Beheviour Of A Cr-Mn-N Austenitic Steel Under Cold And Hot Deformation Conditions

Mechanical behaviours and structures of 32Mn-7Cr-1Mo-0.3N austeniticsteel had been investigated under cold and hot deformation conditions. Thedeformation and strengthening mechanism under different conditions wasclarified, which was significant for developing high strength and ductility highmanganese austenitic steel.Hot compressive and tensile tests were carried out on 32Mn-7Cr-1Mo-0.3Naustenitic steel on Gleeble 3500 thermal simulator. Tensile and compressivetests at different strain rate and deformation temperature were carried on MTSuniversal material testing machine and split Hopkinson bar(SHB), respectively.Moreover, the deformation structures and phase composition and tensile fracturesurfaces were analysed using light microscope(LM) and transmission electronmicroscope(TEM) and X-ray diffraction(XRD) and scanning electronmicroscope(SEM ), respectively.The results of hot compressive tests show that the flow stress and the strainto peak stress increase with increasing strain rate or decreasing deformationtemperature. When true strain is 0.6 and deformation temperature is 1423K, fulldynamic recrystallization occur at the strain rate of 0.1¹0s^-1. When thedeformation temperature bellows 1373K, dynamic recrystallization occurredpartially. The value of hot deformation activation energy Q is 469.03kJ/mol.The hot deformation equation is obtained as followingε|-= 6. 398×10¹⁷[sinh(0.00538σ_p)]^6.3423exp[-469030/RT]The results of hot tensile test indicate that hot-work plasticity ofexperimental steel is excellent in the temperature range from 1223K to 1423K.From the processing map of experimental steel, it can be seen that the efficiencyof power dissipation increases gradually with increasing deformationtemperature and decreasing strain rate, which achieves the maximum 31% atstrain rate 0.1s-1 and at about 1373K.The results of different strain rate and deformation temperature indicatethat with decreasing deformation temperature, yield and tensile strength increaseremarkably while the percentage reduction of area and elongation decreaseslightly with the exception of elongation at 77K increasing slightly at low strainrate. The tensile strength increases rapidly while the percentage reduction ofarea and elongation vary slightly with increasing strain rate and decreasingtemperature at high strain rate. Compressing flow stress at room temperatureincreases with increasing strain rate, average flow stress increases increasesabout 300MPa, when the strain rate increases from 0.1s-1 to 3000s-1.Tensile fracture surfaces are mainly composed of dimples and exhibittough fracture character at high strain rate . The excellent combination of highstrength and ductility and high structural stability under different deformationconditions is related to interaction among twin and dislocation and ε-martensitein deformation structure.