GB2340506A

GB2340506A - Rolling member and device

Info

Publication number: GB2340506A
Application number: GB9924497A
Authority: GB
Inventors: Shigeru Okita; Susumu Tanaka; Manabu Ohori; Koji Ueda; Akihiro Kuichi
Original assignee: NSK Ltd
Current assignee: NSK Ltd
Priority date: 1996-09-19
Filing date: 1997-09-18
Publication date: 2000-02-23
Anticipated expiration: 2017-09-18
Also published as: GB2340130B; GB9924494D0; GB2340506B; GB2340130A; GB9924497D0

Abstract

A rolling contact device comprising: ```rolling elements of the rolling contact device; and ```a mated member of the rolling contact device which contacts said rolling elements and is rotated, rolled, slid or moved relative to said rolling elements, ```in which said mated member is made of carbon steel containing 0.6% - 0.9% by weight of C, 0.1% - 0.7% by weight of Si, 0.5% - 1.1% by weight of Mn, 0.1% - 0.6% by weight of Cr and with the remainder, apart from inevitable impurities being Fe, said mated member being subjected to a hardening heat treatment; and, ```said rolling elements of said rolling contact device being made of an alloy steel containing Cr, and said rolling elements being subjected to a hardening heat treatment, ```wherein at least one of said mated member and rolling elements have an ideal critical diameter DI value calculated by satisfying a following equation in the range of 1.5 - 4.0 inches (38 to 101 mm), where <F>```DI = (0.311 X C%<SP>0.498</SP>) X ([0.7 X Si%] + 1) X ([3.33 X Mn%]+1) X ([2.16 X Cr%]+1)</F>.

Description

2340506 ROLILING MBER AND DEVICE This invention relates to a rolling

device and Its components, and In particular relates to, an improvement an material for the components of various kinds of rolling devices such as long-life and 2ow-cost rolling bearings made of a bearing steel utilized for automobiles.. construction equipment,, machine tools, etc., and also rolling devices used as comparativly small-eized precision bearings such as spindle support bearings of a hard disk drive (HDD), a videocassette recorder (VCR), etc., and bearings of a cooling fan motor, etc.

Generally, as well as in the present invention, for example, rolling bearings, ball Screws, linear guides, ball bushes$ ball splines, etc., are well-krunm as representative or typical rollinq devices. In additiont as rolling member defining each components constituting the zolling devices, following rolling members are we12-3mcwn- Races (inner races, outer races) and rolling elements (balls, rolling beaxing rolls) are known as components of the rolling bearings. 14uts, screw shaft, and-rolling elements (balls) are 2C knmm as components of the ball screws. Sliders (nuts), guide rails, and rolling elements (balls) are known as components of the linear guides. Bearings, guide races, and rolling elements (balls) are known as components of the ball bushes. Ball bushes, spline shafts, and rolling el nts (balls) are known - I - as components of the ball splines.

in the rolling devices, the rolling members are ref ereed/def ined &is parts /components for making up each rolling device. The rolling member comprises the rolling elements and component5 rotated, slid or moved relative to the rolling elements for guiding the rolling elements. The rolling elements and the components are refereed/defined as mated members relative to each other.

The races and rolling element of a bearing are utilized as components of a rolling bearing which is one example of the rolling devices. The races and rolling element make rolling motion between rolling surfaces and receive a contact stress repeatedly, and also they make slide motion between a flange portion of each races and a rolling element of a roller bearing is such as a cage or a component part of a rolling device. Then, for the materials, hardness for resisting against a load, long rolling fatigue strength, good wear resistance to slide, and the like are recraired. Since the bearings are highly precise mechanical parts as dimensions, sufficient dimension stability is requixed. Then, as the matemial of the members, generally STJJ2 is used for bearing steel or steel equivalent to SCR420 is used for case hardening steel.

The loss and gain to use the materials of SUJ2 and SCR420 for rolling bearings are described belows SInce SUJ2 contains much C and Cr in alloy constitution, macro carbide or segregation easily occurs at the Steel Making time and soaking, etc., is perf ormed to remove it, leading to an increase in the material cost as Compared with SCOR420.

Generally, inner and outer races for small bearings are molded by hot (warm) forging, then undergoessoftening successively; because of the carbon amount of the material, SUJ2 has large hardness after softening, is hard to cut, and increases the working cost as compared with SCR420. However, SVJ2 is only hardened and tempered to provide hardness required for a bearing; SCR420 is carburized or carbonitrided, then is hardened and tempered to provide hardness required for a surface layer, thus drastically increases the heat treatment cost as compared with SUJ2. smsultantly, SUJ2 hag; the total bearing manufacturing cost lower than SCR420 has.

is However, for the rolling bearing function, the bearing provided by carburizing or carbonitriding SCR420 contains much yR (retained austenite) on the surface layer and a residual compressive stress allso occuzer thus the bearing made of S.CR420 tends to be a long life particularly under lubrication mixed with foreign zaaterial and also show good fatigue strength and act strength. SCR420 in superior to SUJ2 in d1mension stability of an important function as a bearing.

On the other hand, for the rolling elements, cold wire drawing matexial,, which will be hereinafter called coil material, Is almost used as a material and is molded like a rolling element by cold forgingi which will be hereinafter called header working, and cutting is not performed. Comparing cold workability between 5UJ2 and SCR420, SUJ2, which contains much C and Cr in alloy constitution, has large hardness after annealing and Is inferlor to SCR420 in cold workability.

However, SCR420 requires carburizing or carbonitriding, thus increasing the heat treatment cost as with the inner and outer races. Resultantly, SCR420 increases the manufacturing cost drastically as compared with SUJ2.

For the rolling element function, the rolling element provided by carburizing or carbcnitriding SCR420 still contains much yR (retained austenite) on the surface layer and a residual compressive stress also occurs, thus the rolling element made of SCR420 tends to he a long life particularly under lubrication mixed with foreign material.

is In contrast, rolling members of spindle support bearings of HDDs and VCRs, air conditioner fan motor bearings.. etc., are used under a c=pc=atively light load, but low vibration and isound produced by the bearing itself are required and in some cases, sound degradation during use may become higher than the upper limit of the usage. This means that a good sound characteristic rather than rolling fatigue strength is required for comparatively small precise ball bearings used for the app.1hiCationE.

Vibration and sound are produced on ball bearings for various reasons; they are produced on comparatively small precise ball bearings used for MD9, etc., because vibration and sound occurring from the bearing raceway surface increase.

That is, if the inner and outer race material of a bearing contains a large retained austenite amount, an impression is easily made on the raceway surface of the finished product of the bearing, thus load or impact load easily causes the bearing raceway surface to be deformed permanently. Such permanent deformation increases vibration and sound occurring from the bearing raceway surface, degrading the sound characteristic.

Thus, reducing the retained austenite amount (TR) or setting the amount (yR) to zero is effective as a sound degradation countermeasure.

Thent a bearing for which sound characteristic degradation is prevented by reducing or setting to zero the retained austenite amount in the material is disclosed in the Japanese Patent Unexamined Publication No. Hei. 7-103241.

As described above,, for the conventional bearing member,, care hardening steel which is carburized or carbonitrided has a higher bearing function than bearing steel, but rolling bearings made of bearing steel a often adopted giving costs priority under clean oil bath lubrication or gkease lubrication.

However, the conventional rolling member made of bearing steel is high in material cost and also has poor cold workability as described above, thus is hard to meet severe cost reduction demand in recent years. This is a first problem in the prior art.

Further, particularly, external water, etc., easily enters rolling bearings used with machines mainly run outdoors, such as bicycles, automobiles, agricultural machinery, and construction equipment, thus it is known that generally the life of the rolling bearings lowers ("Jidousha no tripology,, Shadan houjin jidousha gijyutukai, 1994. p.272). As its causes, it is known that the lubrication state becomes f ault or damage occurs due to corrosion such as a rust, etc., because water, etc., enters ("Korogari jikuuke handbook" J.Blendline et al., 1996f p-382). To prevent trouble caused by entry of external water, etc., sealing is enhanced for axle bearings and water pump bearings of engine auxiliary machinery for preventing water, etc., from entering.

However, if sealing is enhanced for improving hermeticity, air in the bearing expands and shrinks and water is sucked in because of the temperature difference during the ope=ation and stop of the bearingr thus life lowering caused by water entry cannot perfectly be prevented. To cope with life lowering caused by water entry, high alloy steel such as stainless steel can be used an bearing material to improve corrosion resistance, but the bearing cost increases.

This is a second problem of the prior art

Furthermore, it is also effective as sound degradation countermeasures to reduce or reduce to zero the retained auste nite to cause permanent deformation to easily occur on the bearing raceway surface because of load or impact However, the conventional reduction method is to parform subzero treatment or tempering treatment at high temperature, thus resulting in the cost equal to or greater than the current cost. This is a third problem in the prior art.

Countermeasures for reducing vibration or sound resulting from the bearing raceway surface are not originally taken; this means that the sound characteristic sti12 has room for improvement.

3.0 1 is a first object cf the invention to solve the first problem in the prior art and to provide a rolling member having higher performance of life, zwchanical strength, etc., than that of the conventional rolling member made of SUJ2 of bearing steel while reducing material and manufacturing costs 13 as much as possible.

According to an experiment of the inventor, the bearing life in not prolonged simply by improving corrosion resistance of inner and outer races; corrosion occurs due to entered water and it is considered that an unknmm cause cf the bearing damage still exists. Therefore, it is a second object of the invention to solve the second problem in the prior art and to provide a rolling member excellent in endurance life even in an environment wherein corrosion such as a rust, etc., occurs due to entry of water, etc.-, and inexpensive more than ever and a rolling device comprising the rolling member.

Fuxthermore, It is a third object of the invention to solve the third problem in the prior art and to provide a comparatively small precise rolling member used for an HDD, a VCR, or an air conditioner fan motor, improved in vibration and sound occurring fron the bearing raceway surface, and. inexpensive more than over and a rolling device comprising the rolling member.

A first aspect of the present Invention will be explained hereinafter.

The inventors have considered reducing the cost of conventional bearing steel and prolonging the life thereof. An a result, they have found that (1) the C, Cr amount is reduced, whereby macro carbides and segregation decrase, soaking treatment can be omitted, and the material cost can be reduced, is that (2) the 14n, S! additive amount is also suppressed within a certain threshold valuee whereby good cold workability and machinability are provided and the machining cost can also be decreased for accoraplishl-ng drastic cant reduction, and that (3) optim= heat treatment is performed, whereby rolling life equal to or greater than that of bearing steel can be provided.

To check whether or not a problem In mass production exists, the inventors have coneldered forging, cutting, heat reatment, grinding, etc., in actual rolling bearings and have also executed bearing function evaluation. As a result, they have found that (1) if the c, cr content is decreased for reducing the material and machining costs and a large amount of Xn is added in order to supplement insufficient hardenability, coarsening crystal grains may be promoted fo= lowering the mechanical strength or a large amount of retained austen-Ite maLy be produced for lowering dimension stability or strength and that (2) if hardenability is enhanced more than necessary by addin; Mn, when the C. Cr content. is low (particularly C: 0. at or less, Cr: 0.1% or loss), the suppression effect of coarsening crystal grains decreases and the Ms points loivrers, whereby surface tenslon of transformation xtreas type at the hardening time increases, so that in rolling elements (particularly rollers) 1 breakage sensibility is raised with an extrusion hole, a chamfer pa=# etc., at the header working time or a small surface flaw or a non-metal inclusion contained in steel as the starting point and breakage occurs in the rolling elements of certain size (particularly rollers) or races (particularly races of bearings) or a sufficient fatigue strength characterislic is not provided.

