JPH0233847B2 - KOONTAIMAMOSEI2SOSHOKETSUBARUBUSHIITO - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an iron-based sintered valve seat used in internal combustion engines. [Prior art] Iron-based sintered alloys are often used for valve seats in internal combustion engines because of their good wear resistance. In order to satisfy the requirement of better thermal conductivity, which is required as performance increases, considerably more expensive materials must be used. In response to this, recently, a two-layer valve seat using an inexpensive material as a base material has been proposed. However, it is not easy to use an inexpensive material to ensure the same level of loosening resistance as conventional high-quality materials and to obtain strong interfacial bonding strength. As a solution to these problems, it may be possible to strengthen the inexpensive base material by infiltrating the sintered alloy with copper, but this would result in high costs and
As the hardness increases, the machinability decreases and the first layer is also infiltrated with Cu, filling the pores of the sintered body.
The problem has been that oxides with a lubricating effect, which were conventionally produced around the pores at high temperatures, are not formed, resulting in a decrease in wear resistance. Therefore, there has been a demand for a two-layer valve seat that can satisfy various requirements for a valve seat. [Object of the invention] The present invention is capable of solving the above-mentioned conventional problems, and aims to provide a low-cost, two-layer valve seat having excellent wear resistance, loosening resistance, and good thermal conductivity. It is something. [Structure of the Invention] The two-layer sintered valve seat of the present invention is an iron-based sintered bond with a two-layer structure consisting of a first layer that includes a valve contact surface and a second layer that is a base material that supports the first layer. Gold, the first layer is Mo2.5~15%, Co1~15% by weight,
Consisting of a composition consisting of 0.5-1.5% C, 5-20% Pb, the balance Fe and less than 2% impurities, and a structure in which hard particles mainly composed of ferromolybdenum with an average particle size of 10-30μ are uniformly dispersed. The second layer has a composition of 0.5 to 1.5% C, 3 to 20% Pb, the balance Fe and less than 2% impurities by weight, and the composition of the first and second layers is Pb is present in the form of infiltration into the pores of the sintered body, and the difference in C content between the first layer and the second layer is 0.3% or less. In the present invention, preferably the second layer is C0.5~
1.5% Pb, 3 to 18% balance Fe and less than 2% impurities. In addition to the first layer components, the first layer of the valve seat of the present invention further includes 0.5 to 5% Cu, 1 to 15% Ni,
Mn0.2~2%, P0.05~0.8%, B0.05~0.8%,
Cr0.5~20%, W0.5~8%, V0.3~8% and
One or more types of Nb can be contained in an amount of 0.1 to 3%. Furthermore, in the valve seat of the present invention, the second layer further contains Cu0.5 to 5% in addition to the second layer components.
Ni0.5~5%, Mn0.2~2%, P0.05~0.8%,
It can contain one or more of B0.05-0.8% and Cr0.5-5%. In addition, in this specification, % indicates weight %. The reason for limiting each component element used in the present invention will be explained below. First, the components of the first layer of the present invention will be explained. Mo (molybdenum) mainly exists as wear-resistant particles, and a part of it is added as a solid solution in the matrix to strengthen it. However, if it deviates from the limited value, it is not preferable because wear resistance in particular decreases. Similarly, when the average particle diameter of the ferromolybdenum particles is less than the limiting value, the wear resistance decreases. Co (cobalt) is solid dissolved in the matrix to strengthen it and improve high temperature strength, oxidation and corrosion resistance, and wear resistance, and a part of it diffuses into the ferromolybdenum particles and strengthens the matrix of these particles. Increase the holding power to. If Co is less than 1%, the effect of adding it will be small, and if it exceeds 15%, not only will the cost increase, but the effect will not improve compared to the amount of addition.
It was limited to 15%. C (carbon) is added as a solid solution in the Fe matrix to strengthen it and is necessary to ensure the strength and wear resistance of the alloy, but if it is less than 0.5%, ferrite will increase and is not preferred. Not again
If it exceeds 1.5%, a liquid phase will appear during sintering and Mo particles will begin to dissolve, which is not preferable. Next, optionally added elements in the first layer will be explained. Cu (copper), Ni (nickel), and Mn (manganese) are dissolved in the matrix to strengthen it, but below their respective limiting values, the effect is small, and beyond the limiting values, Cu becomes expensive. The dimensional accuracy of the resulting alloy decreases, the cost of Ni increases, residual austenite increases, sub-zero transformation occurs when the valve seat is cooled and press-fitted into the cylinder head, and the material is unstable, which is a constraint on use. In addition to the drawback that the oxidation rate increases, surface oxides generated by high-temperature oxidation tend to peel off, which is not preferable. In addition, Mn is set at 2% or less since it causes the alloy to become brittle due to oxidation if it exceeds a limited value. P (phosphorus) and B (boron) are Fe-P-C,
