Mechanical Properties And Microstructures Of Cold-rolled TRIP/TWIP Steel With High Mn-content Atfer Annealing

Fe-Mn-Al-Si TRIP/TWIP steels with high Mn-content have an excellent strength andductility and extraordinary strain hardening phenomenon．The effect of annealing temperatureon microstructures and mechanical properties of the cold-rolled Fe-25Mn-3Al-3Si TWIP wasstudied by means of X-ray diffraction， electron backscatter diffraction technology，transmission electron microscope and tensile test．The Hall-Petch relationship was analyzed indetail．Meanwhile，the microstructure，the texture evolutions and the strain hardening rate ofthe Fe-20/25/29Mn-Al-Si steels subjected to tensile tests at room temperature wereinvestigated as well．The results showed that the microstructure of the cold-rolled Fe-25Mn-3Al-3Si steelmainly consisted of dislocations pile-ups， deformation bands and nanometer grainsaccompanying with a little of mechanical twins．The recrystallization of the cold-rolled TWIPsteels started at500℃and finished at600℃when the holding time of annealing was anhour．The microstructure of the fully recrystallized samples consists of the equiaxed grainsand annealing twins．With the increase of the annealing temperature，the grain sizes werecontinuously increasing but the fraction of the Σ3grain boundaries was discontinuouslyincreasing．After annealing at850℃for1h，the fraction of the Σ3grain boundaries reached to44%．The tensile strength of the annealed Fe-25Mn-3Al-3Si TWIP steel obeys the Hall-Petchrelationship at room temperature，but the K(ε) of the Hall-Petch relationship is different fromthat of ordinary steels，which K(ε) is monotonically increasing with the strain．With thestrain increasing，the K(ε) of the TWIP steel first increases to the peak and then keepsunchanged, finally it decreases．The deformation process of the Fe-20Mn-3Al-3Si steel was always accompanied withphase transformations when the annealed samples of the Fe-20Mn-3Al-3Si steel was tensiletested，so the Fe-20Mn-3Al-3Si steel must be the TRIP steel．The main texture in the tensilefracture samples of the Fe-20Mn-3Al-3Si steel are mainly the copper texture with {112}<111>and the rotated brass texture with {110}<1-11> as well as the cube texture with {100}<001>，except the weak Goss texture with {110}<001>． The deformation processes ofFe-25/29Mn-3Al-3Si steels with higher Mn contents were accompanied with deformationtwinning in the process of tensile testing，which was the TWIP effect．In the tensile fracturesamples of Fe-25/29Mn-3Al-3Si steels，there are the dominant <111> texture and the weak<100> texture．...