Inflatable Tubes Design And Mechanical Properties Of Carbon Micro-alloyed High Strength Steel Calculations

According to the performance requirements of expandable tubular steel with low-cost and large expansion rate, low-carbon micro-alloyed ferrite-martensite dual-phase steel(07MnSi) which was making Mn-Si as the main alloying element and small addition of V elements was designed, the transformation point of the steel was calculated and determined; mechanical properties of the steel though different subthermal quenching process were calculated using the method of developed EET theory and the electronic structure analysis of alloys and phase, interface analysis and statistical average; the organization structural analysis and mechanical testing of samples though different subthermal quenching process(740℃,780℃,820℃,860℃) were compared to theory calculation, the following results was obtained:1. It is declared that Acl, Ac3and Ms of the steel were734℃,883℃and411℃though the transformation point calculation.2. It was verified that strengthening of ferrite region in07MnSi ferrite-martensite dual-phase steel included solid solution strengthening caused by C, Mn, Si, V and other alloying elements, precipitation hardening caused by changes in amount of solid solution, dispersion strengthening caused by precipitation, as well as interface strengthening caused by different forms of ferrite subgrain and precipitates according to the analysis of phase electronic structure and strengthening in ferrite region of07MnSi ferrite-martensite dual-phase steel though different subthermal quenching process (740℃,780℃,820℃,860℃). The electronic structure were nAα-Fe,nAα-Fe-M,NACV and so on, interfaces of the phases included α-Fe//α-Fe-C, α-Fe//α-Fe-M, α-Fe//CV, α-Fe-C//α-Fe-C-M and so on; the strengthening of the phases in martensite region were phase transformation strengthening caused by a large number of microscopic defects (twins, dislocations and stacking faults, etc.), the aging strengthening caused by diffusion and segregation of C atoms in the process of quenching to room temperature, as well as solid solution strengthening and interface strengthening caused by alloying elements.3) Valence electron structure parameters of the dual-phase steel though different subthermal quenching process (740℃,780℃,820℃,860℃) were calculated though the method of the developed EET theory and most robust statistical average method; dual-phase steel mechanical properties (tensile strength, yield, elongation, impact energy) formulas were obtained though the improvement on the basis of non-quenched and tempered steel calculation theory of Liu zhiling, after taking into account that martensite and ferrite organization of dual-phase steel though different subthermal quenching process were in the different proportions, carbon content of the samples were different(martensite was high carbon twinned martensite though the water quenching below the temperature of780℃, martensite was low-carbon bit wrong martensite though the water quenching above the temperature of820℃) and sub-structure in ferrite were changed. The formulas were as follow:4. The result was showed in below table though the comparison of the calculated results and the analysis of the organizational structure and determination of mechanical properties on07MnSi though different subthermal quenching process (740℃,780℃,820℃,860℃).It was showed that the calculation and the experimental data were in high degree (relative error was less than10%)...