The Effect Of Chromium Content On Microstructure And Mechanical Property Of Fe-Mn-Cr-C TWIP Steel

Three kinds of Fe-20Mn-1.2C-XCr TWIP steels with different weight addition ratios of chromium are fabricated in this paper.The specific weight addition ratios of chromium in the Fe-20Mn-l.2C-XCr TWIP steels are controlled to be 0.464,0.875,1.30.The effect of chromium content on stacking fault energy,microstructures,mechanical properties and strain hardening behavior of TWIP steels are studied by means of X-ray diffraction(XRD),scanning electron microscope(SEM)and transmission electron microscope(TEM).And the deformation mechanism and the twinning-induced plasticity mechanism of Fe-20Mn-1.2C-XCr TWIP steels are systematically investigated.The main conclusions are described as follows:(1)The stacking fault energy of TWIP steels with different chromium contents is investigated by means of X-ray diffraction Peak-shift method and thermodynamic modeling,and the phase identification of prior to and after deformed TWIP steels is analyzed by X-ray diffraction.The results show that,with the increase of chromium,the stacking fault energy of TWIP steel decreases and the addition of chromium suppresses the occurrence of ???martensite transformation and promots the generation of deformation twins and TWIP effect.Fe-20Mn-1.2C-XCr TWIP steel specimens are fully composed of austenite without phase transition.(2)The microstructures of TWIP steels during tensile deformation are observed by OM.The results show that,the microstructures of the sample is austenitic and the number of deformation twins and the intensity in austenite increase with the addition of Cr.Moreover,the increase of Cr element is advantageous to the alloy TWIP effect.(3)The results of mechanical properties of TWIP steels with different chromium content showed that,the yield strength,tensile strength and elongation of TWIP steel are significantly improved with the increase of chromium content.The Fe-20Mn-1.2C-1.3Cr TWIP steel has an extraordinary mechanical property,the yield strength,tensile strength and elongation were 498.76MPa,1248.6MPa and 81.9%,respectively.The excellent strain hardening ability of TWIP steel is attributable to the interaction of dislocation glide and deformation twins strengthen.At low strain stage,the dislocation strengthening plays the dominant role,the twins strengthening plays the leading role when strain increases to a certain extent.(4)The microstructures of TWIP steels after tensile deformation are observed by SEM.It is found that the fracture of Fe-20Mn-1.2C-XCr TWIP steel is typical ductile fracture pattern with small and uniform equiaxed dimples.The chromium addition is beneficial to the improvement of TWIP steel's fracture toughness.(5)The microstructure of Fe-20Mn-1.2C-1.3Cr TWIP steel during tensile deformation and the mechanism of twinning-induced plasticity are investigated by TEM.The results show that the dislocation glide and multiplication is the primary mechanism of plastic deformation at low strain,whereas the twins strengthening plays the dominant role as the deformation twins and secondary twins are formed with the increase of strain.The generations of a large number of dislocations provide potential nucleation sites to deformation twins,and the increase of strength and plasticity is attributable to large quantity of dislocation pile-up,the generation of deformation twins and the interaction of each other.