JP4565561B2 - Method for casting cast iron and method for manufacturing cylinder head for internal combustion engine using the method - Google Patents

Description

  The present invention relates to a casting method for improving wear resistance and heat resistance in a part of cast iron, and a method for manufacturing a cylinder head for an internal combustion engine using this casting method.

  Conventionally, an alloy member having wear resistance and heat resistance, such as a cylinder head in an internal combustion engine, which is partially required for wear resistance and heat resistance, is fixed with a cold fit. However, there has been a problem that the above-mentioned members may be loose and fall off, and the cost may be significantly increased.

  Therefore, the present inventors have proposed a casting method as described below in a previous patent application (Japanese Patent Application No. 2004-059455).

In other words, the casting method of this prior application is
“In a casting mold for casting cast iron, 0.5 to 1.5 wt% graphite powder, 3 to 10 wt% copper powder, 10 to 20 wt% nickel powder, and 10 to 15 wt% iron-chromium An alloy powder, 15 to 30 wt% cobalt-molybdenum-chromium alloy powder, and the rest of the metal powder compact formed by mixing and compacting pure iron powder are disposed, and then molten into the casting mold. By pouring the cast iron, and using the heat of the molten cast iron to sinter and diffuse the metal powder compact, a sintered layer of the metal powder compact is formed on a part of the cast during casting. As it is formed, the sintered layer is bonded to the cast matrix. "
That's it.

  In the casting method of the prior application, the addition of graphite powder to the metal powder green compact facilitates sintering and has the effect of making the base metal structure of the metal powder green compact into heat-resistant austenite in the cast product. However, if the blending ratio is less than 0.5 wt%, the effect of promoting the sintering is small, and if the blending ratio exceeds 1.5 wt%, the formation of carbides increases, resulting in a decrease in toughness and machinability. Arise.

  The addition of copper powder to the metal powder compact is intended to promote sintering by the generation of a liquid phase with copper having a low melting point. However, if the blending ratio is less than 3 wt%, the effect of promoting sintering is achieved. However, if the blending ratio exceeds 10 wt%, the amount of liquid phase generated increases and the sintered layer is deformed, resulting in poor dimensional accuracy.

  The addition of nickel powder to the metal powder green compact is intended to diffuse the pure iron powder to make the base metal structure of the metal powder green compact of the cast into austenite having heat resistance. When the blending ratio is less than 10 wt%, the amount of austenite produced decreases, while the ferrite in the portion where pure iron powder remains undiffused (the more ferrite, the less austenite is produced) and graphite powder. The amount of pearlite in the part that remains in a diffuse state (the more pearlite increases, the less austenite is generated), which leads to a decrease in heat resistance. If the ratio exceeds 20 wt%, an effect commensurate with the amount added cannot be obtained.

  The addition of the iron-chromium alloy powder to the metal powder green compact allows a part of chromium to diffuse into the pure iron powder to make the base metal structure of the metal powder green compact of the cast into austenite having heat resistance. This is to achieve the effect and the effect of improving the wear resistance by the non-diffusion iron-chromium alloy powder. When the blending ratio is less than 10 wt%, the austenite generation amount is reduced, while the pure iron powder is not diffused. The amount of pearlite in the part that remains in the state where only the ferrite and graphite powder in the remaining part is diffused increases, resulting in a decrease in heat resistance, and the addition amount exceeds 15 wt%. In addition to being able to obtain an effect commensurate with the above, it is difficult to compact into metal powder compacts.

  The addition of cobalt-molybdenum-chromium alloy powder to the metal powder compact is effective in improving wear resistance by dispersing the cobalt-molybdenum-chromium alloy because it is a hard particle with high hardness. In order to achieve the effect that a part of cobalt and / or chromium is diffused into pure iron powder and the base metal structure of the metal powder compact in the cast is made austenite having heat resistance. If the ratio is less than 15 wt%, the effect of improving wear resistance is small, and if the blending ratio exceeds 30 wt%, the compactibility to metal powder compacts deteriorates, so that sufficient sintering cannot be obtained during casting. Wear resistance is reduced.

  The addition of pure iron powder to the metal powder compact has the effect of improving formability when the powder mixture is compacted into a predetermined shape, and increases the density of the porous material after compaction and decreases the porosity. It is for aiming at the effect to do.

