, P, S, B, N, Mo, W, Ti, Co, Cu and Al.

5. The sintered sliding member according to clause 4, wherein said ferrous sintered sliding body contains at least one of Si of 1 to 3.5wt% and Al of 0.5 to 2wt%.

6. The sintered sliding member according to clause 5, wherein a content of carbon in said ferrous sintered sliding body satisfies the following equation: 0.l43xCr(wt%)_l.41+0.15XSi(Wt%)+14)<MCtYPe carbide (volume fraction) Carbon(wt%) 0. l56xCr(wt%)- 0.58+0.l5xSi(wt%)+14xMC- type carbide (volume fraction), wherein said ferrous sintered sliding body has martensi.te phase, said martensite phase forming a solid solution with carbon of 0.2 to 0.45wt%, Cr of 6.5 to l2wt% and at least one of Si of 1 to Swt% and Al of 0.5 to 4wt%, and containing Mo or Mo and W in a total amount of 0 to 4.0-0.5x(Si(wt%)+Al(Wt%)).

7. The sintered sliding member according to clause 4, wherein said ferrous sintered sliding body contanS either one of Mo of 1.6 to 6.5wt% or Mo and W in a total amount of 1.6 to 6.5wt%, and said martensite phase contains one or more elements selected from the group consisting of Mo of 1.5 to 4wt%, Mo and W in a total amount of 1.5 to 4wt% and V of 0 to 0.6wt%.

8. A sintered sliding member comprising a back metal and a ferrous sintered sliding body which is combined to the back metal, wherein said ferrous sintered sliding body contains carbon of 1.8 to 4.5wt%, Cr of 12 to 3Owt%, V of 3.5 to lOwt% and either one of Mo of 2 to 6.4wt% or, Mo and W, in a total amount of 2 to 6.4wt%, and has martensite phase, in which said martensi-te phase, forming a solid solution with carbon of 0.2 to 0.45wt%, Cr of 6.5 to l2wt% and further one or more elements selected from the group consisting of Mo of 1 to 3.5wt%, Mo and W in a total amount of 1 to 3.Swt% and V of 0.4 to O.6wt%, contains dr,c3-type carbide in a content of 10 to 35% by volume and MC-type carbide in a content of S to 15% by volume dispersed therein with a total content of said carbides being 15 to 40% by volume, and wherein said ferrous sintered sliding body contains one or more elements selected from the group consisting of Si, Mn, Ni, P, S, B, N, Mo, W, Co, Cu and Al.

9. A sintered sliding member comprising a back metal and a ferrous sintered sliding body which is combined to the back metal, wherein said ferrous sintered sliding body contains carbon of 0.6 to l.9wt%, Cr of 1 to 7wt%, V of 0 to 3wt%, Mo of 3.5wt% or more and Mo+0.5xW of 4.5 to 3Owt%, in which O.5xW represents half of a real amount of W, and 1as martensite phase, in which said martensite phase, having a solid soluble carbon concentration of 0.2 to 0.45wt%, contains M6C-type carbide in a content of 5% or more by volume and MC-type carbide in a content of 5 to 40% by volume dispersed therein, and wherein said ferrous sintered sliding body contains one or more elements selected from the group consisting of Si, Mn, Ni, P, S. B, N, Ti, Co, Cu and Al.

10. The Sintered sliding member according to clause 9, wherein a content of carbon in said ferrous sintered sliding body satisfies the following equation: O.OSX(MO(Wt%)+O.5X(wt%))+llxMC type carbide (volume fraction)Carbofl(wt%)0.038x(M0t+05XWt% xMC-type carbide (volume fraction) 11. A sintered sliding member comprising a back metal and a ferrous sintered sliding body which is combined to the back metal, wherein said ferrous sintered sliding body contains carbon of 1.3 to 3wt%, Cr of 1 to 5wt%, V of 3 to l2wt%, Mo of lOwt% or more and, Mo and W, of 10 to 23wt% and has a structure in which martensite phase, having a solid soluble carbon concentration of 0.2 to O.45wt%, contains M6C-type carbide in a content of 15 to 35% by volume and MC-type carbide in a content of 5 to 15% by volume dispersed therein, and wherein said ferrous sintered sliding body contains one or more elements selected from the group onsist1nq of Si, Mn, Ni, P, 5, B, N, Ti, Co, Cu and Al.

12. A sintered sliding member comprising a back metal and a ferrous sintered sliding body which is combined to the back metal, wherein said ferrous sintered sliding body contains carbon of 0.8 to 3.4wt%, Cr of 9 to 28wt%, V of 0 to 5wt%, Mo of Swt% or more and, Mo and W, of 5 to l8wt%, and has martenSite phase, in which said martensite phase, having a solid soluble carbon concentration of 0.2 to 0.45wt%, contains Cr7C3-type carbide in a content of 5 to 25% by volume, M6C-type carbide in a content of 5 to 25% by volume and MC-type carbide in a content of 0 to 5% by volume dispersed therein with a total content of said carbides being 10 to 40% by volume, and wherein said ferrous sintered sliding body contains one or more elements selected from the group consisting of Si, Mn, Ni, P, S. B, N, Ti, Co, Cu and Al.

