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利用示波冲击试验机对X100管线钢直缝埋弧焊实际焊接接头热影响区不同位置处的冲击韧性进行了测试.结果表明,当缺口穿过不完全重结晶粗晶区(ICCGHAZ)时冲击韧性很低(平均为51 J),而当缺口不穿过ICCGHAZ时冲击韧性则高达183 J.还利用Gleeble热模拟试验机对热影响区不同区域的组织进行了模拟,得到均一组织的粗晶区(CGHAZ),细晶区(FGHAZ)和不完全重结晶区(ICHAZ)的冲击韧性较高,平均分别为244,164和196 J,而ICCGHAZ的冲击韧性只有32 J.因此,ICCGHAZ是导致冲击韧性骤降的主要原因.ICCGHAZ由粗大的原奥氏体晶粒及沿晶界呈链状分布的马氏体-奥氏体(M-A)组元构成,晶粒内部为粗大的粒状贝氏体或者上贝氏体.断口分析表明,ICCGHAZ是整个断面的起裂源,且裂纹扩展过程中M-A组元易成为解理刻面的起裂源.示波冲击结果显示,ICCGHAZ的存在使得起裂功显著降低.对断口下方二次裂纹的研究表明,CGHAZ处的断裂机制为形核控制型,而在ICCGHAZ处则为扩展控制型.因此,ICCGHAZ中链状M-A组元的存在是导致热影响区韧性恶化的根本原因,并且使得断裂行为和断裂机制发生显著变化.
The impact toughness at different locations in the HAZ of the actual welded joints of X100 pipeline LSAW steel was tested by using an oscillometric impact tester.The results show that when the notch passes through the ICCGHAZ Toughness is low (average 51 J) and impact toughness is as high as 183 when the notch does not pass through ICCGHAZ. The structure of different regions in the HAZ was also simulated using a Gleeble thermal simulator to obtain a homogenous coarsened crystal The impact toughness of CGHAZ, FGHAZ and ICHAZ were higher with an average of 244, 164 and 196 J, respectively, whereas ICCGHAZ had an impact toughness of only 32 J. Therefore, ICCGHAZ is the major component of impact toughness The main reason for the sudden drop of ICCHAHAZ consists of the coarse primary austenite grains and the martensite-austenite (MA) elements distributed in a chain along the grain boundaries. The grains are coarse granular bainite or Upper bainite fracture analysis shows that ICCGHAZ is the starting source of the whole cross section, and the MA component is easy to be the cleavage facet when the crack propagates.Impact results show that the existence of ICCGHAZ makes the cracking work Significantly reduce the secondary cracks under the fracture research The fracture mechanism at CGHAZ is controlled by nucleation and extended at ICCGHAZ. Therefore, the presence of medium-chain MA elements in ICCGHAZ is the root cause of the toughness deterioration in heat-affected zone, and the fracture behavior and Fracture mechanism has changed significantly.