Microstructure of laser metal deposited duplex stainless steel: Influence of shielding gas and heat treatment

Abstract

This research work is the first step in evaluating the feasibility of producing industrial components by using Laser Metal Deposition with duplex stainless steel Wire (LMDw). The influence of Ar and N2 shielding gases was investigated in terms of nitrogen loss and in the microstructure and austenite content of different deposited geometries. The evolution of the microstructure in the build-up direction of the Ar and N2-shielded blocks was compared in the heat-treated and as-deposited conditions. The susceptibility for oxygen pick-up in the LMDw deposits was also analyzed, and oxygen was found to be in the range of conventional gas-shielded weldments. Nitrogen loss occurred when Ar-shielding was used; however, the use of N2-shielding prevented nitrogen loss. Austenite content was nearly doubled by using N2-shielding instead of Ar-shielding. The heat treatment resulted in an increase of the austenite content and of the homogeneity in the microstructure regardless of the shielding gas used. The similarity in microstructure and the low spread in the phase balance for the as-deposited geometries is a sign of having achieved a stable and consistent LMDw process in order to proceed with the build-up of more complex geometries closer to industrial full-size components.

Wire Laser Metal Deposition Additive Manufacturing of Duplex Stainless Steel Components—Development of a Systematic Methodology

“…The results of the first and second stages were investigated in [ 3 , 4 ], and full details of the studies of the block produced in stage 3 and the cylinder produced in stage 4 will be within the scope of separate publications. In this paper, the application of the systematic methodology is presented, and examples of microstructures, chemical compositions, and mechanical properties leading up to the cylinder as the final components are presented.…”

“…Laser Metal Deposition with Wire (LMDw) is an AM technique in which the wire is melted with a laser beam and deposited layer-by-layer (bead-by-bead) to build a component. In LMDw, the implementation of a laser beam in combination with an advanced controlling system allows appropriate monitoring and control of the process [ 3 , 4 ]. In addition to the low cost of raw material (the wire) [ 5 ] and high material usage efficiency (up to 100%), LMDw has provided the opportunity to reach comparatively high productivity [ 6 ] and is, therefore, suitable for the production of full-size near-net-shape parts for industrial applications.…”

“…In addition, although there have been many studies on AM of DSS, no systematic and generally applicable approach to the fabrication of real components has yet been addressed. Recently, Valiente et al [ 4 ] studied the production of a single-bead wall DSS by LMDw as an initial stage of the work presented in more detail here. They produced a single-bead wall and studied the microstructures in both as-deposited and heat-treated conditions.…”

Hot-Wire Laser-Directed Energy Deposition: Process Characteristics and Benefits of Resistive Pre-Heating of the Feedstock Wire

“…As this study focuses on the stability of the process and interaction effects of the electrical and the laser power, the included metallographic investigation is restricted to the morphology of the beads and the defect evaluation. An extended metallurgical investigation on Duplex stainless steel processed with HW-LDED can be found in [35].…”

“…Selected levels of the set voltage U set and corresponding hot-wire levels. Chemical composition (wt%)[35].…”