  By the way, in the casting method of the prior application, when the mixing ratio of the iron-chromium alloy powder is less than 10 wt%, the amount of heat-resistant austenite is reduced, while the pure iron powder remains undiffused. Since the pearlite in the remaining portion increases in the state where only the ferrite and graphite powder in the remaining portion is diffused, the heat resistance is lowered, so the lower limit of the mixing ratio of the iron-chromium alloy powder is 10 wt%. On the other hand, when the blending ratio of the cobalt-molybdenum-chromium alloy powder exceeds 30 wt%, sufficient compaction is required to reduce the compactibility of the metal powder compact. Therefore, the wear resistance is lowered without obtaining the above, so the upper limit value of the blending ratio of the cobalt-molybdenum-chromium alloy powder is regulated to 30 wt%.

  That is, in the casting method of the prior application, the improvement of the wear resistance by the metal powder compact is limited to the case where the blending ratio of the cobalt-molybdenum-chromium alloy powder is added so as not to exceed 30 wt%. Therefore, it was thought that the wear resistance could not be improved further.

  Although the present invention basically follows the casting method of the prior application, it is a technical object to further improve the wear resistance by the metal powder compact.

In order to achieve this technical problem, the casting method according to the present invention is as described in claim 1,
“In a casting mold that casts cast iron, graphite powder, copper powder, nickel powder, iron-chromium alloy powder, cobalt-molybdenum-chromium alloy powder, and the remaining pure iron powder are mixed and molded. Next, by pouring molten cast iron into the casting mold, and sintering and diffusing the metal powder green compact using the heat of the molten cast iron, In a casting method in which, during casting, a sintered layer of the metal powder compact is formed on a part of the casting, and the sintered layer is bonded to the base material of the casting.
The composition ratio of the graphite powder is 0.5 to 1.5 wt%, the composition ratio of the copper powder is 3 to 10 wt%, the composition ratio of the nickel powder is 10 to 20 wt%, The blending ratio is set to 3 wt% or more and less than 10 wt%, and the blending ratio of the cobalt-molybdenum-chromium alloy powder is set to more than 15 wt% and 70% or less, while the particle size of the iron-chromium alloy powder is set to the cobalt-molybdenum- The particle size is made smaller than that of the chromium alloy powder. "
It is characterized by that.

Further, the casting method in the present invention, as described in claim 2,
"In the description of the claim 1, wherein the cobalt - molybdenum - against particle diameter in the chromium alloy powder is less than 1 49 microns, wherein the iron - particle size in the chromium alloy powder is less than 7 4 microns."
It is characterized by that.

Next, a cylinder head manufacturing method according to the present invention includes:
“In the first or second aspect of the present invention, the metal powder green compact is formed into a ring shape, and the ring-shaped metal powder green compact is used as a cylinder in a casting mold for casting a cylinder head in an internal combustion engine. The cylinder head is cast in this state at one or both of the intake port and the exhaust port of the head, and the cylinder head is cast in this state. Machined to expose the sheet. "
It is characterized by that.

  When the upper limit of the mixing ratio of the iron-chromium alloy powder to the metal powder compact is less than 10 wt%, as described above, the amount of heat-resistant austenite produced is reduced, while the pure iron powder Although there is more pearlite in the part where only the ferrite and graphite powder are diffused in the part that remains undiffused, the particle size in the iron-chromium alloy powder is reduced by the cobalt-molybdenum-chromium. This is the same as the particle size in the alloy powder, and the particle size in the iron-chromium alloy powder is made smaller than the particle size in the cobalt-molybdenum-chromium alloy powder added simultaneously to the metal powder compact. Therefore, the total surface area of the iron-chromium alloy powder is the same as that of the cobalt-molybdenum-chromium alloy powder. Therefore, even if the austenite generation amount of the base metal structure of the metal powder compact is reduced to less than 10 wt%, the diffusion to the pure iron powder in chromium is promoted. On the other hand, it is possible to reduce the pearlite in the portion where only the ferrite and graphite powder remain in the state where the pure iron powder remains undiffused.

On the other hand, while the mixing ratio of the iron-chromium alloy powder is reduced to less than 10 wt%, the cobalt-molybdenum-chromium alloy powder is prepared by simultaneously adding the particle size of the iron-chromium alloy powder to the metal powder compact. When the blending ratio of the cobalt-molybdenum-chromium alloy powder is increased beyond the upper limit of 30 wt% in the invention of the prior application, the compactibility to the metal powder compact is reduced. In other words, the blending ratio of the cobalt-molybdenum-chromium alloy powder can be reduced to the metal powder green compact without incurring deterioration of the moldability and, therefore, sufficient in casting. such under sintering as possible out to obtain a state, since it is possible to much exceeds 30 wt%, the abrasion resistance and heat resistance, the preceding invention It can be significantly improved as compared to the case.

