JP6228409B2 - Sliding member and manufacturing method thereof - Google Patents

Description

  The present invention relates to a sliding member having a sliding surface that slides with another member and a method for manufacturing the same.

  For example, a bearing used for a joint portion of an arm of a construction machine is required to have excellent wear resistance because a very large surface pressure is applied to the bearing surface. As this type of bearing, there are, for example, those obtained by cutting a cast alloy, and those in which graphite pieces are embedded in spots on the sliding surface. Therefore, instead of these, a sintered bearing made of a sintered metal having excellent formability has been proposed. For example, Patent Document 1 discloses a sintered bearing in which copper is dispersed in an iron-carbon alloy containing a martensite structure as a bearing for a construction machine. In this sintered bearing, the entire sintered body is quenched (for example, oil-quenched) after sintering, and then the inner and outer peripheral surfaces and end surfaces are cut and ground to finish to a predetermined size.

  In addition, in order to make the material different for each part in the sintered body and make the function different for each part, the two-layer structure in which the material is made different on the inner peripheral surface side and the outer peripheral surface side of the sintered body. Japanese Patent Application Laid-Open No. 2004-228561 describes a method for forming the green compact. Specifically, the outer peripheral surface side of the green compact is formed with a high-strength first powder, and the inner peripheral surface side is formed with a second powder excellent in low friction, and then the green compact is sintered. I am going to conclude.

JP 2003-222133 A JP 2005-95979 A

  In the two-layer structure sintered body described in Patent Document 2, in order to make the inner peripheral surface have a low friction coefficient, it is necessary to form a copper rich layer on the inner peripheral surface of the sintered body. On the other hand, in order to ensure high strength on the outer peripheral surface side of the two-layer structure sintered body, particularly high strength required for a bearing provided in a joint part of an arm of a construction machine described in Patent Document 1. It is necessary to form the outer peripheral surface side of the sintered body with a structure mainly composed of iron-carbon (pearlite structure). In this case, the green compact is sintered at a temperature of 1130 ° C. or higher in order to obtain a pearlite structure.

  However, when sintered at a temperature exceeding the melting point of copper (1083 ° C.), the copper contained in the copper-rich layer on the inner peripheral surface is completely melted. Since the molten copper is drawn into a layer having a low copper concentration on the outer peripheral surface side, a sufficient copper structure is not formed on the inner peripheral surface after sintering. On the other hand, the strength required on the outer peripheral surface side of the sintered body cannot be ensured simply by lowering the sintering temperature. Therefore, the original purpose of the two-layer structure sintered body cannot be achieved as it is.

  Then, an object of this invention is to provide the sliding member which can improve the slidability and durability of a sliding surface, and its manufacturing method, ensuring the intensity | strength of a sintered compact.

  In order to achieve the above object, the present invention is a sliding member that is formed of a sintered body and has a sliding surface that slides on other members, and contains Fe, Cu, and C containing alloy elements as main components. And a base layer mainly composed of Fe, Cu, C, and a metal having a lower melting point than Cu, in contact with the sliding layer. A sliding surface is provided in the dynamic layer.

  By including Cu and a low melting point metal in the base layer, the low melting point metal contained in the base layer is first melted during sintering. The melt of the low melting point metal diffuses deep inside the Fe particles by capillary action. Further, since the melt of the low melting point metal wets the surface of the Cu particles, the Cu melts at a temperature lower than the melting point, and the molten Cu and the low melting point metal penetrate into the Fe particles and diffuse into the Fe particles. . As a result, the Fe particles are firmly bonded to each other and the strength of the base layer is improved, so that the bearing strength can be ensured even when the sintering temperature is lowered. By setting the sintering temperature to a temperature lower than the melting point of Cu, the Cu particles contained in the sliding layer are not melted even during the sintering, and the solid state is maintained. Therefore, Cu particles contained in the sliding layer are not drawn into the base layer, and it is possible to distribute a target amount of Cu structure on the sliding surface. From the above, it is possible to achieve both the slidability on the sliding surface and the strength of the sintered body.

