Grain boundary assembly in a 316 L steel produced by selective laser melting and annealing

Abstract

The effect of recrystallization annealing on the grain boundary assembly of a 316 L-type austenitic stainless steel produced by selective laser melting was studied. The primary recrystallization readily developed upon heating to 1373-1473 K. Using the orientation imaging microscopy, the recrystallization development could be evaluated using the grain orientation spread and/or the kernel average misorientation. The recrystallization kinetics was mainly controlled by the grain nucleation rate rather than the grain growth rate. The recrystallized microstructures were characterized by large fractions of special sigma 3n CSL (coincident site lattice) grain boundaries above 0.7 that were associated with a high number density of annealing twins. The change in the fraction of sigma 3n SCL boundaries could be expressed by a unique linear function of the recrystallized fraction irrespective of annealing temperature. The development of sigma 3n CSL boundaries interrupted the network of ordinary grain boundaries when the number of triple junctions with 3 ordinary boundaries decreased and that with 1 ordinary and 2 sigma 3n CSL boundaries increased. An increase in the fraction of triple junctions with 1 ordinary and 2 sigma 3n SCL boundaries correlated with the recrystallized fraction.