JPH0210218B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to wear-resistant cast iron made by die casting, and more specifically, in practical use, a die that exhibits excellent wear resistance even under severe wear conditions such as sliding parts under high speed and high surface pressure loads. Concerning wear-resistant cast iron by casting. Wear-resistant cast iron is widely used as a base material for various mechanical parts that are used under severe wear conditions, such as sliding machine parts such as cylinders of internal combustion engines and rollers of rotary air conditioners. These sliding parts are
Normally, in order to slide at high speed and under high surface pressure load,
There are inconveniences such as reduced strength of minute parts on the surface of the part, resulting in mechanical breakage, resulting in abnormal wear, or the generated heat causing seizing of the lubricant. Therefore, it is preferable that such sliding parts not only have high hardness, high strength, and excellent wear resistance, but also have as few irregularities on the surface of the parts as possible, and do not cause problems such as destruction of minute parts. . Japanese Patent Publication No. 53-6929 discloses a wear-resistant cast iron whose components are adjusted in order to eliminate such inconveniences such as abnormal wear. This cast iron suppresses the precipitation of soft ferrite phase in the structure of the as-cast state, and mainly by the effect of adding vanadium, coarsens the precipitated graphite, resulting in fine particles that are generated by crushing the coarse graphite during initial wear. Graphite improves lubricity. However, such coarse graphite under high surface pressure load,
If it is present on the sliding surface of parts that slide at high speed and the surface roughness of the sliding surface is large, it has the disadvantage that problems such as abnormal wear described above are more likely to occur. The present inventors conducted extensive research to develop a wear-resistant cast iron that does not have the disadvantages of abnormal wear caused by the destruction of such minute parts, and found that such cast iron generally has a soft ferrite phase in its matrix structure. It is preferable that the precipitated graphite does not become coarse, and more specifically, the base metal has a pearlite structure (layered structure of ferrite and cementite).
, and graphite is formed by the precipitation of fine and dispersed eutectic graphite, such as the D-type (non-directional alignment) graphite form established by the American Foundry Society-American Society for Testing and Materials (AFS-ASTM). The conclusion was reached that one having a phase is preferable. Conventionally, in order to obtain cast iron with such eutectic graphite and a pearlite matrix by sand casting, the carbon content of the cast iron should be 3.0% by weight or less, the sulfur content should be 0.05% by weight or less, and a trace amount of Ti, Mo,
Products containing Ni, Cr, Cu, etc. as alloying elements were manufactured. However, even in such a composition, the graphite is not entirely eutectic, or because of the sand mold, the shape and structure of the graphite are non-uniform on the surface and inside. On the other hand, in the case of mold casting, the solidification rate is generally higher than that in sand mold casting, so the graphite structure becomes heterogeneous as cementite (Fe ₃ C) crystallizes, or eutectic graphite crystallizes. There was an inconvenience that a ferrite phase precipitated as the liquid was removed. Conventionally, the composition of wear-resistant cast iron produced by die casting includes 3.1 to 3.5% by weight of C, 1.6 to 2.6% by weight of Si, and 0.05 to 0.5% by weight of Cu as other components.
Those containing 0.01 to 0.1% by weight of Sn as an alloying element were commonly used. According to this composition, a small amount of ferrite still precipitates around the eutectic graphite, and 1000
Even by quenching at temperatures below ℃, the matrix structure is difficult to become completely martensite. Therefore, for practical purposes, cast iron does not have sufficient wear resistance. The purpose of the present invention is to eliminate the above-mentioned disadvantages of conventional wear-resistant cast iron, and to create a microstructure in an as-cast state in which the base is a pearlite structure and has a precipitated phase of eutectic graphite. Furthermore, by quenching at temperatures below 1000°C, the pearlite base easily becomes an all-martensitic structure, and therefore can be used at high speeds.
The object of the present invention is to provide a wear-resistant cast iron made by die casting that exhibits excellent wear resistance even under severe wear conditions such as sliding parts under high surface pressure loads. That is, the wear-resistant cast iron produced by die casting of the present invention is
Carbon (C) 2.2-2.4% by weight, silicon (Si) 3.6-4.4
