JPS6140001B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a valve seat made of an Fe-based sintered alloy that has excellent wear resistance and is structurally extremely stable. Conventionally, valve seats made of Fe-based sintered alloy generally have a C: 0.5.
~1.5%, Cr: 1 to 10%, and optionally either Ni or Co, or both: 1
~15% and/or Mo and/or W: 1~15%, the remainder being Fe.
It was manufactured by rapidly cooling a sintered body having a composition (all percentages by weight, all percentages by weight) consisting of and unavoidable impurities. However, since the conventional valve seat made of Fe-based sintered alloy mentioned above usually has a mixed structure of martensite and retained austenite, for example, when it is used by being attached to the cast iron head of an engine by shrink fit, , the retained austenite undergoes martensitic transformation due to the temperature increase during shrink fitting or use, and this martensitic transformation causes the valve seat to undergo dimensional changes (expansion).
The valve seat often falls off from the engine head, and furthermore, the presence of the retained austenite makes it difficult to maintain desired wear resistance. Therefore, conventional methods with such an unstable structure, that is, a structure in which retained austenite exists,
Attempts have been made to stabilize the structure by subjecting the valve seat made of Fe-based sintered alloy to a tempering process, but even with this tempering process, it is not possible to completely eliminate residual austenite. This resulted in a decrease in hardness and a decrease in wear resistance. From the above-mentioned viewpoint, the present inventors have proposed
As a result of research to solve the problems of valve seats made of Fe-based sintered alloy, we have found that Cu can be added to the raw material powder as an alloying component to the conventional valve seats made of Fe-based sintered alloy, or sintered Later, Cu is added through impregnating treatment to increase the solid solution amount of C in the Fe base, and then, due to the Cu inclusion, after quenching, the valve seat contains a large amount of retained austenite. Sub-zero treatment is performed to transform the retained austenite to martensite, and C
By creating a martensitic structure with a large amount of solid solution of C, and then subjecting it to a tempering treatment to precipitate the solid solution C as carbide, an Fe-based sintered alloy with extremely high hardness and a stable structure that is completely unaffected by heat can be created. This led to the discovery that a valve seat could be produced. This invention was made based on the above findings, and includes C: 0.5 to 1.5%, Cr: 1 to 10%,
Contains Cu: 1 to 30%, and further Ni as necessary.
and one or two of Co: 1 to 15%,
and/or one or two of Mo and W: 1 to 15%, and the remainder is Fe and inevitable impurities, or a Co-impregnated sintered body is heated to 900 to 1200°C. Quenched from a temperature of -
Subzero treatment at temperatures below 20°C followed by 400°C
Fe consisting of tempering treatment at a temperature of ~700℃
This method is unique in the manufacturing method of a valve seat made of sintered alloy. Next, in the Fe-based sintered alloy valve seat of the present invention, the reason why the components, composition range, quenching temperature, sub-zero treatment temperature, and tempering temperature are limited as described above will be explained. (a) Component composition C The C component has the effect of forming a solid solution in the base material and strengthening it, as well as forming carbide and improving wear resistance, but if its content is less than 0.5%, the above effect will not be achieved. If the desired effect is not obtained, and on the other hand, if the content exceeds 1.5%, embrittlement will become significant, hardness will also increase significantly, and the aggressiveness of the valve, which is the mating material, will increase. The amount was determined to be 0.5-1.5%. Cr The Cr component combines with most of the C to form carbides and improves wear resistance, as well as solid solution in the base material and improves heat resistance, but if the content is less than 1% However, if the content exceeds 10%, the strength will rapidly decrease and the damage to the valve will increase significantly due to the increase in hardness. Therefore, the content was set at 1 to 10%. Cu As mentioned above, the Cu component increases the solid solution amount of C in the matrix, thereby ensuring a fine martensitic structure that does not contain residual austenite through sub-zero treatment, and preventing the precipitation of carbides through tempering treatment. In addition, when it is contained in a large amount, it has the effect of improving thermal conductivity and increasing the cooling efficiency of the valve, but the content is 1%.
If it is less than the desired effect, the desired effect cannot be obtained;
If the content exceeds 30%, the strength decreases significantly, so the content was set at 1 to 30%. Ni and Co These components have the uniform effect of solid-dissolving in the base material, strengthening it, and improving heat resistance, so they can be used as needed when particularly high strength and heat resistance are required. However, if the content is less than 1%, the desired improvement effect on the above action cannot be obtained, and on the other hand, even if the content exceeds 15%, no further improvement effect will be obtained, and economic efficiency should be considered. The content was determined to be 1-15%. Mo and W These components, like Cr, combine with C to form carbides, and also disperse in the base material as undiffused ferromolybdenum particles and ferrotungsten particles to improve wear resistance. In addition, it is dissolved in the base material and has a uniform effect of improving its heat resistance, so it is included as necessary when particularly abrasion resistance and heat resistance are required, but the content is less than 1%. However, if the content exceeds 15%, not only will embrittlement become significant and the strength will deteriorate.
The content was set at 1 to 15% since machinability would be significantly impaired. (b) Quenching temperature At a quenching temperature of less than 900℃, after tempering treatment,
While unable to ensure the desired high hardness, 1200
Since 1200°C is the upper limit of sintering temperature, a quenching temperature exceeding 1200°C will result in significant coarsening of the structure.
It was determined that (c) Sub-zero treatment temperature If the temperature is higher than -20℃, only a structure with a large amount of retained austenite will be obtained, and martensite will not be refined, so by setting the upper limit to -20℃, , we ensured a fine martensitic structure with no retained austenite. (d) Tempering temperature When attaching the valve seat to the engine head by shrink-fitting and using the valve seat, the valve seat will be heated to a temperature of 300°C or higher, so it must be tempered at a temperature of 400°C or higher. It is necessary to stabilize the structure and increase hardness through carbide precipitation through treatment. However, tempering treatment at a temperature exceeding 700°C causes a significant decrease in hardness, so the upper limit temperature must be set at 700°C. Next, the method of the present invention will be explained using examples and comparing with comparative examples. Example 1 As raw material powders, Fe powder with a particle size of -100mesh, Fe-Cr alloy (containing Cr: 12%) powder with a particle size of -100mesh, Cu powder with a particle size of -100mesh, and -
100mesh carbon powder, -200mesh Ni powder, -200mesh Co powder, -200mesh Fe-Mo gold (Mo: 60% content) powder, and -200mesh Fe
- Prepare W alloy (W: 75% content) powder, blend these raw material powders into the composition shown in Table 1,
The mixture was mixed and formed into a green compact under a pressure of 6 tons/cm ² , and then sintered in a hydrogen atmosphere at a temperature of 1170°C for 1 hour. using liquid nitrogen, temperature: -
Sub-zero treatment is carried out by holding at 150℃ for 15 minutes, and finally at 550℃ in ammonia decomposition gas.
Valve seats 1 to 1 of the present invention having substantially the same composition as the blended composition by subjecting to time-maintenance tempering treatment.
22 were produced respectively.

