JPH0559982B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a sintered alloy for valve seats during internal combustion, and more particularly to an iron-based sintered alloy that has improved wear resistance of the alloy itself and is less aggressive against mating valves. [Conventional technology] Recently, internal combustion engines for automobiles have been increasing in output and rotation speed.
There is a trend towards lower fuel consumption and measures against exhaust gas. For this reason, valves and valve seat components are now exposed to more severe conditions than ever before. In order to improve wear resistance at high temperatures, iron-based sintered alloys containing alloying elements such as Cr, Ni, Co, and Mo are increasingly being used for valve seats. [Problems to be solved by the invention] By the way, the valve seat is required to improve its own wear resistance and reduce its aggressiveness to the mating valve, and the selection of the material of the valve seat is dependent on the mating valve and the valve seat. If this selection is incorrect, it will not only weaken the wear resistance of the valve itself, but also increase its aggressiveness against the mating member, which will have an undesirable effect on the entire valve mechanism. Therefore, if conventional valve seats, for example, which have extremely high wear resistance by simply adding intermetallic compounds such as ferromolybdenum or composite carbides, are used as they are, engine valve wear will increase. . The present invention applies to general-purpose engine valves that do not have particularly high wear resistance (e.g., manufactured by JIS NFC 751).
The aim is to avoid abrasion of the mating material or a significant increase in wear of the mating material even when the mating material is used as a mating material. [Means for Solving the Problems] The iron-based sintered alloy for valve seats of the present invention contains, by weight, chromium (Cr) 10 to 70%, tungsten (W) 5 to 20%, and molybdenum (Mo) 5%. ~20%,
5 to 25% alloy particles consisting of 0.5 to 3% carbon (C), 20% or less iron (Fe), and the balance cobalt (Co), 0.5 to 2% carbon (C), and optionally nickel (Ni).
It is characterized by being uniformly dispersed in a matrix mainly composed of pearlite, which is composed of 1 to 10% iron (Fe) and inevitable impurities. Further, the present invention provides that the sintered alloy contains 1 to 10% of lead (Pb).
Characterized by 20% infiltration. In the present invention, % indicates weight % unless otherwise specified. The reason for limiting each component element used in the present invention will be explained. First, each component element of the alloy particles added as hard particles will be explained. Cr (chromium) in the alloy particles combines with C (carbon) to form carbides, and a portion also forms an alloy with Co, which has the effect of improving the hardness of the alloy particles. If it is less than 70%, the above effect is insufficient, and if it exceeds 70%, the diffusion of Cr will proceed too much to the surrounding base, creating voids inside and at the periphery of the alloy particles, making the alloy particles brittle. Therefore Cr is 10
Limited to ~70%. However, 40-70% is more preferred. W (tungsten) combines with C to form a double carbide of MC-type hard carbide and Co, improving the hardness of the alloy particles, but this effect is not exhibited when W is less than 5%. If the W content exceeds 5%, the alloy particles become too hard and attack against the valve, which is the mating material, increases, so W is set at 5 to 20%. Mo (molybdenum) combines with C to form hard carbides and increases the hardness of alloy particles, but Mo
If it is less than 20%, the effect will not appear, and if it exceeds 20%, the alloy particles will become too hard and attack the mating material.
~20%. C combines with Cr, Mo and W to form carbides and improves the hardness of alloy particles, but when C is 0.5%
If it is less than 3%, the effect will not be exhibited, and if it exceeds 3%, the amount of carbide will be too large and it will become brittle. Therefore, C is
It was set at 0.5 to 3%. Co (cobalt) forms the remainder of other metal components in the alloy particles, and it improves the heat resistance of the particles, and a portion of it diffuses into the matrix, improving the bonding properties between the particles and the matrix, and preventing the particles from falling off. It has the effect of preventing This effect is difficult to obtain when it is less than 5%, and there is no change in the effect even when it exceeds 30%.
It is preferably 5 to 30%. Fe (iron) does not need to be particularly added, but if there is no problem with the strength required for the valve seat, it can be used in any range of 20% or less in place of the expensive Co. Furthermore, when Cr, W, and Mo are used as raw materials for alloys as ferroalloys rather than as single substances, they are added. Alloy particles are used because they are effective in improving wear resistance. When the particle size is less than 20 μm, wear resistance decreases, and when it is 200 μm or more, moldability and compressibility decrease, resulting in a decrease in wear resistance. Therefore 20~200μm
It is preferable that Also, more preferably 30
