| 摘要 |
PROBLEM TO BE SOLVED: To obtain a case hardening steel having high-deformability and low deformation resistance and excellent in cold workability as hot-rolled by setting the area ratio and average grain size of ferrite occupied in the metallic structure after hot rolling to specified falue. SOLUTION: This steel has a compsn. obtd. by being added with, by mass, <=8.0% Cr, <=2.0% Mo, <=2.0% V, <=2.0% Nb and <=2.0% Ti (0% not included in any cases), and in which the value of A expressed by the following formula is regulated to >=3.0: A=[Cr]+3[Mo]+5[V]+4[Nb]+4[Ti], where [X] denotes the mass % of the element X. Or, it has a compsn. contg. <2.5% Ni, <1.0% Cu or specified small amounts of one or more kinds among S, Ca, Zr, Pb, Te, Sb and Se. This case hardening steel excellent in cold workability is the one in which the area ratio of ferrite occupied in the metallic structure of the steel after hot rolling is regulated to >=90%, and moreover, the average grain size of ferrite is regulated to <=40μm.
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