JPH0978178A - Cast iron material having gradient function and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce a cast iron material having a gradient function in which the form and distribution of graphite are continuously shifted. SOLUTION: A cast iron material having a gradient function, in which one part is composed of spheroidal graphite cast iron and another part is composed of flake graphite cast iron and, further, the form and distribution of graphite are continuously shifted in the part between them, is produced by previously disposing a graphite-spheroidizing agent, preferably MgF2 , fixedly in the prescribed position in a mold and then pouring a molten metal, having a composition corresponding to flake graphite cast iron, onto the above agent. By this method, a gear, in which a tooth part is composed of spheroidal graphite cast iron, a boss part is composed of flake graphite cast iron, an arm part is composed of C/V cast iron, and the form and distribution of graphite are continuously shifted from the tooth part toward the boss part, can be produced.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a functionally graded cast iron material having a composition and a microstructure continuously transitioning from one site to another site and a method for producing the same. More specifically, the present invention relates to a functionally graded cast iron material having a part made of spheroidal graphite cast iron and another part made of flake graphite cast iron, and a method for producing the same.

[0002]

2. Description of the Related Art Some automobile parts are required to have mutually contradictory characteristics. For example, the brake drum
While it is required that the portion in contact with the mating material has high wear resistance and high thermal conductivity, it is also required that the drum itself has high mechanical strength and damping performance. Further, the gear of the motion system part of the internal combustion engine is also required to have high wear resistance and high thermal conductivity because the tooth portion meshes with the mating gear, while the boss portion and the rib portion, especially the boss portion, It is required that the function and strength of damping the transmission vibration of gears, especially the repeated impact strength, be high. The above-mentioned parts are FC having a flake graphite cast iron structure that is easy to mold and is low in cost when the brake performance and meshing performance, that is, wear resistance are important.
It can be made from ordinary cast iron of 10 to FC25 (JIS standard), but in this case, the strength and damping of vibration are sacrificed to some extent. On the other hand, when importance is attached to damping performance and strength, a cast product made of spheroidal graphite cast iron or C / V cast iron is prepared, and subsequently flame-hardened, induction-hardened, etc. is applied to a site where high wear resistance is required as post-treatment. The surface hardening treatment was performed. However, since the heat treatment inevitably involves deformation and distortion of the cast iron product, when the heat treatment is performed, the magnitude of the impact load that can be applied to the teeth is limited to some extent.

In recent years, demands for higher output, lighter weight, and scale-down have been increasing, so that the above-mentioned contradictory characteristics have been required to a very high degree, but it is difficult to respond to them by heat treatment. Is.

As a solution to the above-mentioned problems, Japanese Patent Application Laid-Open No. 60-24260 discloses a structure in which a flake graphite cast iron structure is provided on the sliding surface and in the vicinity thereof, and a spheroidal graphite cast iron structure is provided in another portion. The manufacture of materials with a vermicular cast iron (C / V cast iron) structure has been proposed. This material is a spheroidal graphite cast iron product placed in a mold, and a molten metal having a flake graphite cast iron composition is injected into the mold cavity corresponding to the sliding surface and its vicinity, that is, a spheroidal graphite cast iron product is cast. It is produced by wrapping, the material obtained, one part is a flake graphite cast iron structure, the other part is a spheroidal graphite cast iron structure or vermicular cast iron structure, consisting of two structures, so-called It is a composite material, and inevitably there is a definite phase boundary between the site of the spheroidal graphite cast iron structure or the vermicular cast iron structure and the site of the flake graphite cast iron structure. If such a boundary surface is present, the composition and the microstructure are different before and after the boundary surface, and the coefficient of thermal expansion is also different. Therefore, when heated or external stress is applied, a crack propagates from the boundary surface and in the worst case, it is destroyed. Therefore, there is still a demand for development of materials having highly opposite properties which can be successfully used as the above-mentioned parts.

[0005]

SUMMARY OF THE INVENTION The present invention, therefore, provides a single highly-combined property of superior mechanical strength and damping performance as well as superior wear resistance and low coefficient of thermal expansion. It is intended to provide a cast iron material.

Further, the present invention is a method of eliminating a heterophase boundary surface in a single cast iron material in which phases such as a flake graphite cast iron structure and a spheroidal graphite cast iron structure coexist, specifically those having different morphology and distribution of graphite. The purpose is to provide.

Another object of the present invention is to provide a single cast iron material which is particularly suitable for automobile brake drums and gears for internal combustion engines.

[0008]

The inventor of the present invention has been keen to develop a single material having a spheroidal graphite cast iron structure in one part and a flake graphite cast iron structure in another part. As a result of research, by using a graphite spheroidizing agent capable of transforming a flake graphite cast iron structure into a spheroidal graphite structure during casting, one part consists of spheroidal graphite cast iron and another part consists of flake graphite cast iron, The present invention finds that a single material, in which a specific boundary surface does not exist unlike a composite material, that is, a functionally graded cast iron material, can be produced, because the morphology and distribution of graphite are continuously transitioned between the sites, and the present invention is achieved. Completed

That is, the functionally graded cast iron material of the present invention is
One part is made of spheroidal graphite cast iron, another part is made of flake graphite cast iron, and the morphology and distribution of graphite are continuously transitioned between these parts. If this material is applied to a gear, the tooth portion is made of spheroidal graphite cast iron, the boss portion is made of one-sided graphite cast iron, the arm portion is made of C / V cast iron, and the form and distribution of graphite from the tooth portion to the boss portion It is possible to obtain a gear that continuously transitions.