~150 μm. If the hardness of the alloy particles is less than 1000 Hv, the particles will easily wear out, so wear resistance will not be exhibited. Therefore, it is preferable to set it to Hv1000 or more. If the alloy particles are less than 5%, the resulting sintered alloy will not exhibit the wear-resisting effect, and if it exceeds 25%, the formability, compressibility, and machinability will decrease, and the mating material, the valve, will be attacked. The alloy particles were limited to 5 to 25% due to the increase in the amount of alloy particles. Next, I will explain the base. C forms a solid solution in the base Fe to form a pearlite structure, improving the strength and hardness of the sintered alloy, and
It combines with Cr, Mo, and W in the alloy particles to form hard carbides, which has the effect of further improving the hardness of the alloy particles, and unreacted free graphite.
C has a lubricating effect by being present in the base to some extent, but if it is less than 0.5%, it has no effect, and if it exceeds 20%, the cementite becomes coarse and there is too much free graphite, making the base brittle. teeth
It was set at 0.5 to 2%. Ni (nickel) dissolves in the Fe base and helps improve the strength of the base, so it is added when further strength is required, but if Ni is less than 1%, its effect will not be exhibited, and 10 If the Ni content exceeds 1%, the base becomes soft and the wear resistance decreases, so the Ni content was set to 1 to 10%. Infiltration of sintered alloys with Pb (lead) is carried out in the case of valve seats used under more severe conditions. The infiltrated Pb acts as a lubricant by forming a Pb oxide layer at the contact area between the valve and the valve seat, improving mutual wear resistance between the valve and the valve seat. If the Pb infiltration is less than 1%, the effect of Pb infiltration will not be exhibited;
If infiltration exceeds 1%, the skeleton of the sintered alloy will weaken and wear will increase, so it was set at 1% to 20%. [Example] The present invention will be explained with reference to an example. In the following examples, percentages refer to percentages by weight. Example 1 Alloy atomized powder (-100 mesh) 15%, graphite powder (-350 mesh) 1.5%, consisting of 30% Cr, 10% W, 10% Mo, 10% Fe, 25% C, and the balance Co.
After mixing 0.8% zinc stearate powder as a lubricant with 4% carbonyl Ni powder (10μm or less) and the balance reduced iron powder (-100 mesh), this mixed powder was filled into a mold and the molding pressure was 7t/cm. ² to obtain a powder compact with a rough valve seat shape. This powder compact was sintered at a temperature of 1150°C for 60 minutes in an ammonia decomposition gas atmosphere to obtain a sintered body. The density of the sintered body is 7.0g/cm ² . The obtained sintered body was processed into the shape of an exhaust valve seat and installed in a 2000 c.c. 4-cylinder diesel engine, and a bench durability test was conducted for 200 hours under full load to increase the surface width of the valve seat. The amount of wear and valve wear were measured. Note that JIS NFC 751 was used for the mating valve. Examples 2 to 4 Each material was blended in the respective composition ratios shown in Table 1 and the same procedure as in Example 1 was carried out to obtain each sintered body. In addition, in Examples 3 and 4, the obtained sintered body was
The sintered body was brought into contact with the Pb lump and heated again at a temperature of 1050°C for 30 minutes in an ammonia decomposition gas atmosphere to infiltrate Pb into the sintered body. Each of the obtained sintered bodies was processed into a valve seat shape, and the increase in surface width per valve seat and the amount of valve wear were tested and measured in the same manner as in Example 1. Example 5 Alloy atomized powder consisting of 45% Cr, 18% W, 10% Mo, 6% Fe, 1% C, and the balance Co (-100 mesh) 15%, graphite powder (-350 mesh) 1.1%, carbonyl Ni powder (10 μm or less) After mixing 0.8% zinc stearate powder as a lubricant with 2% and the balance reduced iron powder (-100 mesh), this mixed powder is filled into a mold and molded at a molding pressure of 7t/cm ² to form a valve seat. A roughly shaped powder compact was obtained. This powder compact was sintered at a temperature of 1140° C. for 60 minutes in an ammonia decomposition gas atmosphere to obtain a sintered body. The density of the sintered body is 7.0g/cm ² . The obtained sintered body was processed into the shape of an exhaust valve seat and installed in a 2000 c.c. 4-cylinder diesel engine, and a bench durability test was conducted for 300 hours under full load, resulting in an increase in the surface width of the valve seat. The amount of wear and valve wear were measured. Note that JIS NFC 751 was used for the mating valve. Examples 6 to 8 Each material was blended in the respective composition ratios shown in Table 1 and the same procedure as in Example 5 was carried out to obtain each sintered body. In addition, in Examples 7 and 8, the obtained sintered body was
The sintered body was brought into contact with the Pb lump and heated again at a temperature of 1050°C for 30 minutes in an ammonia decomposition gas atmosphere to infiltrate Pb into the sintered body. Each of the obtained sintered bodies was processed into a valve seat shape, and the amount of increase in surface width per valve seat and the amount of valve wear were tested and measured in the same manner as in Example 5. In addition, the particle diameter and hardness of the alloy particles are shown in Table 2. Comparative Examples 1 and 2 JIS FC 30 cast iron as Comparative Example 1 and JIS heat-resistant steel SUH4B as Comparative Example 2 were processed into a valve seat shape, and tested in the same manner as Example 1 to increase the face width per valve seat. The amount of wear and valve wear were measured. The above measurement results are summarized in Table 1.

