提高齿轮钢8620RH( K)末端淬火内控符合率的工艺实践

齿轮钢8620RH(K)(/%:0.18～0.22C,0.17～0.26Si,0.70～0.90Mn,≤0.025P,0.015～0.025S,0.4～0.6Cr,0.4～0.7Ni,0.15～0.25Mo,0.015～0.045Al,≤0.010 0N)的冶炼流程为60 t BOF-LF-VD-300 mm×360mm铸坯。分析了工艺改进前BOF终点残余元素,出钢量,精炼合金调整量,VD增N方式和铸坯C偏析,得出BOF出钢量不稳定、中间包钢水过热度高、内控成分合格率低,铸坯C偏析指数高是导致末端淬火试验AHRC值4～5带宽符合率偏低的主要因素。通过稳定转炉装入量和出钢量,LF吹氮气增氮,空置红钢包加盖,控制中间包钢水过热度15～25℃,优化连铸电磁搅拌参数等工艺措施,使8620RH(K)钢末端淬火内控符合率由原<60%提高至82.93%。

Process Practice to Increase Qualified Rate of Internal-Controlled End-Quenched Hardenability of Gear Steel 8620RH(K)

The steelmaking flowsheet of gear steel 8620RH ( K) (/% ： 0.18 ~0.22C, 0. 17 ~0. 26Si, 0.70 ~ 0. 90Mn,≤0.025P, 0.015 ~ 0.025S, 0.4 ~0.6Cr, 0.4 ~0.7Ni, 0.15 ~0.25Mo, 0.015 ~ 0.045A1, ≤0.0100N) is 60 t BOF-LF-VD-300 mm x360 mm casting bloom. The BOF end residual elements and tapping amount of steel, alloying adding amount in refining process, adding N method in VD process and carbon segregation of casting bloom in original process have been analyzed, it is obtained that the main causes of hardenability band width AHRC 4 ?5 being on low side in end-quench test are BOF liquid tapping amount not stable, higher superheating temperature extent of liquid in tundish, lower qualified rate of internal controlled compound of liquid and higher casting bloom carbon segregation index. With using the process measures including stabilizing BOF charging and tapping amount, blowing nitrogen to increase nitrogen in liquid in LF, idle hot ladle adding covering plate, controlling tundish liquid supeiheating temperature 15 ~25 ℃., and optimizing casting electromagnetic stirring parameters, the qualified rate of internal-controlled end-quenched hardenability of steel 8620RH(K) increases from original <60% to 82.93%.