低碳贝氏体钢双面埋弧焊接头的组织和低温韧性

Microstructure and Low Temperature Toughness of Weld Joints Prepared by Double-sided Submerged Arc Welding for Low Carbon Bainite Steel

对低碳贝氏体钢进行双面埋弧焊焊接,并用光学显微镜和PSW750型示波冲击试验机对焊接接头进行表征,研究了钢的显微组织和低温韧性。结果表明:低碳贝氏体钢双面埋弧焊后,焊缝区的组织为针状铁素体和粒状贝氏体;HAZ的组织为贝氏体铁素体和粒状贝氏体;HAZ熔合线附近的硬度最高,远离熔合线硬度降低并逐渐接近母材金属的硬度;随着温度的降低焊接过程中的凝固偏析、高度集中的位错源来不及松弛应力集中以及分布在晶界上的Ti、Mo等微合金元素形成的碳氮化物,导致焊接接头焊缝区和HAZ韧性降低并在-20℃和-60℃发生韧脆转变。

The low carbon bainite steel was welded by double-sided submerged arc welding and the microstructure and low temperature toughness of the joints was studied by optical microscope and PSW750 instrumented impact testing machine. The results show that the microstructure of the weld seam consisted of acicular ferrite and granular bainite, however the HAZ shows a microstructure consist- ed of bainite ferrite and granular bainite. The hardness at HAZ near the weld bond is the highest and then decreases gradually approaching to the hardness of base metal. In comparison to the matrix the weld seam and HAZ show a lower toughness with a ductile brittle transition temperature at -20℃ and -60℃ re- spectively, which may be ascribed to the occurrence of solidification segregation, highly concentrated dis- locations and formation of carbon nitrides of alloying elements such as Ti and Mo at grain boundaries etc. in the weld joints durinq rapid coolinq after weldinq.