NL1011805C2 - Method for manufacturing a ball bearing steel. - Google Patents

Description

Method for manufacturing a ball leather sample.

The present invention relates to a method of manufacturing a steel grade comprising providing a steel grade containing: 5-0.9-1.03 wt% C; 0.15-0.35 wt% Si; 0.75-1.00 wt% Mn; 0.70-0.90 wt.% Cr; and - other Fe and impurities, said steel being produced by continuous slab casting followed by rolling. The use of continuous block casting is well known, and the description of block casting is that the cast part requires two heat treatment steps for rolling the strand into the end rod or bar. See Hengerer et al. "Evaluation of the Continuous Casting ASTM STP 1195, 1993", pp. 237-251.

In order to limit the costs of manufacturing construction material, it is proposed in the prior art to manufacture such a steel grade for continuous slab casting, see J. Lichtenstein, Brunei's Steel World Quaterly Vol. Issue 4, pp. 25-29.

The most commonly used ball bearing steel ASTM A295 52100 includes about 1 wt% C, 0.25 wt% Si, 0.35 wt% Mn, and 45 wt% Cr and can be used for this purpose. However, it is necessary to introduce a homogenization treatment after continuous casting and before rolling. This is necessary because during solidification, segregation of the alloy elements C and Cr produces primary carbides which will continue to evolve in the steel if reheating and homogenizing heat treatment are not used. The segregation and primary carbides create voids after elevated machining and other errors in a final rolling element bearing.

Such a homogenization treatment will necessarily take place at a relatively high temperature and for a relatively long time. This means that the advantage of continuous casting of ASTM A295 52100 steel is at least partially reduced due to the increased energy costs. In general, such a homogenizing heat treatment is not carried out in a special atmosphere and steel losses are caused by skin formation. In view of 101 1805 2 the above disadvantages, continuous casting of steels has not realized the full economic potential as suggested.

A ball bearing steel is known from GB 2294270A comprising 0.70-0.93 wt.% C, 0.15-0.50 wt.% Si, 0.50-1.10 wt.% Mn 0.3-0.65 wt% Cr with the ratio 5 over the Cr / C being in the range 0.4-0.7.

From EP 0825270A1 a ball bearing steel is known comprising 0.95-1.10 wt.% C, 0.15-0.70 wt.% Si, maximum 1.15 wt.% Mn, 0.90-1.60 wt. .% Cr.

In view of the cost reduction currently possible through the use of continuous casting, the object of the invention is to provide a method for manufacturing a steel grade in which such a homogenization treatment to remove segregation can be avoided and thus achieve the full possible cost saving without a major drawback in quality.

According to the invention, this is accomplished by a method as described above, wherein said steel grade comprises 0.25 wt% Si; 0.85 wt% Mn and 0.8 wt% 15 Cr with the Cr / C ratio being between 0.78 and 0.87, and that either immediately after casting that steel is rolled or rolled after casting and again without a homogenizing heat treatment.

Surprisingly, it has been found that a steel with a lower carbon and chromium content and a slightly higher manganese content does not exhibit the segregation and formation of primary carbides is found in ASTM A295 52100 steels. This means that it is now possible to roll or roll steel immediately after continuous casting, in which case the steel can be rolled immediately after the slab has been heated without a homogenization treatment.

It is believed that because of a slightly lower carbon content and a significantly reduced chromium content, segregation and primary carbide problems are (substantially) avoided. However, it should be understood that this is only a theory on which the validity of the appended claims does not depend.

Preferably, the steel described above nominally comprises 0.96 wt.% C, 0.25 wt.% Si, 0.85 wt.% Mn and 0.80 wt.% Cr. Such a steel type is also known as ASTM A295 5195. Hardening of this steel can either be achieved by martensitic hardening or surface (induction) hardening.

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The suitability of ASTM A295 5195 steel as a replacement for ASTM A295 52100 is illustrated in Figures 1 and 2 showing martensitic through hardening ability and reaction to temper.

Although the steel described above can be used for all kinds of rolling bearings 5, it is particularly suitable for bearings that are not subject to a heavy load. A particular application is where the life of the bearing is not determined the life of the product in which it is applied, that is to say where the life of the bearing is much longer. Typical examples are rolling bearings for electric motors. However, it should be noted that the present invention is not limited to this application and those skilled in the art will find further application within the scope of the appended claims.

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Claims (7)

1. A method of manufacturing a steel grade comprising providing a steel grade containing 0.9-1.03% by weight C; 0.15-0.35 wt% Si; 0.75-1.00 wt% Mn; 0.70-0.90 wt.% Cr, other Fe and impurities wherein said steel is made by continuous casting followed by rolling, characterized in that said steel comprises 0.25 wt% Si; 0.85 wt.% Mn and 0.80 wt.% Cr, the ratio Cr / C being between 0.78 and 0.87 and that either the steel is rolled immediately after casting or is rolled after casting and reheating without a homogenization heat treatment. The method of claim 1, wherein said steel comprises about 0.96 wt% C. Method according to one of the preceding claims, wherein said steel comprises a rolling bearing steel. A method according to claim 3, wherein a part of said steel is hardened by continuous martensitic hardening or surface induction hardening. A method according to claim 3, wherein the part of said steel type has a hardened martensitic structure. 6. Rolling bearing element manufactured by the method according to any one of the preceding claims. Rolling element bearing according to claim 6, comprising a bearing ring. 10 11 80s