粗晶热影响区比例对09MnNiDR焊接接头冲击韧性的影响

通过对09MnNiDR低温压力容器用钢埋弧焊焊接接头热影响区不同位置处的冲击吸收能量的测试、冲击断口以及微观组织的观察分析，确定了09MnNiDR焊接接头的组织特征以及最薄弱区域，并深入讨论了最薄弱区域对焊接接头冲击韧性的影响. 结果表明，在?70 ℃时，焊接接头母材、亚临界热影响区、临界热影响区、细晶热影响区平均冲击吸收能量均在270 J以上，表现出良好的韧性. 焊缝的平均冲击吸收能量为139 J. 焊接接头韧性最薄弱区域为粗晶热影响区，当缺口完全位于粗晶热影响区时，冲击吸收能量为20 J，相比于母材冲击韧性损失高达92.7%. 粗晶热影响区的显微组织为粗大的粒状贝氏体、板条贝氏体以及块状铁素体组成的复合组织. 随着缺口尖端前沿粗晶热影响区比例的增加，其分布位置越靠近缺口尖端，试样的冲击吸收能量越小，充分体现出最薄弱区域对冲击韧性的影响.

Influence of fraction of coarse-grained heat affected zone on impact toughness for 09MnNiDR welded joint

The impact absorbed energy of various regions of the heat affected zone(HAZ) of submerged arc welding actual welded joint for 09MnNiDR low temperature pressure vessel steel was measured, the microstructures, fracture surface were observed and anlyzed. Based on the experimental results, the microstructures of all regions of HAZ, the weakest region can be determined, and the effects of the weakest region on impact toughness of the welded joint were further discussed. The results show that at ?70 °C, the average impact absorbed energy of the base metal, subcritical heat affected zone, intercritical heat affected zone, and fine grain heat affected zone of the welded joint is above 270 J, which all show good toughness. The average impact absorbed energy of the weld metal is 139 J. The coarse grain heat affected zone (CGHAZ) is the weakest region of the welded joint. When the notch tip is completely composed of CGHAZ, the impact absorbed energy of 20 J is reached. The impact energy of CGHAZ decrease to 92.7% of the base metal. The microstructure of CGHAZ is composed of coarse granular bainite, lath bainite and block ferrite. With the increase of the fraction of CGHAZ in front of the notch tip, the closer from notch location is, the lower the impact absorbed energy of the specimen is, which fully reflects the influence of the weakest region on the impact toughness.