Investigation of microstructure evolution and its effect mechanism on high temperature tensile properties of 304L stainless steel processed by laser powder bed fusion

Laser Powder Bed Fusion (LPBF) 304L stainless steel has garnered significant attention due to its unique blend of strength and ductility at room temperature. However, there is limited understanding of its high-temperature tensile properties. In this study, we conducted tensile testing on LPBF 304L at temperatures ranging from 623K to 1023K in its as-built state. Additionally, we performed a comparative tensile test on traditionally hot-rolled (at 1433K) 304L stainless steel under equivalent test conditions. The results revealed that LPBF 304L steel exhibited high ductility at 973K (ultimate tensile stress (UTS) is 257.3 ± 3.6 MPa)-1023K (UTS is 218.7 ± 3.8 MPa), but its strength (yield strength (YS) decreased from 346.0 ± 4.5 MPa to 182.7 ± 3.8 MPa) and plasticity (UTS decreased from 405.7 ± 5.3 MPa to 218.7 ± 6.4 MPa) decreased slowly as the testing temperature increases. We also delved into the microstructure and its impact on high-temperature tensile deformation. The fine grains and ensuing dynamic recovery were found to be responsible for the reduced strength and ductility of LPBFed 304L samples at elevated temperatures. Furthermore, a sawtooth fluctuation emerged in the stress-strain curve at 873K, which could be attributed to dynamic strain aging (DSA) and the interaction between solute elements and dislocations.