Effect of Heat Treatment on the Microstructure Evolution and Sensitization Behavior of High-Silicon Stainless Steel
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JMEPEG https://doi.org/10.1007/s11665-020-05060-w
Effect of Heat Treatment on the Microstructure Evolution and Sensitization Behavior of High-Silicon Stainless Steel Prince Setia, Ayush Anand, T. Venkateswaran, K. Thomas Tharian, Sudhanshu S. Singh, K. Mondal, and Shashank Shekhar (Submitted April 19, 2020; in revised form July 24, 2020) The microstructure and sensitization behavior of high-silicon stainless steel containing 4.0 wt.% Si was studied after stabilization heat treatment followed by isothermal heat treatment. Isothermal heat treatment for 6 h was carried out on the alloy at two different temperatures, viz. 500 and 750 °C, after stabilization heat treatment at 950 °C. Phase fraction of the high-silicon stainless steel remained constant after isothermal heat treatment. Fine (Ti,C) precipitates of angular and spherical morphology were observed throughout the microstructure, in all the heat-treated sample conditions. Their number density was measured and related to the processing conditions that they were exposed to. Additionally, the presence of Cr and C was confirmed by compositional analysis, and they appeared at the grain boundary in the sample isothermally heat-treated at 750 °C for 6 h. Sensitization study of the heat-treated samples was carried out with the help of double-loop electrochemical potentiokinetic reactivation test in specially prepared acid etchant, and it was observed that degree of sensitization depended strongly on the formation of Cr-depleted zone along the grain boundary. Based on our study, we conclude that stabilization heat treatment significantly reduces the sensitization behavior, even for steel containing significant fraction of Si. Keywords
duplex steel, EBSD, high-silicon stainless steel, intergranular corrosion, sensitization
1. Introduction Stainless steel is one of the most widely used structural materials owing to its outstanding combination of very good mechanical properties and excellent corrosion resistance that can be achieved through the incorporation of various alloying elements, albeit up to a certain limit. These steels are utilized in a wide range of industries, such as nuclear industry, food industry, chemical industry, automobile industry, etc. Most of the austenitic stainless steels and duplex stainless steels undergo severe intergranular corrosion when exposed to a temperature in the range of 450 to 750 C (Ref 1). In the austenitic stainless steel and duplex steel, the intergranular corrosion is directly related to the depletion of Cr near the grain boundary region, concomitant with the formation of chromium carbide in the grain boundaries. This is termed as sensitization. Several studies have been carried out to ascertain the role of various alloying elements in modifying the sensitization characteristics of the steel and thereby improving its intergranular corrosion behavior. Pardo et al. (Ref 2) conducted a systematic study of the role of alloying elements such as Ti, C and N on the intergranular Prince Setia, Ayush Anand, Sudhanshu S. Singh, K. Mondal, a
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