【table】

[Table] For the purpose of comparison, the same manufacturing conditions as the above-mentioned valve seat of the present invention were used, except that one of the constituent components had a composition outside the scope of the present invention, as shown in Table 1. Comparative valve seats 1 to 6 were manufactured under the following conditions. Furthermore, as shown in Table 1, the quenching temperature,
Comparative valve seats 7 to 11 were manufactured under the same manufacturing conditions as the valve seat 2 of the present invention described above, except that either the sub-zero treatment temperature or the tempering treatment temperature was outside the scope of the present invention. Note that in Table 1, conditions that are outside the scope of the present invention are marked with * regarding these comparative valve seats 1 to 11. Next, Rockwell hardness was measured for the resulting valve seats 1 to 22 of the present invention and comparative valve seats 1 to 11, and valve material: austenitic steel, valve temperature: 900°C, valve lift amount: 6.8 mm, Valve seat temperature:
350℃, seating load: 40Kg, rotation speed: 3000r.pm
(A wear resistance test was conducted under the conditions of atmosphere: LPG combustion gas and test time: 50 hours to determine the wear resistance of the valve and valve seat. These measurement results are shown in Table 1. The above-mentioned valve seats 1 to 22 of the present invention and comparative valve seats 1 to 11 were made of head material: FC20 (cast iron) and
AC5A (A alloy), press-fit surface head dimensions: 44.00±
0.01mm, press-fit face valve seat dimensions: 44.1±0.01mm, press-fit allowance: 100μm, head dimensions: 44mmφ×90mmφ×2.0
mm, valve seat dimensions: 44.1mmφ x 34mmφ x 8mm, press-fit load: 800 to 1000Kg (for cast iron head) and
1000 to 1300 kg (in case of A alloy head), fit and install on cast iron head and A alloy head, heat and hold in the atmosphere at 500℃ for 10 hours, and then remove the valve seat from the head. The extraction load of each was measured. The measurement results are also shown. As is clear from the results shown in Table 1, in the common valve seats 1 to 11 in which any of the conditions is outside the scope of the present invention, at least any of the wear resistance, attack resistance, and extraction load On the other hand, valve seats 1 to 22 of the present invention all have excellent wear resistance, are less likely to attack others, and have an extremely large extraction load. It's getting old. Example 2 As raw material powders, Fe powder with a particle size of -100mesh, Fe-Cr alloy (containing Cr: 12%) powder with a particle size of -100mesh, carbon powder with a particle size of -100mesh, and -
100mesh Cu powder, -200mesh Ni powder, -200mesh Co powder, -200mesh Fe-Mo alloy (Mo: 60% content) powder, and -200mesh
Prepare Fe-W alloy (containing 75% W) powder,
These raw material powders were blended into the composition shown in Table 2, mixed, and molded into a green compact at a pressure of 6 tons/cm ² .
Then, in a hydrogen atmosphere, the temperature was maintained at 1170°C for 1 hour for sintering, and the amounts shown in Table 2 (total percentage amounts) were added to the resulting sintered body.
A predetermined amount of Cu powder is placed on top so that the Cu powder is impregnated, and Cu infiltration treatment is performed in ammonia decomposition gas at a temperature of 1130℃ for 30 minutes. By oil quenching, followed by sub-zero treatment and tempering treatment under the same conditions as the valve seats 1 to 22 of the present invention in Example 1, a final product with substantially the same composition and Cu impregnation amount as described above was obtained. Valve seat of the present invention having a component composition 23~
40 were produced each.