13. The sintered sliding member according to clause 12, wherein a content of carbon in said ferrous sintered sliding body satisfies the following equation: O.O43X(MO(Wt%)+0.5(t%)) 5t7C3_type carbide (volume fraction)+14XMCtYPe carbide (volume fraction) Carbon(wt%) 0. 038x(Mo(Wt%) +0.

5xCr7C3-type carbide (volume fractiofl)+14XMCtYPe carbide (volume fraction) 14. A sintered sliding member comprising a back metal and a ferrous sintered sliding body which is combined to the back metal, wherein said ferrous sintered sliding body contains carbon of 1.5 to 3.2wt%, Cr of 7 to 25wt%, Mo of 3.5wt% or more, Mo and W of 5 to l5wt% and at least either one of V or Ti in a total amount of 3 to 8wt%, and has martensite phase, in which said martensite phase, having a solid soluble carbon concentration of 0.2 to 0.45wt%, contains Cr7C3-type carbide in a content of 5 to 20% by volume, M6C-type carbide in a content of 5 to 20% by volume and lID MC-type carbide in a content of 5 to 15% by volume dispersed therein with a total content of said carbideS being 15 to 50% by volume, and wherein said ferrous sintered sliding body contains one or more elements selected from the group consisting of Si, Mn, Ni, P, S, B, N, Ti, Co, Cu and Al.

15. The sintered sliding member according to clause 1, wherein a composition of said ferrous sintered sliding body is adjusted so as to contain one or more carbides selected from the group consisting of Cr7C3-tYPe carbide, M6C-type carbide and MC-type carbide, which are coarsened to have an average grain size of 4Opm or more, dispersed and precipitated therein in a content of 3% or more by volume by adding Cr powder, Mo powder, w powder, V powder or ferrous alloy powder contained high alloying element.

16. The sintered sliding member according to clause 3, wherein said ferrous sintered sliding body contains one or more elements selected from the group consisting of Ni of 1 to 5wt%, Mn of 1 to 2wt%, Co of 2 to l2wt% and Al of 0.2 to l.5wt%.

17. The sintered sliding member according to clause 16, wherein said martensite phase contains retained austenite phase dispersed therein in a content of 5 to 40% by volume.

18. The sintered sliding member according to clause 1, wherein said ferrous sintered sliding body contains at least one of P of 0.1 to 1.5wt% and B of 0.01 to 0.2wt% so as to contain one or more compounds selected from the group consisting of Fe3P, Cr2P, FeMoP, V2P, and lib FeTiP dispersed therein in a content of 10% or less by volume - 19. The sintered sliding member according to clause l wherein said ferrous sintered sliding body contains Cu based alloy, containing one or more elements selected from the group consisting of P. Sn, Al, Fe, and Ni, dispersed therein in a granular form in a content of 1 to 10% by volume.

20. The sintered sliding member according to clause 18, wherein said ferrous sintered sliding body contains at least one of Mo metal partic1es metal particles and graphite particles dispersed therein in a content of 1 to 10% by volume, in which said dispersed particles are surrounded with Cu or Cu alloy phase.

21. The sintered sliding member according to clause 3, wherein said ferrous sintered sliding body is formed with closed pores scattered therein in a content of 1 to 10% by volume, said closed pore having an average size of 0.03 to 3.0mm.

22. The sintered sliding member according to clause 3, wherein said ferrous sintered sliding body is formed with recesses scattered at a sliding surface thereof ifl an area ratio of 3 to 10%.

23. The sintered sliding member according to clause 1, wherein said martensite phase comprises tempered martensite phase tempered at 150 to 600 C.

24. The sintered sliding member according to clause 1, wherein said back metal comprises a cylindrical member and a collar formed at one end surface of the cylindrical member, said collar having a sliding surface, wherein said ferrous sintered sliding body having a thickness of 0.5mm or more is combined to said s:Lidiflg surface.

25. The sintered sliding member according to clause 1, wherein said ferrous sintered sliding body is formed into a doughnut shape and at least a part of an inner surface and an under surface thereof is sintering_b0nd to said back metal, in which a part of a bonded surface of said ferrous sintered sliding body and said back metal is formed with at least either one of ventholes or grooves through which gas generated from the ferrous sintered sliding body at sintering-bonding is discharged.

26. The sintered sliding member according to clause 3, wherein said sintered sliding member is a thrust bearing, in which said ferrous sintered sliding body contains CrC3-type carbide, M6C-type carbide and MC-type carbide dispersed therein in a total content of 5 to 25% by volume and said back metal has a hardness of Hv170 or more.

