JP5979118B2 - Wear-resistant iron-based sintered metal and valve seat for internal combustion engine - Google Patents

Description

  The present invention relates to a wear-resistant iron-based sintered metal and a valve seat for an internal combustion engine using the same.

  Conventionally, a valve seat for an internal combustion engine using wear-resistant iron-based sintered metal maintains the airtightness of the combustion chamber by combining with a valve and has high wear resistance in a high temperature and dry environment. The characteristic that the aggressiveness to a valve is low and it has excellent machinability is required.

  In recent years, it has become indispensable to improve engine output performance and fuel efficiency in order to respond to the environment. In addition to high temperatures and high surface pressure, the use of valve seats has increased heat conductivity. Improvement of various conditions, such as low thermal expansion, is required.

  Under such circumstances, an iron-based sintered alloy material having a mixed structure of pearlite and bainite in which hard particles are dispersed in a matrix phase is known and used as a valve seat (for example, see Patent Document 1). In this iron-based sintered alloy material, the composition of the base part including hard particles is C: 0.7 to 1.6%, Si: 0.1 to 1%, Mn: 0.05 to 1%, Cr: It contains 1 to 8%, Mo: 1 to 10%, V: 0.1 to 2%, Co: 1 to 20%, and is composed of the balance Fe and inevitable impurities.

  This iron-based sintered alloy material is composed of 5-25% hard particle particles made of Cr—Mo—Si—Co intermetallic compound having a particle size of 10 to 150 μm, and solid material made of CaF 2 having a particle size of 1 to 50 μm. Lubricant particles are dispersed in an amount of 0.1 to 7%, and the structure of the base portion is 40 to 90% pearlite and 7 to 40% in an area ratio where the base total area excluding hard particles is 100%. By being made of bainite and a 3-20% Co-rich high alloy phase, it is said that it is excellent in machinability, has little opponent attack and is excellent in wear resistance.

Japanese Patent Laid-Open No. 11-021659

  However, in the wear-resistant iron-based sintered alloy material described in Patent Document 1, while being excellent in machinability, appropriate wear resistance cannot be obtained due to the density of carbides precipitated in the bainite phase. There was a problem. That is, sufficient wear resistance cannot be obtained when the density of carbides precipitated in the bainite phase is excessively coarse, and work hardening is not achieved when the density of carbides is excessively dense. There is a problem that it becomes smaller and lower bainite where high wear resistance cannot be obtained, or martensite which has high wear resistance but high opponent attack.

  The present invention has been made to solve the above-described conventional problems, and provides an wear-resistant iron-based sintered metal that eliminates the addition of hard particles and is excellent in both machinability and wear resistance. For the purpose.

  In order to achieve the above object, the wear-resistant iron-based sintered metal according to the present invention includes (1) Mo: 0.0025-2.0%, C: 0.2-1.2% by weight. The balance is composed of Fe and inevitable impurities, and the metal structure is composed of a mixed layer of upper bainite and pearlite or pearlite and pro-eutectoid ferrite, and the area ratio of upper bainite and pearlite or pearlite and pro-eutectoid ferrite is 95: 5 The configuration is 5:95.

  Here, the reason why the content ratio of Mo is limited to a numerical value of 0.0025 to 2.0% is as follows. Mo is a material that improves wear resistance and hardenability. If the weight ratio is less than 0.0025%, a sufficient effect cannot be obtained, and if the weight ratio exceeds 2.0%, the density decreases rapidly. As a result, sufficient wear resistance cannot be obtained.

  The reason why the C content is limited to 0.2 to 1.2% is as follows. C is a material that improves the wear resistance by forming carbides during sintering. When the weight ratio is less than 0.2%, sufficient hardness cannot be obtained, and when the weight ratio exceeds 1.2%. A large amount of pro-eutectoid cementite, which is a high-hardness cementite that precipitates from austenite during cooling after sintering, is generated, which increases the attack of the opponent and deteriorates the machinability.

  When Mo and C are contained in the above range, by appropriately controlling the cooling rate of cooling from the sintering temperature, upper bainite and pearlite or pearlite and proeutectoid ferrite in the wear-resistant iron-based sintered metal A metal structure that provides a mixed layer with an area ratio of 95: 5 to 5:95 is obtained. In this metal structure, pearlite or pearlite and pro-eutectoid ferrite have softer and superior machinability than upper bainite, and upper bainite has pearlite or pearlite and pro-eutectoid ferrite before plastic hardening. It has a slightly higher hardness and excellent machinability, and has excellent wear resistance due to large and deep plastic hardening at an early stage by continuously repeating contact with the counterpart material with impact.

