Effect Of Temperature,strain Rate And Strain On Microstructure And Tensile Properties Of Fe-10Mn Steel

At present,how to solve the problems of energy shortage and environmental pollution has become the focus of social concern.The research proves that the reduction of body mass is beneficial to the reduction of fuel consumption.As the third generation advanced high strength steel,TRIP/TWIP steel can ensure the lightweight of automobile without reducing the safety of automobile.The purpose of this paper is to obtain different microstructures by adopting different Quenching and Partitioning(Q&P)heat treatment for Fe-10Mn steel.The tensile property of Fe-10Mn steel at different temperatures and strain rates was also analyzed.The micro structures of Fe-10Mn steel were observed by scanning electron microscopy(SEM)and transmission electron microscopy(TEM)under different conditions;the content of austenite in Fe-10Mn steel before and after tensile deformation was measured by vibrating sample magnetometer(VSM);electron probe(EPMA)was used to analyze the distribution of elements in Fe-10Mn steel.The main results are as follows:Fe-10Mn steel was treated by Quenching and Partitioning(Q&P)heat treatment to investigated the effects of intercritical annealing temperature,partitioning temperature,intercritical annealing time and partitioning time on the micro structures and mechanical properties of Fe-10Mn steel.The experimental results show:the microstructures of the Fe-10Mn steel after Quenching and Partitioning(Q&P)heat treatment contained lath and block austenite,ferrite and a small amount of martensite.Under the heat treatment process of 630?/20 min+100?/5 s+340?/5 min,the content of austenite was 68.6%,the content of austenite with martensitic transformation after tensile deformation was 49.4%.Stress induced martensitic transformation of austenite improved the strength and plasticity of Fe-10Mn steel.Compared with intercritical annealing process,after Quenching and Partitioning(Q&P)heat treatment,the yield strength of Fe-10Mn steel increased from 346 MPa to 432 MPa,increasing by 25%;the tensile strength increased from 1256 MPa to 1334 MPa,increasing by 6%;the elongation increased from 38%to 41%,increasing by 8%;the product of strength and elongation increased from 47.72 GPa·%to 54.69 GPa·%,increasing by 15%.The tensile tests of Fe-10Mn steel after intercritical annealing were carried out at different temperatures and strain rates.The experimental results show:when the strain rate was fixed,the tensile strength of the steel decreased with the increase of temperature;when the strain rate was 1×10-3 s-1,the elongation reached the maximum value of 48%at 100?;decreased from 48%to 40%at-50? and from 48%to 35%at 300? respectively.When the temperature was fixed,the product of strength and elongation of Fe-10Mn steel decreased with the increase of strain rate.When the temperature was 100? and the strain rate was 1×10-3 s-1,Fe-10Mn steel obtained the best comprehensive mechanical properties.The tensile strength was 1168 MPa,the elongation was 48%,the product of strength and elongation was 56.06 GPa·%.The microstructures of Fe-10Mn steel after tensile tests were analysed at different temperatures and strain rates,the experimental results show:when the strain rate was 1×10-3 s-1,the content of austenite decreased from 67.5%to 18.2%at-50?,the elongation is 40%;when the temperature rised to 100?,the content of austenite decreased from 67.5%to 32.0%and the elongation was 48%.The deformation mechanism of the former was phase transformation induced plasticity(TRIP)effect,while the latter was TRIP effect and twin induced plasticity(TWIP)effect,so the latter had the highest elongation.When the temperature continued to rise to 200? and 300?,the content of austenite with martensitic transformation gradually decreased,resulting in a decrease in the elongation.Fe-10Mn steel shown obvious dimples at various temperatures and strain rates,which was a typical ductile fracture.Tensile tests of Fe-10Mn steel under different strains were carried out and the content of austenite was analyzed by VSM.The experimental results show:when the strain was less than 20%,the content of austenite with martensitic transformation was more,while when the strain was more than 20%,the content of austenite with martensitic transformation was less,it shown that TRIP effect mainly occured in the early stage of tensile deformation.