The achievable mechanical properties of SLM produced Maraging Steel 300 components

Abstract

Purpose Selective laser melting (SLM) is a process that produces near net shape parts from metallic powders. A concern with SLM-produced metals is the achievable materials performance with respect to mechanical properties. Particularly, three important aspects strongly affect the mechanical properties of the material: internal stresses resulting from steep temperature gradients and high cooling rates, the resulting microstructure and the occurrence of pores and flaws. Design/methodology/approach This paper presents SLM-produced maraging steel 300 (18Ni-300), an iron-nickel steel alloy often used in applications where high fracture toughness and strength are required. The steel’s achievable tensile, crack growth and hardness properties and the manner in which these compare to the wrought counterpart are reported. In addition, this paper investigates the porosity distribution and achievable density, residual stress levels and post-processing procedures using heat-treatments. Findings It is found that tensile properties, hardness and microstructure compare well to its wrought counterpart. Fatigue growth rates are also comparable, though they are influenced by residual stresses and microstructure. Originality/value The investigation into the mechanical performance addresses two issues: the achievable mechanical properties and the understanding of the link between the manufacturing process and the achievable material performance.

Comparison of Maraging Steel Micro- and Nanostructure Produced Conventionally and by Laser Additive Manufacturing

“…The almost complete lack of interstitial alloying elements leads to a good weldability of this class of alloys [7]. This, in turn, makes them amenable to metal additive manufacturing (AM) processes, in particular Laser Metal Deposition (LMD) and Selective Laser Melting (SLM) [8,9,10,11,12,13,14,15,16]. Since these processes involve a small melt pool generated by a laser beam for the consolidation of powder feedstock to a dense material, they share similarities with micro-welding processes.…”

Effect of Process Parameters on Residual Stresses, Distortions, and Porosity in Selective Laser Melting of Maraging Steel 300

“…Metals 2019, 9,1042 6 of 16 layer thicknesses were also quite similar (approximately 98.5% for both) at 180 W and 500 mm/s. The porosity results for both layer thicknesses at the same levels of laser power and scanning speed are presented in Table 2.…”

“…The samples were weighed in air as well as distilled water at 20 • C temperature and standard pressure with the aid of a precision scale. The theoretical density of maraging steel 300 was taken as 8.1 g/cm 3 which is in line with related literature [9,34]. An important consideration when measuring density using this method is to ensure that no open pores exist that would allow the penetration of water into the specimens [35].…”

“…Metals 2019, 9,1042 4 of 16 ( Figure 3) equipped with two detectors was used to determine the Fe-α {211} lattice deformations at 25 kV and 4 mA. The X-ray anode tube used was Cr K-α with a wavelength of 2.291 Å.…”

“…The mechanisms of residual stresses in SLM are well explained in [4]. The major effects of residual stresses include form and dimensional deviations [5], delamination, stress-induced cracking [6,7] and accelerated crack growth, which leads to early fatigue failure [8,9]. Warping distortions and cracking are irreversible by post-processing techniques such as stress relief heat treatment.…”