  Therefore, the wear-resistant iron-based sintered metal according to the present invention having the above-described configuration has excellent machinability and excellent wear resistance by eliminating the addition of hard particles.

  Further, the wear-resistant iron-based sintered metal according to the present invention is the wear-resistant iron-based sintered metal described in (1) above, (2) V: 0.02 to 4.0% by weight. It is the structure containing.

  The reason why the content ratio of V is limited to 0.02 to 4.0% is as follows. V has the effect of refining crystal grains, and if the weight ratio is less than 0.02%, a sufficient effect cannot be obtained. If the weight ratio exceeds 4.0%, a large amount of high-hardness V carbide is present. Formed, and the opponent's aggression becomes large.

  When V is included in the range of 0.02 to 4.0%, the crystal structure does not include martensite, and the mixture becomes a mixture of upper bainite and pearlite or pearlite and pro-eutectoid ferrite, and the opponent attack is suppressed. In addition to having excellent wear resistance and excellent machinability, it is obtained in a state in which V carbide crystal grains are appropriately refined, and has excellent wear resistance with suppressed opponent attack.

  Further, the wear-resistant iron-based sintered metal according to the present invention is the wear-resistant iron-based sintered metal according to (1) above, (3) Cr: 0.05 to 2.0% by weight It is the structure containing.

  The reason for limiting the Cr content ratio to 0.05 to 2.0% is as follows. Cr moves the pearlite region of the CCT diagram to the slow cooling side and has the effect of expanding the bainite region. If the Cr content is less than 0.05%, this effect is insufficient, and if it exceeds 2.0%, a large amount of hard martensite is easily generated, and the machinability deteriorates.

  When Cr is included in the range of 0.05 to 2.0%, the crystal structure does not include martensite, and the mixture becomes a mixture of upper bainite and pearlite or pearlite and proeutectoid ferrite, and the opponent attack is suppressed. In addition to having excellent wear resistance and excellent machinability, it is obtained in a state in which V carbide crystal grains are appropriately refined, and has excellent wear resistance with suppressed opponent attack.

In addition, the valve seat for an internal combustion engine according to the present invention preferably uses (3) the wear-resistant iron-based sintered metal described in (1) or (2) above in order to achieve the above object.

  With this configuration, the valve seat for an internal combustion engine according to the present invention has excellent machinability, excellent wear resistance, and high durability.

  According to the present invention, it is possible to provide a wear-resistant iron-based sintered metal and a valve seat for an internal combustion engine that are excellent in both machinability and wear resistance by eliminating the addition of hard particles.