Generally, such breakage -4& caused by the temperature difference between the surface and the care produced in the cooling process. That is, martensitic tzansformation develops ift the portion in the pxoximity of the surface earlier arriving at the Ma point in the cooling process, but the core is not transformed and temporari2y a compressive stress of heat stress type is received in the proximity of the surf ace. When the Z5 core then becomes martensitically transformed and expands, a surface tensile stress of transformation stress type (residual stress) is received In the proximity of the surface and if the effect is la--ge, the constitution becomes deformed in the proximity Of the surface or the material strength does not bear the tensile stress and a minute crack occurs with a complicated form part easily most affected, a surface flawe o= a non-metal inclusion as the starting point.. grcminc3 to a bretikage.

Furthex, if crystal grains are coarsened due to overheating at the heat treatment time, etc., the breakage sensibility tends to increase. The magnitude of the residual stress changes depending on its alloy compositiont form, volume, etc. That is. an the alloy composition increasest the effect of lowering the Ms point is produced, thus the tendency becomes strong (see Figure 1) and if the volume grows, the absolute expansion amount. Increaser. Purthor, if the úo= is becomes complicated, the stress is thrown out of balance and a.Locally large tensile stress occurs with deformation.

For the effect of the voluixe, hmmver, it the thermal stress ber-omes larger then the transformation stress or an incomplete hardening phase is produced in the core, sensibility to breakage may lowers; it Is very difficult to make out the effect of the volum. it is often unavoidable that the bearing form also becomes complicated on design.

Various countermeacures are taken for such a breakage problem caused by the surface tensile stress of transformation Z5 stress type accompanying hardening. First,, the foIllowing preventive countermeasures for breakage are taken on the heat treatment aspect:

(1) Perf orning mild quenching treatinent under control of the hardening oil type and oil temperature; (2) holding proper temperature after hardening; (3) perf o=ing tempering 1 diately after he=dening; (4) repeating t=ing treatment; (5) setting the hardening atmosphere to a slight carburizing atmosphere and adding cliarcoali thereby giving a residual compressive stress onto the surface; and (6) for races, performing press quenching treatment to prevent deformation.

However, fox zoss production, it may be difficult at cost to change hardening oil, control oil temparaturo whenever necessary, hold to proper temperature after hardening, or 13 irmediately porforming tampering in view of problems on lots and facilities. Further, production inanagement Is very difficult to execute because the occurrence frequency becoraes co=parativoly high in winter.

Secondary, countermeasures with respect to the material aspect are taken by highly purifying steel, namely. reducing non-metal inclusions bec=ing the occurrence origin paint of microcracks, thereby accomplishing improvement on the material aspect. In recent years, the high purifying technologies of the steel manufacturers have been developed remarkably for accomplishing the in-steel oxygen concentratior of about 5-7 ppm as a leap upward in the rolling life under clean lubrication. The non-metal inclusions in steel are reduced, whereby the sensibility to breakage also lowers and the heat treatment productivity tends to improve. Howeveri renuLrkable reduction in the in-steel oxygen level results in a rise in the material cost, which does not meet the object of the invention.

Therefore, the inventors have considered not only the material cost or life, but also the breakage sensibility of the material itself viewed from the alloy compositions, and have developed rolling members al so good 1.n productivity.

The first object is accomplished by a rolling member of a rolling devicee according to the first aspect of the present inventionr in which the rolling member Is made of carbon steel containing 0. 6%-0. 91 by weight of C, 0. 14-0. 74 by weight of Si, 0.5t-1.1% by weight of Mn, and 0.14-0.6% by weight of Cr, and 2.5 re and inevitable impurity elements in the remaining part, and the rolling member is subjected to a hardened heat treatment.

in the above -ment ioned construction of the rolling me=ber, the retained austenite amount after subjecting to the hardened heat treatment is preferably 22% by volume or less.

Further to the above -raent loned construction of the rolling mr, the retained austenite amount after subjecting to the hardened heat treatawnent is preferably 8% by volume or More.

In the above-mentioned construction of the -rolling member, an!dual critical dlameter DI value calculated by satisfying a following equation is prefe=ably In the range of 1.5 - 4.0, where DI = (0.311 X C%0.498) X (0.7 X Si% 1) X (3.33 x mn% +1) X (2.16 X CA -i-l).

In the above-mentioned construction of the rclling member, the carbon steel preferably contains 0.8%-0.9% by weight of C.

2n the abcve-mentioned construction, an ideal critical diameter DI value calculated by satis,&1y.;.ng a following equation is preferably in the range of 1.5 - 4.Of DI = (0. 311 X C10.&91) X (0.7 X SA +1) X (3.33 A Rnt +2) X (2.16 X Cx.1).

X In the above-mentioned construction, the carbon steel preferably contains D.WO.9% by weight of C.

A second aspect of the present invention will be explained hereinafter.

is The inventors have made detailed study and analysis of damage conditions occurring on the market for axle bearings of bicycles and automobiles and water pump bearings ef engine auxú1.iary mach:Lnca=y that. external water, etc., easily enters, and have found out the following features:

1) Most of shcrt-life parts that water, etc.t enteris axe fixed outer races.

2) Breakage posItions are not only the maxim= load position, but also the load zone exit and entrance before and after the maximum load position.

2 5 3) Some of rusted outer racea'are not broken.

The lhventors have found out the following ch.Rzdcter,isti.C8 by assuming the use conditiong, carrying Out c life experiment with water mixed in a lubricmntl and reproducing the damage state on the market:

4) As the amount of water mixed in the lub=icant is increased, the short life tendency become strong.

5) When corrosion resistance of inner and outer races and rolling elements is enhanced, the life prolonging effect is produced a little.

6) Although corrosion resistance of inner and outer races is enhanced, the life prolonging effect is not produced.

7) When corrosion resistance of Inner and outer races is lowered a little with respect to rolling elements, the life prolonging effect Is produced.

According to 1)3), if water, etc., in mixed in the lubricant, flaking occurs in the general load zone of the fixed outer races, thus it is expected that the damage state in not simple fatigue caused by load. Some of the rusted outer races have a long life; it in considered thet the d=age state Is not damage caused by simple corrosion either. Further, if the corrosion resistance of the Inner and outer races is lowered a little with respect to the rolling elements. the bearing life prolonging effect is produced. Thus, the effect is produced according to corrosion resistance combination of the inner and outer races and the rolling elements.

To accomplish the second object of the Invention, it is important to produce the life prolonging effect although water, etc., is mixed in the lubricant and to reduce costs, From Ithis viewpoints, most of balls of rolling elements of a ball bearing use the StJJ2 mater'll-al except for some special environment application. The balls are mass-manufactured consecutively by cold working from coil material and the manufacturing cost is reduced to the limit at present. Furtherr the balls cannot be sculptured or marked, thugs are all manulactuxed under lot control. That is, even if low-cost material is used to reduce the cost containing workability, process set change and foreign material management costs are added largely and the cost of the balls can be scarcely reduced. Thus, considering ball bearing cost reduction, SUJ2 is used as the rolling element material even if water, etc., is mixed in the lubricant.

Considering the corrosion resistance combination of the inner and outer races and the rolling elements, the corrosion resistance of the inner and outer races is lowered with respect to the -021ing elements,. thus it is necessary to decrease Cr most affecting the corrosion xesistance from the main compositions of SUJ2. Then,, in the invention, Cr of the inner and outer races is decreased and for other compositiona, optimum compositions are set considering hardness af ter hardening required as bearings, hardenabilitys workability, etc., and are combined with the balls made of SUJ2, thereby providing rolling bearings excellent in endurance life even under an environment wherein corrosion such as rust, etc., occurs due to entry of water, etc.t and moreover inexpensive more than ever.

That Is, to accomplish the second object, according to the second aspect of the Invention, there is provided a rolling device comprising:

rolling elements of rolling member; and a mated member of the rolling member rolled, slid or moved relative to the rolling elements, in which the mated member is made of carbon steel containing 0 - 6%-0.9% by weight of C, 0. 1%-0. 7% by weight of 51,, by weight of 14n, and O.A-0.6% by weight of Cr and Fe substantially in the remaining part. and the mated lnr is subjected to a hardened heat treatment; and the rolling elements of the rolling member are made of an alloy steel containing Cr, and the rolling elements are subjected to a hardened heat treatment, wherein a difference between a matrix Cr content of the mated member and a matrix Cr content of the rolling elements is 0.6% or more.

In the above-nentioned construction of the rolling device, the nLating member in preferably made up of 0.84-0.9% by weight of C, 0.14.0.5% by weight of Si, by weight of Mn, and O.A-0.6% by weight of Cr, and Pc and inevitable impurity elements in the remaining parts wherein the rolling elements are preferably made up of by weight of C, 0.154-0.35% by weight of 51, 0.1% 0.5% by weight of 24n, and 1.3%-1.6% by weight of Cr, and Fe and inevitable impurity elements in the remaining part.

Further, in the above-zentioned cc-wistruction of the rolling device, jjCr of the matrix Cr may have the relationship with the Cr, C content and carbide area coefficient cm as HCr = Cr (I - 28 (1 + 4C) X CM/10000) A third aspect of the present invention will be explained herelnafter.

The inventors have furthermore considered the sound chazacteristic of ball bearings of comparatively small precise rolling devices used with HDDe,, VCRs, air conditioner fan motors, etc.

For the ball bearings used for the applications, vibration and noise still occurring if defects of accessories such as cages and seals as vibration and noise generation sources are removed by the current excellent working techniques for finishing and excellent lubrication material is used are "race sound" occurring from the raceway surface. The race sound" is produced by a microswell on the raceway surface, selects an exciting force component izi the vicinity of the natural frequency of the race, and vibrates, to thereby produces a noise (OlKorogazi jiku-ukeno sinndou onkyou" Noda; NSK Technical Journal No. 661j, 1996, pIS) - Circumferential swell at continuous crest height with respect to the number of continuous crests exists on the raceway surface of the races of the ball bearing and the ball surface and when the ball bearing rotates, vibration occurs and proper vibration of the race is enhanCed, producing sound ("Tamajikuukeno souonn igarashi.

Nippon Kikai Gakkai Ronbunshuu Vol. 30, issue 220, 1964, plIS), This means that if the arwell" as the vibration source is reduced, the sound characteristic occurring from the bearing raceway surface can be improved. Howeverr under present circumstances, the "race sound" is already reduced to the limit by precise working according to working techniques at high level and f=ther reduction needs to be considered from aspects other than the working techniques.

