Effect of thermal cycles of DSAW on microstructure in low alloy high strength steel

According to the low alloy high-strength steel thick plate welding, a new high efficiency technique which does not need back chipping-double-sided double arc welding(DSAW)was provided. Backing run with double-sided double pulsed gas metal arc welding, and other passes with double-sided double gas metal arc welding.The temperature fields of single TIG (tungsten inert-gas) welding and DSAW near the bond area were measured by the method of hiding thermal-couple in drilled hole.Compared the thermal cycles of two methods, the t_8/5 and t_8/3 of DSAW are higher.In DSAW, fore pass provides the rear pass with a preheat action and rear pass provides the fore pass with a postheat treatment.In single TIG welding, microstructure of weld and coarse grain zone is coarse martensitic, but in DSAW weld contains a few of acicular ferrilite besides of martensitic.Moreover, microstructure of coarse grain zone is smaller than that of single TIG welding.Microhardness distribution results indicated that hardness of DSAW was lower than that of single TIG welding.