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...

AI Technical Summary

Benefits of technology

This patent presents a new type of steel that can be used to make gears and other parts for machines. This steel has a higher hardness after a heat treatment, which makes it better for cold forging and helps it resist wear and corrosion. This results in better performance and efficiency of the machines that use these parts. Additionally, this steel is easier and less expensive to produce, which can help companies improve their products and lower costs.

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 in Patent Document 3 does not consider prevention of crack initiation during cold forging.

Therefore, there is a problem of that cracks initiate from inclusions when large inclusions are present in the portion in which the working ratio increases during cold forging and there is still much room for improvement.

However, there is no description of cold forging in any of the above Patent Documents.

However, there is no description of a technique of improving temper softening resistance.

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