Microstructure and Mechanical Properties of 18Ni-300 Maraging Steel Fabricated by Selective Laser Melting

Abstract

High-strength 18Ni-300 maraging steel parts were fabricated by selective laser melting (SLM) additive manufacturing. Aging treatment at 490 ºC for 6 hours was applied for improving the mechanical properties of SLM fabricated parts. The microstructure and properties of the as-fabricated SLM 18Ni-300 parts were carefully characterized and analyzed. The results show that the relatively low surface roughness, with 4.16μm for horizontal surface and 4.79μm for vertical surface, certified the high accuracy of forming process. The almost fully dense microstructures of the as-fabricated SLM specimens were consisted of sub-micron dendritic cellular structures for horizontal cross-section and elongated acicular structures for vertical cross section. Due to precipitated-phase strengthening, the hardness increased from 35~36 HRC to 51~55 HRC after heat treatment. Meanwhile, the ultimate tensile strength (Rm) increases from 1165 MPa to 2014 MPa, which increased by about 73%; while the break elongation (ε) was reduced from 12.44% to 3.28%, owing to the increased embrittlement caused by the heat treatment. The substantial plastic deformation and dispersively distributed dimples in the fracture morphologies indicated a ductile fracture of as-fabricated tensile specimens, while the age-hardened tensile specimen encountered with a main fracture mode of brittle fracture.

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

“…The evolution mechanisms of these growth formations relate to the melt-region thermal flux direction which changes for successive layers and is theoretically explained in a recent study by Tan et al [30]. Assisted by rapid cooling rates (circa 10 3 to 10 8 K.s −1 ), these very fine cellular formations orientate themselves concurrent with the direction of heat flow/removal [29,27,26,33,23,34]. Interestingly, other research [27,47] has failed to identify any dominant crystallographic or fibre texture with a preferred grain growth orientation from the AM processed alloy.…”

“…Recently, Monkova et al [17] examined the tensile properties of EOS MS1 fabricated at 0 • , 45 • , and 90 • , and contrary to the EOS published MDS [11] they observed no significant orientation dependence in the tensile stress-strain behaviour for as-built, solution heat-treated (1h at 820 • C), and aged (6h at 490 • C) material. Other available test-data is mainly limited to static testing (tensile, and/or hardness) of maraging steel 300 fabricated in one [19,14,7,20,6,21,22,3,23,24], or two [25,26,12,16,27] of the primary AM build orientations. The most comprehensive of these studies in terms of the reported mechanical properties is [7], which monitors the effect of an array of aging heat-treatments on the static properties of AM fabricated maraging steel 300.…”

“…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.…”

High Strength X3NiCoMoTi 18-9-5 Maraging Steel Prepared by Selective Laser Melting from Atomized Powder

“…The most important properties are very high hardness, good weldability, high ductility, and easy machinability after solution annealing. Spatial stability during aging is one more positive feature of the maraging steels [8][9][10][11][12][13]. Their properties and range of applications are one of the reasons for the interest in their production by using modern technologies, including 3D printing.…”

A Review of Factors Affecting the Mechanical Properties of Maraging Steel 300 Fabricated via Laser Powder Bed Fusion

“…The typical low-magnification microstructure of maraging steel 300 has a complex appearance, with bundled interconnections of fan-shaped solidification cells between molten lines [17,45]. An example of the sectioned microstructure is shown in Figure 4.…”