In the method for producing a functionally graded cast iron material of the present invention, a graphite spheroidizing agent is fixedly placed in advance at a predetermined position in a mold, and then a molten metal having a composition corresponding to flake graphite cast iron is placed in the mold. Is injected.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

The graphite spheroidizing agent that can be used in the present invention is not particularly limited, and additives that are widely used for spheroidizing graphite crystallized from the melt of flake graphite cast iron composition can be used. As the graphite spheroidizing agent, pure Mg, MgF ₂ , C
u-Mg, Ni-Mg, Fe-Si-Mg, Ni-Si
-Mg, Ca-Si-Mg, Fe-Si-Mg-Ca,
Fe-Si-Mg-RE having Ca-Si, Ce, and Mg contents of 4 to 6% and containing 1 to 2% of a rare earth element is generally used, but MgF ₂ is preferable.

In order to fix and arrange the graphite spheroidizing agent in the mold, a mold usually consisting of an upper mold and a lower mold is used.
After placing the graphite spheroidizing agent at a predetermined position of either or both of the molds, that is, at a position corresponding to the site of the cast product where the graphite is to be spheroidized, the upper mold and the lower mold are combined. When arranging, be careful that the graphite spheroidizing agent is fixedly arranged at a predetermined position in the mold. This is to keep the spheroidization of graphite locally. Although various arrangement methods are possible, for example, as shown in FIG. 1a, when a sand mold is used as a mold, the graphite spheroidizing agent is crushed into particles having a size of about 145 mesh and After shaping the sand mold, it is embedded in the sand mold 1 before drying and the sand mold is dried to fix and arrange the spheroidizing agent, or, as shown in FIG. The graphite spheroidizing agent 9 can be fixedly arranged by applying to the graphite. The latter method can be used with a sand mold or a mold. Furthermore, there is also a method of mixing a spheroidizing agent and a binder such as water glass, or a method of mixing with a mold coating agent and coating the mixture on a mold.

By adjusting the amount and arrangement of the graphite spheroidizing agent, a desired site can be made to have a spheroidal graphite cast iron structure.

As the mold, various sand molds (green mold, dry mold) and molds including a commonly used CO ₂ mold can be used.

After arranging the graphite spheroidizing agent, the lower mold and the upper mold are combined to form a mold according to the casting method. For example, if the target casting is a gear, the mold is constructed as shown in Figure 2a. FIG. 2a is a cross-sectional view of a mold (sand mold) used when casting a gear. Here, the mold 1 is
It is composed of an upper mold 2 and a lower mold 3, and the molten metal is poured into a mold from a sprue 4 through a runner and a weir (not shown). The structure of the gear manufactured in the mold is the boss portion 5, the arm portion 6, the rim portion 7
And a tooth portion 8 used for gear grinding. A completed gear, which is cast using this mold and whose teeth are ground, is shown in FIG. 2b. In addition, 10 shows a rib part. In the case of gears, in consideration of the balance of the cooling rates of the rim and boss and the arm, it is necessary to determine the casting method so that the rim cools as fast as possible and the thin arm cools gradually. There is. As shown in the cross-sectional view of FIG. 2a, the graphite spheroidizing agent 9 is arranged as shown by the diagonal lines so that the tooth and rim portions have a spheroidized structure of graphite.

After the mold is constructed, a molten metal having a composition of flake graphite cast iron is poured from a sprue, and an inoculant, typically S, is added.
Add i.

The preferable composition of the molten metal is C: 2.5 to 4.2 Si: 1.0 to 2.5 Mn: ≤0.5 P: ≤0. 02 S: ≦ 0.02 Fe: balance (provided that C + 1 / 3Si = 2.8 to 5.0).

Since the composition of C and Si is preferably cast iron having a hypereutectic composition because of graphite precipitation, C: 2.5-4.
2% by weight, Si: 1.0 to 2.5% by weight, provided that C + 1
It is preferable to satisfy /3Si=2.8 to 5.0. M
n is preferably 0.5% by weight or less in order to preferentially make the flake graphite cast iron structure portion a ferrite ground and secure a satisfactory impact strength. P is an element that does not adversely affect the spheroidization of graphite, but in order to promote the precipitation of steadite that deteriorates ductility, and to impart satisfactory ductility to the flake graphite cast iron structure part, 0.02 wt% or less Is preferred. S has a great effect on the spheroidization of graphite. When the entire cast iron product is spheroidized after adding the graphite spheroidizing agent, the graphite will not be spheroidized unless it is less than 0.03% by weight. Further, since Mg has a large affinity with S, when S is present in cast iron in an amount of 0.03% by weight or more, Mg is first used for desulfurization, so that the yield of Mg also deteriorates. In the present invention, since the graphite is not spheroidized over the entire cast iron product, the S content is preferably further reduced to 0.02% by weight or less.

