  In this study, a post-heat treatment design for additively manufactured
copper-bearing high-strength low-alloy (HSLA)-100 steel is performed by
understanding the process-structure-property relationships. Hot isostatic
pressing (HIP) is designed to reduce the porosity from 3% to less than 1% for
the HSLA-100 steel processed by laser powder bed fusion (LPBF). Quenching
dilatometry is employed to design the HIP parameters with the optimized cooling
rate for the maximum amount of martensite transformed after HIP. Afterward, a
post-heat treatment step with cyclic re-austenitization is introduced for an
effective grain refinement to compensate the coarsened microstructure after
HIP. Finally, tempering is optimized through microstructure characterization
and microhardness. A two-fold increase in the yield strength of the HSLA with
tailored microstructure during post-heat treatment is achieved in comparison
with the as-built HSLA.
