Effects of Build Direction on the Mechanical Properties of a Martensitic Stainless Steel Fabricated by Selective Laser Melting

Abstract

Mechanical properties and microstructure are investigated for a martensitic stainless steel (AISI 420) fabricated by selective laser melting (SLM) in three build directions. The tensile specimens built by SLM are classified into three groups. Group A is horizontally built in the thickness direction, Group B is horizontally built in the width direction, and Group C is vertically built in the length direction. The loading direction in tensile test is parallel to the build direction of Group C, but perpendicular to that of Groups A and B. Experimental results indicate build direction has significant effects on the residual stress, hardness, and tensile properties of SLM builds. Microstructural analyses indicate the as-fabricated SLM AISI 420 builds exhibit elongated cells and acicular structures which are composed of martensite and retained austenite phases growing along the build direction. Such anisotropy in the microstructure leads to anisotropic mechanical properties as Group C specimens (length direction) exhibit greater yield stress, ultimate tensile stress, and elongation than the specimens of Groups A (thickness direction) and B (width direction). The residual compressive stress in the gauge section also contributes to the superior tensile properties of Group C (length direction), as compared to Groups A (thickness direction) and B (width direction), which exhibit residual tensile stress in the gauge section.

Effects of Laser Spot Size on the Mechanical Properties of AISI 420 Stainless Steel Fabricated by Selective Laser Melting

“…Dimensions of gauge section, in the tensile specimen, were of 32 mm (length) × 6 mm (width) × 3 mm (thickness). Detailed geometry and dimensions of the tensile specimen were given in our earlier study [ 26 ]. The AISI 420 stainless steel powder (Sanyo Special Steel Corporation, Ltd., Hyōgo-ken, Japan) is supplied with a particle size, ranging from 10 μm to 88 μm.…”

“…X-ray diffraction (XRD) analysis was applied to determine the crystalline phases in the given SLM specimens. Details of the XRD analysis technique were given elsewhere [ 26 ].…”

“…SLM is a favorite process in fabricating a mold with conformal cooling channel, and AISI 420 is suitable for such application, due to its low cost and high absorption of laser radiation [ 8 ]. However, only a few studies have been focused on the characteristics of AISI 420 fabricated by SLM [ 8 , 24 , 25 , 26 ]. In order to be applicable to the plastic injection mold, a SLM process window of laser power and scanning speed has been obtained for AISI 420, with a high density and hardness [ 8 ].…”

“…In order to be applicable to the plastic injection mold, a SLM process window of laser power and scanning speed has been obtained for AISI 420, with a high density and hardness [ 8 ]. Effects of build direction on the mechanical properties of AISI 420, fabricated by SLM, have been studied by Shen et al [ 26 ]. Saeidi et al [ 24 ] and Krakhmalev et al [ 25 ] have investigated the effects of heat treatment on the microstructure and mechanical properties of SLM builds of AISI 420.…”

“…However, there is lack of study on the effects of laser spot size on the microstructure, surface finish, and mechanical properties of AISI 420 fabricated via SLM. As an extension of our earlier work [ 26 ], the aim of this study is to investigate the relationship of the spot size with the surface finish and mechanical properties of SLM built AISI 420 parts. The results of this study, and our previous study [ 26 ], can hopefully contribute to improving the quality of the SLM builds of AISI 420, for applications in the plastic injection mold and other industries.…”