Q690钢焊接接头微观组织对冷裂纹的影响研究

Effect of Microstructure in Welded Joint on Cold Cracking of Q690 Steel

分析了Q690钢手工电弧焊与气体保护焊焊接冷裂纹产生与微观组织的联系。结果表明:焊接冷裂纹起源于斜Y坡口根部,沿熔合区、焊缝扩展至焊缝表面;2种工艺焊接的接头组织硬度均较母材高,而塑性较差。热影响区为马氏体、贝氏体与铁素体混合组织,焊缝组织由先共析铁素体、侧板条铁素体、贝氏体和针状铁素体等组成,针状铁素体抗裂纹扩展能力较其他组织强。在2种焊接方法对应断口中观察到了冷裂纹起裂、扩展与断裂区的不同形貌,起裂与扩展区存在塑性变形,而断裂区为解理断裂。

The relationship between microstructure of Q690 and cold cracking by using manual arc welding and gas shielded welding was investigated. The result shows that the cold cracks initially occur at the root of oblique Y groove and then propagate towards the surface along the fusion zone and the weld seam. Those two welded joints have the hardness higher than that of the base metal, but the poor plasticity. The heat-affected zone includes martensite, bainite and ferrite. The weld seam′s microstructure is composed of pre-eutectoid ferrite, side-plate ferrite, bainite and acicular ferrite, in which the acicular ferrite is stronger in resisting crack extension than others. Different morphologies of cold cracking, crack propagation and fracture zones are observed in the corresponding fractures by those two welding methods. There is plastic deformation in the cracking and crack propagation regions, and there is cleavage fracture in the fracture region.