Dislocation structures and residual stresses in duplex stainless steel fabricated by laser powder bed fusion with 430 and 316L powders

Abstract

The duplex stainless steel is fabricated using laser powder bed fusion (LPBF), with raw materials prepared by mechanically mixing 430 and 316 L powders in a 1:1 mass ratio. The as-built alloys exhibit good overall mechanical properties, and theoretical strength calculations are performed based on the flow strength model. Uniquely, the distribution of dislocations, residual stresses, and strain accommodation mechanisms are investigated using electron backscattered diffraction and transmission electron microscopy. The results show that the microstructure of the as-built alloys is predominantly ferritic phase, with an austenitic phase content of approximately 4 %. The ultimate tensile strength is 938 ± 4 MPa and the elongation is 19 ± 0.58 %. The as-built alloys possess high dislocation densities, with the dislocation density in the ferritic phases being higher than in the austenitic phases. In particular, austenitic phases present barely any local misorientation and minimal rotations within grains, stacking faults are introduced to accommodate the solidification strains. However, ferritic phases exhibit a high dislocations density, with dislocations present on the (101), (011‾) and (211) planes, accommodating solidification strains and cooling stresses through elastoplastic deformation, and building up geometrically necessary dislocations.