热连轧高碳带钢65Mn边裂原因分析及改进

Cause analysis and improvement of edge crack in hot continuous rolling high carbon strip steel 65Mn

高碳钢65Mn由于碳含量高、硬度大,在热轧生产中易出现边部开裂缺陷。为彻底解决高碳钢65Mn边裂问题,采用断口分析、金相组织观察、硬度检测等方法,分析了热轧高碳钢65Mn边裂缺陷的成因,并通过热模拟试验,研究了不同冷却速率对65Mn钢相变过程的影响。结果表明,冷却速率显著影响65Mn钢相变过程,当冷却速率大于25℃/s时会发生马氏体相变。在热轧生产过程中,带钢边部过冷形成马氏体,马氏体硬度高,变形能力差,在卷取张力作用下,边部易产生开裂缺陷。通过减弱层流冷却强度、提高卷取温度和减少边部侧喷水等措施可有效改善带钢边部过冷问题,从而避免边裂缺陷的产生,并改善其组织和硬度均匀性。

High carbon steel 65Mn is prone to edge cracking defects in hot rolling production due to its high carbon content and high hardness.In order to completely solve the edge crack problem of high carbon steel 65Mn,the cause of edge crack defect in hot-rolled high carbon steel 65Mn was analyzed by means of fractography,metallography and hardness examination.Thermal simulation test was also carried out to study the effect of cooling rate on the transformation behavior of 65Mn.The results show that cooling rate significantly affects the phase transformation process of 65Mn steel,and martensitic transformation occurs when the cooling rate is greater than 25℃/s.Martensite has high hardness and poor deformation ability.During hot rolling,the edges of strip with martensite microstructure due to a high-rate cooling tend to form cracks under the effect of coiling tension.Improvement measures,such as reducing laminar cooling intensity,increasing coiling temperature and reducing side water spraying,can effectively prevent the edges from overcooling,thereby avoiding edge cracks and improving the uniformity of microstructure and hardness.