  If this sliding member contains an element (at least one selected from Ni, Mo, Mn, and Cr) that improves hardenability as an alloy element contained in the sliding layer, carburizing and quenching, etc. Without performing the heat treatment, at least a part of the Fe structure of the sliding layer can be martensitic and bainite transformed in the cooling process after sintering (sinter hardening). Thereby, since the sliding layer containing a sliding surface is hardened, the abrasion resistance of a sliding surface can be improved. In addition, since the strength of the base layer is increased by penetration and diffusion of Cu and low melting point metal into Fe particles in the base layer, the strength of the entire sintered body is improved. Accordingly, the impact load is frequently applied, and it can be used as a sliding member used under a high surface pressure, for example, a bearing used in a joint part of an arm of a construction machine.

  On the other hand, since the base layer that occupies most of the sintered body basically does not contain the above alloy elements, the majority of the base layer is not sintered hardened even after cooling, and therefore the Fe of the base layer The structure does not undergo martensitic transformation or bainite transformation. Thus, by blending only the sliding layer with an element that improves hardenability, the amount of the expensive element used can be reduced and the cost can be reduced. In addition, since the base layer is softer than the sliding layer, it is possible to perform dimensional correction of the sintered body by sizing (a step of compressing and shaping the sintered body in the mold). In the configuration of Patent Document 1, since the entire sintered body is cured by oil quenching after sintering, dimensional correction of the sintered body is inevitably performed by machining such as cutting and grinding. The sliding member can be dimensionally corrected by sizing, and machining is not necessary. Moreover, the quenching process after sintering is unnecessary. Thus, since the quenching process and machining process after sintering can be omitted, the cost of the sliding member can be further reduced as compared with the invention described in Patent Document 1.

  It is preferable to use phosphorus as the low melting point metal contained in the base layer. The concentration of the low melting point metal in the base layer is preferably in the range of 0.1 to 0.6 wt%.

  By making Cu density | concentration of a sliding layer 10 wt% or more and 30 wt% or less, the cost increase by excessive use of copper can be prevented, ensuring the slidability of a sliding surface. In order to bind the Fe particles of the base layer, it is necessary to also contain Cu in the base layer. At that time, the Cu concentration of the base layer is made smaller than the Cu concentration of the sliding layer, so that expensive copper is used. The cost can be reduced by reducing the amount.

  The sliding member described above prepares a first powder mainly composed of a metal having a lower melting point than Fe, Cu and Cu, and C, and contains Fe, Cu and C containing alloy elements as main components. The second powder is prepared, a partition member is arranged in the mold to form a first cavity and a second cavity, the first cavity is filled with the first powder, and the second cavity is filled with the second powder. The composition corresponding to the first powder is filled, and the first powder and the second powder in the mold are simultaneously compressed with the partition member removed to form a green compact, and the green compact is sintered. The base layer and the sliding layer having a composition corresponding to the second powder are formed, and then the obtained sintered body is subjected to sizing and oil impregnation.

  When the green compact is formed by simultaneously compressing the first powder and the second powder, if the difference in the apparent density between the two powders is large, the green compact is hindered. On the other hand, the green compact can be formed by making the thickness of the base layer larger than the thickness of the sliding layer and making the apparent density of the first powder smaller than the apparent density of the second powder. . That is, the green compact can be easily formed even if there is a slight difference in the apparent density between the first powder and the second powder.

  As described above, according to the present invention, it is possible to improve the slidability and durability of the sliding surface while ensuring the strength of the sintered body.

It is sectional drawing of the joint part incorporating the sintered bearing of this invention. It is a front view of the said sintered bearing. It is sectional drawing which shows the state with which the 1st powder was filled in the compression molding process of the said sintered bearing. It is sectional drawing which shows the state with which the 2nd powder was filled in the said compression molding process. It is sectional drawing which shows the state which lowered | hung the partition member in the said compression molding process. It is sectional drawing which shows the state which removed the excess powder in the said compression molding process. It is sectional drawing which shows the state which compressed the mixed powder with the upper punch in the said compression molding process. It is sectional drawing which shows the state which took out the green compact from the metal mold | die in the said compression molding process. It is a schematic sectional drawing which shows the sintering furnace used at the sintering process of the said sintered bearing. It is sectional drawing which shows the metal mold | die used at the sizing process of the said sintered bearing. It is sectional drawing which shows the manufacturing process after a compression molding process. It is a graph which shows the concentration gradient of the alloy element which improves hardenability. It is sectional drawing of the sintered bearing which concerns on other embodiment. FIG. 14A is a diagram showing the microstructure of the sliding layer, and FIG. 14B is a diagram showing the microstructure of the base layer.

