355 MPa级别低合金钢板边部裂纹的原因与改进措施

Reason Analysis and Improvement Measures for Edge Cracks in 355 MPa Low Alloy Steel Plate

针对355 MPa级别低合金钢板边部出现微裂纹问题,采用金相组织分析及扫描电镜检验等技术手段,对其裂纹成因进行研究分析。结果表明,钢基体组织为珠光体+铁素体,晶粒度约9.5级,成分、组织均符合标准要求;裂纹深度30~70μm,裂纹周边晶粒明显长大,存在氧化铁皮及Si-Mn氧化物析出。综合分析认为连铸坯的角部存在原始横裂纹,经加热炉二次加热,造成表面脱碳及氧化物析出,是诱发终端钢板产品边角裂纹的主要原因。实际生产中,严控钢水浇筑过热度,合理控制拉坯速率,采用结晶器非正弦有序振动,并对出现问题的连铸坯及时下线缓冷精整,强化铸坯边角处氧化铁皮等杂质及缺陷吹扫清理质量,可有效避免该类问题。

In response to the problem of micro cracks appearing at the edges of 355 MPa grade low alloy steel plates,metallographic structure analysis and scanning electron microscopy inspection were used to study and analyze the causes of the cracks.The results show that the microstructure of the steel matrix is pearlite plus ferrite,with a grain size of about grade 9.5 levels.The composition and structure meet the standard requirements.Crack depth is 30-70μum.The grains around the crack grow significantly,and there are iron oxide scales and Si-Mn oxide precipitates.Based on comprehensive analysis,it is believed that there are original transverse cracks at the corners of the continuous casting slab.After secondary heating by the heating furnace,surface decarburization and oxide precipitation are the main reasons for inducing edge and corner cracks in terminal stel plate products.In actual production,strict control of the superheat of molten steel casting,reasonable control of the casting speed,use of non sinusoidal ordered vibration of the mold,and timely offline slow coling and finishing of the problematic continuous casting slab can effectively avoid such problems by strengthening the quality of impurities and defects such as iron oxide scales at the edges and corners of the slab,and blowing and cleaning.