JPH0347947A - Bearing steel excellent in rolling fatigue life - Google Patents

Abstract

PURPOSE:To obtain a particularly inexpensive bearing steel having superior rolling fatigue life by providing a composition consisting of respectively prescribed amounts of C, Si, Mn, Mo, S, O, and Al and the balance essentially Fe with inevitable impurities. CONSTITUTION:The above bearing steel has a composition consisting of, by weight ratio, 0.50-0.90% C, 0.30-2.00% Si, 0.50-2.50% Mn, 0.03-0.50% Mo, <=0.20% S, <=0.0050% O, 0.002-0.08% Al, and the balance essentially Fe with inevitable impurities. In this bearing steel, properties equal to those of conventional high carbon chromium bearing steel while obviating the necessity of expensive alloying elements and homogenizing annealing at high temp. for a long time. Moreover, this bearing steel has excellent workability in the as-hot-rolled state, and further, it shows a characteristic of having rolling fatigue life, which is the most important property required of bearing steel, comparable to that of conventional high carbon chromium bearing steel frequently used. Accordingly, the effects of reducing steel stock manufacturing costs and improving productivity can be attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to steel for bearings, and particularly to provide steel for bearings that is low in price and has an excellent rolling fatigue life.

[Prior Art] Conventionally, carbon steel for machine structures, alloy steel for machine structures, and high carbon steel chromium bearing steel have been used as steel for bearings.

Among these, high carbon steel and chromium support steel are used in the largest quantities in automobiles, industrial machinery, etc. as pole bearings or roller bearings. This steel contains about 1% carbon and 0.9
~1.6% chromium is added and the cost is extremely high. In addition, Cr co-carbides may be formed during the manufacturing process of steel materials, which has an adverse effect on the rolling fatigue life, which is the most important characteristic of bearing steel. Currently, a high-temperature, long-term homogenization treatment is employed to eliminate such eutectic carbides. In addition, since the rolled material is extremely hard and has significantly poor workability, it requires softening annealing prior to machining, which significantly increases manufacturing costs.

From the above viewpoints, it is desired to develop a low-cost steel material that has a rolling fatigue life equivalent to that of high carbon chromium bearing steel and has excellent cold workability.

On the other hand, in Special Publication No. 46-19425, C: 0.5
8-0.88% by weight Cr: 0.50-2. OO weight% Mn: O, l O~1.15 weight% Si・0.15
A bearing steel consisting of ~2.00 tons π% balance and impurities and having a carbon content of 0.35 to 0.55% in the martensite matrix has been developed and put into practical use.

Also, C, V, Gullott, i et al. 0.70%C1
0.28%Si, 0.41%Mn, 0.11%Mo, 0
．． 5AE52100 with 28% Cr, 0.91% Ni
We are developing bearing steel with performance equivalent to (!1l)
etal Progress, Nov/1965, pp.
2-41° However, in these steels, Cr and Ni, which are expensive alloying elements, are still added to a large extent, and there are many problems in terms of cost reduction.

[Problem to be Solved by the Invention J] The object of the present invention is to solve the problems of the prior art as described above, and to produce a conventional high carbon chromium bearing steel without using expensive alloying elements and without requiring long-term homogenization annealing at high temperatures. Our objective is to provide low-cost steel for bearings that has performance equivalent to that of steel.

[Means for Solving the Problem 1 The present inventors have conducted extensive research on the problems of the prior art, and have investigated C, Si, Mn, S, 0, Al1, Mo, Cr, Ni.
, Cu, Nb and V are limited to specific ranges,
They discovered that it is possible to impart two properties: excellent rolling fatigue life and cold workability. As a result, it has become possible to obtain a bearing steel with excellent rolling fatigue life and the original performance required of high carbon chromium bearing steel. That is, the present invention
C: 0.5 (1 to 0.90% by weight Si: 0.30 to 2.00% by weight Mn: 0.5 C1-2, 50% by weight Mo + 0
．． 03-0.50ffiff1% S: 0.20% by weight or more 1 0: 0.0050% by weight or less Ar1: 0.002-0.08 @% by weight, the remainder being substantially Fe and unavoidable impurities This is a bearing steel with excellent rolling fatigue life.

In addition to the same basic components as in the above invention, Cr:
0.05~0.50ittM%Ni:0.05~0.5
0% by weight Cu: 0.05-0.50jTNn%V: 0.02
-0.20 wt% Nb: 0.02 to 0.20 wt% Nb: 0.02 to 0.20 wt% Nb: 0.02 to 0.20 wt% A steel for bearings with excellent fatigue life.

[Effect 1 The reasons for limiting the ingredients in the present invention are as follows.

C: C is a fundamental element in maintaining the strength and hardness required for bearings1, and it is necessary to add at least 0.50% by weight, but if it is included in a large amount, excessive carbides may be formed. This not only deteriorates impact resistance and cold workability and reduces rolling fatigue life, but also requires high-temperature and long-term homogenization annealing to eliminate this negative effect. The weight was 0.90%.

Sl: Sl is an element effective in promoting deoxidation and increasing strength, and is also effective in reducing Mj+I: 1L of surface defects in steel ingots. Furthermore, it contains elements that are extremely effective in strengthening the hardened structure and preventing softening during tempering. This effect is 0.3
This effect becomes noticeable at 0% by weight or more, so the lower limit is 6. However, if it exceeds 2.00% by weight, this effect is saturated. Therefore, the upper limit was set at 2.00% by weight.

Mn.

Mn improves hardenability and increases strength and toughness.
This is effective in preventing deterioration of hot working = rL due to S. This effect becomes noticeable at 0.50 tonne percent or less, with the lower limit being the value. However, if it exceeds 2.50% by weight, this effect is saturated and the impact resistance and machinability deteriorate, so 2.50% by weight was set as the limit.