  A sintered bearing is given as an example of the sliding member of the present invention, and an embodiment thereof will be described below with reference to the drawings.

  The sintered bearing according to the present invention is suitable for use in a joint portion that connects arms (including a boom and a bucket) of construction machines such as a hydraulic excavator and a bulldozer. FIG. 1 shows the schematic structure of such a joint. As shown in FIG. 1, in this joint part, the tip of the second arm 7 is inserted inside the first arm 6 formed in a bifurcated shape. A mounting hole 7a is provided at the tip of the second arm 7, and the outer peripheral surface 3a of the sintered bearing 1 made of a sintered body is fixed to the mounting hole 7a using appropriate mounting means such as press fitting. The first arm 6 and the second arm 7 are rotatably connected by inserting the pin 4 into the pin hole 6a provided in each of the bifurcated portions of the first arm 6 and the inner peripheral surface 2a of the sintered bearing 1. . The pin 4 is fixed to the first arm 6. Therefore, when the first arm 6 and the second arm 7 are swung relative to each other, the pin 4 rotates relative to the inner peripheral surface 2 a of the bearing 1. . Reference numeral 8 is a stopper that prevents the pin 4 from coming off. In this joint portion, the head 4a or the retaining member 8 of the pin 4 is removed from the shaft portion of the pin 4, and the first arm 6 and the second arm 7 are separated by removing the pin 4, and maintenance of the bearing 1 and the pin 4 is performed. Can be done.

  As shown in FIG. 1 and FIG. 2, the sintered bearing 1 is formed of a cylindrical sintered body, and the sliding layer 2 on the inner diameter side and the base layer 3 on the outer diameter side are in contact with each other. Have one. In the illustrated example, the sintered bearing 1 comprises only the sliding layer 2 and the base layer 3, and each layer has a cylindrical shape, particularly a cylindrical shape. The inner peripheral surface 2a of the sintered bearing 1 (the inner peripheral surface of the sliding layer 2) has a perfect circular cross section that is straight in the axial direction, and the shaft portion of the pin 4 (hereinafter referred to as the shaft 4) inserted into the inner periphery. The sliding surface A (bearing surface) is supported so as to be relatively rotatable. The outer peripheral surface 3a of the sintered bearing 1 (the outer peripheral surface of the base layer 3) has a perfect cross-sectional shape that is straight in the axial direction, and constitutes an attachment surface B that is attached to other members such as the second arm 7. Both axial end surfaces of the sintered bearing 1 are flat surfaces extending in a direction orthogonal to the axial direction. Chamfering is provided between both axial end surfaces of the sintered bearing 1 and the inner peripheral surface 2a and the outer peripheral surface 3a.

  When used in the above joint, the sintered bearing 1 is formed so that the inner diameter is 30 to 100 mm and the thickness in the radial direction is 5 to 50 mm, for example. The thickness of the sliding layer 2 in the radial direction is about 1 to 20% (preferably about 2 to 10%) of the radial thickness of the sintered bearing 1, and the actual thickness is, for example, 0.3. About 2 mm. If the sliding layer 2 is too thin, the filling ability of the raw material powder at the time of molding is deteriorated and the allowable wear limit is lowered. If the sliding layer 2 is too thick, an element for improving hardenability, which will be described later, This is because the amount of copper used increases and costs increase. The fine pores of the porous sintered bearing 1 are impregnated with lubricating oil. When the sliding surface A and the shaft 4 rotate relative to each other, the lubricating oil held in the fine holes inside the sintered bearing 1 oozes out from the surface opening of the sliding surface A, and the sliding surface A and the shaft 4 During the lubrication.

  The sintered bearing 1 of the present invention has a two-layer structure in which the metal composition is different between the sliding layer 2 and the base layer 3. The sintered bearing 1 having a two-layer structure is manufactured by sequentially performing a compression molding process, a sintering process, a sizing process, and an oil impregnation process described below.

