The case hardening steel and the production mannered null mass which are superior in bulky grain prevention property and fatigue property

摘要

PROBLEM TO BE SOLVED: To provide case hardening steel in which the generation of coarse grains can be stably suppressed in a carburizing quenching stage, the generation of strain and bending after the carburizing quenching can be prevented, further, the generation of coarse grains can be prevented even in high temperature carburizing, and sufficient strength properties such as rolling fatigue strength can be obtained, and to provide its production method.;SOLUTION: Steel in which 0.05 to 0.2% Ti and the other specified components are comprised in specified ranges, the content of N is limited to 0.0051%, or further, 0.04% Nb is comprised, the precipitation amount of AlN after hot rolling is limited to ≤0.01%, or further, the structural fraction of bainite after the hot rolling is limited to ≤30%, or further, the ferrite crystal grain size number after the hot rolling is controlled to No. 8 to 11 prescribed in JIS G0552, or further, in the cross-section in the longitudinal direction in the matrix after the hot rolling, the maximum diameter of Ti based precipitates by the statics of the extremes measured under the following conditions is controlled to ≤40 μm is produced.;COPYRIGHT: (C)2005,JPO&NCIPI