Steel for case hardening which has excellent cold workability and machinability and which exhibits excellent fatigue characteristics after carburizing and quenching, and process for production of same

摘要

Provided is a steel for case hardening, which is to be subjected to cold working, machining, and carburizing and quenching, and in which the occurrence of coarse particles is prevented. The steel for case hardening has excellent cold workability and machinability and further exhibits excellent fatigue characteristics after carburizing and quenching. The steel for case hardening is characterized by: containing, by mass, 0.001 to 0.15% of S, 0.05 to 0.2% of Ti, at most 0.04% of Al, at most 0.0050% of N, and specific amounts of other specific components, and further containing at most 0.003% of Mg, and/or at most 0.01% of Zr, and/or at most 0.005% of Ca; having a content of precipitated AlN of 0.01% or less; and satisfying the relationship: d ≤ 1700[S]+20 [wherein d is the density (particles/mm) of sulfides which have equivalent circle diameters exceeding 20μm and aspect ratios exceeding 3; and [S] is the content (mass%) of S].