120 t BOF-LF-RH-410 mm×530 mm大方坯连铸18CrNiMo7-6钢的工艺实践

Practice of Steel 18CrNiMo7-6 Bloom by Process of 120 t BOF-LF-RH-410 mm × 530 mm Continuous Casting

采用铁水+废钢-120 t转炉-LF-RH-410 mm×530 mm大方坯连铸-步进式加热炉-750轧机轧制-退火的流程生产规格Φ115～250 mm 18CrNiMo7-6(/%:0.15～0.19C,0.25～0.40Si,0.40～0.60Mn,1.50～1.80Cr,1.40～1.70Ni,0.25～0.35Mo,≤0.020P,≤0.020S,0.020～0.040Al,0.010 0-0.020 0N)。通过控制出钢预脱氧和合金化,深真空时间≥15 min,软吹氮气,控制中间包钢水过热度,拉速0.48 m/min,全过程Ar气保护,连铸M-EMS和F-EMS,轧制后退火等工艺措施,生产的产品宏观夹杂物检测含量≤20 mm/dm^3,碳中心偏析指数≤1.10,晶粒度≥7级,钢材各项指标满足协议要求。

The steel grade 18CrNiMo7-6 with diameter of Φ115 ~250 mm round from process route of hot metal +scrap-120 t BOF-RH-410 mm×530 mm continuous casting-bloom heating by walking forward heating furnace-750 rollingannealing.Its chemical composition is(/%: 0.15~0.19 C,0.25 ~0.40 Si,0.40~0.60 Mn,1.50~1.80 Cr,1.40 ~1.70 Ni,0.25 ~0.35 Mo,≤0.020 P,≤0.020 S,0.020~0.040 A1,0.010 0~0.020 0 N).Through deoxidization and alloy addition during tapping, deep vacuum degassing not less than 15 minutes, soft bubbling with Nitrogen, super heat control in tundish, casting speed of 0.48 m/min, full process argon protection and applications of F-EMS and M-EMS, annealing after rolling etc., the final product’s macro-inclusion not more than 20 mm/dm^3, carbon center segregation not more than1.10 and grain size finer than 7, which meet the specification requirements.