[Table] Regarding the valve seats 23 to 40 of the present invention obtained as a result,
Hardness, wear amount, and extraction load were measured under the same conditions as in Example 1, and the measurement results are shown in Table 2. As shown in Table 2, the valve seats 23 to 40 of the present invention also have excellent wear resistance, extremely low attack resistance, and a large extraction load, similar to the valve seats 1 to 22 of the present invention. It is clear that As mentioned above, the Fe-based sintered alloy valve seat of the present invention has a stable fine martensitic structure with no residual austenite, so it has excellent wear resistance and does not damage the mating material of the valve. Moreover, since it has a stable structure that is completely unaffected by heat, it has industrially useful properties such as not falling off from the head during use.

Claims (1)

[Claims] 1 C: 0.5-1.5%, Cr: 1-10%, Cu: 1-1
A sintered body or Cu having a composition (more than 30% by weight) with the remainder consisting of Fe and unavoidable impurities.
An Fe-based sintered alloy characterized in that the impregnated sintered body is quenched at a temperature of 900 to 1200°C, subjected to sub-zero treatment at a temperature of -20°C or less, and subsequently tempered at a temperature of 400 to 700°C. Manufacturing method for valve seats. 2 C: 0.5~1.5%, Cr: 1~10%, Cu: 1~
A sintered body or a Cu-impregnated sintered body having a composition (weight %) containing 1 to 15% of one or two of Ni and Cu, and the remainder consisting of Fe and unavoidable impurities. A valve made of Fe-based sintered alloy, characterized in that the body is quenched at a temperature of 900 to 1200°C, subjected to sub-zero treatment at a temperature of -20°C or less, and subsequently tempered at a temperature of 400 to 700°C. Manufacturing method for seats. 3 C: 0.5~1.5%, Cr: 1~10%, Cu: 1~
A sintered body or Cu-impregnated sintered body containing 30% of Mo and W, and 1 to 15% of one or two of Mo and W, with the remainder consisting of Fe and unavoidable impurities (weight %) A valve seat made of Fe-based sintered alloy, characterized in that the body is quenched at a temperature of 900 to 1200°C, subjected to sub-zero treatment at a temperature of -20°C or less, and subsequently tempered at a temperature of 400 to 700°C. manufacturing method. 4 C: 0.5~1.5%, Cr: 1~10%, Cu: 1~
30%, further contains one or two of Ni and Co: 1 to 1.5%, one or two of Mo and W: 1 to 15%, and the rest is
Composition consisting of Fe and unavoidable impurities (more than % by weight)
sintered body or Au-impregnated sintered body with
A method for manufacturing a valve seat made of an Fe-based sintered alloy, characterized by quenching at a temperature of 1200°C, subzero treatment at a temperature of -20°C or lower, and subsequent tempering treatment at a temperature of 400 to 700°C.