在某宽厚板的等离子切割工序中,其板厚1/2处产生中心裂纹。采用宏观观察、化学成分分析、金相检验、扫描电镜及能谱分析、硬度测试等方法分析该钢板开裂的原因。结果表明:在钢板1/2 厚度处存在明显的偏析带,基体和偏析带的显微组织分别为回火马氏体和淬火马氏体,在偏析带中分布有长条状夹杂物,裂纹从夹杂物处萌生并扩展;等离子切割后的淬硬层硬度较大,具有很大的淬硬倾向,在热应力和组织应力的作用下,钢板最终开裂。

In the plasma cutting process of a wide and thick plate, a central crack was generated at 1/2 thickness of the plate. The causes of cracking of the steel plate were analyzed by means of macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscope and energy spectrum analysis and hardness test. The results show that there was an obvious segregation band at 1/2 thickness of the steel plate. The microstructures of the matrix and the segregation band were tempered martensite and quenched martensite, respectively. There were long strip inclusions in the segregation band, and the cracks initiated and propagated from the inclusions. The hardened layer after plasma cutting had a large hardness and a great tendency to harden. Under the action of thermal stress and structural stress, the steel plate eventually cracked.