In this case, as described in claim 2, wherein the iron - the particle size of the chromium alloy powder, the cobalt - molybdenum - if the particle size of the chromium alloy powder is less than 1 49 microns, substantially half or less of 7 4 microns It is preferable to make it.

  Further, according to the manufacturing method described in claim 3, the heat resistance of the valve seat portion of either one or both of the intake port and the exhaust port is improved, and the wear resistance of the valve seat in the valve seat portion, A cylinder head that simultaneously improves both the wear resistance on the valve side that repeatedly sits on the valve seat can be manufactured at low cost.

  Hereinafter, the case where the embodiment of the present invention is applied to casting of a cast iron cylinder head in an internal combustion engine will be described.

  FIGS. 1 and 2 show a cast iron cylinder head 1 in an internal combustion engine. The cylinder head 1 includes an intake port 2 and an exhaust port 3 and cooling water, as is well known in the art. A valve seat 6 having a valve seat 6a on which a poppet type intake valve 5 is seated is formed at the opening to the lower surface 1a of the cylinder head 1 in the intake port 2. Valve seat portions 8 each having a valve seat 8a on which a poppet type exhaust valve 7 is seated are provided at openings on the lower surface 1a of the cylinder head 1.

  FIG. 3 shows a casting mold A for casting the cylinder head 1. The casting mold A includes a lower mold A1 that forms the lower surface of the cylinder head 1 and an upper mold that forms the upper surface of the cylinder head 1. A 2, a core A 3 that forms the intake port 2, a core A 4 that forms the exhaust port 3, and a core A 5 that forms the cooling water jacket 4. The cylinder head 1 is cast by pouring molten cast iron into the space.

  At the time of casting, as shown in FIG. 4, various kinds of metals described below are provided at the valve seat portions 6 and 7 in the core A3 for the intake port 2 and the core A4 for the exhaust port 3. A metal powder compact B formed by compacting a powder mixture into a porous ring shape is fixedly mounted so that the metal powder compact B protrudes from the surfaces of the cores A3 and A4. In this state, the molten cast iron is poured, and the metal powder green compact is sintered and diffused using the heat of the molten cast iron, so that the intake port of the cylinder head 1 is cast during casting. 2 and the valve seats 6 and 7 in the exhaust port 3 are formed with a sintered layer of the metal powder green compact B, and the sintered layer is bonded to the base material of the casting.

  5 and 6 show the cylinder head 1 after casting. The cast cylinder head 1 is machined so that its lower surface 1a is indicated by a two-dot chain line D1, and its intake port is shown in FIG. 2 and the exhaust port 3 are machined so that the inside of the opening with respect to the lower surface 1 a is indicated by a two-dot chain line D 2, so that the sintered layer of the metal powder compact B is formed on the intake port 2 and the exhaust port 3. The valve seats 6 and 8 are exposed to the conical valve seats 6a and 8a, whereby the wear resistance and heat resistance of the valve seats 6 and 8 of the intake port 2 and the exhaust port 3 can be improved.

  By the way, the metal powder green compact B is composed of graphite powder, copper powder, nickel powder, iron-chromium alloy powder, cobalt-molybdenum-chromium alloy powder, and the remainder mixed with pure iron powder. The composition ratio of various powders is 0.5 to 1.5 wt% for the graphite powder, 3 to 10 wt% for the copper powder, and 10 to 20 wt% for the nickel powder. %, The iron-chromium alloy powder is made less than 10 wt%, and the cobalt-molybdenum-chromium alloy powder is increased to more than 15 wt%, while the particle size in the iron-chromium alloy powder is increased to the cobalt-molybdenum. -It is smaller than the particle size in the chromium alloy powder.

  Here, the addition of the graphite powder is for the purpose of promoting the sintering and making the base material structure in the vicinity of the valve seat parts 6 and 8 of the cylinder head 1 austenite having heat resistance. If the ratio is less than 0.5 wt%, the effect of promoting the sintering is small, and if the blending ratio exceeds 1.5 wt%, the formation of carbides increases, resulting in a decrease in toughness and a machinability.

  The addition of the copper powder is for the purpose of promoting the sintering by generating a liquid phase with copper having a low melting point. When the blending ratio is less than 3 wt%, the effect of promoting the sintering is small, and other alloy powders are used. If many undiffused portions remain and the blending ratio exceeds 10 wt%, the amount of liquid phase generated increases, so that the sintered layer is deformed, resulting in poor dimensional accuracy.

