Grain Boundary Engineering of Stainless Steel Via Additive Manufacturing

Additive manufacturing followed by thermomechanical processing was investigated as a means to achieve grain boundary engineering. Different combinations of a 930°C recovery treatment, 0-30% cold-rolling, and a 1150°C solution annealing treatment were systematically applied to 316L stainless steel samples produced by laser powder bed fusion. The resulting microstructures were analyzed, including calculations of the special boundary and triple junction statistics, in order to assess the effects of each processing route. It was determined that a temperature above the recovery temperature was necessary to recrystallize the as-built microstructure and to relax internal strain created by the additive process. The lowest amount of cold-rolling resulted in the highest twin boundary length percentage in each sample set, so applying additional cold work did not help toward achieving grain boundary engineering. Longer time at the solution annealing temperature, however, did improve the grain boundary character distribution. While one sample was able to reach a twin boundary length percentage over 60%, none of the samples showed a breakup of the random-angle grain boundary network. Further research on breaking up the random-angle grain boundary network is recommended.