Effect of multiscale Ti(C,N) particle addition on microstructure and mechanical properties of H13 steel fabricated by laser powder bed fusion

In this study, a novel Ti(C,N) particles-modified H13 steel was fabricated by laser powder bed fusion (LPBF) of H13 steel powder surface-coated with 0.5 wt% or 1 wt% multiscale Ti(C,N) ceramic particles with a median particle size (D 50 ) ranging from 0.41 to 2.35 μm. It was found that within the melt pool (temperature>2510 K), Ti(C,N) particles larger than 3.5 μm underwent partial dissolution and effectively served as heterogeneous nucleation sites for δ-ferrite, while the Ti(C,N) particles smaller than 3.5 μm dissolved completely, leading to the formation of nanoscale (Ti,V)(C,N) precipitates during cooling. The addition of Ti(C,N) particles significantly enhances the intrinsic heat treatment (IHT) effect, leading to a marked reduction in retained austenite (RA) content. Furthermore, it also promotes the columnar-to-equiaxed transition (CET) of prior austenite grains (PAGs), refines the PAGs, and attenuates the <110>||BD crystallographic texture. This effect significantly alters the propensity for martensite variant selection, thereby facilitating the randomized growth of martensite laths and mitigating the overall texture of the H13 steel. The addition of 1 wt% Ti(C,N) particles significantly increases the yield strength of the H13 steel from 1509 ± 10 to 1843 ± 15 MPa, but the ductility and work-hardening rate are compromised. The latter effect can be attributed to the residual micron-sized (Ti,V)(C,N) particles serving as sites for microcrack formation during deformation, and the decrease in RA content in the microstructure which diminishes the transformation induced plasticity (TRIP) effect. This work provides a solid theoretical framework and design guidelines for the LPBF fabrication of multiscale ceramic particle-modified martensitic steels.