Unless special requirements of co=osion resistance, long life, etc exist, the SUJ2 material is used for the ball bearings and carbides about I pm proper to SUJ2 are distributed on the bearing raceway surface of a finished product. The inventors have thought that the carbide distribution proper to is the SUJ2 material has an effect as one of the "swell,, causes on the races, have examined the sound characteristic by changing the carbide distribution in various Ways, and have found the followingi For a ball bearing comprising inner and outer races and rolling elements made of SUJ2, 1) if only the carbide area coefficient of the inner and outer races is made higher than that of SUJ2, vibration increases; 2) if only the carbide area coefficient of the inner and outer races is made lower than that of SUJ2, vibration lessens; and 3) if the carbide area coefficients of the inner and outer races and the rolling elements are made lower than that of 5UJ2,, vibration lessens, but is the same or worsens a little as compared with the case where only the carbide area coefficient of the inner and outer races is made lower.

The "swells 1' of the inner and outer races and the rolling elements involved in production of the wrace soundu have irregular nature and produce ininute alternating change in the contact spring force between the inner and outer races and the rolling elements at the rotation tIme and torcible vibration is added tc the inner and outer races,, producing proper vibrat.hcn, which propagates through air, producing sound ("Korogari jikuukeno onkyala,, lgarashi.. Jyunkatut vol. 22, issue 12.. 19771 p15).

Then. the inventors have thought that a minute uneven form on the worked Lin-Ished surface depending an the carbide is amount, particularly placement of carbides forming projections rather than simple asperities or coarseness depending on the finished work accuracy or. the surface is involved in the swell" characteristic of the inn= and outer races and the rolling elements and as a result of consideration, have found that vibration added to the contact spring force way decay depending on the combination of the inner and outer races and the rolli.-.ig elements l namelyr the vibration reduction effect is produced depending on the cozibinat-ion of carbide aroa coefficients in the inner and outer =aces and the rolling elements.

In view of the third object of the invention to decrease vibration and sound of precise ball bearings of cOmParativOlY small rolling devices used for EDD spindles, air conditioner fan motors, etc., for which low vibration and sound produced from the bearings themselves are required, and to reduce the coat, the manufacturing state of the ball bearings is outlined below:

Most of balls of rolling elements of the ball bearing use the SUJ2 material except for some special environment application. The balls are mass-manufactured consecutively by cold working from coil material and the manufacturing cost is reduced to the limit at present. Further, the balls cannot be sculptured or marked, thus are all manufactured under lot control. That is, even if low-cost material is used to reduce the costcontaining workability, the cost of the balls can be scarcely reduced in points of p ocess set change and particularly, foreign material management. Thus, considering ball bearing cost reduction, SUJ2 must be used as the rolling element material even if importance is attached to the sound characteristic.

Therefore, considering the carbide area coefficient combination of the inner and outer races and the rolling elements producing the vibration reduction effect as described above,, the carbide area coefficient of the inner and outer races needs to be lowered with respect to the rolling elements, thug it in necessary to decrease C and Cr affecting the carbide area coefficient from the main compositions of SUJ2. Then, to accomplish the third object of the invention, C and Cr of the inner and outer races are decreased and at the same time, for other compositions r optimum compositions are set considering hardness after hazdening required an bearings, ha--denability, workability, etc., and are combined with the balls made of SVJ2, thereby reducing vibration and sound occurring from the bearing raceway surface and providing bearing devices more inexpensive than the conventional ball bearings.

That is, the third object in accomplished by a rolling deiice comprising:

rolling elements of rolling member; and a mated member of the rolling member rolled, slid or moved relative to the rolling elements, in which the mated member is made of carbon steel containing 0. 6%-0.9% by weigplit of C, 0. 1%-D. 7% by weight of Si, 0.5%-1.1% by weight of Ma, and 0.14-0.6% by weight of Cr, and "ements in the remaining partr and Fe and inevitable impurity e the mated member is subjected to a hardened heat treatment; and the rolling elements are made of an alloy steel containing Cr, and the rolling elements are subjected to a hardened heat treatment, wherein the retained austenite amount of at least one of the mated member and the rolling elements is not more than 6% by volume.

Further, in the aLbov-mentioned construction of the rolling device, a carbide area coefficient ratio defined by dividing the carbide area coefficient of the mated member by that of the rolling element is preferaj)ly not more than 0.9.

The third object may also be accomplished by a rolling device comprising:

rolling eioments of rolling member; and a mated member of the rolling mr rolled, slid or moved relative to the rolling elements, in which the mated mr is made of carbon steel containing 0. 64-0. 94 by weight of C j 0. 1%-0. 7% by weight of. Si 1 0.54-1.1% by weight of Mn, and 0.14-0.6% by weight of Cr, and Fa and inevitable impurity elements in the remaining part,, and the mated member is subjected to a hardened heat treatment; and the rolling elements are made of an alloy steal containing Cri and the rolling elements are subjected to a hardened heat treatment, wherein a carbide area coefficient ratio being defined de area coefficient of the mated member by by dividing the carb.

that of the rolling element in not more then 0.9.

In the above-inentioned rolling devices, the mating member may be made up of 0. 6%-0. 9% by weight of C r 0. A-0. 51h by weight of Si, by weight of Kn, and 0.14-0.6% by weight of er, and F@ and inevitable Impurity elements in the remaining part, wherein the rolling elements may he made up of 0.95%-1.1% by weight of C, 0.154-0.35% by weight of Si, 0.1t 0. 54 by weight of Mn, and 1. 34-1. 6 4 by weight of Cr# and Fe and inevitable impurity elements in the remaining part.

Preferred embodiments in accordance with this invention will now be described with reference to the accompanying drawings, in which:- Figure I is a graph representing the off act of Ks point on the transformation expansion amount of steel material; Figure 2 is a graph to show a DI value in the relationship between material diameter and hardness after hardening; Figure 3 is illustrations of quench crack test pieces; (a) is a plan view of a rolling element test piece, (b) is a side view of the rolling element test piecer (c) is a plan view of a race test piece, (d) is a side view of the race test piece, and (a) is a notch part form view; Figure 4 (a) is a schematic diagram to show a rolling element static crushing test method and (b) is a schematic diagram to show a ring rotation breakage fatigue test method; Figure 5 is a graph to show the life test (material carbon content and life) results under lubrication mixed with a foreign material; Figure 6 is a graph to show the life test (matrix Cr content difference and life) results under lubricaticn mixed with water; Figure 7 is a graph to show the measurement results of an initial sound evaluation test (retained austenite amount on finished product sr,-face of inner and outer races and anderon value); 215 Figure 8 is a graph to show the measurement results of a sound degradation test (retained austenite amount on finished 23 product surface of inner and outer races and anderon value); and Figure 9 is a graph to show the measurement results aff an Inittial sound evaluation test (carbide area coefficient ratio between inner and outer races and rolling elements and anderon value).

The critical meaning of numeric value limits etc. according to the first aspect of the present invention will be discussed hereinafter.

First, the reason why the constitution range of the alloy compositions used In the first aspect of the present invention is limited will be discussed.

[C: Content 0.6b-0.9%, preferably Content OM-0.9%, is inore preferably Content 0.831-0.94) Since bar steel or tubular material is used and hot forgIng, warm forging, and ciutting are performed to manutacture inner and outer races of bearings. the workability of the inner and outer races la--gely affect the bearing costs. Generally, as the carbon amount of a material is decreased, its workability is improved. llowever, if the carbon amount is lowered too much.. hardness required for the bearing after hardening is not obtained. thus the lower limit in considered to be about 0.0.

However. the result of detailed study of the use state 24 - of ball bearings on the market, carried out by the inventors indicates that most of oven ball bearings of grease seal type with a seal generally considered to he clean environment except some "pure clean environments (in this case, the surrounding of a non-metal inclusion at the maximum shearing stress depth position becomes the start point of flaking)" chow a fatigue state of surface damage type containing the case where ccr=osion of rust, etc.i occurs due to entry of water, etc.

Therefores to provide bearings excellent in endurance life, the bearings must have a sufficient life in an environment in which corrosion of rust, ate., occurs due to entry of water. etc., and also a sufficient life for damage of surface start point type.

Then, the inventors have examined the bearing life is under lubrication mixed with a foreign material to reproduce damage of surface start point type. Figure 5 shows the examination result. The result clarifies that C% of 0.8% or =ore (p=eforaLblys, 0.93% ox ==c) in required to maintain the life from damage of surface start point type. Therefore, the lower limit of C% is sat to 0.8%. However. 11 C% exceeds 0.9%, soaking is required to remove macro carbides and segregation at the steel making time and in addition. deformation resistance increases and cold workability is also lowered, resulting in a rise in cc3t.

is Thusi the carbon content of the material is set to the range of 0.64 to 0.9%, preferably the range of 0.8% to 0.9% and more preferably the range of 0.83% to 0.9%.

[Cr: Content 0.1%_0.6%] Cr is dissolved in a matrix to enhance hardenabiiity, the resisting property for temper softening, etc., and after annealing, fo=e minute carbides for preventing crystal grains from being coarsened at the heat treatment timef lowering breakage sensibility and also raising the fatigue strength characteristic and crushing strength. To produce the effect, at least 0.1% or more of Cr is required. however, if 0.6% is exceeded, soaking needs to be performed to improve generation of macro carbides and segregation In the steel making process and the Cr addition cost and material cost rise. As t he content of Cr increasesi defo=mation resistance increases and cold wo=kability is lowered as with carbon.

Thus, the Cr content of the material is set to the range of 0.1% to 0.6%.

[": Content 0.54-1.14) Generally, co imp=ove ha=donabilityp r_n or Cr 15 added. Since er is a carbide preparation element, not all added Cr contributes to improvement in the hardenability of a matrix and if the content of Cr is too large, soaking Is required, thus Cr cannot rauch be expected from the viewpoint of the hardenability. Mn Is lower at cost than Cr. Then, to provide sufficient hardenability In a small Cr amount and paying attention to the fact that En is also a retained austenite preparation element effective for the rolling life under lubrication mixed with a fo=eign material, at least o.s% or more of mn 15 added. However, Mn is also an element enhancing iorrlte of material and particularly, 1.10 the carbon amount of the material is large (0.7% or mo=ch), when the content of mn exceeds 1.1%, the cold workability is lowered rema=kably.

Further, lú the content of Hn is too le=ges crystdl grains may be coarsened or the retained cuztenito anount may increase more than nociassary# raising the sensibility to breakage or lowering the crush strength. Thus. the Mn amount of the material Is set to the range of 0.5% to 1.14.

(S1: Content 0.1t-0.741 51 acts as a deoxidizer at the steel making time of material and is an element effective for improving hardenability like Cr and Rn, enhancing matrix martensite, and prolonging the bearing life. Thus, 0.1% or more, preferably 0.2% or more of 51 in added. Rowever, if the content of S! is too large, machinability, forgeability. cold workability are lowered; the uppe= limit in 0.71h or legs@,, preterably 0.5% or loss.

Next, the critical meaning of item other then the constitution range of alloy c=positions in the first aspect of the present invention will be hereinafter discussed.

