液化天然气储罐用9Ni超低温钢的冶炼和连铸生产实践

9Ni超低温钢(/%:0.03～0.05C、0.15～0.30Si、0.60～0.70Mn、≤0.003P、≤0.002S、9.0～9.5Ni、0.02～0.04Al)的冶金流程为180 t铁水预处理-180 t复吹转炉-LF-喂硅钙线-RH-180～250 mm板坯连铸。通过转炉出钢时钢包脱磷控制[P]≤0.0015%,LF脱硫使[S]≤0.001%,加铝粒和喂铝线控制[A1]0.02%～0.03%;RH前喂硅钙线RH真空度≤200 Pa,RH处理20 min以控制[N]≤25×10^-6,[H]≤1.0×10^-6;连铸使用电磁搅拌、轻压下和全程保护浇铸工艺,提高铸速使铸坯矫直温度≥950℃,铸坯在300℃缓冷坑40 h,使[P]、[S]、[H]、[N]、[0](/10^-6)分别降至15、9、0.5、26、10,铸坯裂纹率降至0,轧制钢板的无损探伤合格率为100%。

Practice of Melting and Concasting Production of Ultra-Low Temperature Steel 9Ni for Liquefied Natural Gas Tank

The metallurgical flow sheet for ultra-low temperature steel 9Ni（/%:0.03～0.05C,0.15～0.30Si, 0.60～0.70Mn,≤0.003P,≤0.002S,9.0～9.5Ni,0.02～0.04Al） is 180t hot metal pretreatment-180t top and bottom combined blown converter-LF-feeding Si-Ca wire-RH-180～250 mm slab casting.With controlling[P]≤0.0015%by dephosphorizing in ladle during converter tapping,[S]≤0.001%by desulphurizing in LF and controlling[Al]0.02%～0.03%by adding Al bullets and feeding Al wire,RH vacuum≤200 Pa in feeding silicon-calcium wire process before RH process,controlling[N]≤25×l0^-6 and[H]≤1.0×l0^-6 in≤200 Pa vacuum for 20 min during RH refining,using electromagnetic stirring,soft reduction and whole shielding casting process,straightening temperature of slab≤950℃by increasing casting speed,and slab cooling in slow cooling pit furnace at 300℃for 40 h,the[P],[S],[H],[N]and [O](/10^-6) decrease respectively to 15,9,0.5,26 and 10,the crack occurring ratio decreases to 0,and the qualified ratio of nondestructive testing is up to 100%.