Fig. 1 Schematic of tensile and microstructure specimens

Fig. 2 TEM images of the as-built samples: a cellular sub-grain structures with dislocation tangles as the cell wall, b needle-like and blocky ferrite observed inside the austenite matrix, c square particles of the σ phase identified by EDS chemical composition, d blocky ferrite revealed at higher magnification

Fig. 3 Optical micrographs showing the microstructural evolution of a as-built material and specimens heat treated at b 600 °C, c 700 °C, d 800 °C, e 900 °C, f 1000 °C, g 1200 °C, h 1300 °C for 2 h, respectively

Fig. 4 XRD patterns of phase identification in the as-built and heat treated samples, with step size of 0.02° and 1 s acquisition time per step. The δ ferrite peak and austenitic peak are marked by black triangle and black dot, respectively

Fig. 5 EBSD unique grain colour maps of equiaxed austenite grains on the horizontal plane under different conditions: a as-built, b 600 °C for 2 h, c 700 °C for 2 h, d 800 °C for 2 h, e 900 °C for 2 h, f 1000 °C for 2 h, g 1200 °C for 2 h, h 1300 °C for 2 h, i curve of grain size evolution with the temperature

Fig. 6 Grain boundary maps with low-angle boundaries in green, high-angle boundaries in blue and twin boundaries in red colour coding of the SLMed 304L SS under as-built and different heat treatment conditions: a as-built, b 600 °C for 2 h, c 700 °C for 2 h, d 800 °C for 2 h, e 900 °C for 2 h, f 1000 °C for 2 h, g 1200 °C for 2 h, h 1300 °C for 2 h, i curve of twin boundaries evolution with the temperature

Fig. 7 Phase distribution maps with the ferrite in green, σ phase in blue and austenite matrix in canary colour coding of the SLMed 304L SS under as-built and different heat treatment conditions: a as-built, b 600 °C for 2 h, c 700 °C for 2 h, d 800 °C for 2 h, e 900 °C for 2 h, f 1000 °C for 2 h, g 1200 °C for 2 h, h 1300 °C for 2 h, i curves of δ ferrite and σ phase fraction evolution with the temperature

Fig. 8 Engineering stress-strain curves of the SLMed 304L SS under as-built and different heat treatment conditions

Fig. 9 Fracture morphologies of tensile specimens under different heat treatment conditions: a macrostructure, b as-built, c 600 °C for 2 h, d 700 °C for 2 h, e 800 °C for 2 h, f 900 °C for 2 h, g 1000 °C for 2 h, h 1200 °C for 2 h, i 1300 °C for 2 h. The inclusions formed at high temperature are calibrated to be oxides containing oxygen, chromium, and iron

Fig. 10 Potentiodynamic polarization curves of the as-built and heat treated samples

Fig. 11 Nyquist plots of the as-built and heat treated samples

Fig. 12 a Fraction of the equilibrium phase versus temperature calculated through Thermal-Calc software according to the specific chemical composition of 304L stainless steel in this study, vertical sections of phase diagrams at b 800 °C, c 1300 °C. The red dots represent the indicator composition of 304L stainless steel