Weight%, manganese (Mn) 0.3-0.5% by weight, phosphorus (P) 0.1% by weight or less, sulfur (S) 0.1% by weight or less, chromium (Cr) 0.3-1.0% by weight, and titanium (Ti) 0.05-0.20% by weight The base structure is pearlite in the as-cast state, and fine eutectic graphite is precipitated in the base structure. . The reasons for limiting the composition of the wear-resistant cast iron produced by die casting of the present invention will be explained below. The main reason why the cast iron of the present invention is limited to the above composition is to transform all the matrix structure of the cast iron in the as-cast state into pearlite, and to make the precipitated graphite into fine eutectic graphite. This is to perform heat treatment to transform the entire base structure into martensite. To explain in more detail, the lower limit of carbon content is set at 2.2% (weight%, hereinafter referred to as
The reason for setting the upper limit as 2.4% is that if it is less than 2.2%, cementite (Fe ₃ C) will crystallize.
This is because the precipitated graphite becomes coarse. The silicon content was limited to 3.6 to 4.4%.
If it is less than %, it will be chilled and cementite will precipitate.
This is because if it exceeds 4.4%, a ferrite phase will precipitate. The contents of manganese, phosphorus, and sulfur are in the normal range, that is, Mn 0.3 to 0.5% and P 0.1% or less, respectively.
S is set at 0.1% or less. Among these, manganese is
It is a pearlite structure stabilizing element, and if it is less than 0.3%, it is difficult to achieve this effect, and if it is added in an amount exceeding 0.5%, cementite will crystallize. The chromium content is 0.3% to 1.0%.
If it is less than 1.0%, a ferrite phase will precipitate, and if it exceeds 1.0%, it will be chilled and cementite will crystallize.
Similarly, the reason for setting the titanium content to 0.05 to 0.20% is that if it is less than 0.05%, a ferrite phase will precipitate,
This is because if it exceeds %, it will be chilled and cementite will crystallize. When casting the cast iron of the present invention, for example, a predetermined amount of each of mild steel, recarburized material, ferrosilicon (commercially available products containing 75% Si, etc.) is cast using a high-frequency melting furnace or the like. , ferromanganese (commercially available products containing 75% Mn by weight), ferrochrome (Cr
In addition, in order to suppress the crystallization of cementite or ferrite, the above-mentioned ferrosilicon is inoculated with 0.2 to 0.3% by weight of Si (Si content) before casting. A molten metal having the above composition is prepared by, for example, inoculation. Next, the obtained molten metal is cast into a desired mold. The mold ratio of the mold used [ratio between the maximum wall thickness of the mold and the (maximum wall thickness x 1/2) of the casting] is 3.
-10 is preferred. If it is less than 3, the life of the mold will be shortened and cracks will easily occur, and if it exceeds 10, the weight of the mold will increase and become uneconomical. The thus obtained cast product can be further subjected to heat treatment such as quenching and tempering, or can be used as-is as cast. According to the wear-resistant cast iron produced by die casting of the present invention,
In the as-cast state, all the matrix structure becomes pearlite, and the graphite precipitated in the matrix becomes fine eutectic graphite, so even in the as-cast state, it has high hardness, high strength, and high durability. Excellent abrasion resistance. In addition, when this cast iron is further subjected to heat treatment such as quenching and tempering, the pearlite structure becomes martensite with even higher hardness, which further improves wear resistance and improves the wear resistance compared to when ferrite is present in the matrix. It has the advantage that the heating temperature for quenching can be kept at a relatively low temperature of 900 to 1000°C, and there is no need to increase the cooling rate to reduce residual ferrite. Therefore, the wear-resistant cast iron made by die casting of the present invention can be used as a base material for various mechanical parts used under severe wear conditions, such as cylinder parts of internal combustion engines or sliding mechanical parts such as rollers of rotary air conditioners. Extremely useful. Examples As Examples 1 to 3 and Reference Examples 1 to 5, each molten metal (hot water temperature 1350°C) having the composition shown in the table was heated at 350°C to
It was cast into a cast iron mold (wall thickness: 50 mm) preheated to 400°C, and a disc-shaped cast product with a diameter of 50 mm and a thickness of 15 mm was obtained under conditions of a mold ratio of approximately 7. In addition, when pouring the molten metal into the mold, Ni80-Al20 alloy powder was coated on the mold surface to a thickness of about 0.2 mm, and acetylene soot was further coated on top.

