重轨钢连铸坯中心偏析的分析和工艺改进

Analysis on Central Segregation of Casting Bloom of Heavy Rail Steel and Process Improvement

研究的重轨钢（/%：0.68~0.73C,0.20~0.30Si,1.05~1.15Mn,≤0.015P,≤0.012S,≤0.003 5 Al,≤0.000 15[H],≤0.006 0[N],≤0.002 0[O]）的冶金流程为铁水脱硫预处理-120 t转炉-LF-RH-280/mm×380 mm坯连铸。分析证实铸坯偏析是钢轨低倍检验和超声波探伤不合格的主要原因。试验研究了钢水过热度、拉速、结晶器电磁搅拌、二冷水量和凝固末端动态轻压下对铸坯中心碳偏析的影响。通过采用优化的工艺措施：钢水过热度15~30℃,拉速0.60~0.75 m/min和恒拉速,结晶器电磁搅拌强度400 A,二冷比水量0.25 L/kg,轻压下6~7mm等,铸坯一般疏松≤1.0级,中心疏松≤0.5级,点状偏析≤0.5级,等轴晶率≥37%,中心碳偏析指数0.94~1.06钢轨超声波探伤合格率提高至99.3%以上。

The metallurgical flow sheet of studied heavy rail steel（/%：0.68-0.73 C,0.20 ~ 0.30 Si,1.05 ~1.15 Mn,≤0.015 P,≤0.012 S,≤0.003 5Al,≤0.000 15[H],≤0.006 0[N],≤0.002 0[O]） is metal desulphurization pretreated-120 t converter-LF-RH-280 mm×380 mm bloom casting.It is identified by analysis that the casting bloom segregation is main cause for unqualified rolled rail by macrostructure examination and supersonic testing.The effect of liquid overheating extend,casting speed,mould magnetic stirring,secondary water cooling rate and dynamic soft reduction at end of solidification on center carbon segregation of casting bloom is tested and studied.With using the optimized process measures including controlling liquid overheating extent 15 ~ 30 ℃,casting speed 0.60 ~ 0.75 m/min and constant speed casting,mould magnetic stirring intensity 400 A,secondary water cooling rate 0.25 L/kg and soft reduction 6 ~ 7mm,the rating of general porosity ≤1.0,of center porosity ≤0.5,of spot segregation ≤0.5,the ratio of equiaxed zone is more than 37%,the center carbon segregation index is 0.94 ~ 1.06 and the qualified ratio of steel rail tested by supersonic method increases up to more than 99.3%.