Regulation of Microstructure, Residual Stress, and Mechanical Properties by Pre-straining and Subsequent Heat Treatment in Selective Laser Melted 304L Stainless Steel

Abstract

The microstructure, mechanical properties, and residual stress of the selective laser melted (SLM) 304L stainless steel (SS) were regulated by pre-straining (ε = 10%, 20%, and 40%) and subsequent heat treatment (650-950 °C). The yield strength increased with the amount of pre-strain, but the ductility decreased. The opposite effect occurred when the heat treatment temperature increased. Upon applying 40% pre-strain and heat treatment at 800 °C, the yield strength and ductility of SLM 304L SS reached equilibrium, and approximately 80% of the residual stresses were eliminated, while the corrosion resistance was improved. The microstructural analysis showed that the dislocation density increased with increasing pre-strain (80% of total dislocations were static statistical dislocations). The dislocation density decreased with increasing heat treatment temperature. After applying 40% pre-strain and heat treatment at 800 °C, part of the cellular structures were retained, and partial recrystallization occurred. The geometrically necessary dislocation density was reduced, and the grains were refined. In addition, part of the static statistical dislocations induced by the pre-strain were retained. These factors resulted in an excellent integrated performance of the SLM 304L SS.