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通过热裂试验和热塑性试验证实,低碳钢焊缝金属中存在结晶裂纹和离温失塑两类裂纹;脆性温度区间分别为1480～1450℃和1100～850℃。高温失塑裂纹表面形态是:沿晶塑性和带孔洞的光滑面,韧窝和孔洞中有(Mn、Fe) S夹杂物。增锰可以消除这种裂纹。对结晶裂纹和高温失塑裂纹的产生条件和形成原因进行了分折。提出硫在晶界的偏析和(Mn、Fe)S 沉淀,引起微裂纹的形成和集聚,产生塑性低落,可能是低碳钢焊缝金属中失塑裂纹形成的原因。
The hot cracking and the thermoplastic tests confirmed that there are two types of cracks in the weld metal of low carbon steel and the temperature-dependent plastic deformation. The brittle temperature range is 1480-1450 ℃ and 1100-850 ℃ respectively. The surface morphology of the high temperature plastic-plastic crack is: along the plasticity and the smooth surface with holes, (Mn, Fe) S inclusions in the dimples and holes. Manganese can eliminate this kind of crack. The conditions and formation causes of the crystal cracks and high temperature plastic-plastic cracks were analyzed. It is proposed that the segregation of sulfur in the grain boundary and the precipitation of (Mn, Fe) S cause the formation and accumulation of microcracks and the plastic ductility, which may be the reason for the formation of plastic-plastic cracks in the weld metal of mild steel.