[Ideal critical diameter D1 value] This DI value in one parameter representing hardenability. That is, the relationship between the diameter of material and hardness after hardening is that when the material diameter increases more than reasonable, the hardness lowers abruptly (b0Cause incomplete hardening state is entered and the portion not made martens itic increases). as shown in Figure 2. The D1 value indicates the critical value of the diameter. As a material has more excellent hardenability. a larger size can be placed in a complete hardening state (namely, the hardness after hardening can be raised); in other wordst the DI value grows. The D1 value is defined in various manners by experiments, etc.,; the D1 value applied in the invention Is defined In AIS1 (American Iron and Steel Institute) and is represented by expression (1) in inch units:

DI - (0.311 X Cl191) X (0.7 X Sil +1) X (3.33 X Yint +1) X (2.16 X Cr +1) ------- (1) By the way, if each alloy compositions of the material is in the rolling mamber maticiles the cond.Ltic>nz deacribed above, a problem may occur depending on the combination of the 1 t ions - For ex"le,, if the C, Cr content is C orapo 5 - ccmpaxatively anall and the 2M content Is comparatively large, the crystal grains are easily coarsened and if the hardenability is raised more than necessary, sensibility to breakage is enhanced. Resultantly, the rolling element or a race may lead to breakage because of various factors depending on the size or the shape; the productivity way lower or minute cracks remain in the bearing, lowering the fatigue life.

When the Cr content is comparatively small, if an attempt Is made to increase the Mn content for providing hardenability, the retained austenite- amount increases and dimension stability or the mechanicall strength may lower, decreasing the bearing function r rkably.

An the content of any of ef Cr, or Y-n increases, the element has the effect of lowering "rkability. Thus, it the contents oú C, ex, and Cri are increased at the same time, workability is impaired inevitably. If the content of C or Cr is increased, macro carbides are easily produced; if the contents of C and Cr are increased at the same time, it becomes necessary to perform soaking.

In the lnvs-bntion,, It is clarified that it Is also effective to thus limit each compositions amount of the rolling m.-; preferably. it is also necessary to define correlation between the compositions at the same time. That is 0 specifically it is found that the DI value defined in expression (1) may he limited to a predetc=ined range in addition to limiting each composition amount of the rolling member; thch D1 value;L limited to 4. 0 or less. On Ue other hand, if the DI vaLue is too smallo the hardenability is insufficient and the DI value can be applied only to small diameter bearings, lacking in convenience, thus the cost effect is low. Therefore, the DI value Is ser. to 2.5 or more to insure sufficient hardenability.

Now, assigning the maximum values of the compositions 23 C, Sle Hn,, and Cr to expression (1) DI t-Y 4.71 inches; assigning the minimum values of the compositions to expression (1), Di iq 0 - 84 inches where C content is 0 - 6% (but DI aR 0.965 inches where C content is 0 - B%).' These values are outside the DI value limit range of the invention (1. 5-4. 0 inches). That is.. if each compositlon amount range in the rolling member is satisfied, the resultant value may be placed outside the range of the invention; preferably, both each composition amount range and the DI value limit range are satisfied at the same time.

[Retained austenitel The retained austenite affects the rolling life desirably and has a large effect in use particularly in an environment wherein the bearing raceway surface is damaged and flakes off in severe use conditions, for example, under lubrication mixed with a foreign material. Therefore, a is rolling bearing exposed to comparatively severe load and lubrication conditions, such as a taper roller bearingo shall contain Ot by volume of the retained austanite of the inner and outer races and the rolling elements (rollers). on %he other hand, if the amount exceeds 22% by volume, the static mechanica2 strength of the rolling elements and the inner and outer races lowers remarkably. Thus, the content is set to St 22% by volume and preferably 12%-22% by volume.

If the life under severe conditions is not required more than necessary and the bearings are used in an environment in which load is comparatively light and it is less feared that a foreign material will be mixed in a lubricant (for example, rolling parts using balls as rolling elements such as ball bearings), importance may be attached to corrosion resistance. dimension stability, sound characteristic, etc more than the life under lubrication mixed with a foreign material. Since the retained austenite is not required more than necessary under such conditions, the lower limit value need not be def ined - As we have discussed, the rolling member of the 'ains a basic composition of carbon steel for invention cont machine structures generally hard to conceive as a bea-ring material; the material or working cost is minimized and the manufacturing cost if; reduced drastically by optimum alloy composition design. Further, considering a production problem of breakage at the heat treatment time, longer-life and more inexpensive rolling members than those made of bHoaring steel from the functional viewpoint are provided.

The "foreign material" in the description made so far refers to a material producing an impression when it is caught between rolling members such as a metal piece, the impression becoming the start point of cracks, having a harmful affect on the rolling life.

The critical meaning of numeric value limits, etc., according to the second aspect of the present invention will be discussed hereinafter.

A case will be discussed where a low-cost rolling device comprising a plurality oi rolling members and mated members used for application wherein water easily anters (namely, to accomplish the second object of the invention) is applied to a rolling bearing.

The rolling bear-Ing usually is made up of an outer race, an inner race, a plurality of rolling elements, a cage, and a seal; the outer race and the Inner race, which will also be hereinafter called inner and outer races, and the rolling elements are as follows:

[inner and outer races] The numeric value Limits and critical meaning of C, Cr, mn, Siy and DI value, and the retained austenite after heat treatnent are the came as those of the material of the above mentioned embodiment according to the first aspect of the present invention except that the upper limit of Si is set to is 0.5% by weight to improve workability. Particularly, It the conditions of lubrication mixed with a foreign material are comparatively moderate as with ball bearings using balls as rolling elements, the lerder limit value of the retained austenite need not he defined.

2C The material of the inner and outer races of the invention Is bearing steel with the Cr amount decreased to lower corrosion resistance moderately and added M increased to provide hardenability and reduces the material and working costs of the Inner and outer races of the bearing drastically.

23 (C cl rolling element: Content 0.95%-1.1%1 the rolling element As described earlier, basically t uses the SUJ2 material from the relationship of the ball manufacturing process. Therefore, the C COMPosition range is 0.95-1.11 as defined in JIS G4805. (Cr of rolling element: Content 1.34-1.6%1 5 For Cr of the rolling 'almaent, as desc=ibed earlier, basically the SUJ2 material is used because SUJ2 is lower cost as a whole (also considering that soaking is required). Then, the Cr amount range is 1.3%-1.6% as defined in ilS G4805.

[mn of rolling element.. Content As described above, basically the rolling element uses the 5UJ2 material. Thus, the 24n amount range is 0.54 or leSS as defined in J1S G4805. if the addition amount is too small, ha=denability proper as a bearIng materlal becomes insufficient, thus the lower lizil: is set to 0.1% or more.

[S! of rolling element: Content 0.15%-0.354] As described above. basically the rolling element uses the SUJ2 material. Thus, the 51 amount range is 0.15%-0.354 as defined in J15 G4005.

[Matrix Cr content difference between inner and outer races and rolling elements: 0.6% or mozel An described earlier. the bearing life in an environment in which corrosion occurs due to entry of water, etc.r is prolonged If the corrosion resistance of inner and outer races is lowered a little with respect to rolling elements. TO check the 1.ife prolonging effect furthermore experimentally, the following life test is conducted:

A ball bearing comprising rolling element-is made of SU32 material and inner and outer races made of material with the Cr content lower than that of the rolling elements is used to conduct a life test in a state in which water is mixed in a lubricant, and the bearing damage state recognized in market research is reproduced. However r the Cr content actually affecting corrosion ri6sistance is the Cz amount contained in a matrix and the Cr amount contained in carbides is a2most insignificant. Then, the area coefficient of the carbides in directly measured, the Cr amount in the carbides is calculated from a conversion expression of applying a Cr distribution coefficient in ferrite and carbides ("Tekkou zairyou" Shadan houjin Nippon kinsoku gakkail 1985, p.44), and all Cr amount minus the calculated Cr amount is used as matrix Cr amount (mCr). That is, assuming that the measurement value of the carbide area coefficient is am, the matrix Cr amount affecting corrosion resistance is represented by the relation:

MCr - Cr (I - 28 (1 + 4C) X Cm/IOCOO) -------- (2) Figure 6 shows the result of the life test. When the matrix Cr content difference resulting from subtracting HCr of the inner and outer races from mCr of the rolling elements falls below 0.6%, the life lowers abruptly. Thus, the matrix Cr content difference between, the inner and outer races and the rolling elements is defined as 0.6% or more. However r considering stability of the life, preferably the difference is set to 0. 75% or more.

34 - The inventors have examined damaged bearings in detail regarding the above-mentioned phenomenon and have found that (1) cracks branching infinitely and having a complicated shape often occur just under the rolling surface and, that (2) the cracks occur at almost constant depth independently of the bearing load. Zt is hard to consider that the cracks occ= due to rolling!atique; it is estimated that water decomposes to generate hydLrocen in an environment in which water is mixed in the lubricant and corrosion occurs, and that hydrogen enters the bearing raceway surface and makes the surface brittle, leading to early breakage.

Since hydrogen generated due to corrosion tends to more enter raetal on the cathode side where corrosion resistance is high and rust does not occur (oxygen generated ai- the same time ls tends to enter the side where corrosion resistance is low), it is considered that the life prolonging effect is produced by making the corrosion resistance of the inner and outer races a little lower than that of the rolling elements. Among the rolling elements and the inner and outer races, the fixed race load 2one is the severest load condition as described above, Thus, the fixed race is not placed on the cathode side, whereby the above-mentioned breakage caused by hydrogen can be made hard to occur.

The critical mear-ing of numeric value limits, etc., according to the third aspect ol the present invention will be discussed hereinafter.

The material constitution and other characteristics of compositions for applying bearing devices to accomplish the third object of the invention to ball bearings used for UDDs. VCT5p air conditioner fan motors, etc., for which a good sound characteristic is required will be discussed.

[Inner and outer races) The numeric value limits and critical meaning of C.. Sif Mn, and Cr am unts are the same as those of the second aspect of the present invention described above. However, fox C, when the retained austenite amount is set to 64 or loss f or the purpose of sound characteristic improvementr the IMMr lirLit con be selected up to 0.6%. In doing noi a long life under lubrication mixed with a foreign material is lowered to acne extent, but both sound characteristic improvement and a long life under lubrication mixed with a foreign material can be acc=plished in good balance.

In the material constitution of the inner and outer races in the bearing device according to the thIrd aspect of the present invention, the C and Cr amounts are decreased relative to the conventional bearing steel to moderately lower the carbide area coefficient of the raceway surface and Kn is increased to provide hardenability for drastically reducing the material and working costs of the inner and outer races of the bearing.

tRolling elements) The numeric value limits and critical meaning of C, Si, w 36 - Nn, and Cr amounts are the same as those to accomplish the second object of the invention described above.

(Retained austenite amount or- finished product surface of Inner and outer races does not exceed 64) The retained austenite amount when rolling devices or rolling mrs are used fox sound characteristic improvement will be discussed.

Sound problems of L-all bearings are that the initial sound of a new product is poor or that sound is degraded as the product in used. The sound of a new product depends on bearing clearance/ working accuracy. surface coarseness, etc. If the factors concerning bearing manialacturing axe standardized (for example, JIS G 1514, grade 5 or =re),, when a bearing is bullt in, rolling elements are pressed against inner and outer races and rdinute impressions occur on the inner and outer races, which becomes the main cause of worsening the initial sound.

Easy occurrance of minute impressions depends on the hardness and structure cú the bea=ing.

In the invention, an ande--On value -4s used in a hoaxing sound evaluation method. The ande=on value is provided by taking bearing sound noise as a vibration component with an anderon meter.