  In the compression molding process, a so-called two-color molding technique is adopted in which the material of the sliding layer 2 and the material of the base layer 3 are supplied to the same mold and molded simultaneously. This two-color molding is one in which two cavities are formed on the outer diameter side and the inner diameter side in the mold, and each cavity is filled with powder, and is performed using, for example, a mold shown in FIG. The mold includes a die 11, a core pin 12 disposed on the inner periphery of the die 11, an outer lower punch 13 disposed between the inner peripheral surface 11a of the die 11 and the outer peripheral surface 12a of the core pin 12, and a partition It has the member 14, the inner lower punch 15, and the upper punch 16 (refer FIG. 7). The outer lower punch 13, the partition member 14, and the inner lower punch 15 have a concentric cylindrical shape and can be moved up and down independently.

  First, as shown in FIG. 3, the partition plate 14 and the inner lower punch 15 are raised to the upper end position, and the outer lower punch 13 is lowered to the lower end position, so that the inner peripheral surface 11 a of the die 11 and the outer periphery of the partition plate 14 are A first cavity 17 on the outer diameter side is formed by the surface 14 a and the end surface 13 a of the outer lower punch 13. The first cavity 17 is filled with the first powder M1 corresponding to the base layer 3. The composition of the first powder M1 will be described later.

  Next, as shown in FIG. 4, the inner lower punch 15 is lowered to the lower end position, and the inner peripheral surface 14 b of the partition plate 14, the outer peripheral surface 12 a of the core pin 12, and the end surface 15 a of the inner lower punch 15 A second cavity 18 is formed. The second cavity 18 is formed in a state of being isolated from the first cavity 17, and the second powder 18 is filled in the second cavity 18 corresponding to the sliding layer 2. At this time, the second powder M2 overflows from the inner cavity 18 so as to cover the upper side of the partition plate 14. The composition of the second powder M2 will be described later.

  Next, the partition plate 14 is lowered as shown in FIG. Thereby, the 2nd powder M2 enters into the space for the partition member 14, and the 1st powder M1 and the 2nd powder M2 contact. As a result, the cavity 19 formed by the inner peripheral surface 11a of the die 11, the end surface 13a of the outer lower punch 13, the end surface 14c of the partition plate 14, the end surface 15a of the inner lower punch 15, and the outer peripheral surface 12a of the core pin 12 is The first powder M1 and the second powder M2 are filled in a two-layer state. Then, excess second powder M2 overflowing from the cavity 19 is removed (see FIG. 6).

  With the partition member 14 removed from the mold in this way, as shown in FIG. 7, the upper punch 16 is lowered, and the end face 16a of the upper punch 16 is pressed against the powders M1, M2, and the upper punch 16, The powders M1 and M2 filled in the cavity 19 are compressed by the punches 13 and 15, the partition member 14, and the die 11, and the green compact M is formed. And as shown in FIG. 8, the outer lower punch 13, the partition plate 14, and the inner lower punch 15 are raised, and the green compact M is taken out from the mold.

Here, the first powder M1 corresponding to the base layer 3 is mainly composed of iron powder, copper powder and graphite powder, and additionally contains a low melting point metal. As the iron powder, reduced iron powder, atomized iron powder, and the like can be used, but it is preferable to use porous reduced iron powder having excellent oil impregnation. As the copper powder, electrolytic copper powder or atomized copper powder can be used, but if the electrolytic copper powder having a dendritic shape as a whole particle is used, the green compact strength can be increased, and copper can be used during sintering. Is more preferable because it easily diffuses into the Fe particles. Further, as the low melting point metal, a metal having a melting point smaller than that of copper, specifically, a metal having a melting point of 700 ° C. or lower, such as tin (Sn), zinc (Zn), phosphorus (P), etc. can be used. . This low-melting-point metal can be added by using a powder alloyed with iron in addition to adding the simple powder to the mixed powder. Among low melting point metals, phosphorus is easily diffused into iron and can be diffused into the iron particles, and further promotes copper diffusion. That is, compatibility with both iron and copper is good. Therefore, it is preferable to use phosphorus as the low melting point metal. For example, if iron-phosphorus alloy powder (Fe ₃ P) is mixed with copper powder and graphite powder, the advantages of easy mixing and forming of the first powder M1 and high safety are obtained.

