Additive Manufacturing of Duplex Steel 2507 via Directed Energy Deposition: Process Optimization, Microstructure, and Mechanical Properties

Abstract

Duplex steels combine excellent mechanical properties and high corrosion resistance through a balanced ferrite-austenite microstructure, which are achieved by post heat treatment in traditional manufacturing. Metal additive manufacturing is a revolutionary manufacturing technique with high freedom of design, and it features a high cooling rate during the solidification of the melt pool, which makes it complex to obtain balanced ferrite and austenite phases. In this study, duplex steel 2507 was fabricated by laser-powder directed energy deposition, and the phase constituent was tuned by powder flow rate at a constant laser power. A high powder flow rate yielded low energy density, suppressing the formation of ferrite and inducing lack-of-fusion pores, while a low flow rate enhanced the ferrite-austenite transformation due to higher energy density. An intermediate powder flow rate achieved a near-equal ferrite/austenite ratio, resulting in the best combination of strength and ductility. This work demonstrates a strategy for tailoring phase constituent in additively manufactured duplex steels and clarifies the process–microstructure–property relationship.