High-temperature oxidation behavior of 9Cr-5Si-3Al ferritic heat-resistant steel
- PDF / 3,008,103 Bytes
- 7 Pages / 592.8 x 841.98 pts Page_size
- 52 Downloads / 180 Views
High-temperature oxidation behavior of 9Cr‒5Si‒3Al ferritic heat-resistant steel Jun-jun Yan, Xue-fei Huang, and Wei-gang Huang College of Materials Science and Engineering, Sichuan University, Chengdu 610065, China (Received: 6 August 2019; revised: 29 October 2019; accepted: 1 November 2019)
Abstract: To improve the oxidation properties of ferritic heat-resistant steels, an Al-bearing 9Cr‒5Si‒3Al ferritic heat-resistant steel was designed. We then conducted cyclic oxidation tests to investigate the high-temperature oxidation behavior of 9Cr‒5Si and 9Cr‒5Si‒3Al ferritic heat-resistant steels at 900 and 1000°C. The characteristics of the oxide layer were analyzed by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. The results show that the oxidation kinetics curves of the two tested steels follow the parabolic law, with the parabolic rate constant kp of 9Cr‒5Si‒3Al steel being much lower than that of 9Cr‒5Si steel at both 900 and 1000°C. The oxide film on the surface of the 9Cr‒5Si alloy exhibits Cr2MnO4 and Cr2O3 phases in the outer layer after oxidation at 900 and 1000°C. However, at oxidation temperatures of 900 and 1000°C, the oxide film of the 9Cr‒5Si‒3Al alloy consists only of Al2O3 and its oxide layer is thinner than that of the 9Cr‒5Si alloy. These results indicate that the addition of Al to the 9Cr‒5Si steel can improve its high-temperature oxidation resistance, which can be attributed to the formation of a continuous and compact Al2O3 film on the surface of the steel. Keywords: ferritic heat-resistant steel; high-temperature oxidation; oxidation kinetics; aluminum
1. Introduction Due to their high-temperature strength and high-temperature oxidation resistance, heat-resistant steels are widely used in equipment that must be operated in high-temperature environments, such as boiler pipelines, steam headers, steam lines, and other parts used in ultra-supercritical power plants, automotive exhaust systems, and solid oxide fuel cells [1‒4]. Among the heat-resistant steels, ferritic heat-resistant steels have attracted much interest due to their good corrosion resistance, excellent thermal properties, and mechanical strength. In addition, the price of these steels is very competitive in comparison to austenitic heat-resistant steels containing high Cr and Ni. One important ferrite heat-resistant steel, 9%–12% Cr martensitic-ferritic steel, has high creep resistance, good oxidation resistance, and high-temperature strength and has been used in the construction of boilers parts and steam pipes in ultra-supercritical power plants and nuclear power plants [5‒9]. To improve creep strength, Mo, W, V, Nb and other alloying elements have been used in 9%–12% ferritic heatresistant steels via solid-solution strengthening and precipitation hardening [10‒11]. Zhou et al [7,10] reported that the refinement of martensitic laths and second-phase particles im-
proves high-temperature performance due to the lack of coarse M23C6 carbide and Laves phases. Fe-based oxide-dispersion-strengthened
Data Loading...
