Effect of Heat Treatment on the Microstructure, Mechanical Properties and Corrosion Resistance of Selective Laser Melted 304L Stainless Steel

The influence of heat treatment holding temperatures from 600 to 1300 °C on the microstructure, mechanical properties and corrosion resistance in selective laser melted (SLMed) 304L stainless steel is investigated in this work. The results reveal that there is no remarkable microstructure change after holding at 600 °C for 2 h, while recrystallization leads to a slight decrease in grain size in the temperature range of 700–900 °C. The heat treatment at temperatures from 1000 to 1300 °C for 2 h obviously affects the morphology of grains in SLMed 304L stainless steel. Combining effects of grain coarsening, delta-ferrite (δ) phases reduction and residual stress release during heat treatment lead to the reduction of yield strength and an increasing elongation. The elongation of the samples heat treated at 800 °C for 2 h is, however, significantly decreased due to the increase in the amount of sigma (σ) phase. A remarkable increase in the amount of δ ferrite results in an increase in yield strength but a decrease in ductility after heat treatment at 1300 °C for 2 h. The corrosion resistance of the samples heat treated at 1300 °C is significantly improved due to the substantial reduction of brittle phase (σ). There is no obvious effect of the presence of δ ferrite on corrosion behavior.