低碳钢开裂原因及轧制工艺参数研究

Study on cracking cause and rolling process parameters of low carbon steel

钢铁厂采用Q215带钢卷制方管时,在折弯处易发生严重开裂。为了降低钢管开裂率,从钢管显微组织和钢中夹杂物2个方面分析了钢管角部开裂的原因,通过探讨组织相变对中低碳钢冷变形性能的影响机理,制定合理的热轧和轧后冷却工艺参数,利用光学显微镜和扫描电镜分析了Q215钢中夹杂物和显微组织的性质,并利用J Mat Pro软件计算Q215钢的相变点、CCT和TTT曲线。结果表明:钢管开裂的主要原因是钢中存在沿着铁素体晶界析出的三次渗碳体,三次渗碳体属于硬脆相,在折弯变形时引起晶界处应力集中而产生裂纹;开裂的次要原因是钢中存在100μm以上的大尺寸硫化物夹杂。设置合理的调整热轧和冷却工艺参数,可以明显减少钢中三次渗碳体数量,增加了珠光体数量,显著降低钢管开裂率,为预防Q215及类似钢种的加工开裂提供参考依据。

When Q215 strip steel is used to coil square tube in iron and steel plant,serious cracking is easy to occur at bending point.In order to reduce the cracking rate of the steel pipe,the causes of the corner cracking of the steel pipe were analyzed from two aspects of the microstructure and the inclusions in the steel pipe.The influence mechanism of the microstructure transformation on the cold deformation properties of medium-carbon and low-carbon steel was discussed.The reasonable hot rolling and cooling processes after rolling were formulated.The properties of the inclusions and microstructure in Q215 steel were analyzed by optical microscope and scanning electron microscope.The transformation point,CCT and TTT curves of Q215 steel were calculated by J Mat Pro software.The results show that the main reason for the cracking of the steel pipe is the existence of ter-tiary cementite precipitated along the ferrite grain boundary in the steel,which belongs to hard brittle phase and causes stress concentration at the grain boundary during bending deformation,and the secondary reason for the cracking is the existence of large-size sulfide inclusions more than 100μm in the steel.By adjusting the hot rolling and cooling process parameters,the amount of tertiary cementite in the steel is significantly reduced,the amount of pearlite is increased,and the cracking rate of the steel pipe is significantly reduced.The research results provide a reference for preventing the processing cracking of Q215 and similar steel grades.