| Expandable Tubular Technology is considered one of the core technology in the oil drilling industry in the 21st century, the final goal of this technology is to develop the monodiameter expandable tubular technology. The selection and optimization of expandable tubular material is an important branch for the research of expandable tubular. Developing suitable steel for monobore technology is the purpose of this study.Austentie high-Mn based twinning-induced plasticity steels has great potential prospect in the applications of expandable tubular technology because of the excellent tensile strength and ductility property. Based on the twinning-induced plasticity steels, combined with the special requirements for the material properties of monobore technology, by means of thermodynamic calculation of stacking fault energy, four new TWIP Steels were developed. The steels are consisted of 0.1～0.3%C,25% Cr,4～10%Mn,2%Ni,2%A1, 1%Si,0.5%Mo, the rest is Fe. The manufacturing process, mechanical properties and corrosion behavior of the TWIP steels were studied by using the universal testing machine with heating insulation unit, OM, XRD, SEM, TEM and EDS. In addition, the expandable deformation constitutive equation of TWIP steels was established under the temperature range from 25℃to 300℃. And then, expansion process of the expandable casing made from the new TWIP steels was simulated by Finite element software. Finally, hardening mechanism of the TWIP steels was investigated.The effect of manufacturing process on organization and performance was studied. The results show that the process is a reasonable process:vacuum melting, then hot rolling followed by annealing under the 1050℃/0.5h/water. The optimized mechanical values are as following:Rp=350-400 MPa, Rm=650-800 MPa, total elongation equals 50～70%, the product of strength and ductility is above 50000MPa%, work-hardening factor may be up to 0.56.The tensile test data of the TWIP steel show that deformation temperature and strain rate have a great impact on material yield strength, tensile strength and elongation. Under 25～300℃, with the deformation temperature increasing, the strength and elongation of the TWIP steel are gradually reduced, whether it is hot rolled, cold-rolled or solution state of steel, The reason is probably that the stacking fault energy of TWIP steel increased with temperature increasing. This makes the main deformation mechanism change from twinning to slipping. In the rate range of 4.2×10-4～6.3×10-3/s, with the acceleration of strain rate, the material strength and elongation decreased. This probably is due to the increased strain rate restricted dislocation movement, which making it difficult to form deformation twins.The material's corrosion resistance of TWIP steel was tested and analyzed by using electrochemical workstation. It can be showed that the corrosion resistance is excellent after solution treatment. The corrosion resistance will reduce after deformation. Mixed with Cr and Ni the corrosion resistance will enhance. The mechanical-chemistry effect of corrosion is the primary factor for corrosion resistance decreasing after deformation.We can obtain the similar dynamic tensile test results as in the condition of underground temperature field by using the finite element simulation method to simulate expansion process of expansion pipe which has large expansion rate.Based on the axiomatic design theory, the material hardening mechanism was discussed. It can be found that the existence of Mn element is the foundation of TWIP. Meanwhile, the existence of C-Mn clusters enhanced the effect of matrix solution strength.In summary, the developed TWIP steel can be used to produce expandable casing with large expansion rate. This will provide necessary materials for the implementing and extending for monobore technology.
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