It is sectional drawing of the principal part of the cylinder head which applied the wear-resistant iron-based sintered metal which concerns on embodiment of this invention to the valve seat. The initial hardness of the upper bainite of the metal structure related to the wear-resistant iron-based sintered metal according to the embodiment of the present invention and the hardness after the hardening, the initial hardness and lower hardness of the lower bainite of the metal structure according to the comparative example It is a graph compared with hardness of. The graph which compared the amount of wear of the upper bainite of the metal structure which concerns on the wear-resistant iron-based sintered metal which concerns on embodiment of this invention with each amount of wear of the pearlite of the metal structure which concerns on a comparative example, and a lower bainite. is there. It is a schematic diagram explaining the surface pressure hardening at the time of applying the wear-resistant iron-based sintered metal which concerns on embodiment of this invention to a valve seat. The wear-resistant iron-based sintered metal whose metal structure according to the embodiment of the present invention is composed only of upper bainite, and the wear-resistant iron-based sintered metal whose metal structure according to the comparative example is composed of only lower bainite. It is a figure to compare, (A) is a graph which compares the relationship between the compressive residual stress and surface depth of upper bainite and lower bainite, (B) is a sectional view near the surface (sliding surface) of upper bainite, (C ) Is a cross-sectional view near the surface (sliding surface) of the lower bainite. It is a graph which shows the relationship between the weight ratio and density of Mo in the wear-resistant iron-based sintered metal which concerns on embodiment of this invention. It is a graph which shows the relationship between the weight ratio of C in the wear-resistant iron-based sintered metal according to the embodiment of the present invention and the wear amount in the axial direction (axial direction of the valve seat shown in FIG. 1). Seven types of valve seats made of the wear-resistant iron-based sintered metal according to the embodiment of the present invention, with the proportion of upper bainite in upper bainite and pearlite being slightly different, are mounted on the cylinder head and the engine is fixed. It is a graph which shows the amount of axial wear of a valve and a valve seat which arises when starting for a time. It is a schematic diagram which shows the dispersion | distribution state of the upper bainite in the pearlite base in the wear-resistant iron-based sintered metal which concerns on embodiment of this invention, and explanatory drawing which shows the crystal structure. It is explanatory drawing which shows abrasion of the base which carries out plastic hardening from the initial stage hardness in the wear-resistant iron-based sintered metal which concerns on embodiment of this invention. It is explanatory drawing which shows the relationship with the surface pressure when the initial hardness in the wear-resistant iron-based sintered metal according to the embodiment of the present invention is harder in the upper bainite than in the base. It is explanatory drawing which shows the relationship with the surface pressure when the initial stage hardness in the wear-resistant iron-based sintered metal which concerns on embodiment of this invention is harder than a base bainite. In the wear-resistant iron-based sintered metal of the example of the present invention, (A) is a chart showing the relationship between the amount of axial wear in the combination of the area ratios of upper bainite and pearlite, and (B) is pearlite and proeutectoid. It is a graph which shows the relationship of the amount of axial wear in the combination of the area ratio according to structure | tissue of the mixed powder of ferrite and an upper bainite. It is explanatory drawing of the material dispersion | distribution state at the time of shaping | molding of the alloy powder in the wear-resistant iron-based sintered metal which concerns on embodiment of this invention, and after shaping | molding. It is a graph which shows the relationship of the axial direction wear amount in the combination of the area ratio according to structure | tissue in the wear-resistant iron-based sintered metal of a comparative example. It is explanatory drawing which shows the relationship with the surface pressure in case the initial stage hardness of a lower bainite is harder than a base. The graph which showed the relationship with the amount of axial wear in the combination of the area ratio according to structure | tissue of the wear-resistant iron-based sintered metal which concerns on the Example and comparative example which were shown in FIG.13 and FIG.15 in the ratio of a valve | bulb and a valve seat. FIG. It is the graph which showed the relationship between the Mo weight ratio and the amount of axial wear in the wear-resistant iron-based sintered metal according to Examples and Comparative Examples of the present invention as a ratio of a valve and a valve seat. It is the graph which showed the relationship with the amount of axial wear in the case of containing V and C in the wear-resistant iron-based sintered metal according to the example of the present invention, as a ratio of the valve and the valve seat. It is the graph which showed the relationship between the weight ratio of V in the wear-resistant iron-based sintered metal which concerns on the Example of this invention, and the amount of axial wear with the ratio of a valve | bulb and a valve seat.

  Hereinafter, embodiments of an abrasion-resistant iron-based sintered metal and a valve seat according to the present invention will be described with reference to the drawings.

  1 to 18 are drawings for explaining the wear-resistant iron-based sintered metal and the valve seat according to the present embodiment. FIG. 1 shows a cross-sectional view of the main part of the cylinder head. In FIG. 1, a valve seat 2 made of a wear-resistant iron-based sintered metal is provided on the bottom side of a cylinder head 1 of an engine (entire drawing is omitted). That is, the valve seat 2 of the present embodiment is formed into a predetermined shape by cutting or polishing the wear-resistant iron-based sintered metal of the primary shape product.

  The cylinder head 1 seals a part of the combustion chamber 3 at its bottom surface, and forms an exhaust passage 4 that opens to the combustion chamber 3. The opening of the combustion chamber 3 is opened and closed by an exhaust valve (hereinafter referred to as a valve) 5 provided in the cylinder head 1. A valve guide 6 is interposed between the shaft portion 5a of the valve 5 and the cylinder head 1 so as to support the shaft portion 5a of the valve 5 so as to be movable along the axial direction.

  The valve 5 normally closes the opening of the exhaust passage 4 with the valve body 5 b by the tensile force of the valve spring 7.

  The valve seat 2 is fitted into the bottom surface of the cylinder head 1, and the valve body 5 b of the valve 5 is seated when the exhaust passage 4 is closed.

  The valve seat 2 is fired with the wear-resistant iron-based sintered metal according to the present embodiment as a primary shape, and is further cut into a chamfered part of the inner peripheral wall surface portion that becomes the seating portion of the valve 5. It becomes.

  Below, the abrasion-resistant iron-based sintered metal which comprises the valve seat 2 is demonstrated.

  The wear-resistant iron-based sintered metal contains Mo; 0.0025 to 2.0%, C; 0.2 to 1.2% by weight, with the balance being Fe and inevitable impurities. The structure is composed of a mixed layer of upper bainite and pearlite or pearlite and pro-eutectoid ferrite, and the area ratio of upper bainite and pearlite or pearlite and pro-eutectoid ferrite is 95: 5 to 5:95.

  The wear-resistant iron-based sintered metal preferably contains V; 0.02 to 4.0% by weight, and further contains Cr; 0.05 to 2.0% by weight. V: It is desirable to contain 0.02 to 4.0%. In the following description, all “%” indicates wt%.