Figure 7 shows the test result of the relationship between the anderon value of a bearing as a new product and the retained austenite anount of inner and outer races of finished product bearing. It the retained austenite amount grows exceeding 6%, minute impressions easily occur. As a result, the initial sound worsens. The initial sound of the conventional S= bearing (9) in higher then that of the bearing of the invention (0) even in the same austenite amount.

On the other hand, for sound degradation as a bearing is used, it the bearing is hold f or a long time In a preload state, particularly at higher temperature, minute impressions easily occur on the contact portions between the rolling elements and the inner and outer races, degrading sound. It an impact load is imposed on the bearing, minute impressions also occur on the contact portions between the rolling elements and the inner and outer races. degrading sound remarkably.

Figure 8 shows the result of imposing a given load on the bearing whose initial sound is measured in Figure 7 for causing minute impressions to occur and then again executing sound measurement. It the retained austenite amount grows exceeding 64, minute Impressions still easily occur. worsening sound ra kably.

Thus, the retained austenlte amount on the finished product surface of the bearing ac--o=ding to the third aspect of the present invention shall not exceed 6%. rurtherf it the initial sound and sound degradation level are required strictly, preferably the retained austenite anount does not exceed 2%. However, the hardness and structure of the rolling elements aúiect the ball bearIng sound characteristics thus treferably, ball coarseness in 3 lin Rms or less, surface 38 - hardened treatment is executed after heat treatment, and tenpering is again executed.

[Ratio between carbide area coefficient of rolling elemen" and that of inner and outer races does not exceed 0. 9] As described above, the sound of a new product depends on bearing clearance, working acc=acy, surface coarseness, etc - if the factors concerning bearing manufacturIng are standardized (for example, JIS G 2514, grade 5 or nore), when a bearing is built in, rolling elements are pressed against inner and outer races and minute impressions occur on the inner and outer races,, thereby worsening sound. However.. the retained austenite amount on the finished product surface is not set exceeding 6%, whereby the initial soundcan be decreased. Also, the retained austenite amount is not set exceeding 64, whereby sound degradation as the bearing is used ted.

can be prevenU The inventors have studied further reduction in the initial sound and have captured suble change In the sound characteristic according to "swell combination of the inner and outer races and the rolling elements - That is, the inventors have found that vibration caused by "swell" is damped if placement of carbides becoming projections particularly in a delicate uneven shape an the work finished face is lowered only for the inner -and outer races by adjusting the carbide a=ount on the bearing flnished raceway surface.

Figure 9 shows the relationship between the rat-Jo - 39 defined by dividing the carbide area coefficient of the inner and outer races by that of the rolling elements and the sound characteristic. In the f igure, (0) denotes the bearing of the invention and (0) denotes the conventional 5UJ2 bearing. The sound decreasing ef fect according to the combination appears in the region in which the carbide area coefficient ratio value defined be dividing the carbide area coefficient of inner and outer races by that of rolling elements (that ist = carbide area coefficient of inner and outerraces 1 carbide area coefficient of rolling elements) does not exceed 0.9.

Note that the carbide area coefficient ratio value is defined by dividing the carbide area coefficient of Inner or outer races by the carbide arect coefficient of rolling elements.

As we have discussed.. if working is performed at the current high working accuracy technical level under bearing specifications considering sound, the ratio of the carbide area coaúiicienz of the inner and out-= =ace& zo that of the =Olling elements needs to be set to a range not exceeding D. 9 to furthermore decrease the initial sound characteristic in the same retained austenite amount. Furtheri iff the initial sound and sound degradation level are required strictlyr preferably the carbide area coefficient ratio is set to the range of 0.5 to 0.9.

Hereinafter, Example 1 according to the first aspect of the present invention will be discussed.

Example 1:

Example I assumes application to roller bearings, etc.,, in particularly severe conditions under lubrication mixed with a foreign material.

Since inner and outer races and rolling elements are manufactured by different methods although they are rolling members, it general manufacturing process is assumed for evaluating material workability.

That iis, to manufacture the inner and. outer races, usually a material is warm- or hot-forged, then spheroidized or softened,, then turned and worked. On the other hand,, to manufacture the rolling elements, a material may be tu=ned and worked as with the inner and outer races; for most small bedrings, cold working (header working, press working) is executed for a coil material. Then, a machinability test with a high-speed lathe is conducted for the inner and outer races and evaluation of cold woxkability by header working is executed for the rolling elesuents.

(1) Alloy compositions and evaluation of necessity for soaking treatment, cutting too! life, metal mold life, and gtindabi2ity Table 1 lists composition constitutions and DI values of steel species of the example and a comparative example.

Table 2 lists necessity for soaking treatment and evaluation and comparison results of cutting tool- life, metal mold life by header working, and grindability.

Table 1

Steel c si mn Cr D! specles (Wtt) (Wtt) (Wt%) (Wt%) value Al 0.87 0.30 0.87 0.25 2.1 A2 0.89 0.35 0.80 0.30 2.2 A3 0,83 0.45 0.91 0.55 3.3 A4 0.85 0.48 0.75 0.35 2.4 Example AS 0.87 0.44 1.07 0.54 3.e A6 0.93 0.54 0.79 0.20 2.0 A7 0.86 0.17 0.65 0.48 2.1 AS 0. Ell 0.25 0.80 0.14 1.6 A9 0.65 0.33 0.82 0.32 1.9 A10 0.78 0.36 0.81 0.32 2.2 All 0.99 0.68 1.09 0.49 4.

A12 0.08 0.46 1.07 0.04 1.9_ A13 0.84 0.32 1.23 0.33 3.1 Comparative A14 0.86 0.74 1.06 0.45 3.9 Example A15 0.89 0.48 1.75 0.04 3.3 A16 0.90 0.62 1.50 0.3s 4.8 A17 0.81 0.18 0.72 0.12 1.3 Ale 1.02 0.35 0.63 0.33 2.5 Alg 0.85 0.34 0.83 0.75 3.

SUJ2_ 1.01 0. 0.3 45 3.

Table 2

Steel Soaking Metall mold Tool No. of Quench crack 1(X10 lif ground C,4LIllatioxL life test SPecles treatment pieces) (z 4 piece Rolling J1) element _ AI No required 21-6 222 30 0 0 A2 NZ required 213 218 29 0 A3 No required 208 210 28 0 A4 NO required 216 223 3D 0 Example AS NO required 211 204 1 28 0 A6 NO required 22a 224 io c c A7 NO required 225 219 29 0 AS NO required 231 224 31 0 0 A9 No required 253 218 30 c Alc 90 required 2.19 225 29 0 All NO re"ired 145 107 29 c X A12 NO required 220 227 38 0 X A13 NO requirwid 75 63 28 CompazatIve 14 50 required 68 61 29 0 0 & Example A15 90 required 69 so 27 X X A16 NO required 54 58 28 X X A17 XCI required 237 228 31 0 0 A18 Required 78 65 28 0 0 Required 152 12 29 0 0 SW2 Required 56 t 55 L28 C> 0 j To determine whether or not the soaking treatment is required, the macro structure and microstructure Of billet i cross section of specimen material are examined and whether macro carbides or thick stripe segregation harmful for the life exists is checked.

The cutting tool life and the metal mold life are evaluated under the following conditions; Cutting tool life:

Cutting machine: High-speed lathe Tool: PIO (JIS B 4053) Cut rate: 180-220 m/sec Feed amount: 0.2-0.3 mm/rev Depth of cut: 0.6-1.0 mm Specimens are cut under these conditions in accordance i5 with a cutting tool cutting test method (JIS E 4011) and the cutting tool is assumed to reach the tool life when the flank wear amount of the cutting tool reaches 0.2 nm. Steel in the examp2e and comparative example is high-carbon bearing material. Before turning and working, the steel is spheroidized (heated to Al point or more of the material) for s-ipply to the test.

Metal mold lile:

Metal mold: V.210 (JIS B 4053) Fractional reduction in upsetting height: 15%-20% working rate; 30D-400 pieces per minute Lubrication: Zinc phosphate coat + lubricant The steel species are worked. when cracks occur on the metal mold or the metal mold is broken and a flaw or deformation appears on a worked workpiece, the metal mold is assumed to reach the metal mold life, which is indicated in the number of workpieces worked so far.

The soaking treatment I&A determined to be recruized for the steel species with the C amount exceeding 0.9t or with the Cr amount exceeding 0.6% as a result of the examination.

For the metal mold life and machinability, workability lowers for the steel species with the C amount exceeding 0.9%, the Mn ai oiount exceeding 1. 1% 1 the Cr amount exceeding 0. 6 t, the Si a-mount exceeding 0. 7%, thus the metal mold life and the tool life tend to lower remarkably. A part of the evaluation test after the heat treatment in not conducted for the steel species other than SUJI for which the metal mold or tool life lowers remarkably.

The heat treatment conditions are as follows:

Harden.ing: Hold at 830C-9700C (In Cp 0.6-0.6 RE gaa atmosphere) f or 30-40 minutes, then harden in an oil bath at 6DOC-900C (after hardening, wash and degrees, then cool to room temperature).

Tempering; At 160OC-1800C for 2 hours An evaluation experiment of grinding workability is conducted for the steel species with good cold workability and machinabi2ity to which the above-mentioned heat treatment is applied. The test conditions are as follows:

[Grinding test] Grind stone; wAIDO Grinding liquid: Soluble type Grind stone peripheral speed: 2800-3000 m/min Samples equivalent to the inner raceway surface of a rolling bearing are ground with a grind stone under these conditions, deformation and plugging of the grind stone are observed, and the number of samples ground by the time the grind stone is dressed (number of ground pieces) is examined.

As a result, all steel species of the invention are equal to or superior to bearing steel and are also good in grinding workability.

The evaluation is workability evaluation. In fact, a large number of breakages may occur at the heat treatment time 13 because of the effect of the size, shape, etc., of the bearing, lowering heat treatment productivity. Then, cluench crack sensibility is also evaluated.

(Quench crack test] Using test pieces of the rolling elements and races shown in Figure 3, a quench crack sensibility test is conducted under the same heat treatment conditions as listed above. With the number of test pieces, n=S, the steel species with a quench crack occurring on at least one test piece is marked with X in Table 2. A quench crack tends to easily occur in steel species with the Cr content less than 0.1% or the Mn addition araount exceeding 1.1%, particular2y the D2 value exceeding 4.0 because Of the effect of coarsening crystal grains and the effect of a transformation stress because the IM point lowers.

(2) Rolling member function evaluation:

A life test, a static crushing test, a rotation breakage fatigue tent, and the like are executed for rolling member test pieces formed using the steel species of the example and comparative ex&mple and the functions of the rolling imembe=e are evaluated and compared.

A thrust type bee-ring steel life tester described on pages 10-21 of 112>kyehukou binran First edi4.tion (edited by D,ezlkioei"kou kenkyujyoo Rikougakushar putlIshed on May25,, 1969) is used for the life test. The cumulative number of stress repetitions to the time when flaking occurs on each sample (life) is examined.. Weibull plots are prepared, and each LIO life in found from the Welbull distrilmtion result. Further, a static crushing test is conducted for the rolling elements and a rotation breakage fattique test is conducted for the races as other function evaluatIon tests.

