Mechanical Properties and Microstructures of High Elongation Steel Used for Expandable Tubular

Making use of the low-carbon and low-alloy component, the new expandable tubular steel was designed. After the optimized α+γ zone annealing treatment, the following properties of steel can be obtained, such as high strength, high elongation, high work hardening ability and good impact ability. And the Mechanical properties under high temperature are also good. At room temperature, tensile strength of the material is more than 700MPa, elongation of it is more than 40%, the products of tensile strength and total elongation of it is more than 30GPa·% and half thickness size impact toughness of it is higher than 50J. At 300℃ high temperature, tensile strength of it is still more than 620MPa, elongation of it is more than 40%, products of tensile strength and total elongation of it is also more than 25GPa·%. By means of SEM and XRD, microstructures of this kind of steel were characterized. The results show that this kind of steel exhibits a multi-phase microstructure including martensite, retained austenite and ferrite. Due to the TRIP effect of the widely distributed small size retained austenite, the sustainable work hardening ability can be obtains, and the good combination of high strength and good plasticity can be achieved.