JPH03294452A - rocker arm material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to materials for rocker arms.

(Prior Art) Since rocker arms are required to have wear resistance, a high C-high Cr bearing steel represented by JIS-5UJ2 is relatively often used as a rocker arm material. The rocker arm is mainly manufactured by cutting.

The material for the rocker arm is subjected to a spheroidizing annealing treatment and then processed using a machine tool such as a lathe. Then, in order to impart wear resistance, the processed material is quenched and tempered to a normal Rockwell hardness of HRC.
Make the hardness 60 or higher.

Cold processing (e.g. cold forging) as opposed to cutting manufacturing methods
If the rocker arm is manufactured by (1)
Reduction of energy, (2) Improvement of processing yield, (3
) It is possible to reduce manufacturing costs, etc.

However, when carrying out such processing, it is necessary to cold forge the material so that its deformation resistance is low and its deformability is large, that is, it can be processed without cracking and the wear and tear of the tools used is small. The material must be of a suitable quality.

(Problem to be Solved by the Invention) However, in the case of JIS-SUJ2, which currently occupies the mainstream of rocker arm materials, the C and Si contents are generally 0.95 to 1.10 wt%, respectively. , S
i: 0.15 to 0.35 wt%. Therefore, during the process of spheroidizing annealing performed for cold working materials, C8i is dissolved in the matrix and promotes solid solution hardening of the material, resulting in a decrease in cold workability. There are some difficulties. In addition, the carbides that precipitate during the spheroidizing annealing process tend to become elongated (for example, when the cooling rate during the annealing process is increased, which also causes a decrease in cold-open formability). ing.

Such problems can be solved to some extent by reducing the contents of C and Si. It is a well-known fact that processability generally improves by reducing the content of C and Si, but
, Si are all essential components for ensuring hardness and strength, and a reduction in these components will reduce wear resistance.

The present invention solves the above-mentioned contradictory problems by defining the weight ratio of each component as described below,
The object of the present invention is to provide a rocker arm material that has excellent cold workability and wear resistance and is used after being cold worked.

(Means for Solving the Problems) The rocker arm material of the first aspect of the present invention for solving the above problems has a composition in wt% of C: 0.45 to 0.7.
0% Si: <0.15% Mn: ≦0.40% Cr: 0. 50-2. 50%P:
50.015% B: 0.0005~o, oiooo% balance consists of Fe and unavoidable impurities, 0.7≦ between C1Cr
[Cr/C]≦5.0, and Mn, Cr, B
Between 0.55≦[Mn+Cr+100B]≦3.5
It is characterized by satisfying 0.

The rocker arm material according to the second aspect of the present invention contains 50% or more of carbides precipitated during annealing, with an average diameter of 1 μm or less, an area ratio of 25% or less, and an aspect ratio of 0.5 or more. It is characterized by Here, the aspect ratio refers to the ratio of the short axis to the long axis of the carbide, and is defined by the following formula, A=X/Y, where the aspect ratio is A, the short axis of the carbide is X, and the long axis of the carbide is Y.

In the rocker arm material of the third aspect of the present invention, the composition further includes 1 of the following wt%: Ni: ≦100%, Mo: ≦0.50%, Nb: ≦0.30%, V: ≦0.50%. Contains one species or two or more species, and if necessary, one of Pb: 50.25% S: 50.25% Ca: 50.15% Rem: 50.15% Te: 60.030% Or it is characterized by containing two or more types.

The rocker arm material according to the fourth aspect of the present invention is characterized in that the unavoidable impurities are 0:50.0015%, Ti:50.0020%, and Aj2:50.0350%.

The reason for determining the lower limit and upper limit of each component described above is as follows.

In the first invention, C is 0.45 to ensure strength.
% or more and 0.70% to improve cold workability.
I made it below. In order to provide the rocker arm with a high Rockwell hardness of 61 or higher, it is desirable that C be 0°55% or higher. Si is
The content was set to less than 0.15% to improve cold workability.

