中碳高锰钢铸坯纵裂原因分析及工艺优化

Cause analysis and process optimization of longitudinal crack in medium carbon high manganese steel billet

针对中碳高锰钢大方坯容易出现表面纵裂纹的问题,采用扫描电镜对裂纹形貌进行观察,利用能谱分析仪对裂纹微区成分进行分析。根据钢种成分用热力学理论分别计算AlN和TiN析出温度,采用热力学模拟软件Thermo-Calc,模拟计算冷却过程相变,为分析连铸坯纵裂提供理论依据。制定工艺优化措施,对钢液进行钛合金化处理,LF离站加入0.040%的w(Ti);真空处理降低钢水中w(N)至0.005%~0.008%;连铸结晶器宽面和窄面的冷却水量分别由850、700 L/min降为750、650 L/min,二冷水量由0.20 L/kg降为0.17 L/kg。通过以上措施,使中碳高锰钢连铸坯纵裂纹得到消除。

In view of the problem of the surface longitudinal cracks on the bloom of medium carbon high manganese steel,the crack morphology was observed by SEM,the composition of the crack micro area was analyzed by energy spectrum analyzer. The precipitation temperature of Al N and Ti N was calculated by thermodynamic theory according to the steel composition,and the transformation of cooling process was simulated by Thermo-Calc soft ware to provide theoretical basis of analyzing the longitudinal crack of continuous casting bloom. During the optimization process,the liquid steel was titanium alloyed,and w( Ti)= 0. 040 % at the end of LF. The nitrogen mass fraction of molten steel reduced to 0. 005 % ~ 0. 008 %by vacuum treatment. The cooling water flow rate of wide and narrow sides of mould decreased from 850,700 L/min to 750,650 L/min,respectively. And the secondary cooling water volume changed from 0. 20 L/kg to 0. 17 L/kg. Through the above measures,the longitudinal crack of the continuous casting slab of medium carbon high manganese steel was eliminated.