焊接HAZ微区转变及晶粒长大规律研究

采用不同热输入对12mm SS400超细晶钢进行焊接,并对焊接接头过热区、正火区及不完全正火区晶粒长大程度与组织变化情况进行分析.结合有限元数值模拟的方法研究焊接热影响区及各子区宽度、组织、硬度随热输入的变化规律,得出焊接热输入与HAZ宽度关系曲线符合Boltzmann平衡态理论.试验结果表明,热输入为9.6~22kJ/cm进行焊接时,HAZ及各子区宽度变化较小;当热输入大于22kJ/cm时,HAZ宽度随热输入的增加而增加,尤其正火区宽度大幅增长.同时,过热区组织随着热输入增加片状贝氏体减少,逐步形成粗大的魏氏组织.接头硬度峰值逐渐升高,局部软化区逐渐扩大.在大热输入焊接时,焊接预热可有效抑制热影响区宽度发展.

Research on Evolution of Subzone Transformation and GrainGrowth in Weld Heat affected Zone

In order to analyze the microstructure evolution and grain growth processes of coarse grain heat affected zone(CGHAZ), fine grained heat affected zone (FGHAZ), and intercritical heat affected zone (ICHAZ), 12 mm SS400 medium plate was welded under different heat input. The varying rules of the HAZ width, microstructure and microhardness with the variation of heat input in welding HAZ and all sub areas were studied using the finite element method in combination with microscopic tests. A relationship between the heat input and HAZ width which follows the Boltzmann distribution was also presented. The result shows that when the steel was welded with heat input of 9.6~22 kJ/cm, the effect of the heat input on the width of HAZ and all sub areas was small; the width of HAZ increased when the heat input was higher than 22 kJ/cm, especially leading to the substantial increase of width in FGHAZ. Moreover, when the heat input increased, the hardness peak of the joint became higher in CGHAZ which was caused by a restraint of the lamellar bainite transformation and the widmanstatten formation, while the softened zone expanded gradually. Preheating can restrain the growth of the HAZ width for the welding with high heat input.