Microstructural Heterogeneity and Mechanical Properties of a Welded Joint of an Austenitic Stainless Steel

Abstract

This research presents the microstructural and mechanical evolution throughout the welded seam of an austenitic stainless steel (ASS) tube. It was found that the main hardness decrement occurred in the fusion zone (FZ), followed by the heat-affected zone (HAZ) and the base material (BM). Optical microscopy indicated a dendritic structure in FZ and heterogeneous austenitic grain size from the HAZ towards the BM, ranging from 100 µm to 10 µm. The welding process generated an intense texture around the FZ and the HAZ, while the BM still showed an extrusion-like texture. In terms of mechanical behavior, the largest austenite grain size in the FZ led to the lowest strength and ductility of all zones due to the earliest strain localization manifested by heterogeneous strain distribution. However, the strain localization in all zones appeared after 0.4 true strain, indicating an overall good ductility of the seam. These high values were related to two microstructure characteristics: 1) the 10% δ-ferrite after solidification in the FZ favored by the Creq/Nieq = 1.67 relationship that delayed the crack propagation along the austenite grains and 2) the heterogeneous microstructure made up of soft austenite and hard martensite in the HAZ and BM producing multiple strain concentrations. Kernel Average Misorientation (KAM) maps obtained by Electron Back-Scattering Diffraction (EBSD) allowed observing higher internal misorientations in the FZ than in the HAZ due to interconnected walls between the δ-ferrite grains. However, the largest KAM values were observed in the BM between γ-austenite and the deformation-induced α’-martensite phases. X-ray diffraction revealed that the residual stresses in the cross-section of the welded seam were compression-type and then switched to tension-type in the outer surface.

Effect of Residual Stress on Mode-I Stress Intensity Factor: A Quantitative Evaluation and a Suggestion of an Estimating Equation

“…A tensile RS was found to be a main factor enhancing the occurrence of brittle fracture, enhancing stress corrosion cracking, and accelerating the fatigue crack growth (FCG) rate. Recent results reported in the literature also suggest that RS has an important influence on the fatigue crack growth behavior rate of welded material, especially at the low-loading regime near the fatigue crack threshold region [30,[33][34][35]. However, the effect of RS on the FCGR properties of materials is more complicated due to the continuous redistribution of RS during the propagation processing of the crack [36].…”

Mitigating Stress Corrosion Cracking of 304L and 316L Laser Welds in a Salt Spray through Micro-Shot Peening

“…AISI 304 SS jointed via the gas tungsten arc welding (GTAW) process shows high microstructural and mechanical heterogeneity in distinct weld zones [33]. To increase the reliability or prolong the service life, the pitting corrosion/SCC of the dry storage canister in a saline atmosphere must be suppressed or under control.…”

The Casting and Hot Forging of Low-Carbon Copper-Bearing Steel and Its Substructural Characterization

“…Post-casting, the widely preferred secondary manufacturing processes are machining, deformation, heat treatment, welding, etc., [4][5][6][7]. Deformation processes like extrusion, rolling, forging, drawing, etc., are the generally carried-out processes [8][9][10][11][12]. Forging is one of the conventional secondary manufacturing processes to produce a homogeneous microstructure by applying a combination of thermal and mechanical energy [13].…”