| TWIP steel has the advantages of high strength,high plasticity,good formability,high energy absorption capacity and no low temperature transition brittleness.And its strong plastic product is also far ahead of advanced high strength steel.However,its lower yield strength limits its more applications in industry.How to improve its yield strength while retaining its excellent elongation is a difficult problem in the development of TWIP steel.This article takes Fe-25Mn-3Al-3Si-0.3C-0.3V TWIP steel as the research object,using optical microscope（OM）,scanning electron microscope（SEM）,X-ray diffractometer（XRD）,transmission electron microscope（TEM）,the tensile test at room temperature and other research methods studied the effects of warm rolling temperature,reduction,rolling pass isothermal rolling parameters on the microstructure and mechanical properties of the experimental steel.At the same time,the microstructure and mechanical properties of Fe-24Mn-0.05C-2Al-1Si TWIP steel under different annealing processes were studied.The main experimental results are as follows:（1）The warm rolling process can effectively improve the strength of TWIP steel while retaining its good elongation.Different warm rolling temperatures can obtain different combinations of mechanical properties.Among them,the strength of the experimental steel which warm rolling at 600℃is the highest and the ultimate tensile strength is 1150 MPa,theσ0.2 yield strength is 1121 MPa,the elongation is 25%,and the best elongation of the experimental steel which warm rolling at 700℃is 49%.A large number of deformed twins did not appear in the experimental steel after warm rolling,and there were a large number of deformed structures such as beam stacking faults and dislocation defects.However,a large number of cluster-shaped deformed twins appeared in the warm rolled experimental steel after the tensile test.This is because the toughening mechanism of the experimental steel during warm rolling changed from twin slip at room temperature to dislocation slip,and the toughening mechanism of the warm rolled steel during tensile deformation remained unchanged.（2）Annealed hot-rolled steel combined with multi-pass warm rolling can obtain TWIP steel with high yield strength and high plasticity.Most experimental steels have aσ0.2 yield strength of more than 800 MPa and an elongation of more than 60%.There are obvious differences in the mechanical properties of the experimental steels with different rolling reductions.When warm-rolled the experimental steel at a large reduction（40%）has a higher strength and when warm-rolled the experimental steel at a small reduction（30%）has better elongation.The warm rolling pass has a smaller increase in the strength of the experimental steel,but it has a greater impact on the elongation of the experimental steel.Multi-pass during small reduction rolling is beneficial to obtain better mechanical properties.And fewer-pass during large reduction rolling is beneficial to obtain better elongation.（3）With the change of the annealing process,the microstructure of the experimental steel gradually changed from the unrecrystallized deformed grains containing high-density dislocations during the recovery annealing to the recrystallized grains during the high-temperature annealing.As the grain grows,straight strip-shaped annealing twins begin to appear in the grain.With the change of the annealing process,the strength of the experimental steel gradually decreases and the plasticity gradually increases.Theσ0.2 yield strength decreased from 969 MPa during warm rolling to 154 MPa during high temperature annealing,the ductility increased from 9%during warm rolling to 120%during high temperature annealing.The main change trend of the hardness of the experimental steel before and after stretching was to decrease first,then not change and finally increase.Beause the toughening mechanism of the experimental steel gradually changed from dislocation slip to twin slip,and the TWIP effect continued to increase. |
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