A liquid phase containing Fe-B-C and some Mo is formed during sintering to accelerate the progress of sintering, make the pores of the sintered body spheroidal, and increase the strength of the matrix. They also act as wear-resistant particles, but if they are less than a limited value, their effect will be small, while if they exceed a limited value, dimensional accuracy will significantly deteriorate and the alloy will become brittle, which is not preferable. Cr (chromium), W (tungsten), V (vanadium), and Mo (molybdenum) mainly exist as ferroalloys or carbides, and improve the wear resistance of alloys, but below their respective limit values, the effect is small and the limit value Exceeding this value increases the cost, becomes too hard, reduces the machinability of the alloy, and increases the aggressiveness of the mating material, the valve, which is undesirable. . In addition, Cu, Ni, Mn, P, B, Cr, W, V,
One or more types of Nb can be added to the first layer component depending on the purpose. When adding,
Elements other than ferromolybdenum may be added in the form of suitable prealloys. Mo may be added in the form of pure Mo or prealloy in addition to the Mo content contained in ferromolybdenum, as long as the total amount satisfies the limited value. Next, the second layer components will be explained. C is added based on the same limiting reasons as C in the first layer. Note that if the difference in C content between the matrix of the first layer and the second layer exceeds 0.3%, the difference between the first layer and the second layer
The diffusion of C from the high C content side to the low C content side near the bonding interface of the layers cannot be ignored, and the materials of both layers will not be stabilized as per the target value, which is not preferable, so the value was set at 0.3% or less. Next, the effect of Nd (lead) infiltration in both layers will be explained. Pb is infiltrated into the pores of the first and second layers and improves the thermal conductivity of the alloy compared to before infiltration.
This reduces the thermal load on the valve and valve seat and improves durability. Furthermore, in the case of the first layer, it acts as a lubricant during wear caused by contact with the valve, thereby significantly improving wear resistance. In addition, Pb infiltration improves the strength of the inexpensive base material and significantly reduces press-fit loosening of the valve seat due to deformation around the pores of the sintered body, which reduces the press-fit allowance with the cylinder head during high-temperature operation. It shows the effect of improving the width. Pb infiltration causes almost no increase in hardness compared to conventional Cu infiltration, and also acts as a lubricant, so it significantly improves the machinability of the alloy and makes processing easier. Furthermore, Pb infiltration significantly improves the bondability at the interface between the first layer and the second layer. The reason is the first
It acts as a buffer material that absorbs the difference in elastic properties between the second layer and the second layer, and it also relieves the stress concentration in the pores.In addition, it is heated in the infiltration process after sintering to prevent the diffusion of each element. In order to proceed further. The above effect of Pb infiltration is insufficient if the amount of infiltration is less than 3%, and in order to infiltrate more than 20%, it is necessary to lower the density of the sintered body, resulting in a decrease in strength. The amount of immersion was 3 to 20%. In particular, in the case of the first layer, 5 to 20
%, and in the case of the second layer, it is preferably 3 to 18% from the viewpoint of improving strength and loosening resistance. The ratio of the thicknesses of the first layer and the second layer is selected depending on the purpose. [Example] The present invention will be explained below with reference to Examples. Example 4% Fe-63Mo in pure iron powder (-100 mesh)
Stearin was added as a lubricant to 100 parts of mixed powder (weight: same below) made by adding alloy powder (-100 mesh), 1% Co powder (-100 mesh), and 0.6% graphite powder (particle size 10μ). 8 parts of zinc oxide was added and mixed for 30 minutes using a V-type powder mixer to obtain a powder for the first layer. Next, 0.8 parts of zinc stearate was added to 100 parts of a mixed powder of pure iron powder and 0.7% graphite powder.
The powder was mixed in the same manner to obtain a powder for the second layer. After that, the powder for the second layer was first filled into a mold having an annular cavity with an outer diameter of 30 mm and an inner diameter of 20 mm, and after preliminary pressurization with an upper punch, the powder for the first layer was further filled. Pressure molding was performed so that the overall height was 8 mm. The ratio of the first layer to the second layer is approximately
The filling amount was adjusted so that the filling amount was 50% each, and the molding was performed so that the joint interface between the first layer 1 and the second layer 2 became a curved surface that descended toward the inner diameter side of the annular body, as shown in the figure. I made it. The obtained powder compact was sintered in an ammonia decomposition gas atmosphere at a temperature of 1150°C for 60 minutes to obtain a sintered body, and then Pb was infiltrated in the same furnace at a temperature of 1120°C to obtain a sintered body. 1st layer component is Fe−2.5Mo−1Co−0.5C
-20Pb, the second layer component is Fe-0.6C-18Pb,
A composite sintered alloy in which both layers were metallurgically bonded was obtained. Thereafter, composite sintered alloys and comparative materials having the compositions shown in Table 1 were produced in the same manner. After each of these materials was processed into a predetermined valve seat shape, it was assembled into a 1600 c.c. aluminum alloy cylinder head engine, and a bench durability test equivalent to continuous high-speed driving of 50,000 km was conducted. The results are shown in Table 1. As can be seen from the results in Table 1, both the wear resistance (change in tappet clearance) and pull-out load show good results.

