Effect of homogenization on precipitation behavior and strengthening of 17-4PH stainless steel fabricated using laser powder bed fusion

TL;DR

This study investigates how homogenization heat treatment affects the microstructure and mechanical properties of 17-4PH stainless steel fabricated by laser powder bed fusion, demonstrating improved strength and ductility through optimized post-processing.

Contribution

It provides new insights into the effects of homogenization on precipitation behavior and microstructure refinement in additively manufactured 17-4PH steel, leading to enhanced mechanical performance.

Findings

Homogenization dissolves incoherent Cu precipitates and promotes coherent Cu-rich clusters.

Optimal heat treatment (1 hour homogenization + aging) improves strength and ductility.

Post-heat treatment exceeds properties of traditionally fabricated 17-4PH steel.

Abstract

Effective post-heat treatment is critical to achieve desired microstructure for high-performance in additively manufactured (AM) components. In this work, the influence of homogenization on microstructure-property relationship in 17-4PH steels has been investigated. Precipitation of NbC, oxides, and {\epsilon}-Cu were observed in the as-built 17-4PH steels. To design an optimum post-heat treatment, homogenization was performed at 1050oC for different times followed by aging at 482oC for 1 hour. It was identified that homogenization for 1 hour followed by aging leads to the best combination of strength and ductility due to the refinement of martensite and prior austenite grains. Improved tensile properties were achieved for the post-heat-treated alloys that exceeded the traditionally fabricated 17-4PH steels. Through comprehensive microstructure characterization, it was deduced that the incoherent {\epsilon}-Cu precipitates in the as-built alloy were dissolved through homogenization, and subsequently, re-precipitated as coherent Cu-rich clusters during aging. This study demonstrates that altering the precipitation behavior using post-heat treatment is an effective pathway to significantly improve the mechanical properties of AM alloys.