Kinetics of Intermetallic Phase Precipitation in Manual Metal Arc Welded Duplex Stainless Steels

The article presents the influence of heat treatment on the kinetics of transformations in lean duplex LDX2101 steel and a weld made of standard duplex 2209 material, which was welded by manual metal arc welding. Changes in the microstructure, hardness, and magnetic phase content were analyzed after heat treatment was conducted at a temperature of 800 °C for a period ranging from 15 to 1440 min. Light and scanning microscopy, Vickers hardness measurements, and magnetic phase content measurements using a ferritoscope were used for the research. In the LDX2101 steel, the presence of δ-ferrite and γ austenite was identified and additional Cr₂N nitrides were observed in the heat-affected zone. After heat treatment, the decomposition of δ ferrite into γ₂ austenite and Cr₂N nitrides was observed in both areas. In the case of weld made by the coated electrode in 2209 grade, a ferritic-austenitic microstructure with allotriomorphic austenite (γ_A), Widmanstätten austenite (γ_W), and idiomorphic austenite (γ_I) and δ-ferrite area with "bee swarms" of fine precipitations of chromium nitrides Cr₂N and non-metallic inclusions (NMIs) of slag, formed during the welding process, are observed in the as-welded state. After heat treatment, the presence of the χ phase (after 15 min of annealing) and the σ phase (after 120 min of annealing) was additionally identified. The kinetics of intermetallic phase evolution in welds made from 2209 material were presented. The obtained results of hardness measurements and metallographic tests were correlated, which allowed for a quick check of the precipitation processes on the used element.