Processing maps and microstructural evolution of the type 347H austenitic heat-resistant stainless steel
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Baoqun Ning School of Materials Science and Engineering, Tianjin University of Technology, Tianjin 300384, People’s Republic of China (Received 7 March 2015; accepted 26 May 2015)
To study the thermal deformation behavior and microstructural evolution of the type 347H austenitic steel, compression experiments were conducted at the temperatures of 800–1100 °C with strain rates of 0.01–10 s1. The activation energy and constitutive equation of the type 347H steel during thermal deformation process were determined according to the flow stress curves. Both the hot processing maps and microstructure characteristics under different deformation conditions were investigated. Based on the thermal processing maps, two unstable regions under 800 °C/0.01–10 s1 and 1100 °C/0.01 s1 were identified. The processing maps were in favor of optimizing thermal processing parameters and improving thermal processing properties of the type 347H austenitic steel. After thermal deformation, the dislocation in the austenite matrix increases significantly. Besides, in the stable regions, the precipitation of carbides is facilitated by thermal deformation.
I. INTRODUCTION
Nowadays, countries worldwide have been developing supercritical and ultrasupercritical generators to reduce pollution and lower costs. Power generation efficiency is affected by generator efficiency, combustion chamber efficiency, coupling efficiency, and so on. To improve the Carnot cycle efficiency, lots of countries have been developing heat-resistant steels. 18Cr–8Ni type austenitic steels have been the focus of many studies due to their excellent combination of high ductility, strength, and steam oxidation resistance at high temperatures. And they are widely used in boiler, petroleum, and other industries.1–3 As one of 18Cr–18Ni type austenite steels, the niobium (Nb)-bearing austenitic stainless steel is frequently used in coal-fired power plants. Over the past decades, a great deal of research activities about austenitic heat-resistant steels has been focused on creep behavior and microstructural evolution at high temperatures,4–7 whereas little attention has been paid to the thermal deformation performance and the carbides precipitation of the austenitic stainless steel. Actually, the hot deformation processing maps of heatresistant steels are favorable to optimize the workability and control the microstructures of the materials.8
Liu et al. defined the processing map of Ni-base superalloy.9 Nkhoma et al. revealed the hot working characteristics of 321 steel and 304 steel.10 In addition, Farahat et al. pointed out that the mechanical properties could be improved with the increase in both the cold deformation strain and the Nb content.11 Using constitutive equations and processing maps, Momeni and Deghani explored the characterization of thermal deformation behaviors of 410 martensitic stainless steel and 2205 austenite–ferrite duplex stainless steel.12,13 In this study, the constitutive equation and the processing maps of type 347H austenitic steel were established to unde
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