Steel for mechanical structures and induction hardened steel parts

Abstract

The chemical components of this steel for mechanical structures include, in mass%, C: 0.40 to 0.70%, Si: 0.15 to 3.00%, Mn: 0.30 to 2.00%, Cr: 0.01% or more but less than 0.50%, S: 0.003 to 0.070%, Bi: more than 0.0001% but not more than 0.0050%, N: 0.0030 to 0.0075%, Al: 0.003 to 0.100%, P: 0.050% or less, and B, Mo, Ni, Cu, Ca, Mg, Zr, Rem, Ti, Nb, V, Sb, Te, and Pb as necessary, the balance being Fe and impurities. Both 290*C + 50*Si + 430>=620 and d + 3sigma<20 are satisfied. In a cross section parallel to the longitudinal direction, the density of MnS having an equivalent circle diameterof less than 2.0 mu m is 300 / mm2 or more.

Description

technical field [0001] The present invention relates to structural steel and high-frequency quenched steel parts, and in particular to power transmission parts (such as gears, bearings, CVT pulleys, shafts, etc.) Induction hardened steel parts used in, etc.) and mechanical structural steel as its raw material. [0002] this application claims priority based on Japanese Patent Application No. 2015-205631 for which it applied in Japan on October 19, 2015, and uses the content here. Background technique [0003] In the past, power transmission parts such as gears were often used after surface hardening treatment. As a surface hardening method, carburizing, nitriding, or induction hardening is used. Among them, "carburizing" is a method of hardening the surface by carbonizing the surface layer of a material with high toughness in the base (base material), and it is mainly used in gears and CVTs for automobiles in order to improve fatigue strength (surface fatigue strength). O...

AI Technical Summary

Problems solved by technology

Patent Document 3 shows that the machinability of the steel for induction hardening is improved, but since no comparative study of the machinability of the steel of the invention and that of the case-hardened steel has been conducted, whether it is possible to obtain a steel that is as good as that of the case-hardened steel Machinability is not clear

In addition, in Patent Document 3, since the Al content needs to be set to exceed 0.100%, it is difficult to complete the transformation to austenite during high-frequency heating, and there is a possibility that the hardenability may be lowered.

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