강재

화학 조성이, 질량%로, C：0.01~0.10%, Si：0.04~0.40%, Mn：0.50~1.50%, Cu：0.10~0.50%, Sb：0.01~0.30%, Al：0.005~0.050%, Mo＋W：0.01~0.30%, P：0.020% 이하, S：0.0005~0.015%, N：0.005% 이하, O：0.0005~0.0035%, Ni：0~0.30%, Sn：0~0.50%, As：0~0.30%, Co：0~0.30%, Cr：0~0.70%, Ti：0~0.050%, Nb：0~0.10%, V：0~0.10%, Zr：0~0.050%, Ta：0~0.050%, B：0~0.010%, Mg：0~0.010%, REM：0~0.010%, 잔부：Fe 및 불순물이며, Si/Al：6.0~16.0, AI：0.06~0.21, EI：2.5~6.0, Ceq：0.180~0.330이며, 강재 중에 MnS 및 MnS 산화물을 포함하고, MnS의 개수 밀도가 50/mm2 미만이며, MnS의 개수 밀도에 대한, MnS 산화물의 개수 밀도의 비가 0.10 이상인, 강재. A steel material in which: the chemical composition contains, in terms of mass%, 0.01-0.10% of C, 0.04-0.40% of Si, 0.50-1.50% of Mn, 0.10-0.50% of Cu, 0.01-0.30% of Sb, 0.005-0.050% of Al, 0.01-0.30% of Mo + W, 0.020% or less of P, 0.0005-0.015% of S, 0.005% or less of N, 0.0005-0.0035% of O, 0-0.30% of Ni, 0-0.50% of Sn, 0-0.30% of As, 0-0.30% of Co, 0-0.70% of Cr, 0-0.050% of Ti, 0-0.10% of Nb, 0-0.10% of V, 0-0.050% of Zr, 0-0.050% of Ta, 0-0.010% of B, 0-0.010% of Mg, and 0-0.010% of REM, the balance being Fe and impurities; Si/Al is 6.0-16.0, Al is 0.06-0.21, El is 2.5-6.0, and Ceq is 0.180-0.330; MnS and MnS oxide are contained in the steel material; and the number density of the MnS is less than 50/mm2, and the ratio of the number density of the MnS oxide to the number ratio of the MnS is 0.10 or higher.