Study On Martensite Microstructure And Properties Of Austenitic Steel After Cold-rolling And Annealing

The austenite steel is widely used since it is characterized by nonmagnetic, highductility, high plasticity and low price. However, the application of the austenite steel isrestricted since the mechanical property is poor. In the present paper, high manganeseaustenite steel (Fe-34.5Mn-0.04C) and18-8austenite stainless steel (1Cr18Ni9Ti) arestudied, the two kinds of austenite steels are cold rolled by a double roller miller andundergo martensite reverse anneal treatment. The tensile property is tested on the coldrolled and annealed specimen, and the microstructure and the fracture morphology areobserved using the metalloscope, transmission electron microscope (TEM) and scanningelectron microscope (SEM).The Fe-34.5Mn-0.04C steel was solution treated at1100C for2h followed bywater quenching, the austenite structure with anneal twin was distributed in the matrix,and the grain size was21μm. The Fe-34.5Mn-0.04C steel was cold rolled to a totalreduction of90%and then annealed at800C for1h after solution treatment, theobserved microstructure was austenite phase with the grain size of4.0μm. The tensilestrength was564MPa, and the elongation was45.1%at ambient temperature (20C);the tensile strength was615MPa, and the elongation was51.3%at-20C; the tensilestrength was697MPa, and the elongation was52.9%at-80C; the tensile strength was765MPa, and the elongation was49.1%at-120C; the tensile strength was811MPa, andthe elongation was48.6%at-150C. Temperature has a significant impact on the tensileproperty, the tensile strength increases with the decreasing of the temperature, theelongation also increases with the decreasing of the temperature and reaches its maximumat-80C.The1Cr18Ni9Ti stainless steel was solution treated at1100C for2h followed bywater quenching, the austenite structure with anneal twin was distributed in the matrix.After solution treatment, the1Cr18Ni9Ti steel was cold rolled to different reductions andannealed at different temperatures. The yield strength was264MPa, the tensile strengthwas728MPa, and the elongation was89.8%after solution treatment; after the first time cold rolled to60%and annealed at800C for40min, the yield strength was342MPa, thetensile strength was839MPa, and the elongation was52.4%; after the second time coldrolled and annealed, the yield strength was423MPa, the tensile strength was847MPa,and the elongation was44.9%; after the third time cold rolled and annealed, the yieldstrength was426MPa, the tensile strength was888MPa, and the elongation was47.9%.Compared with the solution treated specimen, the tensile and yield strength of the coldrolled and annealed1Cr18Ni9Ti steel have a significant promotion at the expense of theelongation. However, after the second and third time anneal treatment, the strength of the1Cr18Ni9Ti steel remains increasing, the elongation drops slightly. While annealing at800-1000C at the third time, the yield and tensile strength decreases with the increasingtemperature, and the elongation increases with the increasing temperature. Whileannealing at800-900C, the work hardening rate of the1Cr18Ni9Ti steel is clearlyseparated into three sections, it is unable to accurately distinguish the sections after950C,the annealing temperature has a significant impact on the work hardening rate.