Crystallographic Features of Microstructure in Maraging Steel Fabricated by Selective Laser Melting

Abstract

This study characterizes the microstructure and its associated crystallographic features of bulk maraging steels fabricated by selective laser melting (SLM) combined with a powder bed technique. The fabricated sample exhibited characteristic melt pools in which the regions had locally melted and rapidly solidified. A major part of these melt pools corresponded with the ferrite (α) matrix, which exhibited a lath martensite structure with a high density of dislocations. A number of fine retained austenite (γ) with a <001> orientation along the build direction was often localized around the melt pool boundaries. The orientation relationship of these fine γ grains with respect to the adjacent α grains in the martensite structure was (111) γ //(011) α and [-101] γ //[-1-11] α (Kurdjumov-Sachs orientation relationship). Using the obtained results, we inferred the microstructure development of maraging steels during the SLM process. The results depict that new and diverse high-strength materials can be used to develop industrial molds and dies.

Effect of Heat Treatment Condition on Microstructural and Mechanical Anisotropies of Selective Laser Melted Maraging 18Ni-300 Steel

“…This indicates that an almost fully hardened state is achievable with an aging temperature of 450 °C for maraging steel fabricated by SLM. It is worth noting that the aging temperature of 450 °C is lower by 30-40 °C in comparison with the aging temperature used for the maraging steel fabricated by the conventional manufacturing process and SLM [6,8].…”

“…Preliminary studies regarding the maraging steels produced by SLM showed that they have a unique microstructure and unique mechanical properties in comparison with those of the conventionally processed ones. For instance, Takata et al [6] investigated the microstructure of maraging steel produced by SLM and found that the alloy had a martensite phase in the as-built state due to an extremely fast cooling rate of up to 10 6 • C/s. It has been also shown that the maraging steel fabricated by SLM has finer structures compared to those of the conventional manufacturing methods due to a sufficiently fast cooling rate, resulting in higher strength [7].…”

Plastic anisotropy of additively manufactured maraging steel: Influence of the build orientation and heat treatments

“…Moreover, the availability of tensile properties for AM fabricated maraging steel 300 for the primary build orientations (0 • , and 90 • ) is limited. Other significant work has been performed to-date in characterizing the microstructure [23,30,31,29,27,32], precipitation reactions [33,6], and austenite reversion behaviours [34,21,7,30] with several of these studies reporting similar microstructures in maraging steel 300 having been produced on a range of AM machines under varying process parameters.…”

Post‐treatment selection for tailored fatigue performance of 18Ni300 maraging steel manufactured by laser powder bed fusion

“…Heat treatments were performed in a vertical tube furnace in argon atmosphere at 10 C/min heating rate. Based on the maraging steel's phase diagram 23,24 and recommended heat treatment procedures reported in literature, 25,26 age-hardening heat treatment was performed at 480 C for 3 h. Some samples underwent a solutionising treatment at 820 C for 1 h, with and without being followed by the designated age-hardening step. The notation of samples in different heat-treated states are as follows: 'AB' for as-built state, '3h480' for age-hardening heat treatment at 480 C for 3 h, '1h820' for solutionising at 820 C for 1 h and '1h820 + 3h480' for solutionising at 820 C for 1 h followed by age hardening at 480 C for 3 h. The chosen heat treatment for fatigue testing is 1h820 + 3h480 as will be seen in Section 3.…”