| Materials computational design is a new field originated from the interdisciplinary intersection. The developed industrial countries regard it as one of the significant research directions in the 21st century. But our research in this area has just begun. Computational design of metal began with nickel-based superalloy in the 1970s, and now it has researches in ceramics, glass, organic materials, metals et al. Austenitic stainless steel is the most important type of stainless steel. Their structures are basically single-phase. The systematic research in computer simulation of structures and performances of austenitic stainless steels is rare. Q. X. Dai and X. N. Cheng have carried out a lot of ground-breaking and meaningful work in the mathematical and modeling of austenitic steels. Based on the research of pioneers and combined with the experimental data of researches, the author and his team have established a mathematical model of austenitic steel's calculation.Based on the experimental data of researchers and the extensive results of the author's research, the author studied the relation between mechanical properties and elements as well as work temperatures of austenitic stainless steels. According to a large number of experimental results, the quantitative calculational equation of strength and computer processing elongation:RP0.2293= R0.20+f(Me); Rm293=Rm0+f(Me) RP0.2=RP0.2293(-GT); Rm=Rm293 exp(-HT); A(%)=K(Me)exp[-(1-N)R0.2300·10-3] were listed. These equations could be applied to the calculation and design of strength and ductility of austenitic stainless steels. The tested results coincided well with the calculated date.Materials computational design system was studied at engineering application level and the austenitic steels were selected as the object. With the principle of intelligence integrity, and considered about the implementation and the operability, we compiled visual austenitic stainless steels expert systems by Visual Studio 2010. Expert system mainly includes the menu bar and toolbars, which contains stainless steels inquiry, structure analysis, properties prediction, elements design and technology design. Elements design and technology design are served as reserve functions, which based on current researches. Stainless steel information database was set up in stainless steel inquiry programe, which includes stainless steel elements, conventional mechanical properties, grades, steel codes and countries, etc., so that users can query the information of different grades of stainless steels easily. The structure analysis module mainly contains Austenitic structure estimate, high-temperatureδ-phase calculation, Austenitic steel structural transformation calculation at moderate temperate and austenitic steel stacking fault energy calculation. The elements prediction function module mainly includes austenitic steel low temperature strength calculation, low temperature ductility calculation and high temperature strength calculationAim at the localization of nuclear power equipments, and breaking the foreign monopoly of nuclear heat transfer tubes, a new low-cost alloy modified with Al was designed by alloying schematic which ensure the better oxidation resistance and sturcture stability of the alloy, based on analysis of international steam generator heat transfer tube mainstream materials.The main research ideas are:①The addition of Al to improve the oxidation resistance.②Nb addition was to increase various performance of alloys contains inhibiting occurrence of intergranular corrosion, promoting protective Al2O3 scale formation. Vacuum induction melting furnace (ZG-0.05) was utilized to melt materials. Hot JSM-7001F field emission scanning electron microscopy and JEM-2100 (HR)-based high-resolution transmission electron microscopy were used to observe microstructure and fracture morphology. Rigaku D/MAX2500PC X-ray diffraction was employed for phase analyses. Choose RDL100 type electronic creep test machine for creep test and high temperature strength tests.Microstructure analysis shows that, both 800H and HDG-Al alloys have an austenit matrix. There are two dominate secondary phases in alloy 800H. One is a small number of TiN with regular shape and the other is bar-like or speckled M23C6 mainly in the grain boundary. Mechanical properties tests of both materials show that the tensile strength of 800H and HDG-Al are much higher than the minimum value of ASME under room temperature, especially HDG-Al which has 40% higher strength than the specified value. Elongation of both materials also meet the specified value; High-temperature short-time strength tests of both materials at 650℃indicates that tensile strength of alloy 800H and HDG-Al are higher than the value of Special Metals Corporation's tests, and alloy HDG-Al is much higher than the given value. Creep test results show that the creep strength of HDG-Al is superior to 800H. Tensile fracture with necking and morphology with a clear cut area which has typical equiaxial dimples were studied. The impact fracture without radiation area has obvious relatively rough fiber area and has equiaxial dimples too; Creep cracking is intergranular brittle and the crack is initiated form microscopic holes and cracks in the grain boundary.Many alloys formed different oxides which due to different oxides' Gibbs forming free energy. (Cr,Fe)2O3 and very little spinel (FeCr2O4) oxides were observed on 800H alloy when oxidation at 700℃in air. (Cr,Fe)2O3,FeCr2O4 and small amount of TiO2 scales at 800℃. At 900℃, lower (Cr,Fe)2O3 was formed and the amount of TiO2 was increasing. Much (Fe2.5Ti0.5)1.04O4 oxides appeared at 900℃. HDG-Al owns obviously superior oxidation resistance compare to 800H. The scales are dense and consist of (Fe0.6Cr0.4)2O3 and a small amount of Al-oxides at 700℃. Mainly (Al0.9Cr0.1)O3 were observed at 800℃and 900℃. The oxidation dynamic curves of both alloys show "Completely oxidation resistence" according to the average speed of oxidation rating standard.
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