稀土对Cr12MoV钢VD工序夹杂物演变的影响

Effect of Rare Earth on Inclusions Evolution of Cr12MoV Steel during VD Process

对国内某钢厂EAF→LF→VD→模铸工艺生产的Cr12MoV钢,VD工序不同时点进行取样,利用ASPEX自动扫描电镜分析统计钢中非金属夹杂物的成分、数量、尺寸等信息。结果表明,钢中夹杂物类型及形貌的演变主要受稀土元素的影响,稀土(La、Ce)添加量为134×10-6,稀土能与钢液中的[O]、[S]结合,置换氧化物类夹杂中的氧和硫化物类夹杂中的硫,将其转变为球状或近球状的RE2O3、RE2S3、RE2O2S,并能与钢液中的[O]、[Al]结合生成REAlO3;夹杂物数量及尺寸的演变与VD工序软吹时间有关,当软吹时间控制在26~45 min时,钢中夹杂物数量和尺寸均随软吹时间的增加不断减小,软吹时间增至55 min时夹杂物尺寸仍在减小但数量有所增加,且主要表现为Al2O3和REAlO3类数量的增加。综合钢种用途,考虑夹杂物改性及VD工序成本,在此稀土添加量情况下,Cr12MoV钢VD工序最佳软吹时间应控制在33~45 min。

For Cr12 MoV steel produced by a domestic steel plant via EAF→LF→VD→die casting process,the amount of rare earth(La,Ce)added is 134×10-6,and the samples is taken from liquid steel during VD process at different times.ASPEX automatic scanning electron microscope was used to analyze the composition,quantity and size of non-metallic inclusions in steel.It is found out that rare earth can improve the type and morphology of inclusions in steel,and transform more than 60%of irregular oxide and sulphide inclusions into spherical or ellipsoidal rare earth inclusions.The influence of rare earth on the amount and size of inclusions is related to the soft blowing time of the VD process.When the soft blowing time is controlled at 26 min^45 min,the number and size of inclusions in the steel are continuously reduced with the increase of soft blowing time.When the soft blowing time is prolonged to 55 min,the size of inclusions is still decreasing but the number is increasing,in particular to Al2O3 and REAlO3 types.Considering the cost for inclusion modification and VD process for studied steel with 134×10-6 rare earth(La,Ce)added,the optimal soft blowing time of the Cr12 MoV steel VD process should be controlled between 33~45 minutes.