M.

It is the most important element in the present invention, promoting the formation of carbides and finely dispersing them, improving wear resistance, properties, and rolling fatigue properties. In addition, it has strong solid solution strengthening properties, improves hardenability, and contains a small amount of ridges, which improves machinability and increases strength and toughness.

This effect becomes noticeable at 0.03% by weight or less, so this value is set as the lower limit. However, if it exceeds 0.50% by weight, the impact resistance and machinability will deteriorate and the addition cost will increase, so 0.50% by weight is set as the upper limit.

0 forms oxide-based inclusions in the steel, which becomes a starting point for peeling during rolling contact fatigue life, and also significantly reduces cutting tool life, so it is necessary to reduce it as much as possible. For this purpose, O needs to be 0.0050% by weight or less, so this value was set as the upper limit.

8 is an element that improves machinability and is a necessary element in the production of bearing steel parts, and this effect increases when added in a large amount, but if added in a large amount, hot workability deteriorates and rolling The upper limit is set to 0.20 because it reduces fatigue and cold workability.
It was expressed as weight%.

The above-mentioned limit amounts of C, Si, Mn, Mo, S, Ag, and 0 are the basic components of the present invention, but Cr, Cu, Ni, Nb, and V may be added to the following limits as necessary. The present invention can also be more effectively achieved in steel containing one or more kinds at the same time. These limits
EThe reasons are as follows.

Cr.

CF improves hardenability and increases strength and toughness.
! , promotes carbide IF hook 11i: and improves 111.1 abrasion resistance. It is effective for This effect is 0.05
This value is set as the lower limit because it becomes noticeable at a volume of % or more. However, if it exceeds 0.50% by weight, the impact resistance and machinability will deteriorate, the addition cost will increase, and excessive carbides will be formed, causing rolling fatigue (rolling fatigue). However, in order to eliminate this negative effect, high tm and long time homogenization annealing is required, so 0-50% by weight was set as 1 limit.

Ni, Cu: Ni and Cu are dissolved in the matrix to improve hardenability and increase strength by 1. In addition, a small amount of content has the effect of improving machinability. If the amount is less than 0.05 small ffi%, no effect will be observed, so 0.05 small ffi% is set as the F limit. -10,000
．． Addition of more than 50% by weight will significantly increase the cost and the intended purpose of the present invention cannot be achieved, so 0.50ff
iiTt% was set as "-eye".

Nb, V: Nb and V are precipitation-strengthening elements, and since the carbides formed together are finely dispersed, the effect of improving ll'Ft wear resistance is remarkable. This value was set as the lower limit because this effect has the effect of increasing the strength even with a small addition of 0.02% by weight. However, if the content exceeds 0.20% by weight, the effect becomes saturated (the ψ direction is exhibited and the cold workability is significantly deteriorated), so 0.20% by weight was set as the upper limit for each.

[Example J Examples of the present invention will be described in detail below.

Steel with the chemical composition shown in Table 1 is melted using a conventional method, and 150 m
After blooming into an m-square billet, it was hot-rolled into a 30 mm diameter steel bar using a conventional method. A cylindrical test piece with a diameter of 12 mm and a length of 22 mm was prepared from this hot-pressed material by machining, quenched and tempered, the hardness was adjusted to Rc60-63, and a cylindrical rolling contact fatigue life test was performed. The test conditions were Hertzian maximum stress Pmax: 600 kgf/mrn'', the lubricating oil was immersed in No. 68 turbine oil, and the stress (' was 46.0 kgf/mrn).
00 times/min.

These test results are expressed as a ratio to the cumulative failure probability value (L 1o) of 10% of rolling fatigue life of 5UJ2 (steel 1) as a comparative material, and are also shown in Table 1.

As shown in Table 1, typical high carbon chromium bearing steel (SU
J2) Steels 3.4.5.6.8.9.10.12 and I5 within the scope of the claims of the present invention have a rolling life equal to or longer than steel I having the composition . On the other hand, comparative example steel 2.7.11.13.
Nos. 17 and 18 do not reach the level of high carbon chromium bearing steel.

In addition, in Steel 14, which exhibits a relatively good rolling fatigue life, Mo
The amount is high and difficult to meet the intended purpose of the present invention.

1 [Effects of the Invention] As is clear from the above examples, the present invention has excellent workability as hot-rolled and a longer rolling fatigue life, which is the most important for bearing steel, by limiting the chemical composition than before. The present invention exhibits properties comparable to those of conventional high carbon chromium bearing steels, and the present invention can bring about two effects: cost reduction and productivity improvement of steel materials.

Outsourcer Kawasaki Steel Co., Ltd.

Claims (1)

[Claims] 1 C: 0.50-0.90% by weight Si: 0.30-2.00% by weight Mn: 0.50-2.50% by weight Mo: 0.03-0.50% by weight % S: 0.20% by weight or less O: 0.0050% by weight or less Al: 0.002 to 0.08% by weight, with the remainder consisting essentially of Fe and unavoidable impurities. Steel for bearings with excellent dynamic fatigue life. 2 C: 0.50 to 0.90 wt% Si: 0.30 to 2.00 wt% Mn: 0.50 to 2.50 wt% Mo: 0.03 to 0.50 wt% S: 0.20 Contains O: 0.0050 wt% or less Al: 0.002 to 0.08 wt%, and Cr: 0.05 to 0.50 wt% Ni: 0.05 to 0.50 wt% Cu : 0.05 to 0.50% by weight, V: 0.02 to 0.20% by weight, Nb: 0.02 to 0.20% by weight, and the remainder is substantially A steel for bearings with excellent rolling fatigue life, characterized by comprising Fe and unavoidable impurities.