Steel parts for machine structure, material therefor, and method for manufacture thereof

Abstract

Steel parts for a machine structure which have a chemical composition in mass % that C: 0.3 to 0.7 %, Si: 0.3 % or less, Mn: 0.2 to 2.0 %, Al: 0.005 to 0.25%, Ti: 0.005 to 0.1 %, Mo: 0.05 to 0.6 %, B: 0.0003 to 0.006 %, S: 0.06 % or less, P: 0.020 % or less, O: 0.0030 % or less and the balance: Fe and inevitable impurities, has a hardened layer formed by induction hardening at least on a part of the surface thereof, wherein the hardened layer has an average old austenite grain diameter of 7 mum or less and it has non-metal inclusions comprising an oxide having a maximum diameter of 15 mum. The above parts exhibit excellent fatigue strength, and thus are suitable for a drive shaft, a constant-velocity universal joint, and the like.

Description

technical field [0001] The present invention relates to a steel part for mechanical construction, such as an automobile drive shaft or a constant velocity joint, which has a hardened layer formed on its surface by induction hardening, and to a raw material for the steel part and to the production of the steel part Manufacturing method. Background technique [0002] Hitherto, for parts for mechanical construction such as automobile drive shafts or constant velocity joints, hot-rolled steel bars were subjected to hot forging, cutting, cold forging, etc. Fatigue strength, such as torsional fatigue strength, bending fatigue strength, and sliding and rolling contact fatigue strength, which is an important performance of the machine structural member, is imparted to the above-treated member for machine structural use. [0003] In recent years, along with the increasing demand for reducing the weight of automobile parts due to environmental problems, further improvement in the fat...

AI Technical Summary

Problems solved by technology

[0008] However, as in the case above, the latest requirements for fatigue strength cannot be fully met by the above components

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