  The blending amount of each powder in the first powder M1 is preferably, for example, copper powder: 2 to 5 wt%, graphite powder: 0.5 to 0.8 wt%, and the remainder is iron-low melting point metal alloy steel powder. . At this time, the ratio of the low melting point metal in the first powder M1 is 0.1 to 0.6 wt% (preferably 0.3 to 0.5 wt%). Copper powder functions as a binder that binds iron powders. If the amount of copper powder is too small, the strength of the base layer 3 is reduced, and if too large, the diffusion of carbon is inhibited and the strength of the sintered body is reduced. -Since the hardness is reduced, the above range is adopted. The low melting point metal is blended in order to increase the strength of the sintered body through the diffusion of the iron into its own iron particles and further the diffusion of copper into the iron particles. If the amount is too large, the low melting point metal segregates and the sintered body becomes brittle, leading to a decrease in strength. Graphite powder is blended to form a hard pearlite phase by reacting iron and carbon during sintering. If the amount is too small, the strength of the base layer cannot be secured, and if it is too large, the iron becomes a cementite structure. Since it becomes brittle and causes a decrease in strength, the above range is adopted.

  On the other hand, the second powder M2 corresponding to the sliding layer 2 is a mixture of iron powder (alloy steel powder) containing an alloy element that improves hardenability, copper powder, and graphite powder. Any one or more selected from Ni, Mo, Mn, and Cr is used as the element for improving the hardenability. In the present invention, Ni and Mo are selected, and Ni, Mo , And iron alloy steel powder (Fe-Ni-Mo alloy steel powder). Elements that improve hardenability are added to cause martensite transformation and bainite transformation as described later to perform sintering hardening, but Ni and Mo are particularly effective in improving hardenability. preferable. Complete alloy powder is preferable as the alloy steel powder of the second powder M2. The copper powder is preferably electrolytic copper powder, but atomized copper powder may be used.

  The blending amount of each powder in the second powder M2 is preferably 10 to 30 wt% (preferably 15 to 20 wt%) of copper powder, 0.5 to 0.8 wt% of graphite powder, and the rest is alloy steel powder. Further, the type and amount of the alloy steel powder are selected so that the Ni ratio in the second powder M2 is 1.5 to 3.5 wt% and the Mo ratio is 0.5 to 1.5 wt%. The blending amounts of Ni and Mo are determined from the effect of improving formability and hardenability. If the amount of copper is too small, the slidability of the sliding surface 2a is lowered. If the amount is too large, the bearing surface becomes too soft and there is a problem in wear resistance. The graphite powder of the second powder M2 is blended to react mainly with iron and carbon during sintering to form a martensite phase and a bainite phase, and further to function as a solid lubricant. The upper limit of the blending ratio The lower limit is determined for the same reason as that for determining the blending ratio of the graphite powder in the first powder M1.

The apparent densities of the first powder M1 corresponding to the base layer 3 and the second powder M2 corresponding to the sliding layer 2 are both 1.0 to 4.0 g / cm ³ . Due to the difference in the composition of both powders, there is a difference in the apparent density of both powders. From this difference, when the first powder M1 and the second powder M2 are simultaneously formed in the compression molding process, the green compact M is formed. It is expected that molding will be difficult due to collapse. However, the thickness of the sliding layer 2 is sufficiently smaller than the thickness of the base layer 3 as in the present embodiment (as described above, the thickness of the sliding layer 2 is 1 to 20 of the thickness of the sintered bearing). %, Preferably 2 to 10%), and in the state where the apparent density of the first powder M1 is lower than the apparent density of the second powder M2, the difference in density is 0.5 g / cm ³ or less. The green compact M can be formed even if the single powder M1 and the second powder M2 are simultaneously formed. Therefore, the apparent density of the first powder M1 is preferably smaller than the apparent density of the second powder M1, and the density difference is preferably suppressed to 0.5 g / cm ³ or less.

  Sintered body M ′ is obtained by sintering the green compact M that has undergone the compression molding process described above in the sintering process (see FIG. 11). At this time, since the base layer 3 is sintered together with the sliding layer 2 in contact with the sliding layer 2, the sliding layer 2 and the base layer 3 can be integrated after sintering. As the sintering furnace, as shown in FIG. 9, a continuous sintering furnace 20 having a sintering zone 20a in which a heater 21 is installed and a cooling zone 20b for performing natural heat dissipation can be used. An atmosphere gas containing CO is used. The sintering temperature (temperature in the sintered structure) is set to be lower than the melting point of copper (1083 ° C.) and higher than the temperature at which iron and carbon start reaction (about 900 ° C.). In order to obtain this sintering temperature, the furnace temperature is set to 1000 ° C. to 1100 ° C., for example. This temperature is lower than a general furnace temperature (1130 ° C. or higher) when sintering an iron-based sintered body.