  The wear-resistant iron-based sintered metal is obtained by mixing a plurality of types of powders and a lubricant, firing them into a predetermined primary shape under high-temperature and high-pressure conditions, and cooling them at a predetermined cooling rate.

  When the wear-resistant iron-based sintered metal contains Mo; 0.0025 to 2.0%, C; 0.2 to 1.2%, and the balance is Fe and inevitable impurities, For example, a mixed powder of a first powder, a second powder, graphite (C powder), and a lubricant is used as a raw material of the sintered metal, and the first powder is Mo; 0.5-2. The balance is 0%, the balance is made of Fe and inevitable impurities, and the second powder is made of powder of Fe and inevitable impurities. FIG. 14 shows the material dispersion state at the time of forming the alloy powder in the wear-resistant iron-based sintered metal and after the forming. As can be seen from FIG. 14, the material dispersion state at the time of molding of the alloy powder and after molding is almost the same.

  Fe-Mo alloy powder can be used as the first powder containing Mo, and the first powder having a particle size in the range of 50 to 250 μm is used. As the Fe-Mo alloy powder, for example, Fe-0.5% Mo alloy powder, Fe-1.5% Mo alloy powder, Fe-2.0% Mo alloy powder and the like can be appropriately selected.

  The particle size of the second powder containing Mo is not particularly limited, but a particle having the same size as the particle size of the first powder can be selected.

  Further, it is desirable that the wear-resistant iron-based sintered metal of the present embodiment contains V; 0.02 to 4.0%. That is, the wear-resistant iron-based sintered metal contains Mo; 0.0025 to 2.0%, C; 0.2 to 1.2%, V; 0.02 to 4.0. %, And the balance is preferably composed of Fe and inevitable impurities.

  V strengthens the base phase and improves wear resistance. V: 0.02 to 4.0%, if less than 0.02%, there is little increase in hardness and the wear resistance deteriorates. On the other hand, if it exceeds 4.0%, the hardness will increase too much and the opponent aggression will increase. For these reasons, V is set in the range of 0.02 to 4.0%.

  The raw material of the wear-resistant iron-based sintered metal in this case is, for example, a mixed powder of a first powder, a second powder, graphite, and a lubricant as a sintered metal raw material. The powder of Mo contains 0.5 to 2.0% and the balance is made up of Fe and inevitable impurities, and the second powder contains V; 0.02 to 1.5% and the balance is made up of Fe and inevitable It consists of powder consisting of mechanical impurities.

  Furthermore, it is desirable that the wear-resistant iron-based sintered metal of the present embodiment contains Cr: 0.05 to 2.0%. That is, the wear-resistant iron-based sintered metal contains Mo; 0.0025 to 2.0%, C; 0.2 to 1.2%, V; 0.02 to 4.0%, and the like. In addition, it is preferable that the content of Cr is 0.05 to 2.0%, and the balance is Fe and inevitable impurities. Note that Cr is added in consideration of the Mo amount, the C amount, the V amount, and the cooling rate after sintering in order to easily form an upper bainite structure.

  The raw material of the wear-resistant iron-based sintered metal in this case is, for example, a mixed powder of a first powder, a second powder, graphite, and a lubricant as a sintered metal raw material. The powder of Mo contains 0.5 to 2.0% and the balance is made up of Fe and inevitable impurities, and the second powder contains V; 0.02 to 1.5% and the balance is made up of Fe and inevitable The first powder or the second powder may contain Cr, or the Cr powder may be mixed with the first and second powders.

  Cr: 0.05 to 2.0% is less than 0.05%, the hardness is lowered and the wear resistance is liable to be adversely affected. On the other hand, if it exceeds 2.0%, the hardness will increase too much and the opponent aggression will increase. Therefore, by blending Cr in the range of 0.05 to 2.0%, the cooling rate can be reduced while suppressing the generation of martensite during sintering, and the bainite region can be expanded.

  The wear-resistant iron-based sintered metal of the present embodiment is sufficiently mixed by mixing the first powder, the second powder, graphite, and the lubricant in a weight ratio of, for example, 49: 49: 1: 1. A raw material obtained by stirring is used, the raw material is filled in a mold, and is compressed and molded by a molding press or the like to form a green compact, and the green compact is sintered in a nitrogen atmosphere at 1120 ° C., for example. For example, it is manufactured by cooling to room temperature at a cooling rate of 100 ° C./min after sintering. For example, zinc stearate can be used as the lubricant. The lubricant evaporates during the firing process and is not included in the sintered metal.