The tent conditions are as follms:

2C (Table 3 list the retained austenite anounts measured ot life tent pieces each 6 = thick and -,.be functIon evaluation results thereof.) table 3 ?hi'ust type i1FE test Steel 7 Llo Me under clean MLIIZ#Cdllfw under lubrication Rolling element Ring t tatIon breakage species (Wtr) lubrication (xler) with foreign material cruchtnIC strent th fatigue Itfe (ton) Lea life (xlo&) AI 17 5.9 15.0 2 5, 4, a 25.4 4.6 AI 17 6.! 1.5.6 23.8 5.2 A4 Is 23.9 4.1 A3 22 8.2 13.6 5.9 A6 is 6.8 13.6 25.4 4.7 A7 12 5.1 11.8 23.3 3.0 A& is 3.0 14.2 24.7 3.7 A9 9 0.5 1.8 20. 1 2.1 Comparative A10 10 1.0 2.1 22.1 2.3 Exateple A12 14 2.2 16.5 16.4 1.1 - AI? is - 1.6 ---- - 11.4 - 1.8 16.4 - j 1 m 1 [Life test] Life test conditions under clean lubrication: Test contact pressure: 5200 Mpa Number of revolutions: 3000 cpm Lubricant: No. 69 turbine oil Life test conditions under lubrication mixed with foreign material:

Test contact press=-: 4900 Mpa Number of revolutions: 3000 cp= Lubricant: No. 68 turbine oil Mixed foreign material:

Constitution: Pe3 C family powder Hardness: IERCS2 Grain diameter: 74-147 gm Mix a=mnt.. 300 pp= in lubricant The rolling nembers of the example show the life exceeding SUJ2 both under clean lubrication and under lubrication mixed with foreign material. Particularly, long life is obtained because of the 9úfect of the retained austealte under lub=ication mixed with foreign material. On the other hand. the steel species with the carbon content lens than 0.8% (comparative example steel species A9 and A10) and those with the C= addition amount less than 0.1% and having a small crystal gra-4n coarsening suppression effect (comparative example steel species) do not 49 - produce a good life particularly under clean lubrication.

[Other function testal Rolling J20Mber static crushing test conditions:

Cylindrical rollers 1-9 = In diameter and 18 mm in length are used as toot pieces and a set of three pieces are tested with a 200t Amslor tester, as shown in Figure 4 (a). The crush value when any one of the test pieces is broken is =ensured ancl an evaluation is made with an average value o! n-S sets.

(Ring rotation breakage fatigue test) ic Figure 4 (b) shows an outline of the tent method. A ring-like tent piece is sandwiched between a press roll and a drive roll and is rotated while a load is imposed on the press roll. The test conditions are listed below. The breakage life is indicated as the number of stress repetitions to breakage from the inner diameter face and is evaluated as LID.

Test load: 400 kgf Number of stress repetitions: 19260 cpsa Lubrican?-,: No. 68 turbine 011 Test ring: 13. 8 mm in inner diameter X 20 = in outer diameter X 8 = thick In the rolling element static crushing test and the ring rotation breakage fatigue test, the example of the first aspect of the present invention (steel species AI-AS) shows the function equal to a= greater than 5UJ2. Particularly, in the ring - so - rotation breakage fatigue test, a gocd life characteristic is provided because the zetained austenite acts on crack retention. Example A7 is a little inferior to Aj-A6 in thrust type life test and ring rotation breakage fatigue life because Si is less than 0.2% and example AS is a little inferior to A1-.A6 in thrust type life test (particularly, under clean lubrication) and ring rotation breakage fatigue life because C is less than 0.83%, but they have sufficiently excellent performance as totally compared with comparative example A9-A17 and SUJ2- In contrast,, in steel species with the carbon content less than 0. 8% (A9 and A10) and those with the Cr content less than 0.2% and having hardenability mainly augmented with Mn (A12) in the comparative example, the Cr effect of suppressing coarsening of crystal grains is too small and a good life particularly in the ring rotation breakage fatigue life test is not provided, Further, for comparative example A12, the retained austenite amount is large exceeding 22% and the crushing strength tends to lower.

In comparative example A17, which has insufficient hardenability, an incomplete hardening phase occurs in the core and both the crushing strength and the fatigue strength lower.

As we have discussed, the rolling members of the invention are equal to or greater than the conventional rolling inembers made of bearing steel (SUJ2) in life and mechanical strength and can be reduced drastically in the material cost and the bearing manufacturing cost as inexpensive rolling members as compared with the conventional rolling members made of bearing steel, producing an extremely large effect on practical use.

The rolling a,ers of the first aspect of the present invention can be preferably applied not only to rolling bearings, but also to parts coming in rolling contact# rotating, or sliding, such as shafts and pins, particularly mechanical parts manufactured by performing cold forging or cold drawing treatment for a material, such as one-way clutch sprags.

Hereinafter, Example 2 according to the second aspect of the present.4,. nvention will be discussed.

Example 2..

Example 2 assumes ball bearings, etc., used particularly in conditions where water can enter.

The material compositions of the inner and =tar races of the invention and necessity for soaking treatnent axe evaluated and material workability is evaluated by assivaing a general manufacturing process. To work the inner and outer races, usually a material often is warm- or hot-forged, then annealed, then turned and worked. [Evaluation conditions] Soaking treatment:

The macro structure and microstructure of billet cross section of 3Pecimen material are examined and whether iT(ac=o carbides or thick stripe segregation harmful for the life exists is checked.

Cutting tool life:

Cutting machine: High-speed lathe Tools P1O (JIS E 4053) Cut rate: 180-220 =/sac reed amount: 0.2-0.3 =/rev Depth of cut: 0.6-1.0 SpecImens are cut under these conditions in accordance with a cutting tool cutting test method (J15 B 4011) and the cutting tool in assumed to reach the tool life when the flank wear amount of.the cutting tool reaches 0.2 mm. However, steel In the example of the invention and comparative exanple is high carbon bearing material. Before turning and wo=king, the steel in spheroldized (heated to A1 point or more of the material).

Table 4 lists the evaluation results.

Table 4

Steel c si mn 1 cr soaking Tool l if 0 specieg (wtZ) (wtl) (wt),t (vtZ) treatment cl 0.86 0.25 0.90 0.27 Not required 225 C2 0.85 0.22 0.85 0.33 Not required 215 C3 0,86 0.34 0.8z 10.23 Nct required 216 C4 0.88 0.36 0.83 0.33 Not required 210 CS -0.81 0.37 0.85 0.34 not required 220 C6 0.82 0.47 0.83 0.32 Not required 2C5 Zx=ple C7 0.54 0.15 0.83 0.33 Not requIred CS 0.85 0.33 1.03 0.32 Not required 202 C9 0.82 0.34 0.58 0.34 Not required 220 CID 0.84 0.35 0.84 0.55 Not required 208 C11 0.83 0.33 0.83 0.17 Not required 219 C12 0.85 0.18 0.05 0.19 Not required 235 C13 1.02 0.31 0.63 0.35 Required 65 C14 0.75 D.33 0.82 0.34 Not required 218 cls 0.70 0.28 0.81 0.38 Not required ZZ3 C16 0.63 0.30 0.95 0.48 Not required 236 C17 0,61 0.29 0.86 0.54 Not required 249 Comparative G18 0.83 0.62 0.83 0.31 Not required 122 Exa=ple C19 0.83 0.05 0.83 0.34 Not required 232 C20 0.84 0.32 1.23 0.33 Not required 63 C21 0.82 0.34 0.3.5 0.32 Not requixed 241 C22 0.85 0.31L 0.83 0.75 Required 112 C23 0,82 0.33 0.84 0.04 Not required 223 1 1_ 5UJ2 1.01 0.23 0.32 1.45 Required 55 54 The inner and outer race material of the second aspect of the present invention need not undergo soaking treatment and is &loo good in machinability; the material and working costs can be reduced as ared with conventional SW2. On the other hand, comparative examples C13 and C22 containing high C% and high Cr% are determined to need soaking treatment, and axe not good in workability. Comparative examples C18 and C20 containing high 51% and high Mn% also lower in workability. C18 contains upper limits or less of C and Mn.

and has Si lese than 0.7%, thus is good as compared with C2D and SUJ2, but worsens a 1Ittle as compared with Cl-C12 containing Si 0.5% or less.

The invention Is intended for satisfying cost reduction and a long lifer thus normal hardening treatment and tempering is treatment most often used for general rolling bearings and at the lowest cost are adopmed for executing an evaluation test; carburizing, carbonitriding. etc.r Is not performed.

The heat treatment conditions in the example according to the second aspect of the present invention are as follows:

Heat treatment conditions:

Hold In the temperature range of 810C-850C for 0.5-1 hour in an RX gas atmosplhere at carbon potential CP = 0.6-0.8, then harden, next temper for 2 hours at 160OC-2000C.

[Life test conditions unde= lubrication snixed with 23 foreign nateriall A thrust type bearing steel life tester described on - C5 - pages 10-21 of "Tokyshukou binran" First edition (edited by Denkiseikou kenkyujyo, RI, kougakusha, published on May25, 19 6 9) is used. SUJ2 balls are used for rolling elements. The cumulative number of stress repetitions to the time when flaking occurs on each sample (life) is examined, Weibull plots are prepared, and each L10 life is found from the weibull distribution result.

Test contact pressure: 4900 Xpa Max.

Number of revolutions: 3000 cpm Lubricant: No. 68 tuibine oil Mixed fo-reign materia2t Constitution: Stainless family powder Hardness: KRCSO Grain diAm ter: 35-95 i5 Mix amount: 30.0 ppm in lubricant Table 5 lists the life evaluation results.

-Table 5

Steel Surf ace Lif C under lubrication mixed speclee hardness with foreign material (HV) L.,Q_ life (x101) cl 750 15.3 C2 746 14.8 Example C3 741 16.3 C4 764 15.6 CS 742 15.1 Comparative C13 745 - 15.1 Example -

C14 737 9.2 C15 723 7.2 C16 719 6.5 C17 706 5.8 C19 683 3.1 C21 658 2.8 C23 694 3.4 745 9.8 The inne= and outer race material according to the second aspect of the present invention has hardness Fiv 700 or mcre after hardening and tempering and shows a long life. ComparatIve example C13 inferior in workability, - but containing C% of about it shows hardness and llf e almost equal to those of the Inner and outer material of the invention. on the other hand. 5UJ2 lowers a little in life at the normal hardening tenperatures adopted In the example as compared with the inner and outer material of the invention. C14-C17 containing less than 0.9% of 0 to enhance only workability tend to lower In hardness and retained austenite; the life 1OW43X5 C19, C21, and C23 containing less than the lower linits of SI, Mn, and Cr have hardness of Rv 700 or less; the life lowers.

[Life tent conditions under lubrication mixed with water] Next, a life test is conducted assuraIng entry of water - 57 in a lubricant under clean lubrication to reproduce the damage state on the market. Grease lubrication is executed, a bearing seal is removed.. and tap water is poured into a bearing housing at a rate of 1 cc/hour.

Test bearing: 6203 (single row deep groove ball bearing) Test contact pressure: 2000 Mpa max.

