Post-Heat Treatment Design of High-Strength Low-Alloy Steels Processed by Laser Powder Bed Fusion

TL;DR

This paper presents a comprehensive post-heat treatment process for laser-processed HSLA steel, significantly improving its microstructure and mechanical strength through tailored heat treatments and microstructure control.

Contribution

It introduces a novel post-heat treatment design involving HIP, cyclic re-austenitization, and tempering to enhance the microstructure and strength of additively manufactured HSLA steel.

Findings

Porosity reduced from 3% to <1% by HIP.

Two-fold increase in yield strength after treatment.

Optimized heat treatments improve microstructure and hardness.

Abstract

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.