Case hardening steel material with little heat-treatment strain

Abstract

This case hardening steel material has a composition that contains, in mass %, 0.05 to 0.45% of C, 0.01 to 1.0% of Si, more than 0 to 2.0% of Mn, 0.001 to 0.06% of Al, 0.002 to 0.03% of N, more than 0 to 0.1% of S and more than 0 to 0.05% of P with the balance being Fe and unavoidable impurities. In the case hardening steel material, the equi-axed crystal region satisfies the relationships (1) and (2), or the columnar crystal region satisfies the relationship (3). Re = (Ae/Ao) 100 <= 30% (1) (Cmin, 1/Co) >= 0.95 (2) (Cmin, 2/Co) >= 0.95 (3)

Description

technical field [0001] The present invention relates to a case-hardened steel material whose surface layer is hardened by carburizing, carbonitriding or carbonitriding (hereinafter sometimes referred to as "carburizing and nitriding") quenching treatment. This case-hardened steel material is particularly useful as a material for mechanical parts such as gears, shafts, and constant velocity joints of automobiles that require high levels of wear resistance and fatigue resistance. [0002] This application claims priority based on Patent Application No. 2012-014474 for which it applied to Japan on January 26, 2012, The content is used for this application. Background technique [0003] In recent years, from reducing CO 2 From the viewpoint of emission reduction and promotion of energy saving, it is required to reduce the body weight of transportation machines including automobiles and motorcycles, and to improve fuel efficiency. As part of measures to reduce the weight of veh...

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Problems solved by technology

[0014] However, the actual situation is that even if any of the above-mentioned methods and steels are used, it is impossible to achieve low-stress changes that meet the strict requirements of recent consumers.

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