Texture, microstructure and mechanical properties of laser beam welded AISI 2507 super duplex stainless steel

Abstract

This study investigates weldability of AISI 2507 super duplex stainless steel (SDSS) sheets with laser welding. The impact of heat inputs and post-weld heat treatment (PWHT) on the mechanical properties, texture, microstructure and the surface of joints were analyzed. The microhardness and tensile strength values of the samples welded with the lowest weld heat input was detected to be greater than samples welded with the high heat input. The highest values for tensile strength, bending force and impact toughness in welded samples have been identified as 891 MPa, 1092 N and 58.4 J respectively. The effect of PWHT caused a decrease in the hardness and tensile strength of all samples, and improved the toughness and ductility properties. While dislocations and stacking faults were observed in the base material microstructure, twinning formation was also detected in the weld metal. Secondary austenite (γ2) and Cr23C6 carbides were also found after heat treatment. Variations in the coincidence site lattice (CSL) boundary proportions and the Schmid factors (SFs) directly affected the mechanical properties. In the 2D- and 3D-orientation distribution function (ODF) base material and weld metal maps, the δ-ferrite and γ-austenite textures performed high-density γ-fiber and α-fiber orientations and a low-density (110) <110> rotated cube component, and showed high-density γ-fiber and low-density α-fiber RD//<110> orientations after heat treatment. When the orientation relationships of the heat-treated sample were examined, Kurdjumov–Sachs (K–S) and Nishiyama–Wassermann (N–W) relationships were determined between the γ/α phases in the base material and weld metal, in addition to these orientation relationships, a occasionally seen (100)γ//(100)α Bain orientation relationship was also found in the non-heat-treated sample. The atomic concentrations of the non-heat-treated and heat-treated weld metals exhibited an increase in the O1s spectrum and decreases in the Ni 2p, Fe 2p, Mo 3d and Cr 2p spectra with increasing sputtering time. Diffusion of H− ion with low density to ferrite and austenite grains on weld metal structure was observed.