High-performance room temperature quenching and partitioning (RT Q&P) steel fabricated through laser powder bed fusion

Abstract

The present investigation focuses on analyzing the microstructure and tensile properties of room temperature quenching and partitioning (RT Q&P) steel manufactured using laser powder bed fusion (LPBF). The as-built specimen reveals a dual-phase microstructure composed of retained austenite (RA) grains within the martensite matrix, with the absence of the conventional Mn banded microstructure. However, the as-built sample demonstrates poor tensile properties, exhibiting only a 2.5% total elongation, largely due to significant residual stress. To mitigate this issue, the as-built sample undergoes tempering at low temperatures (300, 350, and 400 °C) for 10 min. This treatment results in a reduction of the average compressive residual stresses from −214.4 to −132.1 MPa, and a transformation of the residual stresses in RA from a compressive state of −52.4 MPa to a tensile state of 136.4 MPa after tempering at 350 °C. Furthermore, the volume fraction of RA increases by approximately 10%, and there is a slight increase in the C content after tempering. The tempered RT Q&P steel demonstrates an ultra-high tensile strength ranging from 1.3 to 1.5 GPa, coupled with a substantial total elongation of 10–15%. This exceptional combination of strength and ductility is attributed to the transformation-induced plasticity (TRIP) effect and the reduction of residual stresses. Notably, this study marks the first confirmation that strong and ductile RT Q&P steel can be produced through the LPBF process.