  By cooling from 1120 ° C. to room temperature, the wear-resistant iron-based sintered metal is produced by dispersing Fe—Mo hard particles that have become upper bainite from the first powder in the matrix phase. In addition, the wear-resistant iron-based sintered metal is such that Fe of the first powder and Fe of the second powder that did not become Fe-Mo hard particles become pearlite of proeutectoid cementite and Fe-V composition, A base phase is generated.

  This will be described in more detail below. In general, bainite is a structure formed when carbon steel is cooled from an austenite state and kept at a constant temperature range between a temperature range where pearlite transformation occurs and a temperature where the martensitic transformation starts (Ms point). . In steel containing alloy elements such as Mo, it occurs not only during such constant temperature holding but also by continuous cooling at a moderate speed.

  Bainite is close to martensite when treated at an upper bainite exhibiting a black feather-like structure close to pearlite when treated at an isothermal treatment temperature of about 450 to 550 ° C. and at a temperature relatively close to the Ms point below that. It is roughly divided into lower bainite that has a needle-like structure.

  As shown in FIG. 2, the upper bainite has an initial hardness that is softer than that of the lower bainite, and is harder than that of the lower bainite after plastic hardening. As shown in FIG. 3, the plastic-cured upper bainite (upper B) has a structural characteristic that the amount of wear (μm) is lower than that of pearlite (P) or lower bainite (lower B).

  Pearlite is generally a structure formed when carbon steel is cooled from an austenite state and gradually cooled to a temperature range where pearlite transformation occurs, and is a structure in which thin plate-like ferrite and cementite are alternately arranged. is there.

  As shown in FIG. 3, pearlite has a structure specification that the wear amount is higher than that of the upper bainite and that plastic hardening is difficult compared to the upper bainite.

  Thereby, this inventor acquired the above novel knowledge about an upper bainite.

  That is, the upper bainite can easily perform cutting and the like at the initial hardness, and it is difficult to damage the processing tool, thereby contributing to the extension of the tool life. Moreover, the amount of wear of the upper bainite is low after curing. As a result, for example, as shown in FIG. 4, when the valve 5 is opened from the open state of the exhaust passage 4, that is, the valve body 5 b is vigorously seated on the valve seat 2. ) Is cured. At the same time, the roughness of the surface of the valve seat 2 is reduced (density is increased) to ensure wear resistance, and wear of the valve seat 2 can be suppressed. That is, the wear characteristics vary greatly depending on the surface roughness.

  The upper bainite is larger in pearlite or pearlite and pro-eutectoid ferrite or lower bainite in the usage environment of the valve seat 2 and has a larger plastic hardening amount and a higher hardening depth and is excellent in wear resistance.

  More specifically, as shown in FIG. 5A, the compressive residual stress (MPa) becomes more disadvantageous in terms of fatigue strength as the surface depth (μm) becomes deeper. Moreover, as shown in FIG. 5B, the upper bainite has an advantage in fatigue strength and lower change with respect to the surface depth than the lower bainite shown in FIG. 5C. That is, when the wear-resistant iron-based sintered metal is applied to the valve seat 2, since the wear phenomenon includes surface pressure fatigue failure (plastic deformation), it is more advantageous to plastically harden into the deep layer. .

  Therefore, in consideration of such characteristics of the upper bainite, in the present embodiment, the valve seat 2 is composed of Mo: 0.0025-2.0%, C: 0.2-1.2% by weight. The balance is composed of an upper bainite having a metal structure composed of an inevitable material and Fe and a wear-resistant iron-based sintered metal composed of pearlite or pearlite and pro-eutectoid ferrite.

  That is, Mo is a material that has excellent wear resistance and improves hardenability. At this time, when the weight ratio of Mo is less than 0.0025%, the above-described effect is hardly obtained. As shown in FIG. 6, when it exceeds 2.0%, the density rapidly decreases and sufficient wear resistance is obtained. Sex cannot be obtained. For these reasons, the Mo content is in the range of 0.0025 to 2.0%.

  C is a material that forms carbides during sintering and improves wear resistance. At this time, as shown in FIG. 7, if the weight ratio of C is less than 0.2%, the amount of axial wear increases rapidly, and sufficient wear resistance cannot be obtained. Coarse pro-eutectoid cementite, which is a high-hardness cementite that precipitates from austenite during subsequent cooling, is produced, resulting in disadvantages in machinability and increased opponent aggression. For these reasons, C is set in the range of 0.2 to 1.2%.

  When Mo and C are included in the above range, the metal structure that becomes a mixed layer of upper bainite and pearlite or pearlite and pro-eutectoid ferrite is polished by appropriately controlling the cooling rate of cooling from the sintering temperature. In the case of a metal structure in which a wear-resistant iron-based sintered metal is obtained and the area ratio of upper bainite and pearlite or pearlite and pro-eutectoid ferrite is a mixed layer of 95: 5 to 5:95, machinability and resistance Excellent wear resistance. In this metal structure, pearlite or pearlite and pro-eutectoid ferrite have softer and better machinability than upper bainite, and upper bainite has low hardness before machinability and machinability. In addition, it has excellent wear resistance by being deeply plastic-cured by sliding contact with the counterpart material.