[Table] Thus, wear-resistant cast irons obtained by die casting of the present invention as Examples 1 to 3, and Reference Examples 1 to 3
When the structure morphology of each of the cast irons obtained in Examples 1 to 3 in the as-cast state was observed using a metallurgical microscope, all of the cast irons of the present invention obtained as Examples 1 to 3 had a pearlite structure as a matrix. The precipitated graphite was also fine and eutectic. On the other hand, the surfaces of the cast irons obtained as Reference Examples 1 and 2 were both chilled and cementite crystallized. Also,
In both of the cast irons obtained as Reference Examples 3 and 4, a ferrite phase was precipitated in the matrix structure, and the precipitated graphite was also partially coarsened. Furthermore, the cast iron obtained as Reference Example 5 had a larger amount of precipitated ferrite and coarse graphite than Reference Examples 3 and 4. Next, each of the as-cast castings obtained as Examples 1 to 3 and Reference Examples 1 to 5 was further heated to 950°C.
It was subjected to oil quenching treatment and then tempering treatment at 400℃. When the structure of the base metal of each cast iron subjected to such treatment was observed using a metallurgical microscope, it was found that
In all of the cast irons of Examples 1 to 3, the base metal had a martensitic structure, but in the case of the cast irons of Reference Examples 1 to 5, a portion of the ferrite phase remained in the base. As-cast cast iron produced as Example 2 (hereinafter referred to as sample a), Examples 1 to 3,
The cast irons produced as Comparative Examples 3 to 5 were further subjected to the above-mentioned quenching and tempering treatment (hereinafter referred to as
15 × 12 × 10 from each cast iron of samples b to g)
Abrasion test pieces of mm were cut out and placed in an Amsler type abrasion tester to perform a wear test under the following conditions. <Test conditions> Mating material: S55C (JIS mechanical structural carbon steel, diameter 40
(mm, thickness 10mm) Load: 70Kg Speed: 2.5-2.7m/sec Lubricating oil: Turbine oil No. 90 The wear amount of the above samples a to g is shown in the drawing. In the figure, curve A, points B, C, D, and curves E to G
shows the relationship between the test distance and the amount of wear for samples a to g, respectively.

【table】

[Table] As is clear from the drawings, the wear-resistant cast iron produced by die casting of the present invention has excellent wear resistance in the as-cast state or in the state where it has been further subjected to quenching, tempering, etc. treatment.

[Brief explanation of drawings]

The drawings show the as-cast cast iron produced in the "Example" or the wear-resistant cast iron produced by die casting of the present invention, which is a cast iron that has been quenched and tempered, and the reference example. It is a diagram showing a comparison of wear resistance, where curve A and points B, C, and D represent the wear resistance of each cast iron according to an example of the present invention, and curves E, F, and G represent a reference example.

Claims (1)

[Claims] 1 Carbon 2.2-2.4% by weight, Silicon 3.6-4.4% by weight,
It contains 0.3-0.5% by weight of manganese, 0.1% by weight or less of phosphorus, 0.1% by weight or less of sulfur, 0.3-1.0% by weight of chromium, and 0.05-0.20% by weight of titanium, with the balance being composed of iron, and the matrix structure is in the as-cast state. A wear-resistant cast iron produced by die casting, which is made of pearlite and is characterized by having fine eutectic graphite precipitated in the matrix structure.