Significant Grain Refinement in the Simulated Heat-Affected Zone (HAZ) of Ferritic Stainless Steels by Alloying with Tun
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gh ferritic stainless steel (FSS) has wide application because of its excellent corrosion resistance and low cost, the reduced ductility and toughness of the weld zone and the surrounding region, limits it use as a structural material.[1] The degradation of weld mechanical properties is generally caused by excessive grain growth in the heat-affected zone (HAZ) during welding thermal cycle.[2,3] Welding is inevitable during manufacturing of automotive exhaust pipes. The subsequent pipe bending and expansion process requires weld seam to have high ductility and toughness in the event there are cracks near the weld joint. Thus, restricting excessive grain growth
LIANGLIANG WEI is with the State Key Laboratory of Rolling and Automation, Northeastern University, 3-11 Wenhua Road, Shenyang 110819, China and also with the Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical, Materials and Biomedical Engineering, University of Texas at El Paso, El Paso, TX 79968, USA LIQING CHEN and HOULONG LIU are with the State Key Laboratory of Rolling and Automation, Northeastern University. Contact e-mail: [email protected] R. D. K. MISRA is with the Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical, Materials and Biomedical Engineering Manuscript submitted December 14, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
in the HAZ and obtaining a high-quality weld joint is important. Fine grain size can be achieved by minimizing rate of growth (or boundary migration velocity).[4] Two effective approaches have been identified for decreasing the velocity of migration of boundaries: Zener pinning by precipitates[5] and solute drag effect.[6] Thus, the presence of precipitates with high stability at high temperatures is a viable approach to hinder the grain growth in the HAZ during the weld thermal cycle. Our previous studies demonstrated that the addition of tungsten in ferritic stainless steels promoted the precipitation of Laves phase in annealed steels, which on being present at the oxide/metal interface had significant influence on the oxidation mechanism of FSSs.[7–9] However, the effectiveness of Laves phase precipitates in impeding grain growth in the HAZ of the newly designed FSSs containing W is unknown. Moreover, the influence of alloying element, tungsten, on the precipitation mechanism needs further study. In this study, the precipitation behavior of Laves phase and its influence on impeding grain growth in the HAZ of W-containing ferritic stainless steels is elucidated. Four different FSSs were studied and their nominal chemical composition is presented in Table I. The details of preparing the experimental steels is described elsewhere.[7] The hot rolled sheets were annealed at 900 C (1173 K) for 5 minutes and the ~ 1 mm thickness cold rolled plates were annealed at 1000 C (1273 K) for 2 minutes. To simulate heat-affected zone (HAZ), samples of dimensions 80 mm 9 12 mm 9 1 mm were cut. The simulated HAZ experiments were carried out using MMS-200 thermomechanical simulat
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