CASE HARDENING STEEL HAVING EXCELLENT COLD FORGEABILITY WITH SUPPRESSABLE ABNORMAL GRAIN GROWTH UPON CARBURIZING

PROBLEM TO BE SOLVED: To provide a case hardening steel which has excellent cold forgeability and in which the occurrence of abnormal grains can be prevented in surface hardening heat treatment such as carburizing and carbo-nitriding.SOLUTION: There is provided the case hardening steel which contains prescribed amounts of C, Si, Mn, P, S, Cr, Al, N, Ti and B, and in which: the density of Ti-containing carbides and carbonitrides having an equivalent circle diameter of 10 nm or greater but less than 200 nm is 10/μmor greater; and the density of Ti- and S-containing deposits having an equivalent circle diameter of 200 nm or greater is 0.2/μmor less. The case hardening steel has metal structure which is a pearlite/ferrite mixed structure, with the area ratio of the mixed structure being 80% or greater, the area ratio of the pearlite being 25% or less of the entire metal structure, and the area ratio of pearlite having an equivalent circle diameter of 100 μm or greater being 10% or less of the entire metal structure. 【課題】冷間鍛造性に優れており、かつ浸炭処理や浸炭窒化処理等の表面硬化熱処理において異常粒発生を防止できる肌焼鋼を提供すること。【解決手段】本発明の肌焼鋼は、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ｃｒ、Ａｌ、Ｎ、Ｔｉ、Ｂを所定量含有すると共に、Ｔｉを含有する円相当直径１０ｎｍ以上２００ｎｍ未満の炭化物、および炭窒化物の密度が１０個／μｍ2以上、Ｔｉ、およびＳを含有する円相当直径２００ｎｍ以上の析出物の密度が０．２個／μｍ2以下であり、金属組織が、パーライトフェライト混合組織であり、該混合組織の面積率が８０％以上であって、パーライトの面積率が金属組織全体に対して２５％以下であり、かつ円相当直径が１００μｍ以上のパーライトの面積率が金属組織全体に対して１０％以下であること。【選択図】図１