  The addition of the nickel powder is to diffuse into the pure iron powder and to make the base material structure in the vicinity of the valve seat portions 6 and 8 of the cylinder head 1 into austenite having heat resistance, and its blending ratio Is less than 10 wt%, the amount of austenite is reduced, while the ferrite in the part where the pure iron powder remains undiffused and the pearlite in the part where only the graphite powder remains diffused increase, and the heat resistance In addition, if the blending ratio exceeds 20 wt%, an effect commensurate with the amount added cannot be obtained.

  The addition of the iron-chromium alloy powder causes a part of chromium to diffuse into the base material structure in the vicinity of the valve seat portions 6 and 8 in the cylinder head 1, and the base material structure in this part is austenite having heat resistance. This is to achieve the effect of improving the wear resistance by the non-diffusion iron-chromium alloy powder.

  The cobalt-molybdenum-chromium alloy powder is added because the cobalt-molybdenum-chromium alloy is a hard particle having high hardness. Is diffused into the base material structure in the vicinity of the valve seats 6 and 8 in the cylinder head 1 to strengthen the bonding of the hard particles to the base material structure and to austenite the base material structure. This is to achieve an effect.

  The addition of the pure iron powder is intended to improve the formability when the powder mixture is compacted into a predetermined shape, and to increase the porosity density and reduce the porosity after compaction. Because.

  In this case, in the above-mentioned prior application, the blending ratio in the graphite powder is 0.5 to 1.5 wt%, the blending ratio in the copper powder is 3 to 10 wt%, and the blending ratio in the nickel powder is 10 to 10 wt%. The blending ratio in the iron-chromium alloy powder was specified as 10 to 15 wt%, and the blending ratio in the cobalt-molybdenum-chromium alloy powder was defined as 15 to 30 wt%.

  That is, in the above-mentioned prior invention, the particle size in the iron-chromium alloy powder is set to about 149 microns, so that the particle size in the cobalt-molybdenum-chromium alloy powder is about 149 microns. The mixing ratio in this iron-chromium alloy powder is such that the austenite generation amount is reduced, while the ferrite in the part where the pure iron powder remains undiffused and the pearlite in the part where only the graphite powder remains diffused. In order to avoid the increase, it is considerably increased to 10 to 15 wt%. On the other hand, the increase in the compounding ratio in the iron-chromium alloy powder deteriorates the compactibility of the metal powder compact. Therefore, the blending ratio in the cobalt-molybdenum-chromium alloy powder is regulated to 15 to 30 wt%. Because must Shikere, said cobalt - molybdenum - improvement of the wear resistance by chromium alloy powder, cobalt - molybdenum - chromium alloy powder, may be added 30 wt% at the upper limit was the limit.

  On the other hand, in the present invention, the particle size in the iron-chromium alloy powder is made smaller than the particle size in the cobalt-molybdenum-chromium alloy powder.

  Thus, by making the particle size of the iron-chromium alloy powder smaller than the particle size of the cobalt-molybdenum-chromium alloy powder, the total surface area of the iron-chromium alloy powder is reduced to the particle size of the iron-chromium alloy powder. Since it increases compared with the case of cobalt-molybdenum-chromium alloy powder, the diffusion of chromium into pure iron powder is promoted, and the austenite generation amount of the base metal structure of the metal powder compact B is determined by the blending ratio. Even if it is reduced to less than 10 wt%, it can be increased, while reducing the pearlite in the part where only the ferrite and graphite powder remain in the state where the pure iron powder remains undiffused. be able to.

On the other hand, while reducing the blending ratio of the iron-chromium alloy powder to less than 10 wt%, the particle size in the iron-chromium alloy powder is made smaller than the particle size in the cobalt-molybdenum-chromium alloy powder, When the compounding ratio in the cobalt-molybdenum-chromium alloy powder is increased beyond the upper limit of 30 wt% in the prior invention, it is possible to reliably avoid the deterioration of the compactibility of the metal powder compact, in other words, the cobalt - molybdenum - compounding ratio of chromium alloy powder, without causing deterioration of the compacted molding of the metal powder compact B, therefore, as possible out to obtain a sufficient sintering during casting state Therefore, the wear resistance and heat resistance can be greatly improved as compared with the invention of the prior application. It is.

  Next, the abrasion resistance was evaluated by the actual single-piece friction test described below for Examples 1 and 2 according to the present invention and the comparative example according to the prior invention.

