摘要
The microstructure evolution of heat-affected zone （HAZ） in the multi-pass underwater welded joints is investigated in the present work, and it can be characterized by four zones, marked as Region A, B, C and D, respectively. The microstructure in Region A is the mixture of lath martensite and residual austenite. Besides this structure, lots of acicular ferrite appears in Region B as well, and the grain size becomes larger. Lath ferrite combined with granular bainite is observed in Region C. In Region D, tempered sorbite, granular bainite and fine acicular ferrite are found within the grains, while massive ferrite and Widmanstatten structure are distributed along the grain boundary： The thermal effect of multi-pass welding makes the microstructure and property more and more uniform in the ttAZ, and the largest hardness 356 HV in the HAZ appears in Region A.
The microstructure evolution of heat-affected zone （HAZ） in the multi-pass underwater welded joints is investigated in the present work, and it can be characterized by four zones, marked as Region A, B, C and D, respectively. The microstructure in Region A is the mixture of lath martensite and residual austenite. Besides this structure, lots of acicular ferrite appears in Region B as well, and the grain size becomes larger. Lath ferrite combined with granular bainite is observed in Region C. In Region D, tempered sorbite, granular bainite and fine acicular ferrite are found within the grains, while massive ferrite and Widmanstatten structure are distributed along the grain boundary： The thermal effect of multi-pass welding makes the microstructure and property more and more uniform in the ttAZ, and the largest hardness 356 HV in the HAZ appears in Region A.
