Case-hardening steel and case-hardened steel member

Abstract

There is provided a case-hardening steel in which in inclusion evaluation using an extreme value statistical method, when an estimated area S is 30,000 mm², an estimated value of the maximum size (√area)_S of sulfide-based inclusions present in the estimated area S is 49 μm or less and an estimated value of the maximum size (√area)_Ox of oxide-based inclusions present in the estimated area S is 80 μm or less, and the number of sulfide-based inclusions having a length of more than 20 μm and a thickness of more than 2 μm per 1 mm² is limited to 200 or less,

Description

TECHNICAL FIELD OF THE INVENTION[0001]The present invention relates to a case-hardening steel and a case-hardened steel member, and particularly to a case-hardening steel, which has excellent cold forgeability and capable of obtaining excellent temper softening resistance after a carburizing treatment or a carbonitriding quenching and tempering treatment, and is suitable for components for automobiles, construction machines, and industrial machines, and a case-hardened steel member.[0002]Priority is claimed on Japanese Patent Application No. 2013-087857, filed Apr. 18, 2013, the content of which is incorporated herein by reference.RELATED ART[0003]Transmission gears used in automobiles, construction machines, etc. and reduction gears used in industrial machines, etc. are mainly configured by gears. These components can be obtained by using a medium carbon alloy steel such as JIS SCr 420, JIS SCM 420, etc. as a material, forming the material into the shape of a component by hot forgi...

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Benefits of technology

[0064]According to the embodiments of the present invention, it is possible to provide a case-hardening steel having higher hardness of a carburized layer after tempering at 300° C. than the hardness of JIS SCr 420 or JIS SCM 420 and excellent cold forgeability and a case-hardened steel member. That is, it is possible to provide a case-hardening steel having excellent tem

Problems solved by technology

The problem when the cold forging is performed is to prevent cracks from initiating during the cold forging and improve die life.

However, in recent years, along with the expansion of application of hard shot peening capable of rapidly increasing tooth root bending fatigue strength, the main point of the problem to achieve high-strengthening of gears is shifted from improvement of tooth root bending fatigue strength to improvement of pitching strength.

However, the technique disclosed

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