  In the actual single body friction test, a poppet type intake valve 5 that is biased by a spring against a valve seat 6a in the valve seat portion 6 with the valve seat portion 6 at 200 ° C. Is continuously seated once per rotation with a motor-driven rotary cam for 16 hours with a rotation speed per minute of the rotary cam of 1200, and the amount of wear on the valve seat 6a, This is an experiment in which both the wear amount on the seated intake valve 5 side is measured.

In this experiment, the components in the various powders used in Examples 1 and 2 and Comparative Example were as shown in Table 1.

  The particle sizes of the various powders were as shown in Table 2 except for the graphite powder.

  And in Example 1, Example 2, and the comparative example, the compounding ratio of various powder was made into Table 3. FIG.

  The results of the “actual single body friction test” for each of Examples 1, 2 and Comparative Example are as shown in FIG.

  That is, as in Example 1 and Example 2, by making the particle size in the iron-chromium alloy powder smaller than the particle size in the cobalt-molybdenum-chromium alloy powder, the blending ratio in the iron-chromium alloy powder is reduced. Can be made lower than the lower limit value in the invention of the prior application, while the blending ratio in the cobalt-molybdenum-chromium alloy powder can be made higher than the upper limit value in the invention of the prior application. Both the wear resistance on the valve seat surface 6a side in the seat portion 6 and the wear resistance on the valve side repeatedly seated on the valve seat surface 6a are more than in the case of the prior invention (comparative example). It was possible to greatly improve.

  Moreover, the improvement of the wear resistance of the valve seat surface 6a and the wear resistance on the valve side is proportional to the increase in the blending ratio in the cobalt-molybdenum-chromium alloy powder.

  In the experiment described above, the lower limit of the blending ratio in the iron-chromium alloy powder is 3 wt%, and if it is less than this, the effect of adding the iron-chromium alloy powder cannot be recognized. There wasn't.

  In the above-described experiment, the upper limit of the blending ratio in the cobalt-molybdenum-chromium alloy powder is 70 wt% or less, and if the amount exceeds this, the particle size in the iron-chromium alloy powder is reduced. It was not possible to recognize an improvement in compaction moldability due to the above.

It is a vertical front view which shows a part in the cylinder head for internal combustion engines. It is a principal part enlarged view of FIG. It is a vertical front view which shows a part of casting mold in the said cylinder head. It is a perspective view of the metal powder compact to be loaded into the casting mold. It is a vertical front view which shows a part of cast cylinder head. It is a principal part enlarged view of FIG. It is a figure which shows the result of a real single-piece | unit friction test.

1 Cylinder head 2 Intake port 3 Exhaust port 4 Cooling water jacket 5 Intake valve 7 Exhaust valve 6, 8 Valve seat 6a, 8a Valve seat surface A Casting mold A1 Lower mold A2 Upper mold A3, A4, A5 Core B Metal powder Green compact

Claims (3)

In a casting mold that casts cast iron, graphite powder, copper powder, nickel powder, iron-chromium alloy powder, cobalt-molybdenum-chromium alloy powder, and the rest are mixed and solidified. The metal powder green compact is installed, and then the molten cast iron is poured into the casting mold, and the metal powder green compact is sintered and diffused by using the heat of the molten cast iron. In some cases, in the casting method, a sintered layer of the metal powder compact is formed on a part of the casting, and the sintered layer is bonded to the base material of the casting.
The composition ratio of the graphite powder is 0.5 to 1.5 wt%, the composition ratio of the copper powder is 3 to 10 wt%, the composition ratio of the nickel powder is 10 to 20 wt%, While the blending ratio is set to 3 wt% or more and less than 10 wt%, and the blending ratio of the cobalt-molybdenum-chromium alloy powder is set to more than 15 wt% and 70 wt% or less, the particle size of the iron-chromium alloy powder is set to the cobalt-molybdenum- A casting method for cast iron, characterized in that it is smaller than the particle size of the chromium alloy powder. In the description of the claim 1, wherein the cobalt - and wherein the particle size of the chromium alloy powder is less than 7 4 microns - molybdenum - against particle diameter in the chromium alloy powder is less than 1 49 microns, wherein the iron Cast iron casting method.   3. The cylinder head according to claim 1 or 2, wherein the metal powder green compact is formed into a ring shape, and the ring-shaped metal powder green compact is used in a casting mold for casting a cylinder head in an internal combustion engine. The cylinder head is cast in this state in one or both of the intake port and the exhaust port in the cylinder, and the cylinder head is cast in this state. A method of manufacturing a cylinder head for an internal combustion engine, wherein the machining is performed so as to be exposed to