考虑焊接热影响区软化的高强钢对接接头强度

为研究焊接热输入对调质态高强钢对接焊缝接头强度的影响，设计了对接焊缝接头的静力拉伸试验，进行了对接接头熔敷金属及热影响区(HAZ)硬度分布测试，并对影响接头强度的关键因素进行了参数分析。试验材料选取Q550和Q690两种调质态高强钢，采取气体保护焊分别以1.0、1.5kJ/mm和2.0kJ/mm三个等级焊接热输入，以涵盖常用焊接工艺参数。静力拉伸试验结果表明：对接焊缝接头的强度随焊接热输入的增大而下降；在焊接热输入1.0kJ/mm下，接头的破坏模式为母材处断裂，而在热输入1.5kJ/mm和2.0kJ/mm下，接头断裂均发生在热影响区处。通过硬度分布测试发现，接头的热影响区存在硬化区和软化区。随着热输入的增加，接头软化区范围增大、最小硬度下降，导致接头强度降低。静力拉伸试验的强度测试结果与硬度分布测试结果在宏观上相互印证。参数分析结果表明，热影响区中软化区与母材强度之比、相对软化宽度是决定接头强度的主要因素，且其与接头强度呈近似线性相关关系。

Strength of high strength steel butt welded connections with consideration of heat affected zone softening

To study the influence of welding heat input on mechanical properties of butt welded connections of quenched and tempered (QT) high strength steels, tensile test and hardness distribution analysis were carried out. Key factors that affect the strength of the butt welded connection were parametrically analyzed. In this study, Q550 and Q690 steel plates delivered in QT condition were adopted and welded by GMAW(gas metal arc welding) with three different heat inputs, i.e., 1.0kJ/mm, 1.5kJ/mm and 2.0kJ/mm. It is found that the higher heat input, the lower strength of the butt welded connection. The failure mode of the specimen with heat input of 1.0 kJ/mm is fracture across base metal, while, for the specimens with heat inputs of 1.5kJ/mm and 2.0kJ/mm, the fracture surfaces are located at the heat affected zones (HAZ). Furthermore, both the hardened zone and softened zone are observed from the obtained hardness distribution of HAZ of all specimens. However, for welded connections with higher heat input, the softening is more severe and the width of softened zone is larger, which results in the degradation of strength of the welded connections in high strength steel. The strength test results of static tensile test and the hardness distribution test results agree with each other. The parametric analysis shows that the strength softening ratio between softening zone and base metal and relative softening width of HAZ are the main factors determining the strength of the connection, and there is almost a linear correlation between them and the strength of the welded connection.