  In the present embodiment, the area ratio between upper bainite and pearlite or pearlite and pro-eutectoid ferrite in the wear-resistant iron-based sintered metal is limited to the range of 95: 5 to 5:95 as follows. Depending on the reason. If the area ratio of upper bainite and pearlite is, for example, as shown in FIG. 8 and the ratio of upper bainite is less than 5, the axial wear is rapidly increased and the wear is deteriorated. Further, when the ratio of upper bainite exceeds 95, the opponent aggression becomes high.

  In the present embodiment, the wear-resistant iron-based sintered metal has a weight ratio to the whole of Mo; a first powder containing 0.5 to 2.0% Mo, the balance being Fe and inevitable impurities, Fe And it shape | molds from the mixed powder which mixed the 2nd powder which consists of an unavoidable impurity, graphite, and a lubricant, and the weight ratio is 49: 49: 1: 1, respectively. Here, the wear-resistant iron-based sintered metal is sintered and cooled, so that all of the first powder becomes upper bainite and all of the second powder becomes pearlite or pearlite and pro-eutectoid ferrite. .

  In the present embodiment, the particle size of the first powder, which is a manufacturing raw material of the wear-resistant iron-based sintered metal, is limited to a range of 50 to 250 μm. This limitation is due to the following reasons. If the wear-resistant iron-based sintered metal is fired with the first powder having a particle size of less than 50 μm, the particle size of the produced upper bainite becomes too small, and sufficient wear resistance cannot be obtained. In addition, if the wear-resistant iron-based sintered metal is fired when the particle size of the first powder is 250 μm or more, the particle size of the produced upper bainite is too large, and the base pearlite or pearlite and the pro-eutectoid ferrite The dispersion density of the upper bainite will decrease. When the density of the upper bainite is lowered, the wear-resistant iron-based sintered metal tends to expose pearlite or pearlite and pro-eutectoid ferrite, and wear resistance is lowered. Since the second powder, pearlite or pearlite and proeutectoid ferrite, serves as a base, it is not necessary to consider the particle size.

  In the present embodiment, lower bainite and martensite are generated by setting the sintering temperature during molding to 1100 to 1200 ° C. and the cooling rate after sintering during molding to a range of 40 to 150 ° C./min. Thus, the wear-resistant iron-based sintered metal having upper bainite and pearlite or pearlite and proeutectoid ferrite can be obtained.

  FIG. 9 (A) shows an example in which Fe-1.5% Mo alloy powder, Fe powder, C powder, and lubricant are molded from a material kneaded so as to have a weight ratio of 49: 49: 1: 1. The schematic diagram of the principal part at the time of cooling at 100 degrees C / min after sintering by nitrogen atmosphere is shown.

  The valve seat 2 shown in FIG. 9A exhibits a structure in which the metal structure is composed only of a mixed phase of the upper bainite 2a and the pearlite (base) 2b. The wear-resistant iron-based sintered metal is produced by dispersing the Fe—Mo hard particles that have become the upper bainite 2a from the first powder into the pearlite 2b that is the base phase from the second powder. In addition, the wear-resistant iron-based sintered metal forms the base 2b when the first powder Fe and the second powder Fe that have not become Fe—Mo hard particles become pearlite.

  At this time, the crystal structure of the upper bainite 2a is shown in FIGS. 9B and 9C, and the crystal structure of the pearlite 2b is shown in FIG. 9D. In the crystal structure of the upper bainite 2a, the apparent hardness 220 (HV10) and the microhardness 270 (HV0.025) are shown in FIG. 9B, and the apparent hardness 250 (HV10) and the microhardness are shown in FIG. 9C. 390 (HV 0.025), and this difference is due to the difference in compression molding force before sintering.

  As shown in FIG. 10, the valve seat 2 made of wear-resistant iron-based sintered metal is preferentially worn by pearlite or pearlite and proeutectoid ferrite (base) 2b by the surface pressure received from the valve 5 in the actual machine, A high surface pressure is applied to the upper bainite 2a. For example, the upper bainite 2a is plastically hardened from an initial hardness of 27 HV to around 600 HV at an early stage, so that the function of hard particles can be achieved as a hard phase.

  As shown in FIG. 11, the upper bainite 2a dispersed in pearlite or pearlite and pro-eutectoid ferrite (base) 2b is rapidly deeply and deeply plastically cured by a load (surface pressure) from the valve 5 in an actual machine.