  The sintered body M ′ that has undergone the sintering process is transferred to the sizing process and dimension correction is performed. In this embodiment, as shown in FIG. 10, the inner peripheral surface, outer peripheral surface, and both end surfaces of the sintered body M ′ are formed using a sizing die having a die 23, a core rod 24, and upper and lower punches 25 and 26. By pressing, the sintered body M ′ is sized. Then, the sintered bearing 1 is completed by impregnating the internal pores of the sintered body M ′ with a lubricant in the oil impregnation process. In order to remove the residual austenite of the sintered body M ′, the sintered body M ′ may be tempered after the sintering.

  At the time of sintering in the sintering step shown in FIG. 9, first, phosphorus contained in the first powder M1 is melted. The phosphorus melt diffuses deep inside the Fe particles by capillary action. In addition, since the phosphorus melt wets the surface of the Cu particles, the Cu melts at a temperature below its melting point, and the molten Cu and phosphorus penetrate into the Fe particles and diffuse into the Fe particles. Thereby, iron particles are firmly bonded to each other, and the strength of the base layer 3 is improved. In addition, since sintering is performed at a temperature higher than the reaction start temperature of iron and carbon, a hard pearlite phase is formed in the Fe structure (partially a ferrite phase). Through the above sintering process, the strength of the base layer 3 is ensured. Therefore, even when the sintering temperature is lower than the sintering temperature of a general iron-based sintered product as described above, the base layer 3 The strength required for 3 can be ensured. By lowering the sintering temperature to a temperature lower than the melting point of copper, the copper contained in the sliding layer 2 (second powder M2) does not melt even during the sintering and maintains a solid state. Therefore, the copper existing on the sliding layer 2, particularly the sliding surface A, is not drawn into the base layer 3, and a target amount of copper can be distributed on the sliding surface A. Therefore, both the slidability of the sliding surface A and the strength of the sintered body M ′ can be achieved.

  Further, since the hardenability improving elements such as Ni and Mo are included in the sliding layer 2, the cooling layer 20b of the continuous sintering furnace 20 shown in FIG. In the meantime, martensite transformation and bainite transformation can be caused in the Fe structure of the sliding layer 2 to increase the hardness (sinter hardening). Thereby, the sliding surface A can be hardened and its wear resistance can be improved. In addition, since the strength of the base layer 3 is increased by diffusion of copper and phosphorus in the base layer 3, the strength of the entire sintered body (compression strength, etc.) is improved. Therefore, the impact load is frequently applied, and can be used as a bearing in the joint portion of the arm of the construction machine used under high surface pressure.

  On the other hand, since the element for improving the hardenability is not added to the base layer 3 occupying most of the sintered body M ′, the amount of the expensive element used in the entire bearing can be reduced, The cost of the bearing can be reduced. Further, since the base layer 3 is not sintered and neither martensite transformation nor bainite transformation occurs, the base layer 3 becomes softer than the sliding layer 2. Therefore, it becomes possible to correct the dimension of the sintered body M ′ in the sizing process. In the configuration of Patent Document 1 described above, since the entire sintered body is cured by oil quenching after sintering, dimensional correction of the sintered body must be performed by machining such as cutting and grinding. The sintered body M ′ of the invention can be dimensionally corrected by sizing, and does not require post-processing by machining. Moreover, even if it does not quench after sintering, sufficient intensity | strength (for example, crushing strength of 500 Mpa or more) required can be ensured. Thus, since the hardening process and machining process after sintering can be omitted, the cost of the sintered bearing 1 can be further reduced as compared with the invention described in Patent Document 1.

  Graphite in the base layer 3 is decomposed by sintering and basically becomes carbon and reacts with Fe. On the other hand, some of the graphite in the sliding layer 2 remains as particles even after sintering. This is because the sliding layer 2 has a higher copper content than the base layer 3, and the copper particles cover a part of the surface of the iron particles, which makes it difficult for Fe and C to react. As described above, since the sliding layer 2 has more graphite particles than the base layer 3, the graphite particles can function as a solid lubricant, and the sliding property of the sliding surface A is improved. be able to.