Nunl>er of revolutions: 7000 cpm Lubricant: Albanial grease (Showa shell) Water mixing; I cc/b6ur (tap water) The carbide area coefficient is used to find the matrix Cr content difference. To directly measure the area coefficient, the issue on the bearing surface is shot under an electron microscope, only carbides are extracted fror, the ground of the electron microscope image by an image analyzer, and the area, the number of pieces, and the like are measured for calculating the area coefficient.

Electron microscope: JSM-T220A manufactured by Nihon densisha Image analyzer: TEM2000 manufactured by Table 6 lists the test results.

- ss - Table 6

No.!=or and Rolling Hat=ix I'= Life under cuter race element steel difference 1.abricart steel species species (X) mixed with water LIO (hour) 1 SW2 0.84 41.2 2 C2 5UJ2 0.79 39.2 3 C3 SW2 0.88 43,6 4 C4 5UJ2 0.80 40.9 C5 SW2 0.78 38.6 6 C6 5UJ2 0. eo 39.2 Example 7 C7 5UJ2 0.79 39.4 a C8 9UJ2 0.80 40.2 9 C9 5UJ2 0,78 38.3 C10 5UJ2 0.61 32.4 ii C11 5UJ2 0.93 44.3 12 C12 BW2 0-9-1 42.6 13 5UJ2 5UJ2 0 9.0 14 CIL 7 S17J2 0.55 15.6 C17 C17 0 8.2 16 cl C1 7 0.30 9.3 Comparative 17 C10 Cl? 0.07 8.5 Exe le is ell C17 0.38 9.7 19 cl cl 0.00 6.3 C11 cl C.03 7.2 1 21 SW2 C17 1 - 0.55 - 6.5 Each of combinations of the inner and outer races of the invontion made of CI-C12 and the rolling members made of SUJ2 contains the matrix Cr content dif f erence of 0. 6 % or more and provides a sufficient endurance life even under lubrication mixed with water.

on the other hand, comparative example containing the cr content difference of less than 0.6% lowers in endurance life. Nos. 13, 15, and 19 comprising the same steel species in combination also contain the Cr content difference of less than 0.6%,, thus lower in life; the same steel species combination having better corrosion resistance is a little better in life. In contrast, No. 21 having lowered corrosion resistance of the rolling el;iment has a short life.

T hue, the life prolonging effect of the bearing of the invention in an environment in which corrosion of rust,, etc. f occurs due to entry of water, etc.,, is produced by making corrosion resistance of the inner and outer races appropriately lower than that of the rolling elements. Since it is difficult to change the steel species of the rolling elements of ball bearings f r= working process control, SUJ2 is used as material and is combined with the inner and outer races made of low-cost material containing the Cz amount decreased f or appropriately lowering corrosion resistance, whereby lower-cost and longer-life bearings than the conventional bearings can be provided.

Hereinafter, Example 3 according to the third aspect of the present invention will be discussed.

Example 3:

Example 3 assumes ball bearings, etc., particularly for application where low vibration and low noise are required.

SUJ2 is used as material of rolling elements. steel species EI-ElS of material compositions 'Listed in Table 7 1e) and steel species B16-E23 and 5UJ2 for compazison (comparative example) are used a:s inner and outer races.

(1) Alloy compositions and evaluation of necessity for soaking treatment and workability First, necessity for soaking treatment is evaluated for each specimen material and a cutting test with a high-speed lathe is conducted based or. a general manufacturing process of the inner and outer races for evaluating workability.

[Evaluation conditions] The soaking treatment and cutting workability evaluation conditions are the same as those of examples 1 and 2. That is# for the soaking treatment, the macro structure and microstructure of billet cross section of specimen material are examined and whether macro carbides or thick stripe segregation ha.-mful for the life exists is checked.

For the cutting workability, specimens are cut under the above-described conditions in accordance with a cutting tool cutting test method (J15 B 4011) and the time (minutes) until the flank wear amount of the cutting tool reaches 0.2 m is assumed to be the tool life. The workability is evaluated according to the tool life.

Table 7 lists the results.

Table 7

Steel c si Mn C. r S oaking Tool life species (vtZ) (vtZ) OftZ) (wt2) treatment (min) El 0.86 0.25 0.90 0.27 Not required 225 X2 0.85 0.22 0.85 0.33 Not required 218 33 0.86 0.34 0.82 0.23 Not required 216 E4 0.88 0.36 0.83.33 Not required 220 0.33 LF5 0.81 0.37 0.05 0.34 Not required 220 E6 0.52 0.47 0.83 0.32 Not required 205 V 0.84 0.15 0.83 0.33 Not required 220 Example E8 0.85 0.33 1.03 0.32 Not required 102 E9 0.92 0.34 0.58 0.34 Not required 220 E10 0.94 0.35 0.54 0.55 Not required 2013 Ell 0.63 0.33 0.83 0.17 Not required 219 E12 0.85 0.18 0.85 0.19 Not requ--red 233 213 0.75 0.33 0.82 0.34 Not required 215 914 0.70 0.28 0.81 0.39 Not required 223 Els 0.65 0.30 0.85 0.441 Noz required 236 X16 1.02 0.31 0.83 0.35 Required 65 E17 0.56 0.29 0.86 0.54 Not required 249 Zia 0.83 0.62 0.83 0.31 Not required 122 E19 0.83 0.05 0.83 0.34 Not required 232 Coffarative- - 0.84 0.32 1.23 0.33 Not required 63 EXORPle Z20 E21 0.82 0.34 0.35 0.32 iNct required 241 322 0.85 0.34 0.83 0.75 1 Required 112 E23 0.82 0.33 0.84 0.04 Not required 223 SUJ2 1.01 0.23 0.32 1.45 Required 55 Steel species E1-ú15 used as tt-he inner and outer race specimen& of the example need not undergo soaking treatment and are also good in machinability; the material and working costs can be reduced as compared with conventional SUJ2. on the other hand, of steel species El-ElS used as the inner and outer race specimens of the comparative example, E16 and E22 containing high C% and Cr% contents are determined to need soaking treatment., and are not good in workability. E18 and ú20 contain.ng high Si and Nnk contents axe also lower in workability.

(2) Evaluation of heat treatment conditions According to the third aspect of the present invention,, hardening treatment and tempering treatment xtogt often used for general rolling bearings and at the lowest cant are i5 applied for executing an evaluation test to provide pieces having a good sound charactexistic at low cost; special treatment such as carburizing or carbonitriding is not performed. However., the retained austenite amount needs to be decreased as a sound countermeasure, thus desirable heat treatment conditions are evaluated.

The following three types of heat treatment A-C changing the tempering trature are applied to inner and outer races and rolling elements made of steel species EI and SW2, and the retained austenite (TR) amounts on the surfaces of the finished product specirmns provided &=c compared.

treatment conditions] [Reat t Hold for 0.5-1 hour at temperatures BIOOC-8500c, then harden. Subsequently, temper under the following heat treatment conditions:

Heat treatment condition: A Temper for two hours at 160IC-2000C.

Heat treatment condition: B Temper fortwo hours at 2OCIC-2400C.

Heat treatment condition: C Temper for two hours at 220OC-2600C immediately after subzero treatment in applied:

Table 9 lists the retained austenite amount measurement results for the f iniehed product specimens provided. As a resultt heat treatment A with the retained austenite amount of the inner and outer races exceeding 124 by volume in 13 improper from the viewpoint of sound countermeasures. Heat treatment B and heat treatment C with the less retained austenite amount are proper; heat treatment B applying no subzero treatment is more desirable if importance is attached to the cost.

(3) Life evaluation under lubrication mixed with icreign terial How general ball bearings are used on the market is examined in detail and a life test of tested ball bearings under lubrication mixed with a foreign material is conducted to reproduce the damage state of surface start point type on I the market. Balls mad of SUJ2 are used as rol.L.Ing elements.

Inner and outer races of the example are made of some steel species selected from among example steel species El-215 in Table 7. Inner and outer races of comparative example are made of steel species selected from among comparative example steel speclea E16-ú23 in Table 7. The c=ulative streis repetition time to the tine when flaking occurs on the inn= and outer races of each tested ball bearing (life) In examined, Weibull plots are prepa=ed, and the L10 li-fe of each inner and outer race specimen is found from the Wedbull distribution result. On the other hand, likewise a life test is also executed for the Inner and outer races inade of the SUJ2material fox finding the L10 life. Each LID life ot the inner and outer race specimens of the example and the inner and culter race specimens of the comparative example is divided is by the L10 life of the inner and outer races made of SW2 to find the life ratio for evaluation.

[Life test conditions under lubrication mixed with foreign material] Test bearing: 608 Test contact pressure: 1500 Xpa Max.

Number of revolutions: 5000 epra Lubricant: No. 68 turbine oil Mixed foreign snaterial; Constitution: Stainless famiiy powdex Ha=dness: MRC 50 Grain diameter: 65-120 gm Mix amount: 200 ppm in lubricant Table 8 lists the lite evaluation results Table 8

Steel Surface Life ratio under lubrication species hardness mixed with foreign material (to inner and outer race made of SUJ2) 21 750 1.53 E2 746 1.48 E3 741 1.63 E4 764 1.56 E5 748 1.51 ú13 737 1.23 E14 723 1.02 EIS 1 719 0.98 E16 745 1.51 B17 706 0.58 Comparative E19 683 0.31 Example E21 658 0.28 B23 694 0.34 The inner and outer race material of the oxwnple has hardness Hv 700 or more after hardening and tompering and shows a lite equal to or longer than that of conventional 5UJ2. On the other hand, comparative example E1:6 shows a lite equal to or longer than that of conventional SUJ2. but is inferior in workability (see Table 7). Steel species E17 containing 1e6z than 0.6% as the C amount to enhance only workability tends to lower in hardness; the life lowers as compared with the conventional inner and outer races made of SUJ2. Steel species E19, E221 and E23 containing less than the lower limits of Si, Xn, and Cr have hardness of Hv 700 or less an; the life lowers if the C amount is set to 0.8% or more.

(4) Sound evaluation test:

Next, a sound evaluation test of tested bearings will be discussed. For the sound evaluation, initial sound evaluation and sound degradailon evaluation are executed. in the example, an anderon value is used in a bearing sound evaluation method. The anderon value is provided by taking bearing scund noise as a vibration component with an anderon meter. AD-0200 manufactured by Sugawara Renkyujo (Kabu) is used as the anderon meter.

(4-1) Initial sound evaluation test Test bearings- 608 Number of revolutions: 1900 zTm Bearing preload: 2 kqf (thrust load) Measurement range: H band (1800-10000 H2) A now bearing is set on the anderon meter and the anderon value is measured under these conditions. The average value of the anderon values found by measuring 30 bearings under the same conditions is evaluated as the 3ound level of the bearing. Table 9 and Figure 7 show the measurement results of the retained austenite amount on the finished product surface of the inner and outer races and the anderon Value.

7 1 Table 9

Inner and outer Rolling element Retained austenite Retained Anderow races Steel Reat Steel Heat Of the Inner and AustOnito after And run value after species treatment species treatment outer races the rolling vaolue load is element Imposed SW2 0.40 0.41 2 SW2 5.7 0.40 0.41 Example 3 E:1 8 8 1.8 5.7 0.41 0.42 4 91 n SU32 a 3.8 5.7 0.43 0.44 91 n 1 1 B 5.6 5.1 0.44 0.46.