  As described above, the wear-resistant iron-based sintered metal of the present embodiment is composed only of upper bainite that does not contain hard particles and has an increased carbide density. That is, the wear-resistant iron-based sintered metal of the present embodiment is composed of only upper bainite that has a small initial hardness and a large and deep plastic hardening compared to pearlite and lower bainite, so that it is excellent in machinability and is offensive to the opponent. Therefore, it is easy to machine the valve seat, and it is possible to suppress the shortening of the life of the machining tool, and when used as a valve seat, It can be plastic hardened deeply to exhibit excellent wear resistance.

(Example)
As an example, a valve seat made of wear-resistant iron-based sintered metal composed only of bainite and pearlite was experimentally manufactured and the wear resistance was examined.

  As shown in the schematic diagram of FIG. 11, the wear resistance of a valve seat made of a wear-resistant iron-based sintered metal consisting only of upper bainite and pearlite, in which the upper bainite 2a is dispersed in the base 2b that is pearlite, was investigated. It was. The valve seat 2 having a metal structure shown in the schematic diagram of FIG. 11 supports the load when the valve 5 is closed by the upper bainite 2a, and the upper bainite 2a is deeply and greatly plastically cured at an early stage.

  If the initial hardness of the upper bainite 2a is smaller than the hardness of the base 2b, which is a pearlite, as shown in FIG. 12, the pearlite 2b receives a load (surface pressure) from the valve seat valve 5, so The bainite 2a is not plastically cured, and simultaneous wear of the pearlite 2b and the upper bainite 2a proceeds. However, since the initial hardness of the upper bainite 2a is not smaller than the hardness of the base 2b which is a pearlite, as shown in the schematic diagram of FIG. 11, the load (surface pressure) from the valve seat valve 5 is applied to the upper bainite 2a. Will receive.

  As shown in FIG. 13 (A), three kinds of powders of Fe100% powder, Fe-1.5Mo% powder, and graphite (Gr) with respect to pearlite were mixed at five ratios of Nos. 1 to 5, Each of the primary molded products was sintered at 1120 ° C., cooled at 100 ° C./min, and cut to obtain valve seats that were No. 1 to No. 5 products. Similarly, Fe-0.25% powder, Fe-1.5Mo% powder, and graphite (Gr) are mixed in two ratios of No. 6 and No. 7, respectively, and primary molded products at 1120 ° C., respectively. After being sintered, it was cooled at 100 ° C./min and cut to obtain valve seats as No. 6 and No. 7 product. Gr is graphite and is used in an amount of 1% or more in order to determine the amount of C in the sintered metal.

  As shown in FIG. 13 (B), Fe60% powder for pearlite and pro-eutectoid ferrite, Fe-1.5Mo40% powder for upper bainite, and three types of powders of graphite (Gr), No. 15, Fe-0.25V 60% powder for pearlite and pro-eutectoid ferrite, Fe-1.5Mo 40% powder for upper bainite, and three types of powders of graphite (Gr) are mixed in two ratios of No. 16. Each of the primary molded products was sintered at 1120 ° C., cooled at 100 ° C./min, and cut to obtain a valve seat as an implemented product. Gr is graphite and is used in an amount of 0.8% or more in order to determine the amount of C in the sintered metal.

  Then, it was attached to the cylinder head as shown in FIG. 1, the engine was started for a certain period of time, and the axial wear amount of the valve seat and the valve was measured.

  As a result, as shown in FIG. 13 (A), the valve seat of the implementation product related to the seven pearlites shows the maximum amount of axial wear of the first implementation product of 62 μm, and All were significantly smaller than this value and were found to have excellent wear resistance.

  In addition, as shown in FIG. 13A, the valve seat of the actual product related to the two pearlites and pro-eutectoid ferrite shows the value of the axial wear amount of the No. 15 actual product of 64 μm, and the No. 16 actual product. The amount of axial wear of each showed a value of 50 μm, and it was found that all had excellent wear resistance.

(Comparative example)
As a comparative example, a wear-resistant iron-based sintered metal valve seat other than the combination of upper bainite and pearlite was prototyped and the wear resistance was examined.

  In FIG. 15, No. 8 is a wear-resistant iron-based sintered metal valve seat made only of lower bainite, and Nos. 9 and 10 are wear-resistant iron-based sintered metal valves made only of upper bainite and lower bainite. No. 11 is a valve sheet made of wear-resistant iron-based sintered metal made only of pearlite, and Nos. 12 to 14 are valve sheets made of wear-resistant iron-based sintered metal made only of pearlite and lower bainite.