  Note that the first powder M1 corresponding to the base layer 3 does not contain elements (Ni and Mo in this embodiment) that improve the hardenability, so that the base layer 3 does not contain these elements in theory. However, in relation to the procedure of the molding process shown in FIGS. 3 to 8, the concentration gradient of the element is actually at the interface between the sliding layer 2 and the base layer 3 as shown in FIG. Arise. As a result, a region containing an element that improves the hardenability is formed in the vicinity of the interface, so that the strength of the interface, and hence the bonding strength between the sliding layer 2 and the base layer 3 is increased. In this case, a region sufficiently separated from the sliding layer 2 in the base layer 3, for example, a surface facing the sliding layer 2 (in this embodiment, the outer peripheral surface of the base layer 3) is hardened. The element to improve is not included. The radial dimension R of the region where the concentration gradient is generated is preferably in the range of 0.1 to 1.0 mm, and preferably in the range of 0.2 to 0.5 mm. The radial dimension R of the region where the concentration gradient is generated can be adjusted by the radial thickness of the partition member 14 (see FIG. 3) of the two-color molding die.

  Similarly, since the second powder M2 corresponding to the sliding layer 2 does not contain a low melting point metal (phosphorus in this embodiment), the sliding layer 3 theoretically does not contain a low melting point metal. However, for the same reason as described above, a low-melting-point metal concentration gradient is generated at the interface between the sliding layer 2 and the base layer 3. In the sliding layer 2, a region sufficiently separated from the base layer 3, for example, a surface facing the base layer 3 (sliding surface A of the sliding layer 2 in this embodiment) has a low melting point metal. It will not be included.

  Of the sintered bearing 1 manufactured by the above procedure, the microstructure of the sliding layer 2 is schematically shown in FIG. 14 (a), and the microstructure of the base layer 3 is schematically shown in FIG. 14 (b).

  As shown in FIG. 14 (a), the sliding layer 2 is mainly composed of an Fe structure having Fe as a base, a Cu structure made of only copper represented by a dotted pattern, and a graphite structure represented by black coating. Fe structure is more than Cu structure and graphite structure is the smallest. The Fe structure mainly includes a martensite phase and a bainite phase, and forms a quenched structure including a pearlite phase in part. Ni and Mo are diffused in the quenched structure. The sliding layer 2 follows the mixing ratio of the second powder M2, and contains Cu: 10 to 30 wt% (preferably 15 to 20 wt%), C: 0.5 to 0.8 wt%, and Ni: 1.5 as main components. It is an iron-based metal structure containing ˜3.5 wt%, Mo: 0.5 to 1.5 wt%, with the balance being Fe and inevitable impurities.

  Further, as shown in FIG. 14B, the base layer 3 is composed of an Fe structure (pearlite phase and ferrite phase) having Fe as a base material. Cu and P are diffused inside this Fe structure, and Cu as particles does not exist in the base layer 3. Moreover, there is no hardened structure and graphite structure. This base layer 3 follows the mixing ratio of the first powder M1, and contains Cu: 2 to 5 wt%, P: 0.1 to 0.6 wt% (preferably 0.3 to 0.5 wt%), C as main components. : An iron-based metal structure containing 0.5 to 0.8 wt% with the balance being Fe and inevitable impurities. Since the copper content of the base layer 3 is less than the copper content of the sliding layer 2, it is possible to reduce the cost by reducing the amount of copper used in the entire bearing.

  In the above embodiment, the case where the sliding surface A is formed on the inner peripheral surface 2a of the sliding layer 2 is shown. However, the present invention is not limited to this, and for example, as shown in FIG. The present invention may be applied to the sintered bearing 1 in which the sliding surface A is formed. In this case, the sliding layer 2 is formed on the outer peripheral surface 3 a of the sintered bearing 1, and the base layer 3 is formed on the inner peripheral surface 2 a of the sintered bearing 1. The configurations and functions of the sliding layer 2 and the base layer 3 are common to the sliding layer 2 and the base layer 3 in the above-described embodiment. In addition, in FIG. 1, when the end surface of the sintered bearing 1 slides with the first arm 6 at a high surface pressure, a sliding surface A can be formed on the end surface of the sintered bearing.

  The form of the sintered body M ′ and the sliding surface A is also arbitrary, and the present invention can be applied to a spherical bush or a flat pad-like member (for example, a boom pad) as the sliding member. In the former case, the sliding surface A is spherical, and in the latter case, the sliding surface A is flat. One or a plurality of recesses (for example, a groove shape) can be formed on the sliding surface A, whereby the recesses can be used as a lubricant reservoir.