[Table] Next, for Inventive Material 1 and Comparative Material 1, the bonding strength between the first layer and the second layer was measured. The results are shown in Table 2. As can be seen from this result, inventive material 2 infiltrated with Pb has double the strength of comparative material 1 before infiltration with Pb.

〔Effect of the invention〕

The present invention has a two-layer structure consisting of a first layer that includes a valve contact surface that requires wear resistance, and a second layer that serves as a base material that supports the first layer. A valve seat can be obtained that has wear resistance, good thermal conductivity, and loosening resistance that cannot be obtained with a sintered body. Moreover, by adjusting the ratio of the thickness of the first layer and the second layer, the thermal conductivity and loosening resistance can be adjusted, so it can be used not only for aluminum alloy cylinder heads but also for conventional cast iron cylinder heads. It also has the advantage of being widely usable.

[Brief explanation of drawings]

The figure is a sectional view showing the valve seat of the present invention. In the figure, 1...first layer, 2...second layer.

Claims (1)

[Scope of Claims] 1 An iron-based sintered alloy with a two-layer structure consisting of a first layer including a valve contact surface and a second layer supporting the first layer, wherein the first layer has a weight ratio of Mo2 .5~15%, Co1~15%,
It consists of 0.5 to 1.5% C, 5 to 20% Pb, the balance Fe and less than 2% impurities, and has a structure in which hard particles mainly composed of ferromolybdenum with an average particle size of 10 to 30μ are uniformly dispersed. Yes, the second layer consists of components consisting of 0.5 to 1.5% C, 3 to 20% Pb, the balance Fe and impurities less than 2% by weight, and Pb in the components of the first and second layers are both sintered. A high-temperature wear-resistant two-layer sintered valve, characterized in that it exists in the form of infiltration into the pores of a compact, and the difference in the amount of carbon between the first layer and the second layer is 0.3% or less. sheet. 2 The second layer has a weight ratio of C0.5 to 1.5%, Pb3 to 18%,
The valve seat according to claim 1, characterized in that the balance consists of Fe and less than 2% impurities. 3 In addition to the above ingredients, the first layer contains Cu0.5-5%,
Ni1~15%, Mn0.2~2%, P0.05~0.8%, B0.05
~0.8%, Cr0.5~20%, W0.5~8%, V0.3~8%
The valve seat according to claim 1, characterized in that the valve seat comprises a component containing one or more of Nb and 0.1 to 3%. 4 In addition to the above ingredients, the second layer further contains Cu0.5 to 5%,
Ni0.5~5%, Mn0.2~2%, P0.05~0.8%,
The valve seat according to any one of claims 1 to 3, characterized in that it is made of a component containing one or more of B0.05 to 0.8% and Cr0.5 to 5%. .