  As shown in FIG. 1, the prototype Nos. 8 to 14 were mounted on the cylinder head, the engine was started for a certain period of time, and the axial wear amounts of the valve seat and the valve were measured. As a result, the comparative valve seats of Nos. 8 to 14 all had a high axial wear amount, resulting in poor wear resistance.

  The schematic diagram of FIG. 16 shows the number 13 valve seat, and when compared with the schematic diagram of FIG. 11, the upper bainite 2a of FIG. 11 is replaced with the lower bainite 2c. Although the lower bainite 2c is harder than pearlite and has an initial hardness higher than that of the upper bainite, the plastic hardening is small and shallow. Since the lower bainite 2c supports the load when the valve 5 is closed, and the lower bainite 2c receives the load (surface pressure) from the valve 5, the lower bainite 2c has a small plastic hardening, so the lower bainite 2c and the pearlite 2b Simultaneous wear progresses.

  FIG. 17 shows the relationship between the amount of wear in the axial direction in the combination of the area ratios by structure of the wear-resistant iron-based sintered metal according to the examples and comparative examples shown in FIGS. 13 and 15, and the ratio of the valve to the valve seat. It is the graph shown by.

  As can be seen from FIG. 17, each example (Nos. 1 to 7) is a valve seat made of wear-resistant iron-based sintered metal composed only of upper bainite and pearlite, and upper bainite, pearlite, and proeutectoid ferrite. Each example (No. 15 and No. 16) which is a wear-resistant iron-based sintered metal valve seat is a wear-resistant iron-based sintered metal valve seat other than the combination of upper bainite and pearlite. Compared to the comparative examples (Nos. 8 to 14), in all cases, the amount of axial wear is small and the wear resistance is excellent.

(Other examples and comparative examples)
FIG. 18 shows the amount of axial wear of a valve seat and a valve in the case of Fe-0.5Mo-0.9C as a comparative example and two valve seats of Fe-2.0Mo-0.9C as an example. It is a bar graph to show. As shown in this bar graph, when Mo is 0.5% or less, the axial wear amount is high, and when Mo is 2.0% or more, the attacking ability against the valve 5 is high.

  Moreover, as shown in FIG. 19, about the valve seat at the time of setting it as Fe-2.0Cr-0.5V-0.02Mo-0.9C as an Example, the bar graph which shows the amount of axial wear of a valve seat and a valve. It is. As shown in this bar graph, it has been found that this example has a low amount of axial wear, good wear, and low attack to the valve 5.

  Furthermore, as shown in FIG. 20, in the case of Fe-0.6Mo- (X) V-0.9C, the weight ratio (X) of V is V (0.0%, comparative product), 0.01 % (Comparative product), 0.02% (commercial product), 0.08% (commercial product), and 4.0% (comparative product) of five valve seats indicate the valve seat and valve axial wear. It is a bar graph. As shown in this bar graph, it has been found that the axial wear amount decreases when the lower limit is 0.02%, and that the attacking ability against the valve 5 increases when the upper limit is 4%.

  In the above embodiment, the valve seat 2 disposed on the exhaust side of the engine has been described. However, the same effect can be obtained even when disposed on the intake side.

  In the present embodiment, the wear-resistant iron-based sintered metal is applied to the valve seat 2 and the structure is hardened by the surface pressure applied by the valve 5. However, for example, the surface is shot by shot peening technology. Various plastic parts such as various parts to be cured, various parts formed by cold forging by compression molding using a mold, or various parts formed by sizing and rolling for shape correction are required. The present invention is also applicable when using an abrasion-resistant iron-based sintered metal as the metal material.

  As explained above, the wear-resistant iron-based sintered metal according to the present invention has the effect of eliminating the addition of hard particles and is excellent in both machinability and wear resistance. For wear-resistant iron-based sintered metals used as metal materials that require plastic deformation, such as valve seats, which are applied under a surface pressure environment and require initial processing and high wear resistance when used. Useful.

  2 ... Valve seat (abrasion-resistant iron-based sintered metal), 2a ... Upper bainite, 2b, (P) ... Pearlite

Claims (3)

  In a weight ratio, Mo; 0.0025 to 2.0%, C; 0.2 to 1.2%, the balance is made of Fe and inevitable impurities, and the metal structure is upper bainite and pearlite or pearlite and proeutectoid. A wear-resistant iron-based sintered metal comprising a mixed layer of ferrite and having an area ratio of upper bainite and pearlite or pearlite and pro-eutectoid ferrite of 95: 5 to 5:95.   The wear-resistant iron-based sintered metal according to claim 1, comprising V; 0.02 to 4.0% by weight. An internal combustion engine valve seat with a wear-resistant iron-based sintered metal according to claim 1-2.