Q355NE风电用钢探伤不合格原因分析

Cause Analysis on Disqualification of Flaw Detection for Q355NE Wind Power Steel

通过对在线探伤不合格的Q355NE钢板进行人工探伤,精确定位探伤不合格所在缺陷的位置,利用光学显微镜、电子显微镜,对探伤不合格处的组织及缺陷进行分析。结果表明,Q355NE风电钢探伤不合格对应的缺陷为钢板心部的微裂纹,心部微裂纹区域的组织为塑性较差的马氏体和贝氏体,马氏体和贝氏体的形成是由C、Mn元素偏析导致的。同时,在裂纹处发现有长条状的MnS夹杂物和呈链状分布的钛、铌化合物,它们与基体的界面结合能低,破坏了基体的连续性,在应力的作用下容易萌生裂纹。通过改善铸坯凝固过程中的偏析和采用钢板下线缓冷的方式,避免了心部的微裂纹,提高了风电钢探伤的合格率。

The locations of disqualification of flaw detection for defects are accurately positioned through manual flaw detection of Q355NE plates with disqualification of online flaw detection as well as the microstructure and defects of the locations of disqualification of flaw detection are analyzed with optical microscope and electron microscope.The results showed that the defect corresponding to disqualification of flaw detection for Q355NE wind power steel was the microcrack in the center of steel plate,microstructure of the microcrack area in the center was martensite and bainite with poorer plasticity,which was caused by segregation of C and Mn.At the same time,MnS inclusions with long strip shape as well as compound of titanium and niobium distributed in chain are found at the crack.The interfacial bonding energy of them and matrix is low,continuity of matrix is destroyed so that cracks are easily initiated with the effects of stress.The microcracks in the center are avoided and qualification rate of flaw detection for wind power steel is increased by improving the segregation during solidification process of casting blank and adopting the mode of offline slow cooling of steel plate.