Applicability evaluation of X-ray stress measurement at weld metal of austenitic stainless steel based on dependence of crystal grain coarsening on welding conditions

This study examines the effect of welding conditions on the applicability of X-ray stress measurement at weld metal with coarsened grains. Testing material was low carbon austenitic stainless steel and 15 welded specimens were prepared through tungsten inert gas (TIG) welding under various welding conditions, in which five kinds of welding currents and three kinds of welding speeds were assigned in all combinations. In the X-ray stress measurement, 2θ-sin²ψ method was applied and then the effectiveness of enlarging a diameter of collimator and applying additional planer oscillation for weld metal with coarsened grains was evaluated. Meanwhile, the effect of welding conditions on crystal grain coarsening at weld metal was examined based on welding thermal conduction theory with a moving point heat source. The results showed that the mean crystal grain size at weld metal correlated linearly with the parameter derived from the welding thermal conduction theory. Based on relation between X-ray irradiation area and the mean crystal grain size, the effect of the welding conditions on the applicability of X-ray stress measurement with or without enlarging a diameter of collimator and applying additional planer oscillation was systematically evaluated. (author)