JPH09202938A - Chromium-molybdenum cast steel excellent in machinability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cast steel excellent in mechanical properties, such as strength and wear resistance, by specifying the composition of a chromium- molybdenum cast steel. SOLUTION: This chromium-molybdenum cast steel has a composition consisting of, by mass, 0.1-0.5% C, 0.15-1.0% Si, 0.3-1.0% Mn, 0.90-1.50% Cr, 0.1-0.5% Mo, 0.005-1.0% Ti, 0.01-0.1% Al, and the balance Fe. This chromium- molybdenum cast steel has excellent turning and planing properties at (0.1 to 1.2)m/s cutting rate. The reasons why contents of the elements in the composition are regulated to the values in the above ranges are as follows: C, to secure strength and machinability; Si, to secure deoxidation, flowability of molten metal, castability, and toughness; Mn, to secure deoxidation, mechanical properties by improvement of hardenability, and wear resistance; Cr, to secure wear resistance and hardenability; Mo, to secure strength, such as high temp. creep resistance, and wear resistance; Ti, to refine structure and secure softening control after hot working; Al, to refine structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromium-molybdenum cast steel which is excellent not only in strength and wear resistance but also in machinability, and is particularly suitable for use as a rocker arm of an internal combustion engine. Is.

[0002]

2. Description of the Related Art Conventionally, as a rocker arm for an internal combustion engine, Fe-based cast alloys and non-ferrous-base sintered alloys, which are rich in wear resistance, have been widely used. Among them, regarding the Fe-based casting alloy, for example, Japanese Examined Patent Publication No. 7-6031 discloses that C: 2 to 4%, Cr: 10 to 25%, and Mo: 1 to 10% as main components. In addition, all of them were relatively high alloys, and the required characteristics were mainly limited to wear resistance.

[0003]

The cast alloy is rarely used as it is because of its manufacturing method.
In many cases, the final product is obtained through machining such as cutting and turning, and further heat treatment. This point is similar to the rocker arm, but as described above, the rocker arm has an alloy design mainly for the purpose of improving mechanical properties such as strength and wear resistance. Many of them are inferior in machinability, so that not only sufficient machinability is not obtained, but also a problem remains where the cutting tool is significantly damaged.

That is, the cast rocker arm is formed into a desired shape by machining after casting for the purpose of use, but if the surface finish after cutting is poor at this time, it must be further ground. In addition, the economic efficiency is lowered due to the increase in the manufacturing process. In addition, wear and damage of the cutting tool can be mentioned as the cause of the poor finish surface, but if the tool wear is remarkable, the tool life will be shortened and frequent tool replacement will be necessary, which is also economical. Will be a problem.

The present invention advantageously solves the above problems, and it is an object of the present invention to propose a chromium-molybdenum cast steel excellent in machinability, not to mention mechanical properties such as strength and wear resistance. And

[0006]

From the above viewpoints, the inventors have attempted a new alloy design in order to improve the machinability of cast chromium-molybdenum steel. As a result, C: 0.1 to 0.5 mass%, Si: 0.15 to 1.0 mass%, Mn: 0.3 to 1.0 mass%, Cr: 0.90 to 1.50 mass%, Mo: 0.1 to 0.5 mass%, Ti: 0.005 to 1.0 mass% , Al: 0.01 to 0.1 mass% and balance Fe and unavoidable impurities in the balance were found to be extremely effective in achieving the intended purpose, and the present invention was completed. is there.

The chromium-molybdenum cast steel having the composition of the present invention is excellent in turning property and planing property at a cutting speed of 0.1 to 1.2 m / s, and is particularly suitable for use as a rocker arm. Is.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The reason why the component composition is limited to the above range in the present invention will be described below. C: 0.1 to 0.5 mass% C is a solid solution in the matrix to improve the strength, form carbides and improve wear resistance, and effectively contribute to the improvement of mechanical properties, but are proportional to the addition amount. And then hardens, which is disadvantageous for machinability. Therefore, in consideration of these points, the range is set to 0.1 to 0.5 mass%, preferably 0.1 to 0.2 mass% as a range that has the minimum strength required for a rocker arm and does not deteriorate machinability.

Si: 0.15 to 1.0 mass% Si has a deoxidizing effect and an effect of improving the fluidity of the molten metal to improve the castability. However, the content is 0.15ma
If it is less than ss%, its addition effect is poor, while 1.0 mass
%, The toughness decreases, so 0.15 to 1.0 mass%
Limited to the range. It is preferably 0.4 to 1.0 mass%, more preferably 0.4 to 0.8 mass%.

Mn: 0.3 to 1.0 mass% Mn has a deoxidizing effect as well as Si, and also has the function of improving hardenability and improving mechanical properties. However,
If the content is less than 0.3 mass%, the effect of addition is poor, while if it exceeds 1.0 mass%, wear resistance deteriorates.
It was limited to the range of 0.3 to 1.0 mass%. Preferably 0.5 to
It is preferably 0.5 to 0.85 mass%, more preferably 1.0 mass%.