27. The sintered sliding member according to clause 3, wherein said sintered sliding member is a thrust bearing, in which said ferrous sintered sliding body contains Cr,C3-type carbide, M6C-type carbide and MC-type carbide dispersed therein in a total content of 5 to 25% by volume and is formed with at least either one of closed pores and recesses at a sliding surface thereof in an area ratio of 1 to 10%, and said back metal has a hardness of Hv170 or more.

-. lib 28. The sintered sliding member according to clause 26 or wherein said back metal comprises a cylindrical member and a collar at one end surface thereof, said collar having a sliding surface sliding under a thrust load, wherein said ferrous sintered sliding body is sintering-bonded to the sliding surface of said collar and a bushing is fixedly mounted to an inner surface of said cylindrical member, said bushing being made of porous sintered material which retains lubricating oil or lubricating compound of lubricating oil and wax, filled therein.

29. The sintered sliding member according to clause 28, wherein said porous sintered material is made of a material having the same property as said ferrous sintered sliding body.

30. The sintered sliding member according to clause 3, wherein said sintered sliding member is a floating seal, in which said ferrous sintered sliding body contains CrC3-type carbide, M6C-type carbide, and MC-type carbide dispersed therein in a total content of 20 to 40% by volume and said back metal has a hardness of l-Ivl7O or more.

31. The sintered sliding member according to clause 3, wherein said sintered sliding member is a floating seal, in which said ferrous sintered sliding body contains Cr7C3-type carbide, M6C-type carbide and MC-type carbide dispersed therein in a total content of 20 to 40% by volume and is formed with at least either one of

I_I p

closed pores or recesses at a sliding surface thereof in an area ratio of 1 to 10%.

32. The sintered sliding member according to clause 30 or wherein said ferrous sintered sliding body is formed with closed pores scattered therein in a content of 3 to 10% by volume, said closed pore having an average size of 0.03 to 1.0mm.

33. The sintered sliding member according to clause 30 or wherein a seal surface of said floating seal is formed with recesses scattered therein in an area ratio of 3 to 10%, said recess having a depth of 1mm or less in a width direction of said seal surface.

34. The ferrous sintered sliding member according to clause 30 or 31, wherein said martensite phase contains retained austenite dispersed therein in a content of 5 to 40% by volume.

35. A connecting device comprising: a bearing made of a sintered sliding member according to clause 26 or 27 comprising a back metal and a ferrous sintered sliding body which is combined to the back metal, in which said ferrous sintered sliding body has rnartensite phase, having a solid soluble carbon concentration of 0.15 to O.Swt%, and contains carbide in a content of 5 to 25% by volume, and another bearing to slide with respect to said bearing.

Claims

What is claimed is: 1. Pi sintered sliding member comprising a back

metal arid a ferrous sintered sliding body which is combined to the back metal, wherein said ferrous sintered sliding body contains carbon of 1.5 to 3.2wt%, Cr of 7 to 25wt%, Mo of 3.5wt% or more, Mo and W of 5 to l5wt% and at least either one of V or Ti in a total amount of 3 to Bwt%, and has martensite phase, in which said martensite phase, having a solid soluble carbon concentration of 0.2 to 0.45wt%, contains Cr,C3-type carbide in a content of 5 to 20% by volume, M6C-type carbide in a content of 5 to 20% by volume and MC-type carbide in a content of 5 to 15% by volume dispersed therein with a total content of said carbides being 15 to 50% by volume, and wherein said ferrous sintered sliding body contains one or more elements selected from the group consisting of Si, Mn, Ni, P, S, B, N, Ti, Co, Cu and Al, wherein a content of carbon in said ferrous 5interecf sliding body satisfies the following equatiOfl 0.O43X(MO(Wt%)+0.51t)+8.5xCr-iC3-type carbide (volume fraction) +14xMC-tYPe carbide (volume fraction) Carbon(wt%) O.O38X(MO(Wt%)+0.5(wt%+0.33+85)r7C3 type carbide (volume fraction) +l4xMc_tYpe carbide (volume fraction), or wherein said ferrous sintered sliding body contains

I

at least one of p of 0.1 to 1.5wt% and B of 0.01 to 0.2wt% sO as to contain one or more compounds selected from the group consi5tiflg of Ee3P, Cr2P, FeMOP, v2P, and FeTiP dispersed therein in a content of 10% or less by volume.
2. A sintered sliding member ccordiig to claim 1, wherein said ferrous sintered sliding body contains one or more elements selected from the group onsistiflg of Si of 0 to 3.5wt%, Ni of 1 to 5wt%, Kn of 1 to 2wt%, Co of 2 to l2wt% and Al of 0.2 to l.Swt%.
3. A sintered sliding member according to claim 1, wherein said ferrous sintered sliding body is formed into a doughnut shape and at least a part of an inner surface and an under surface thereof is sjnteriflg bonded to said back metal, in which a part of a bonded surface of said ferrous sintered sliding body and said back metal is formed with at least either one of ventholeS or grooves through which gas generated from the ferrous sintered sliding body at sinteringbofldifl9 is discharged.