On the relation between microstructure and impact toughness of 17-4__PH stainless steel produced by powder bed fusion laser beam (PBF-LB)

TL;DR

This study explores how heat treatments affect the microstructure and impact toughness of 17-4 PH stainless steel made by PBF-LB, revealing a significant strength-toughness trade-off and microstructural influences on mechanical behavior.

Contribution

It provides a detailed multiscale microstructural analysis linking processing, microstructure, and impact toughness, highlighting the strength-toughness trade-off in PBF-LB 17-4 PH steel.

Findings

PBF-LB specimens have high tensile strength but lower impact toughness.

Strain-induced transformation of reversed austenite improves ductility and toughness.

SiO2 inclusions act as nucleation sites for micro-cavities, reducing toughness.

Abstract

This work investigated the effects of aging heat treatments on the microstructure and, consequently, the quasi-static (tensile properties) and dynamic (impact toughness) mechanical behaviour of a 17-4 PH stainless steel produced by powder bed fusion laser beam (PBF-LB). Multiscale microstructural characterization, using X-ray diffraction, scanning and transmission electron microscopy and electron backscatter diffraction, was conducted to establish quantitative correlations between microstructural evolution and mechanical performance, providing insight into the mechanisms governing plasticity and fracture. The PBF-LB specimens exhibited tensile strengths comparable to or exceeding those of conventionally manufactured counterparts but consistently showed significantly lower impact toughness, regardless of heat treatment conditions. Within the complex microstructure, strain-induced transformation of reversed austenite was found to enhance ductility and impact toughness. SiO2 inclusions, originating from the starting powder, were identified as nucleation sites for micro-cavities and proved detrimental to impact toughness. Meanwhile, the distribution of Cu-rich nanoprecipitates could be tailored to favour either tensile strength through Orowan strengthening or impact toughness by enhancing local plasticity, but not both simultaneously. This work highlights the pronounced strength-toughness trade-off inherent in PBF-LB-produced 17-4 PH alloys and reveals the interplay between strength, ductility, and toughness. These findings underscore the need for further research into dynamic loading mechanical properties, especially for demanding applications such as those in the nuclear sector.