Si-Mn-Mo系低碳贝氏体钢焊接热影响区的脆化机理

Embrittiement mechanism of simulated HAZ of low carbon Si-Mn-Mo bainitic steel

关键词:  贝氏体钢  焊接热影响区  脆化机理

Key words:  bainitic steel  HAZ  cmbrittlement mechanism

摘要:

用焊接热模拟,普通光学金相,透射、扫描电镜及电子探针,X射线和常规拉伸、冲出等手段研究了一种新型Si-Mn-Mo系低碳贝氏体钢焊接热影响区过热区的组织和性能的关系,重点探讨了过热区的脆化机理.结果表明,在焊接热模拟条件下,原始奥氏体晶粒尺寸是影响机械性能的主要因素.少量准下贝氏体与低碳马氏体的混合组织具有最佳的强韧性配合.随线能量增加,影响韧性的主要因素是奥氏体晶粒粗化以及高温时碳原子在奥氏体晶界及其附近的偏聚;而且碳原子的这种偏聚是经过较高线能量热循环后出现沿晶脆性断口的主要原因.粒状贝氏体及粒状组织中的M-A岛不是该钢焊接热影响区过热区脆化的原因.

Abstract:

An investigation into the structure-property relationship,cspeeially the embrittlement mechanism of the over-heated band of the simulated HAZ of a low carbon Si-Mn-Mo bainitic steel has been carried out with welding simulation,photomicroscope,TEM,SEM,EPM,X-ray diffraction,tension and impact and other tests.Results show that after various welding simulations,the grain size of austenite imposes the most significant effect on the tensile and impact properties;and the complex structure of small quantity of lower meta-bainite together with dominant low carbon martensite is of the best match of strength and toughness.With heat input increasing,the predominant factors affecting room temper ature toughness and low temperature toughness are the coarsened austenite grains and the segregation of carbon atoms at and near the grain boundaries at high temperatures,and the lalter leads to intergranular brittle fractures at high heat input.The M-A units in granular bainite and granular structure are not the cause of embrittlement.