【table】

〔Effect of the invention〕

As mentioned above, the iron-based sintered alloy for valve seats of the present invention has alloy particles uniformly dispersed in an iron base mainly composed of pearlite, so it has excellent wear resistance and is less aggressive against the mating material of the valve. It is a low alloy sintered alloy suitable for valve seats.

Claims (1)

[Claims] 1. Chromium (Cr) 10 to 70%, tungsten (W) 5 to 20%, molybdenum (Mo) 5 to 70% by weight
20% carbon (C), 0.5 to 3% carbon (C), 20% or less iron (Fe), and the balance cobalt (Co) 5 to
An iron-based sintered alloy for valve seats, characterized in that 25% of carbon (C) is uniformly dispersed in a pearlite-based matrix consisting of 0.5 to 2% of carbon (C) and the balance iron (Fe) and inevitable impurities. 2. The iron-based sintered alloy for a valve seat according to claim 1, wherein the content of chromium (Cr) in the alloy particles is 40 to 70% by weight. 3. The iron-based sintered alloy for a valve seat according to claim 1, wherein the alloy particles have a particle diameter of 20 to 200 μm and a hardness of Hv1000 or more. 4 By weight, chromium (Cr) 10-70%, tungsten (W) 5-20%, molybdenum (Mo) 5-5%
20% carbon (C), 0.5 to 3% carbon (C), 20% or less iron (Fe), and the balance cobalt (Co) 5 to
25%, carbon (C) 0.5-2%, nickel (Ni) 1
An iron-based sintered alloy for valve seats, characterized by being uniformly dispersed in a pearlite-based matrix consisting of ~10% iron (Fe) and inevitable impurities. 5. The iron-based sintered alloy for a valve seat according to claim 4, wherein the content of chromium (Cr) in the alloy particles is 40 to 70% by weight. 6. The iron-based sintered alloy for a valve seat according to claim 4, wherein the alloy particles have a particle diameter of 20 to 200 μm and a hardness of Hv1000 or more. 7 By weight, chromium (Cr) 10-70%, tungsten (W) 5-20%, molybdenum (Mo) 5-5%
20% carbon (C), 0.5 to 3% carbon (C), 20% or less iron (Fe), and the balance cobalt (Co) 5 to
Lead (Pb) is added to a sintered alloy in which 25% of lead (Pb) is uniformly dispersed in a pearlite-based matrix consisting of 0.5-2% carbon (C) and the balance iron (Fe) and inevitable impurities.
An iron-based sintered alloy for valve seats characterized by infiltration of 1 to 20%. 8. The iron-based sintered alloy for a valve seat according to claim 7, wherein the content of chromium (Cr) in the alloy particles is 40 to 70% by weight. 9. The iron-based sintered alloy for a valve seat according to claim 7, wherein the alloy particles have a particle diameter of 20 to 200 μm and a hardness of Hv1000 or more. 10 Weight ratio: chromium (Cr) 10-70%, tungsten (W) 5-20%, molybdenum (Mo) 5
Alloy particles 5 consisting of ~20%, carbon (C) 0.5 to 3%, iron (Fe) 20% or less, and the balance cobalt (Co)
~25% carbon (C) 0.5~2%, nickel (Ni)
It is characterized by infiltrating 1-20% of lead (Pb) into a sintered alloy that is uniformly dispersed in a pearlite-based base consisting of 1-10% lead (Pb) and the balance iron (Fe) and unavoidable impurities. Iron-based sintered alloy for valve seats. 11. The iron-based sintered alloy for a valve seat according to claim 10, wherein the content of chromium (Cr) in the alloy particles is 40 to 70% by weight. 12. The iron-based sintered alloy for a valve seat according to claim 10, wherein the alloy particles have a particle diameter of 20 to 200 μm and a hardness of Hv1000 or more.