Mn was added to ensure hardenability, and was set to 0.40% or less to improve cold workability. Cr was set to 0.50% or more to ensure fatigue properties, and 2.50% or less to prevent deterioration of machinability. P was set to 0°015% or less in order to improve cold workability.

B is set to 0.0005% or more to ensure hardenability, and O, to improve hot workability during blooming, etc.
0IO05'o or less.

The reason for setting 0.7≦Cr/C between C and Cr is to improve fatigue properties, and the reason for setting Cr/C to 50°0 is to suppress the generation of large carbides that precipitate during steel ingot casting. This is because even if the Cr/C value exceeds 5.0, the fatigue properties do not improve much. The reason for setting 0 55≦Mn+Cr+100B is to improve hardenability, and Mn+Cr
The reason for setting +100B≦3.50 is that cold workability is improved, and even if the amount exceeds 3.50, hardenability does not improve much.

In the second invention, the average diameter and area ratio of carbides precipitated during annealing treatment are set to be below a predetermined value, and carbides with an aspect ratio of 0.5 or more are included in 50% or more of the rocker arm. This is to improve the cold workability of the material.

In the third invention, Ni is added to improve fatigue properties and hardenability, and is set to 1.00% or less to prevent deterioration of machinability. Mo was added to improve fatigue properties and hardenability, and was made less than 0.50% to prevent cold workability. Nb and ■ were added to improve fatigue properties, and in order to prevent deterioration of cold workability, Nb was set at 0.3% or less, and ■ was set at 0.50% or less.

In the third invention, pb and S as selective elements are
Each is added to improve machinability, and the content is set to 0.25% or less to prevent deterioration of cold workability and fatigue properties. Both Ca and Rem (rare earth element) are added to improve machinability, and 0.0% is added to prevent deterioration of fatigue properties. It was set to 15% or less. Te is added to improve machinability, and Te is added to prevent deterioration of fatigue properties.
030% or less.

In the fourth invention, the reason why 0, Ti, and A° C. are set to be below a predetermined percentage is to reduce inclusions in the steel material and improve fatigue properties and workability.

(Example) Examples of the present invention will be described below.

Steel with a predetermined chemical composition was melted in a vacuum induction furnace and cast. The obtained ingot was hot forged, heated at 850°C for 60 minutes under the heat treatment conditions shown in Figure 1, normalized, and then spheroidized under the prescribed heat treatment conditions shown in Figure 2. The resulting steel was made into a piece with a diameter of 6 mm and a height of 10 mm.
The specimen was cut into a cylindrical specimen.

The chemical components of various steel materials are shown in Table 1.

(The following is a blank space.) For each steel shown in Table 1, the hardness after spherical annealing was measured by a Rockwell hardness test. Furthermore, samples were cut out from various test pieces, the surface was puff polished to a mirror finish, and immersed in a corrosive solution to corrode.
Observation was made using an electron microscope at 0x magnification, and image analysis was performed. the result,
The average diameter of carbides, the area ratio of carbides, and the amount of carbides with an aspect ratio of 0.5 or more were measured, and the results shown in Table 2 were obtained.

(The following is a blank space.) U=Lk and then various steel materials were evaluated for cold workability. 1st
The test was conducted by measuring deformation resistance and critical compressibility. The results are shown in Table 3.

(Hereafter, margin.) Here, the "deformation resistance" was determined as follows.

The test piece of the predetermined size was compressed and deformed, and the load and height of the test piece at that time were measured. When the height after deformation is Ho, the amount of strain ε is expressed as ε” 12 /HO, and the formula ρn
The value obtained by dividing the load by the cross-sectional area when the value of (ε) was a predetermined value was defined as the deformation resistance. The "critical compressibility" was a value determined by the following formula, % (%), where H3 is the height of the test piece where cracking occurred.

As shown in Table 3, in Comparative Examples 1 and 2, the deformation resistance is relatively thick compared to Examples 1 to 15 (and the critical compression ratio is also relatively small compared to Examples 1 to 15). It can be seen that cold workability is poor.On the other hand, Example 1
It was found that Samples 1 to 15 had relatively better cold workability than Comparative Examples 1 and 2.

