Bearing part, steel for bearing part and method for producing thereof

Abstract

A bearing part according the present invention includes: C: 0.95% to 1.10%; Si: 0.10% to 0.70%; Mn: 0.20% to 1.20%; Cr: 0.90% to 1.60%; Al: 0.010% to 0.100%; N: 0.003% to 0.030%; P: 0.025% or less; S: 0.025% or less; O: 0.0010% or less; optionally one or more of the group consisting of Mo: 0.25% or less, B: 0.0050% or less, Cu: 1.0% or less, Ni: 3.0% or less, and Ca: 0.0015% or less; and a remainder including Fe and impurities; wherein a metallographic structure includes a retained austenite, a spherical cementite and a martensite; in which an amount of the retained austenite is 18% to 25%, by volume %; an average grain size of a prior-austenite is 6.0 μm or less; an average grain size of the spherical cementite is 0.45 μm or less; and a number density of the spherical cementite is 0.45×106 mm−2 or more in the metallographic structure.

Description

TECHNICAL FIELD OF THE INVENTION[0001]The present invention relates to a bearing part such as needle bearings, roller bearings and ball bearings, steel for a bearing part which is a material for the bearing part, and a method for producing thereof.[0002]Priority is claimed on Japanese Patent Application No. 2014-3338, filed on Jan. 10, 2014, and Japanese Patent Application No. 2014-84952, filed on Apr. 16, 2014, the contents of which are incorporated herein by reference.RELATED ART[0003]Bearing parts such as needle bearings, roller bearings and ball bearings are continually used under a situation where a foreign material such as burr or abrasion powder is mixed into lubricating oil, that is, are continually used even in contaminated environments. Therefore, it is important to improve rolling contact fatigue life of a bearing part in contaminated environments. In order to improve the rolling contact fatigue life of the bearing part in contaminated environments, it is known that an in...

AI Technical Summary

Benefits of technology

The present invention provides a method for improving the rolling contact fatigue life of bearing parts by controlling the average grain size of prior-austenite, the amount of retained austenite, and the number density of spherical cementite. Additionally, the invention provides a method for achieving this without performing carburizing, nitriding, and spheroidizing annealing for a long period of time. The method also involves performing spheroidizing annealing for a short amount of time and once, even in contaminated environments. The resulting steel material for bearing parts can also be obtained by controlling the metallographic structure. This invention can extend the life of machines and reduce manufacturing costs, making it significant for the industry.

Problems solved by technology

However, there are some problems that not only a surface treatment such as carburizing or nitriding for the steel for the bearing parts is high cost, but also a variation in qualities of a bearing part occurs due to the influence of variations in the treatment atmosphere.

As a result, a supercooled structure such as martensite is generated during cooling after hot rolling, and the workability, ductility and toughness of hot rolled wire rod is deteriorated.

However, in the method disclosed in Patent Document 2, spheroidizing at high temperature is performed for long period of time.

As a result, C is solid-soluted into an austenite phase and the number density of spherical cementite is insufficient.

Furthermore, the grain size of austenite is coarsened and an improvement effect of rolling contact fatigue life cannot be obtained sufficiently.

Since the treatment time of spheroidizing annealing is long, when the number of times of the annealing is increased, it is known that production efficiency is deteriorated by increasing a manufacturing cost.

However, the method disclosed in the Patent Document 4 is not intended to shorten the treatment time of the spheroidizing annealing.

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