Effect of arc distance on HAZ thermal cycles and microstructural evolution 10CrNi3MoV steel

Double-sided double GTAW and GMAW (DSGTAW and DSGMAW) have been proposed to reduce hydrogen induced crack (HIC) susceptibility in recent years. This paper is mainly to investigate the effect of arc distance on thermal cycles and microstructural evolution of HAZ. To clarify this, DSGTAW and single gas tungsten arc welding (SGTAW) were employed in backing welding of 10CrNi3MoV low-alloy high-strength steel. The thermal processes were studied by numerical simulation in this paper. The heat input of each pass was 21.7 kJ/cm. The thermal cycles of SGTAW and DSGTAW with different arc distances (d) were compared and analyzed. The microstructural evolution of coarse grained heat affected zone (CGHAZ) of SGTAW and unaltered coarse grained heat affected zone (UACGHAZ) of DSGTAW was observed by confocal laser scanning microscope (CLSM). The results show that DSGTAW can significantly decrease the cooling rate of HAZ. As the arc distance increases, the trough temperature (T_t) between the two peak temperatures induced by the fore and rear arc will decrease and the HAZ temperature gradient of rear pass will increase which can lead to the change of thermal cycles. When arc distance increases to 60 mm, brittle intercritically reheated CGHAZ (IRCGHAZ) will form.