Influence of Various Heat Treatment Cycles on the Phase Transformation and Microstructure Evolution of AISI 329 Super-Duplex Stainless Steel

Abstract

AbstractThe importance of duplex stainless steel in the global steel industries takes from its application because of its utilization in the environment, the paper industries, and pipelines and reactions champers found in the gas, oil, and chemicals industries. This research investigates the effect of various heat treatment cycles on the intermetallic compound precipitation and different constituents' evolution of the AISI 329 steel. Also, this investigation aims at exploring the relationship of the microstructure evolution at various heat treatment cycles and its effect on the tensile properties of selected steel. The phase transformation studies were conducted theoretically utilizing the JMatPro program and experimentally employing differential scanning calorimetry tests and dilatation; the obtained microstructure was inspected by exploiting a light metallographic microscope, a field-emission scanning electron microscope, and x-ray diffraction. The results illustrated that the microstructure includes ferrite, austenite phases, and dispersive particles. The dispersive particles are carbide particles and intermetallic compounds. Furthermore, the sigma phase settled at the boundaries of the ferrite grains. Intermetallic compounds were observed in both cast and heat-treated steel microstructures. Observed intermetallic compounds have no specific engineering geometry with various sizes, and the main alloying elements are Cr, Fe, and Mn. Special heat treatment, including solid solution and aging at high temperatures, leads to thinning of the sigma phase while diminishing the size of the intermetallic compound. Tensile properties were enhanced by controlling the volume fraction of different constituents that are adjusted by heat treatment. The fracture morphology is consistent with the microstructure and tensile properties of the investigated steel.