The joining of 14.8 mm thick pipeline steels was achieved with developments in high-power fiber laser by laser welding or hybrid laser arc welding. However, there were few studies on the… Click to show full abstract
The joining of 14.8 mm thick pipeline steels was achieved with developments in high-power fiber laser by laser welding or hybrid laser arc welding. However, there were few studies on the effects of single-pass welding heat input on the M-A component and impact toughness of the heat-affected zone. In this study, single-pass welding thermal cycle was performed on Gleeble 3800 thermal simulation tester; the effect of heat input on microstructure, M-A constituent, hardness, toughness and corrosion resistance of coarse-grained heat-affected zone of X100 pipeline steel was studied. The results showed: The microstructure was lath martensite with a heat input of less than 8 kJ/cm. When the heat input was 26-36 kJ/cm, the microstructure was granular bainite. The heat input had not obvious effect on hardness (only 16% hardness reduction in this heat input arrange). However, the impact toughness was strongly influenced by heat input, with an 88% hardness reduction compared to base metal, due to M-A constituent and prior austenite grain size. Few finer M-A constituent dispersing in austenite was obtained instead of necklace-like M-A constituent at the prior austenite grain boundary when the welding heat input was less than 15 kJ/cm, which was beneficial to improve the impact toughness and corrosion resistance of welded joints of X100 pipeline steels.
               
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