低合金钢Q355B加工开裂原因分析及改善

ANALYSIS AND IMPROVEMENT OF CRACKING CAUSES OF LOW ALLOY STEEL Q355B PROCESSING

针对Q355B钢板加工过程中开裂问题,分析了缺陷试样的化学成分、力学性能、金相组织和电镜夹杂物等。认为:钢板内部大量的MnS夹杂以及芯部严重的带状组织,是导致钢板加工开裂的主要原因。通过分析MnS夹杂和带状偏析产生的原因,提出了在不改变原有成分的前提下,通过增加LF钙处理用量,对硫化物夹杂改质,采用LF炉造渣工序前移,严格保证净吹时间≥6 min;连铸机全程恒定拉速控制,减少夹杂物数量,改善夹杂物形貌。连铸工序通过实施低过热度浇注,避免出现铸坯凝固“搭桥”现象;同时优化设备冷却效果,避免因出现坯壳鼓肚变形而加重偏析程度;采用合适电磁搅拌、动态轻压下技术减少铸坯中心偏析程度,提高钢板内部质量。通过一系列工艺优化,夹杂物含量得到有效控制,铸坯中心偏析程度进一步弱化,加工开裂问题得到解决。

Aiming at the cracking problem during the processing of Q355B steel plate,the chemical composition,mechanical properties,metallographic structure and electron microscopy inclusions of the defective specimen were analyzed.It is believed that a large number of MnS inclusions inside the steel plate and the serious band structure of the core are the main reasons for the cracking of the steel plate processing.By analyzing the causes of MnS inclusion and band segregation,it is proposed that the net blowing time≥6 min is strictly guaranteed by increasing the amount of LF calcium treatment and modifying the sulfide inclusion.The constant pull speed control of the continuous casting machine reduces the number of inclusions and improves the morphology of inclusions.The continuous casting process avoids the phenomenon of"bridging"of casting billet solidification by implementing low superheat pouring;At the same time,the cooling effect of the equipment is optimized to avoid aggravating the degree of segregation due to the deformation of the bulge belly of the blank shell;Suitable electromagnetic stirring and dynamic soft reduction technology are used to reduce the degree of segregation in the center of the casting blank and improve the internal quality of the steel plate.Through a series of process optimizations,the inclusion content is effectively controlled,the segregation degree of casting billet center is further weakened,and the processing cracking problem is solved.