The temperature of the molten metal is as high as possible, preferably 1,450 to 1,500 ° C., in order to promote spheroidization of graphite. The molten metal may be injected not only at normal pressure but also under reduced pressure or increased pressure. The shape and distribution of any graphite are continuously changed to obtain a cast product having no boundary surface. After the molten metal is completely solidified, it is taken out of the mold. After that, in the case of a gear, the tooth portion is subjected to tooth profile grinding.

[0021]

EXAMPLE CO ₂ having the stepwise cross section shown in FIG.
It was actually cast using a mold. In FIG. 3, the same parts as those in FIG. 2 are designated by the same reference numerals as those in FIG. 2.

The graphite spheroidizing agent used was MaF ₂ and was melt coated onto the upper mold as shown in FIG. The thickness of the MaF ₂ coating film was 0.5 to 2 mm. Then, after the upper mold and the lower mold were combined, a molten metal at 1450 ° C. was injected from the spout under atmospheric pressure or under pressure of 30 K to 50 KPMa, and Si was further added as an inoculant. The component of the molten metal after the addition of the inoculant had a chemical composition of C: 3.8 Si: 2.43 Mn: 0.16 P: 0.03 S: 0.008 Fe: balance by weight. It was This molten metal is 1450 ° C
Was poured into the mold. Then, after the casting was completely solidified, it was taken out of the mold. The obtained cast product had the shape shown in FIG. The height T _{1 of} part A is 5 mm,
The height T _{2 of} part B is 20 mm, the height T _{3 of} part C is 30 mm
Met.

FIGS. 5, 6 and 7 are micrographs (magnification × 10, respectively) of the A, B and C parts of the obtained cast product.
0). These figures show that the graphite morphology of the cast product transitioned from flaky to spherical, and the transition of distribution was also continuous, and no boundary surface was formed. Generally, spheroidal graphite cast iron has a larger shrinkage ratio than ordinary cast iron (flake graphite cast iron), so it is easy to create shrinkage holes,
In the present example, micropores were not confirmed although the structure changed from flake graphite cast iron to C / V cast iron and then to spheroidal graphite cast iron.

5, FIG. 6, and FIG. 7, according to the manufacturing method of the present invention, a cast iron material is made of spheroidal graphite cast iron even at a small thickness, and another portion is flaky. It is composed of graphite cast iron, and it is shown that the morphology and distribution of graphite are continuously transitioned between these portions.

[Brief description of drawings]

FIG. 1a schematically shows a graphite spheroidizing agent placed in a mold. FIG. 1b schematically shows another embodiment.

FIG. 2a is a cross-sectional view of a mold for a gear used in the practice of the present invention. FIG. 2b shows a gear manufactured using the mold of FIG. 2a.

FIG. 3 is a cross-sectional view of a mold used in Examples.

FIG. 4 shows cast products obtained in the examples.

FIG. 5 is a micrograph showing a metal structure of a cross section of a portion A of the cast product obtained in the example.

FIG. 6 is a micrograph showing a metal structure of a cross section of a B part of the cast product obtained in the example.

FIG. 7 is a micrograph showing a metal structure of a cross section of a C portion of a cast product obtained in an example.

[Explanation of symbols]

1: Mold, 2: Upper mold, 3: Lower mold, 4: Gate, 5: Boss part, 6: Arm part, 7: Rim part, 8: Tooth part, 9: Graphite spheroidizing agent, 10: Rib part, 11: riser, 6: weir

Claims (5)

[Claims] 1. A gradient characterized in that one part is made of spheroidal graphite cast iron, another part is made of flake graphite cast iron, and the morphology and distribution of graphite are continuously transitioned between these parts. Functional cast iron material. 2. The tooth portion is made of spheroidal graphite cast iron, the boss portion is made of one-sided graphite cast iron, the arm portion is made of C / V cast iron, and the form and distribution of graphite are continuous from the tooth portion to the boss portion. Cast iron parts made of functionally graded cast iron material characterized by transitions. 3. A graphitizing agent is fixedly arranged in advance at a predetermined position in the mold, and a molten metal having a composition corresponding to flake graphite cast iron is poured on the graphitizing agent. A method for manufacturing the functionally graded cast iron material according to claim 1 or the cast iron component according to claim 2. 4. The method according to claim 3, wherein MgF ₂ is used as the graphite spheroidizing agent. 5. The components of the molten metal, including the inoculant, are C: 2.5 to 4.2 Si: 1.0 to 2.5 Mn: ≤0.5 P: ≤0. 02 S: ≦ 0.02 Fe: The balance (however, C + 1 / 3Si = 2.8-5.0) has a chemical composition consisting of, The manufacturing method of Claim 3 or 4 characterized by the above-mentioned.