Cr: 0.90 to 1.50 mass% Cr not only has the effect of forming carbides to improve wear resistance, but also has the effect of significantly increasing the quench-hardenability of the material. Therefore, the addition of a large amount has the disadvantage of reducing the machinability. Like the present invention, from the viewpoint of wear resistance and creep strength required for rocker arms, it is not necessary to contain 10 mass% or more of Cr like ordinary Ni-Cr steel,
From this viewpoint, the range is limited to 0.90 to 1.50 mass%.
A more preferable range is 0.95 to 1.15 mass%.

Mo: 0.1 to 0.5 mass% Mo not only effectively contributes to the improvement of strength such as creep resistance at high temperature but also acts to form carbides to improve wear resistance. When used as an arm, it does not reach a temperature higher than 500 ° C, so high strength at a higher temperature is not required. Also, from the viewpoint of economy, it is not preferable to add a large amount. Further, as in the present invention, when the chromium content is about 1 mass%, 0.5 mass of Mo is added.
Even if added in excess of%, no further effect can be expected. Therefore, in the present invention, the Mo content is 0.1 to 0.5 mass.
% Preferably 0.1-0.3 mass%, more preferably 0.1-0.
It was limited to the range of 2 mass%.

Ti: 0.005 to 1.0 mass% Ti forms carbides and disperses uniformly in the material, so that it has the effect of suppressing the refinement of the structure and softening after hot working, so at least 0.005 mass% % Addition is required. However, if added over 1.0 mass%, these dispersed carbides increase hardness and deteriorate machinability, so the content was limited to the range of 0.005 to 1.0 mass%. Preferably 0.005-0.5 mass%, more preferably
It is 0.005 to 0.05 mass%.

Al: 0.01 to 0.1 mass% Al effectively contributes to the refinement of the structure by coexisting with Ti in addition to the deoxidizing action, but if the content is less than 0.01 mass%, the addition effect is poor. If it exceeds 1.0 mass%, the toughness in the cold will drop significantly, so the content should be 0.01-1.0 mass%.
Limited to the range.

Although the essential components have been described above, the other impurity elements are as follows. S: 0.020 mass% or less If S is contained in excess of 0.020 mass%, inclusions such as MnS are significantly formed. Therefore, it is preferable to suppress the inclusion of S as much as possible, and 0.020 mass% or less. Is desirable. P: 0.010 mass% or less If P is contained in excess of 0.010 mass%, the castability deteriorates, so it is preferable to suppress its inclusion as much as possible.
It is desirable that the content be 010 mass% or less. N: 0.005 mass% or less When N exceeds 0.005 mass%, it is strengthened by solid solution N and reduces machinability. Therefore, it is preferable to suppress the mixture as much as possible, and the content should be 0.005 mass% or less. Is desirable. O: 50 ppm or less When O is contained in excess of 50 ppm, the contribution of S to the immobilization is reduced, so it is preferable to suppress the contamination as much as possible, and it is preferable to set it to 50 ppm or less.

Next, the manufacturing method will be described. When casting the steel of the present invention, the method is not limited at all, and any of the ordinary lost wax method, the shell mold method, the sand mold casting method and the like can be used. Fits in an advantageous way. The main use of the invention material is a rocker arm of an internal combustion engine, but other uses such as various wear resistant parts are also conceivable.

[0017]

Example: Molten steel having the composition shown in Table 1 was melted in a high-frequency induction melting furnace and then 60 mmφ was formed by the lost wax method.
It was cast into a rod of × 200 mmH and cooled with water. The machinability survey is
A turning test was conducted. The tool used for the test is made of cermet. The machinability was evaluated by the surface roughness of the material after cutting and the amount of wear of the cutting tool. FIG. 1 shows the results of an examination of the relationship between the cutting speed and the finished surface roughness (Ra) of the material, and FIG. 2 shows the results of an examination of the relationship between the cutting speed and the amount of tool wear.

[0018]

[Table 1]

As is clear from FIG. 1, all the invention materials have smaller surface roughness and better finished surface properties than the comparative materials. Further, as shown in FIG. 2, when Ti is at the upper limit of 1.0 mass%, the tool wear amount tends to increase, but the tool wear amount is still smaller than that of the comparative material, and excellent wear resistance is exhibited. ing.

[0020]

As described above, according to the present invention, it is possible to inexpensively obtain a chrome-molybdenum cast steel which is excellent in machinability, not to mention strength and abrasion resistance, and particularly as a rocker arm for an internal combustion engine. Delivers a great effect when used.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between cutting speed and surface roughness of a material.

FIG. 2 is a graph showing the relationship between cutting speed and wear amount of cutting tools.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hidekazu Todoroki 4-2 Kojima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Nihon Metallurgical Industry Co., Ltd.

Claims (2)

[Claims] 1. C: 0.1 to 0.5 mass%, Si: 0.15 to 1.0 mass%, Mn: 0.3 to 1.0 mass%, Cr: 0.90 to 1.50 mass%, Mo: 0.1 to 0.5 mass%, Ti: 0.005 to 1.0 A chromium-molybdenum cast steel with excellent machinability, characterized by containing mass% and Al: 0.01 to 0.1 mass% and the balance being Fe and inevitable impurities. 2. The chromium-molybdenum cast steel for rocker arms according to claim 1, which has excellent turning properties and planing properties at a cutting speed of 0.1 to 1.2 m / s.