Casting Method for Bi-S free cutting steel

PURPOSE: A casting method for suppressing formation of pin holes and blow holes inside casting slab by controlling concentration of dissolved oxygen in molten low carbon Bi-S free cutting steel is provided. CONSTITUTION: The casting method for Bi-S free cutting steel comprises the process of casting molten steel comprising 0.05 to 0.21 wt.% of carbon (C), 0.5 to 2.0 wt.% of manganese (Mn), 0.04 to 0.40 wt.% of sulfur (S), 0.01 to 0.1 wt.% of phosphorus (P), 0.03 to 0.30 wt.% of bismuth (Bi), 0.02 wt.% or less of silicon (Si), 0.003 to 0.009 wt.% of nitrogen (N), 0.005 wt.% or less of soluble aluminum (Al), and 0.003% or less of oxygen (O) or 0.003 to 0.005% of oxygen (O) and 0.0040 to 0.0100% of boron (B) at a temperature of 1,550 to 1,600 deg.C. 본 발명은 정밀부품, 기계구조용 등으로 사용되는 쾌삭강 주편에서 발생되는 기공(pin hole and blow hole)의 생성을 억제하는 주조방법에 관한 것이다. 이 주조방법은 중량%로 탄소(C):0.05~0.21%, 망간(Mn):0.5~2.0%, 유황(S):0.04~0.40%, 인(P):0.01~0.1%, 비스무스(Bi):0.03~0.30%, 실리콘(Si):0.02%이하, 질소(N): 0.003~0.009%, 고용 알루미늄(soluble Al):0.005%이하이고, 여기에 (1) 산소농도:0.003% 이하, 또는 (2) 산소농도:0.003~0.005% 이하와 보론:0.0040~0.0100% 이하의 조건을 만족하는 용강을 1550~1600℃에서 주조하는 것을 포함한다.