Next, as a second test for evaluating cold workability, the cracking incidence was measured. The conditions for this cracking test are: first, the diameter is 30 mm;
For a cylindrical test piece with a height of 45 mm, when the height after compression deformation is H, the compression ratio [(1-H2/45) x
The probability of occurrence of cracking was determined in the range of 50% to 80%.

The test was conducted for 10 examples and 10 comparative examples. The results are shown in Table 4.

(Hereinafter, margin.) As is clear from Table 4, in Comparative Examples 1 and 2, 6
Occurrence of cracks was confirmed at a compression rate of 0%. On the other hand, in Examples 1 to 15, no cracks occurred at a compression rate of 60%. This revealed that the steel materials of Examples had good cold workability.

Hideto Crazy Standing Ninu± The rocker arm is subjected to repeated impact loads.

As a result of various experiments, the inventor of the present application found that the fatigue characteristics of a rocker arm are correlated with the rolling life, which is used to determine the fatigue characteristics of bearing steel. Therefore, the fatigue life of the rocker arm can be evaluated by the transfer life.

The transfer lifespan was measured for the various Examples and Comparative Examples described above. The test conditions are as follows.

Sample Radial life test piece (diameter 12mm, length 22mm) Test conditions: Load stress 600kgf/mm2 rotation speed
46240 rpm Heat treatment conditions for test piece: After spheroidizing annealing treatment, the following quenching/tempering quenching = 850°C x 30 minutes Oil cooling tempering: 180°C x 60 minutes Air cooling was used.

The Rockwell hardness (HRC) and rolling life of the obtained test piece were measured. The results are shown in Table 5.

(Hereinafter, blank space.) In Table 5, the transfer life is the standard life r1 of Comparative Example 2. OJ, and the ratio of each transfer lifespan to this is shown. Note that Examples 1 to 4 have not been measured.

As is clear from Table 5, it was found that Examples 5 to 15 had relatively long transfer lives compared to Comparative Examples 1 and 2.

Next, a second transfer lifespan test was conducted under different conditions. The difference from the above-mentioned transfer life test is that the applied stress is 40
0 kgf/mm2. Other test conditions and heat treatment conditions were the same as those described above. The results of this transfer life test were as shown in Table 6.

(The following is a margin.) Table 5 Transfer life test results Table 6 Transfer life test results Table 2 As is clear from Table 6, in Examples 1 to 8, Comparative example 1
6 (Effects of the Invention) As explained above, the rocker arm material of the present invention is easy to cold work and has excellent fatigue properties. Therefore, the manufacturing cost of the rocker arm can be reduced.

[Brief explanation of drawings]

FIG. 1 is a heat treatment process diagram showing a normalizing process, and FIG. 2 is a heat treatment process diagram showing a spheroidizing annealing process.

Claims (4)

[Claims] (1) Composition is wt%: C: 0.45-0.70% Si: <0.15% Mn: <0.40% Cr: 0.50-2.50% P: <0.015% B : 0.0005 to 0.0100% The balance consists of Fe and unavoidable impurities, satisfies 0.7≦[Cr/C]≦5.0 between C and Cr, and Mn, Cr, B A material for a rocker arm, which satisfies 0.55≦Mn+Cr+100B≦3.50. (2) The average diameter of carbides precipitated during annealing is 1
2. The material for a rocker arm according to claim 1, wherein the rocker arm material contains 50% or more of micrometers or less, an area ratio of 25% or less, and an aspect ratio (minor axis/longer axis) of 0.5 or more. (3) The composition further includes one or more of the following in wt%: Ni: ≦1.00%, Mo: ≦0.50%, Nb: ≦0.30%, V: ≦0.50%. and, if necessary, one or two of the following: Pb:≦0.25% S:≦0.25% Ca:≦0.15% Rem:≦0.15% Te:≦0.030% The rocker arm material according to claim 1 or 2, comprising the above. (4) The rocker arm according to any one of claims 1, 2, or 3, wherein among the inevitable impurities, O: ≦0.0015%, Ti: ≦0.0020%, Al: ≦0.0350%. material.