  Further, in the above embodiment, the case where the interface between the sliding layer 2 and the base layer 3 is a cylindrical surface has been shown. Spline-like) (not shown). Thereby, the bonding strength between the sliding layer 2 and the base layer 3 is further increased. Since the shape of the interface follows the shape of the partition member 14 (see FIG. 3 and the like) in the compression molding process, the shape of the interface can be changed by changing the shape of the partition member 14.

  Moreover, although the case where the sintered bearing 1 was applied to a construction machine was illustrated in said embodiment, not only this but the sliding member of this invention is used on a sliding surface on high surface pressure conditions. It can be suitably applied to various uses.

1 Sintered bearing 2 Sliding layer 3 Base layer 4 Pin (shaft)
6 First arm 7 Second arm 20 Sintering furnace A Sliding surface (bearing surface)
B Mounting surface M Green compact M ′ Sintered body M1 First powder M2 Second powder

Claims (12)

A sliding member formed of a sintered body and having a sliding surface sliding with another member,
And Fe, and Cu, and a sliding layer composed mainly and C, and a hardenability improving element which is alloyed Fe,
Sintered together with the sliding layer in a state of being in contact with the sliding layer, and Fe, and Cu, Sn, Zn, and a low melting elements of the low melting point than Cu, which is selected from among P, a main component and a C And a base layer
A sliding surface is provided on the sliding layer, and a Cu structure made of only copper is formed on the sliding surface,
Fe structure of the sliding layer is a quenched structure,
A sliding member characterized in that neither martensitic transformation nor bainite transformation occurs in the Fe structure in a region separated from the sliding layer in the base layer . The sliding member according to claim 1, comprising at least one selected from Ni, Mo, Mn, and Cr as the hardenability improving element. The sliding member according to claim 2, wherein at least a part of the Fe structure contained in the sliding layer has undergone martensitic transformation and bainite transformation. The sliding member according to claim 1, wherein the low melting point metal contained in the base layer is P. The sliding member according to claim 1, wherein the concentration of the low melting point elements was 0.1～0.6Wt% in the base layer. Wherein the Cu concentration of the sliding layer and 10 to 30 wt%, the base layer sliding member according to claim 1, wherein the Cu concentration was less than the Cu concentration of the sliding layer of. The sliding member according to claim 1, wherein the sintered body is sintered at a temperature lower than the melting point of Cu and higher than the reaction start temperature of Fe and C. The sliding member according to claim 1, wherein the sliding member has a region where a concentration gradient of a quenching improving element is generated at an interface portion between the sliding layer and the base layer.   The sliding member according to claim 1, wherein the sliding member is used as a bearing of a joint portion of an arm of a construction machine. A method for producing a sliding member comprising a sliding layer and a base layer, wherein the sliding layer is formed with a sliding surface sliding with another member,
And Fe, and Cu, Sn, Zn, prepared with a low melting point elements of the low melting point than Cu, which is selected from among P, a C, and a first powder mainly composed of,
And Fe, Cu and, C and, a second powder mainly composed of the hardenability enhancing elements were alloyed Fe prepared,
A partition member is arranged in the mold to form a first cavity and a second cavity,
To fill the first powder in the first cavity, filling the second powder in the second cavity,
The first powder and the second powder in the mold, the green compact formed by compression at the same time in a state of detaching the partition member,
And sintering the green compact, and the base layer of the composition corresponding to the first powder to form a sliding layer of a composition corresponding to the second powder, and by the sintering, the sliding layer In the base layer, neither the martensite transformation nor the bainite transformation occurs in the Fe structure in the region separated from the sliding layer, and the sliding surface is made of copper. Forming a sintered body formed with a Cu structure consisting of only,
Then, the manufacturing method of the sliding member characterized by performing sizing on the obtained sintered compact. The manufacturing method of the sliding member of Claim 9 containing at least 1 sort (s) selected from Ni, Mo, Mn, and Cr as said hardenability improvement element. The thickness of the base layer is larger than the thickness of the sliding layer, and the sliding of claim 9, wherein the apparent density of the first powder characterized by less than the apparent density of the second powder Manufacturing method of member.

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