用插销法研究CO2气保焊条件下SA106C铸件的冷裂纹敏感性

用插销试验法研究了CO2气保焊条件下SA106C铸件的冷裂纹敏感性及断口特征。结果表明，在不预热和16kJ／cm热输入条件下，SA106C铸件的抗冷裂性好，临界断裂应力σer为560MPa，接近其抗拉强度σb，可在不预热条件下焊接该钢。当拘束拉伸应力高于σb。时，将发生失效断裂，断裂性质为典型的氯致延迟裂纹引起的断裂，断裂方式为棱角分明的沿晶(IG) 准解理穿晶(QC)。晶内出现较多短小、锋利、笔直的二次裂纹；启裂区的IG比例较大，随着裂纹的缓慢扩展．扩散氢含量逐渐降低．断口中IG减少，QCHE和二次裂纹都明显增加，而且QCHE中撕裂棱的塑性变形增大。CO2气保焊条件下，SA106C铸件的抗冷裂纹性好，主要与该方法能得到超低氢的焊接条件有关，此外还与该钢的碳当量(CEHW=0．48)不高，HAZ淬硬不明显有关，过热区组织主要为贝氏体，硬度为321HV．低于350HV的临界硬度。

Study of cold cracking susceptibility of CO2 gas shielded arc welded SA106C cast steel using implant tests

Implant tests were performed on the SA106C cast steel welded using CO_2 gas shielded arc welding, which intended to investigate the susceptibility of cold cracking(CR) and the fracture morphology.The results show that in the case of heat input being 16kJ/cm and no preheating , the critical fracture stress of implant is 560 MPa ,near to the value of tensile strength, consequently ,its resistance to CR is so high that it can be welded without preheating. If the restraint stress is higer than tensile strength, the fracture will occur.The features of the fracture is typical hydrogen-induced crack (HIC). The rupture mode of the fracture is found to consist of sugar like intergrannular(IG) and quasi-cleavage(QC_(HE)), some sharp,perfectly straight,short sub-crack can be also observed additionally.With the crack propagating ,the content of hydrogen is cut down,as a result ,the proportion of IG decrease ,wheras those of QC_(HE) and sub-crack increase signifcantly, and more plastic deformation appears clue in QC_(HE) . The reason for high resistance to CR of SA106C cast steel is mainly due to the lower content of hydrogen of CO_2 arc welding process,and also related to the microstructures and as-quenched hadness of over heated zone near the weld interface,which is largely bainite with hardness of 321HV,less than critical hardness of 350 HV.