Wire Arc Additive Manufactured Mild Steel and Austenitic Stainless Steel Components: Microstructure, Mechanical Properties and Residual Stresses

Abstract

Wire arc additive manufacturing (WAAM) is an additive manufacturing process based on the arc welding process in which wire is melted by an electric arc and deposited layer by layer. Due to the cost and rate benefits over powder-based additive manufacturing technologies and other alternative heat sources such as laser and electron beams, the process is currently receiving much attention in the industrial production sector. The gas metal arc welded (GMAW) based WAAM process provides a higher deposition rate than other methods, making it suitable for additive manufacturing. The fabrication of mild steel (G3Si1), austenitic stainless steel (SS304), and a bimetallic sample of both materials were completed successfully using the GMAW based WAAM process. The microstructure characterization of the developed sample was conducted using optical and scanning electron microscopes. The interface reveals two discrete zones of mild steel and SS304 deposits without any weld defects. The hardness profile indicates a drastic increase in hardness near the interface, which is attributed to chromium migration from the SS304. The toughness of the sample was tested based on the Charpy Impact (ASTM D6110) test. The test reveals isotropy in both directions. The tensile strength of samples deposited by the WAAM technique measured slightly higher than the standard values of weld filament. The deep hole drilling (DHD) method was used to measure the residual stresses, and it was determined that the stresses are compressive in the mild steel portion and tensile in austenitic stainless steel portion, and that they vary throughout the thickness due to variation in the cooling rate at the inner and outer surfaces.

A critical investigation of the anisotropic behavior in the WAAM-fabricated structure

“…However, an improvement in the hardness along the upper regions of the fabricated part was observed. A similar variation in the hardness profile of a WAAM-printed wall has been reported in the literature (Rani et al, 2022):…”

“…However, the average grain size in the upper region of the WAAM-built structure marginally decreases compared to the middle region. This is because the final deposited layer of the built walls does not experience the thermal effect of the successively deposited layers, which resulted in a slightly higher cooling rate (Rani et al , 2022). Further, with the increase in built height, the surface area for heat loss increased compared to the lower regions, also the direct exposure of the final layer with the ambient atmosphere for a longer period compared to those in the middle region together contributed toward fast heat dissipation, responsible for nonuniform grain size distribution along the top region of the WAAM-built structure, as shown in Figure 4(a).…”

“…The strong existence of crystallographic texture leads to a significant degree of anisotropy in the properties of the fabricated part. The texture intensity depends on several parameters, including the steel chemistry, amount of deformation, initial structure and grain size and cooling rate during transformation (Ray et al, 1994). Among the three examined surfaces, owing to an increase in the cooling rate, a slight increase in the intensity of the crystallographic texture was observed for the top and bottom regions of the fabricated sample when compared to the middle region (Javaheri et al, 2021).…”

Stress Relieving Heat Treatment of 316L Stainless Steel Made by Additive Manufacturing Process

“…Additive manufacturing also expresses technologies using the welding techniques that are used Materials 2023, 16, 6461 2 of 20 traditionally for the joining of separate parts. A principle of such Wire Arc Additive Manufacturing (WAAM) technologies lies in the deposition of material in the form of wire, which creates 3D components layer by layer [5]. A specific standard, with the label ISO/ASTM 52900:2021 [6], includes the Selective Laser Melting (SLM) method into the group of technologies, during which the metal in the form of powder, with desired composition, is fully molten in the set thickness, using the laser power.…”

Research on Residual Stresses and Microstructures of Selective Laser Melted Ti6Al4V Treated by Thermal Vibration Stress Relief

“…Casavola et al [ 14 ] reported that residual stresses in AISI 18 Maraging steel first increase and then decrease with sample height. Rani et al [ 15 ] found that the distribution of residual stresses is related to the path direction, and longitudinal stresses are more dominant than transverse stresses. Chen et al [ 16 ] found that solid phase transformation is also one of the factors that cannot be ignored for the formation of residual stress in the AM process of Ti-6Al-4V.…”