Aging Behaviour and Mechanical Performance of 18-Ni 300 Steel Processed by Selective Laser Melting

TLDR

Rapid cooling during selective laser melting gives the as‑built 18‑Ni 300 alloy full potential for precipitate strengthening, eliminating the need for a prior solution treatment. The study investigates how aging conditions affect the microstructure and mechanical behavior of 18‑Ni 300 maraging steel processed by selective laser melting. Selective laser melting produces a submicrometric structure and phase distribution that, together with aging, determines tensile strength and ductility mainly through strengthening precipitates, with minor influence from γ‑Fe reversion. Aging increases reversed austenite proportion, raises strength while reducing ductility, yet tensile properties show no systematic correlation with the amount of austenite.

Abstract

An 18-Ni 300 grade maraging steel was processed by selective laser melting and an investigation was carried out on microstructural and mechanical behaviour as a function of aging condition. Owing to the rapid cooling rate, the as-built alloy featured a full potential for precipitate strengthening, without the need of a solution treatment prior to aging. The amount of reversed austenite found in the microstructure increased after aging and revealed to depend on aging temperature and time. Similarly to the corresponding wrought counterpart, also in the selective laser-melted 18-Ni 300 alloy, aging promoted a dramatic increase in strength with respect to the as-built condition and a drop in tensile ductility. No systematic changes were found in tensile properties as a function of measured amount of austenite. It is proposed that the submicrometric structure and the phase distribution inherited by the rapid solidification condition brought by selective laser melting are such that changes in tensile strength and ductility are mainly governed by the effects brought by the strengthening precipitates, whereas the concurrent reversion of the γ-Fe phase in different amounts seems to play a minor role.