Mechanism Of Effect Of Deformation On Continuous Annealing Process Of Medium Manganese Steel

In the stduy,taking micro alloyed medium manganese steel as the research object,simulation of thermal deformation and reversion annealing process of austenite in austenite region and two-phase region of medium manganese steel were studied.The microstructure was characterized by optical microscopy,scanning electron microscopy,transmission electron microscopy and X ray diffraction.The mechanical properties of medium manganese steel were characterized by room temperature micro-tensile test,and the effects of thermal deformation parameters on the microstructure evolution and mechanical properties were analyzed.Experimental results are as follows:(1)On the basis of the traditional C-Mn steel,trace alloying elements niobium,molybdenum and titanium were added.The composition of the experimental steel was Fe-0.15C-1.2Si-5Mn-0.09Nb-0.08V-0.07Mo(wt.%).The static CCT curve of the experimental steel is made.The experimental results show that the alloy element expands the austenite temperature zone,and the temperature of AC1 and AC3 of the experimental steel is lower than that of the traditional C-Mn steel.Therefore,the low temperature critical annealing process can be realized.(2)The thermal deformation temperature has a great influence on the grain size of martensite.The grain size of martensite reaches the minimum at 750?.The average lamellar thickness is only 2.61 um,The martensite structure is obviously refined.The fraction of the residual austenite with thermal deformation increased gradually,The fraction of retained austenite can reach above 20% at the deformation temperature of950?;(3)Effect of the deformation temperature on the elongation,the tensile strength and the yield strength are different.The influence of deformation temperature on elongation and tensile strength is greater than that of yield strength.The tensile strength reaches the maximum at the deformation temperature of 750?,but the plasticity is poor and the product of strength and ductility is low.Under the deformation temperature of 850?,the plasticity reaches the maximum,and the product of strength and ductility reaches over30Gpa·%.The experimental results show that when the deformation in the austenite zone,low temperature can accelerate the formation of residual austenite,high dislocation density matrix to promote the diffusion of carbon and manganese element to improve the stability of retained austenite,mechanical performance are the best;(4)The effect of deformation on the size of duplex microstructure is different.The size of martensite grain decreases with the increase of deformation,and the size,content and carbon content of austenite increase with the increase of deformation.And with the increase of deformation amount,the precipitation of carbide increases gradually,and strain induced precipitation occurs.In terms of mechanical properties,the effect of deformation on the elongation is larger.Under the 30% deformation,the product of strength and ductility of the experimental steel reached a maximum value of 29.2Gpa%.The results show that when the deformation occurs in the full austenite zone,the small deformation can improve the plastic properties and the mechanical properties are the best.