SW2 6 cl 15 0UJ2 a 7.5 5.7 0.32 0.57 5UJ2 a 9.9 5.1 0.54 0.91 Comparative A SUJ2 a 12.0 5.1 0A9 0.74 txample 9 I5UJ2 C. 9UJ2 5.1 0.45 0.46 -LO- E: A - SUJ2 - IN 12.5 5.7 0.62 0.73 1SU:3 2 - 2 1 0% qu 1 Example bearings Nos. 1-5 are good in initial sound. in contrast, comparative example bearings Nos. 6-9 and 10 with retained austenite of inner and outer races exceeding 6% by volume are poor in initial sound because minute impreesions easily occur alt the bearing assembly time. Cc"arative example bearing No. 9 provided by applying heat treatment A to the bearing comprising inner and outer races made of the conventional material SW2 for reducing the retained austenite -han that of example amount to zero has higher initial sound t bearing No. 1 having the sam austenite amount.

(4-2) Sound degradation test:

* The measurement conditions are the came as those of (4 1) initial sound evaluation test. A 50-60 kgú axial load is imposed on the bearing af tar the initial sound measurement for 5-10 seconds, then, sound measurement-is, again executed for evaluating Impression resistance according to the imposed load.

The average value of the anderon values found by measuring 30 bea=ngs under the same conditions is evaluated as the Bound level of the bearing.

Table 9 and Figure 6 show the measurement results of the retained austenite amount on the finished product surface of the inner and outer races a-nd the anderon value.

Example bearings Nos. 1-5 are good with' less sound degradation from the initial sound. In contrast, comparative example bearings Nos. 6-8 and 10 with retained auEtenite of inner'and outer races exceeding 6% by volume are degraded in sound because minute Impressions occur due to the imposed load.

Comparative example bearing No. 9 provided by applying heat treatment C containing subzero treatment to the conventional Inner and outer races made of 5UJ2 tor reducing the retained austenite amount to zero has a small sound degradation amount, but higher sound than that of example bearing No. 1 to which heat treatment C in applied.

This means that if the retained austenite amount on the surface of the finished product inner and outer races exceeds 61h by volume, both the inItial sound and sound degradation increase. When the retained austenite iLaount is 6% or less by vol=e, it the initial sound Is low, the sound after the load is imposed can also be lowered.

13 (5) Initial sound evaluation test according to carbide area coefficient combination of Inner and outer races and rolling elements inner and outer races and rolling elements different in carbide area coefficient are combined and initial sound is evaluated. The measurement conditions: a= the same as those of (4-1) initial sound evaluation test.

The ratio defined by dividing the carbide area coof ficient of Inner and outer races by that of rOlling elements (that Isi a carbide area coefficient ratio - carbide 2.5 area coefficient of inner and outer races 1 carbide area coefficient of rollinc j elements) is used as the evaluation - 71 criterion. To directly measure the carbide area coefficient, the issue on the surface of each finished product of the inner and outer races and the rolling elements is shot under an electron microscope, only carbides are extracted from the ground of the electron microscope image by an image analyzer, and the carbide area, the number of pieces, and the like are measured for calculating the area coefficient.

Electron microscope: JSX-T220A manufactured by Nihon densisha Image ana2yzer: IBAS2000 manufactured by Table 10 and Figure 9 show the measurement results.

72 1 Table 10 loner and outer races Roll lin L-e leffient Steel Heat Steel Heat carbide area initial Anderon --lncies tr!Ratzmnt --2petieo -tceatmltnt traction ratio value 11 - cl 8 - 5UJ2 B- --- -- 068---- 0.41 12 F. a 0 SUJ2 0.73 0.40 - 13 Z3 5UJ2 0.65 0.42 14 ú4 a '41 is ES B 5UJ2]B 0.61 0.42 __A6 %S a 5UJ2 B 0,65 0.4Z 17 97 -8 9UJ2 a 0.69 0.41 trample is -- U a 2 -0.71 0.40 - 19 SW2 0.67 20]RIO 0.02 0J42 21 ú11 8UJ2 0. 9 0.42 2a sit SW2 0.61 0.42 23 all sniz - a 0.51 0.42 Z4 ú14 5UJ2 B 0.39 0.43 xis a buiz IB 0.21 0.44 26 syla b 5UJ2 5 1 2.46 -27 SUJ2 B Iti B 1.147 0.45 Cumparative 28 91 a 91 - B 1 0-45 Example 5UJ2 8 J1 1 0.83 - 0.49 91 a 41 0.57 0.48 31 Ell a cl a 0.86 - - - - - - - 0.44 1 -4 4.0 Table 11 lists element examples of SUJ2, El steel, and 31 steel in Table 10.

Table 11

Example specimen Nos. 11-25 with the carbide areo coaffici_ent ratio not exceeding 0.9% are low in initial sound and good. However, exa=le specimen Nos. 24 and 25 with a low carbide area coefficient of inner and outer races and the carbide area coefficient ratio less than 0.5% lower a little in 1Wression resistance because the hardness of the. inner and outer races lowers, thus the initial sound Is a little high. Therefore# preferably the carbide area coefficient ratio is 0.54-0.9%.

On the other hand, the combination effect produced by decreasing the carbides of the inner and outer races does not appear on comparative example specimen Nos. 26-28 with the carbide aLrea coefficlent ratio exceeding 0.9%; vibration caused by swell of the inner and outer races grows and the initial sound does not lower.

For comparative example speciiaen Nos. 29 and 30 comprising rolling elements made of steel species J1 having Steel c si mn C= Speci a (Wtt) (wt -(wtqr) (Wtt) j_ Example SUJ2 1.00 0.25 0.33 1.47 Comparative E1 0.86 0.25 0.90 I 0.27 Example J1 1.23 0.23 0.32 1.65 a high carbide a-rea coefficient containing the C amount exceeding the composition range of the invention although the carbide area coefficient ratio is 0.911 or less, vibration caused by swell of the rolling elements grows and the initial sound does not lower.

Comparative example specimen No. 3.1. comprises rolling elements made of steel species El having a low carbide area coefficient containing the C amount falling below the composition range of the invention and sound is a little decreased because of the combination effect with respect to comparative example specimen lRo. 28 comprieIng the inner and outer races and the rolling elements made of steel species 31.

However, if parts having a low carbide area coef f icient are thus combined, a large effect cannot be produced. Further, when the rolling elements are balls, if low-cost material is used to reduce the cost containing workability, the cost is increased in points of process set change and particulaxly, foreign material management. Thus, in the invention, use of steel species STJJ2 for the rolling elements becomes optimum.

As we have discussed, %to accomplish the third object of the invention, the carbide area coef f icient of the inner and outer races is made moderately lower than that of the rolling elements, whereby the,swell" characteristic of the inner and outer races and the rolling elements as a source of vibration and noise of baCrings is changed and the low-cost bearings excellent in sound characteristic are provided. The conventional "swell" characteristic depends an the magnitude of simple unevenness and coarseness corresponding to the finished working accuracy or. the surfaces of the inner and outer races and the rolling elements. However, in the invention, attention is focused on placement of carbides particularly becoming projections in a delicate uneven shape on the work finished face depending on the carbide amount in the material constitution of the inner and outer races and the rolling elements and the inner and outer races and the rolling ele:wnts made of materials different in carbide amount are combined, whereby vibration added to the contact spring force can be damped for improving the sound characteristic.

The invention can be effectively applied not only to bearing parts, but also to other parts coming in rolling is contact,, rotating, or sliding, such as balls, shafts, and pins, particularly other mechanical parts used in an environment in which corrosion of ruet# etc., occurs due to entry of water, etc., and mechanical parts, etc., particularly meeting strict requirements of initial sound and sound degradation. In this case, the members with stricter load conditions are made of a material equivalent to the inner and outer races and the mated members are made of SUJ2. For example, a linear guide device comprising a slider made of a material equivalent to the inner and outer races and rolling elements made of SUJ2 and a linear kmaring device such as a ball screw device comprising nuts made of a material equivalent to the inner and outer races and rolling elements made of SUJ2 can be nazed.

[Effect of the Invention] As we have discussed, according to the rolling members of the fixst aspect of the present. the contents of er, C, etc., of the compositions causing cost increase in bearing steel are limited, whereby the material and:manufacturing costs are reduced as much as possible. The contents of Mn caus.bng breakage and strength degradation and Si causing io workability degradation are limited and the DI value defined from the mutual amount relationship among the compositions is also 12.=toci at the saw time, whereby hardenability and workability are provided and functionabjlity la enhanced without pe-rfor=Ling car)>urizing or car)>onitriding. Thus 1 the 13 material and manufacturing costs are reduced as much an possible and the rolling members having higher perfozmtance than the rolling members xade of conventional bearing steel can be provided.

According to the second aspect of the present invention. a constitution material equivalent to SUJ2 is used for the rolling elements of members of a rolling device. On the other hand, Cr is lowered in the constitution of other members coming in contact with the rolling almants and the matrix Cr content difference therabetween is set to 0.6% or more,.whazeby a long-life and inexpensive rolling device even in an environment in which corrosion off rust, etc., occurs due to entry of water, etc., can be provided.

Further, according to the third aspect of the present invention, the carbide area coefficient of other members is made moderately lower than that of the rolling elements, whereby the "swell" characteristic of other members and the rolling elements coming in contact therewith and rolling as a souzce of vibration and noise of bearings is changed and the low-noise, low-vibration, and low-cost bearing devices excellent In sound characteristic can be provided.

- 78 79

Claims

CLAIMS 1. A rolling contact device comprising: rolling elements of the

rolling contact device; and a mated member of the rolling contact device which contacts said rolling elements and is rotated, rolled, slid or moved relative to said rolling elements, in which said mated member is made of carbon steel containing 0.696 - 0.9% by weight of C, 0.1% - 0.7% by weight of Si, 0.5% - 1.1R5 by weight of Mn, 0.1% 0.6% by weight of Cr and with the remainder, apart from inevitable impurities being Fe, said mated member being subjected to a hardening heat treatment; and, said rolling elements of said rolling contact device being made of an alloy steel containing Cr, and said is rolling elements being subjected to a hardening heat treatment, wherein at least one of said mated member and rolling elements have an ideal critical diameter DI value calculated by satisfying a following equation in the range of 1.5 - 4.0 inches (38 to 101 mm), where - X Co I DI = (0.311 60-498) X ([0.7 X Siok] 1) X ([3.33 X Mn%1+1.) X ([2.16 X Cr%l+i).
2. A rolling contact device according to claim 1, wherein at least one of said mated member and rolling elements have a retained austenite amount after being / subjeced to said hardening heat treatment in a range of 80o to 22-o by volume.
3. A rolling contact device according to claim 1, wherein at least one of said mated member and rolling elements have a retained austenite amount after being subjected to said hardening heat treatment in a range of 12-06 to 22-. by volume.
4. A rolling contact device according to any one of the preceding claims, wherein the rolling elements are made up of 0.950-1; - 1.1% by weight of C, 0.15%-0.35% by weight of Si, 0.1% -0.5% by weight of Mn, and 1.3% 1.6% by weight of Cr, and Fe and inevitable impurity elements in the remaining part.
5. A rolling contact device substantially as herein 5 described.