A continuous casting process of the steel containing high Ni for LNG tanks

PURPOSE: A continuous casting method of high nickel contained steel for LNG tanks is provided to secure superior surface and internal qualities in the casting slab state by optimizing refining and continuous casting conditions of the high nickel contained steel when manufacturing high nickel contained steel by continuous casting. CONSTITUTION: In a method for continuously casting a casting slab in a continuous casting machine, the method comprising the processes of refining a steel ingot comprising 0.05 to 0.10 wt.% of C, 0.15 to 0.35 wt.% of Si, 0.50 to 0.80 wt.% of Mn, 0.005 wt.% or less of P, 0.003 wt.% or less of S, 0.020 to 0.060 wt.% of soluble Al, 3.5 to 9.5 wt.% of Ni, a balance of Fe and other impure elements in a converter so that composition of the other impure elements is minimized, degassing the refined molten steel, and injecting the degassed molten steel into tundish and mold, the continuous casting method of high nickel contained steel for LNG tanks comprises the processes of degassing the refined molten steel under a low degree of vacuum for 20 minutes or more so that the refined molten steel contains 30 ppm or less of N; continuously casting molten steel at a casting speed of 1.17 to 1.19 m/min after charging molten steel into tundish as controlling degree of superheat of the degassed molten steel to the range of 13 to 17 deg.C; and cooling the casting slab by spraying cooling water onto casting slab coming out of the mold by continuous casting in the second cooling zone, wherein roll gap of pass line is tapered to 0.19 to 0.20 mm/m from the lower part of the mold to a point where a ratio of solid phase thickness to casting slab thickness in the continuous casting machine is 0.9, and roll gap of pass line in which the casting slab passes through the vicinity of solidification completion is tapered to 2.75 to 2.85 mm/m in the section where solidification fraction is 0.3 to 0.7. LNG 탱크용 고니켈 함유강의 연속주조방법이 제공된다. 본 발명의 방법은, 고Ni함유 용강을 전로 정련하고, 정련된 용강을 탈가스 처리하고, 탈가스 처리된 용강을 턴디쉬 및 몰더에 주입하여 연주기에 의해 주편을 연속주조함에 있어서, 상기 정련된 용강을 그 N함량이 30ppm이하가 되도록 저진공도에서 20분 이상 탈가스처리하는 공정; 상기 탈가스처리된 용강을 과열도를 13~17℃범위로 제어하면서 턴디쉬에 장입한후 1.17-1.19m/min의 속도로 연속주조하는 공정; 및 상기 연속주조에 의해 몰드로부터 빠져나오는 주편을 2차냉각대에서 냉각수를 살수하여 냉각하는 공정을 포함하고, 상기 주편이 통과하는 패스라인(Pass Line)의 롤갭(Roll Gap)을 몰드하단으로부터 연주기내의 고상두께/주편두께 비가 0.9까지는 0.19~0.20 mm/m로 테이퍼 되도록 하고, 그리고 상기 주편이 응고완료 부근을 통과하는 패스라인의 롤갭은 고상율(Solidification fraction)이 0.3~0.7인 구간을 2.75~2.85mm로 테이퍼 되도록 하는 것이다.