The effect of the surface on grain boundary migration in austenitic stainless steel weld metal

The direction of grain boundary (GB) migration that occurs after solidification in the original surface of the weld of an austenitic stainless steel was compared to that in the interior (the depth 100 mum from the original surface). The results are as follows. In the interior, the direction of GB migration was decided by the moving direction of the triple junctions that bring about their equilibrium. This equilibrium results from the GB approaching a cross angle of 120 deg with another GB in the vicinity of the triple junction. Meanwhile, in the original surface, the direction of GB migration was decided by the direction that makes the GB plane, which is just at solidification, being perpendicular to the surface. That is, the GB plane migrates to be perpendicular to the original surface. This GB migration was often observed when the angle between the GB plane and the original surface had been less than 40 deg. Furthermore, the amount of the GB mi,oration had rapidly increased with the decrease in the angle. The validity of these results is examined with a discussion of the reduction of the interfacial energy.