Microstructure and mechanical properties of simulated unaltered coarse grained heat affected zones of 10CrNi3MoV steel by double-sided double arc welding

This paper aims to reveal the influence of different welding conditions on unaltered coarse grained heat affected zones (UACGHAZs) of backing passes by double-sided double gas tungsten arc welding (DSGTAW) of 10CrNi3MoV steel. UACGHAZs were also compared with coarse grained heat affected zones (GGHAZs) of single gas tungsten arc welding (SGTAW). At lower heat input (21.7 kJ/cm for each run without preheating), CGHAZ mainly consisted of lath martensite (LM) while UACGHAZs composed of LM and small amount of lath bainite (LB). At higher heat input (33.2 kJ/cm for each run with 150 °C preheating), the microstructures of CGHAZ were LM and LB. In UACGHAZs, the microstructures would transform from LB + LM + granular bainite (GB) to LB + GB as arc distance (d) decreased. The toughness of UACGHAZs was related to martensite/bainite packet sizes instead of prior austenite grain sizes. At higher heat input, the formation of granular bainite deteriorated the toughness of UACGHAZs and negated the positive effect of LB on toughness. DSGTAW can significantly improve the toughness of coarse grained zones when lower heat input is adopted.

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