Composition Optimum Design and Strengthening and Toughening Mechanisms of New Alumina-Forming Austenitic Heat-Resistant Steels

Abstract

In order to promote the development of ultra-supercritical technology, the optimum composition design of three new alumina-forming austenitic heat-resistant steels, based on Fe–22Cr–25Ni (wt. %), with low cost and excellent performance, and used for 700 °C ultra-supercritical unit was carried out using Thermo-Calc software. A comparison of the mechanical properties presented that with increasing Al content, the plasticity of the system was further improved. Based on the composition system, a systematic investigation regarding the structure stability, thermodynamic properties, and mechanical properties of these new steels was carried out to reveal possible strengthening and toughening mechanisms by employing the first-principles method. Calculation results showed that when Al existed in the Fe–Cr–Ni alloy system as a solid solution, the new structures were stable, especially under high temperature. The solution of Al and Al + Si could increase the value of B/G, namely improving the plasticity of the system, particularly in case of alloying with Al + Si. The inclusion of Si in the Fe–Cr–Ni–Al system was conducive to further improving the plasticity without affecting the strength, which provided references for the subsequent optimum composition design and performance regulation of alumina-forming austenitic heat-resistant steels.

Analysis of the effects of alloying with Si and Cr on the properties of manganese austenite based on AB INITIO modelling

“…6) indicates the similarity of their electron structure, and the lack of energy cracks near the Fermi level (zero energy point) is a sign of the bond of metallic type. According to [14], the number of electrons at the Fermi level determines the level of electrochemical stability of a structure, namely, when it increases, the level of stability decreases. According to this, the model austenite structures in the order of growth of their electrochemical stability can be placed in a series: Fe 32 C→Fe 24 Mn 8 C(Fe 18 Mn 8 Si 6 C)→Fe 18 Mn 8 Cr 6 C. Thus, dissolving Mn in austenite increases its electrochemical stability while the further dissolution of Si in it does not significantly affect its value.…”

“…The construction of new, as well as the continuous improvement of existing algorithms of quantum-mechanical calculations of the crystalline structure and properties allow them to be used for modeling the most important phases in steels, in particular austenite of different compositions [12,13]. In order to study the impact of Si and Al additives on the elastic characteristics, structure, and energy state of nickel-chromium austenite, the authors of work [14] modeled its crystalline structure in accordance with the Fe 8 Cr 4 Ni 4 formula. To simulate an unordered solution, the atoms of dissolved components were symmetrically arranged in the FCC (face-centered cubic) nodes of the supercell: 2×2×1, based on γ-Fe, which contained 16 atoms.…”

Research Progress of Alumina-Forming Austenitic Stainless Steels: A Review

“…Y. Yamamoto et al [ 42 ] and Dong et al [ 49 ] designed AFA steels consisting of low nickel and high manganese, or high chromium based on Fe-22Cr-25Ni alloy using ThermoCalc. On the other hand, ThermoCalc can be used to analyze the nitriding depth [ 50 ], the volume fraction of precipitates [ 51 ] and predict the corrosion resistance of AFA alloy in the liquid lead environment [ 52 ].…”

“…AFA steels have complicated microstructures, which generally have several types of precipitates both in the matrix and along the grain boundaries (GBs). It is well known that the alloy properties are closely affected by the microstructure of alloys [ 49 ], forming conditions [ 50 ], and the microstructure evolution.…”

Effects of Mn content on austenite stability and mechanical properties of low Ni alumina-forming austenitic heat-resistant steel: a first-principles study

“…They concluded that Mn reduced the local electrochemical corrosion behavior of the γ-Fe/Cr 2 N interface by reducing the voltage potential difference (VPD) between them. Dong et al 17 studied the effect of Al on the composition optimization and mechanical properties of an AFA heat-resistant steel. When Al was present as a solid solution in the Fe–Cr–Ni alloy system, the austenitic matrix was stable at high temperatures; the solid solution of Al and Al + Si improved the system's plasticity.…”