Microstructure And Mechanical Properties Of Low Carbon 15Mn-3Al Steel

In recent years,in order to meet the automotive industry's requirements for vehicle safety performance,economic performance,environmental protection and other performance and quality.Research institutions such as universities,research institutes,and steel research institutes are constantly making reformation and innovation.Transformation Induced Plasticity(TRIP)steel and Twinning Induced Plastic(TWIP)steel have become the main research hotspots at this stage.However,research is mainly focused on high-carbon,ultra-low-carbon,carbon-free TWIP steel,and research on low-carbon TWIP steel is rare.In addition,the research on hot-rolled low-carbon high-manganese TWIP steels is relatively rare.The production process of hot rolled high strength steel is relatively simple and the cost is low,which not only can be applied to the automobile industry,but also can be used as a structural part and has great potential application space.Therefore,in this paper,a new type of low-carbon silicon-free manganese steel(Fe-15Mn-3Al-0.19C steel)was designed to systematically study the mechanical properties and microstructure of hot rolled Fe-15Mn-3Al-0.19C steel during different annealing processes,the microstructure evolution and deformation mechanism during tensile deformation and the microstructure,impact performance and deformation mechanism during temperature-changing impact.The main research contents and results of this paper are as follow:(1)The hot rolled and air-cooled steels were annealed for different temperature and time.The results showed that as the annealing temperature increased,the ultimate tensile strength of investigated steels decreased firstly and then increased,while the total elongation increased firstly and then decreased.As the annealing time increased,the ultimate tensile strength of the investigated steels increased firstly and then decreased,while the total elongation decreased firstly and then increased.The investigated steel obtained excellent mechanical properties with ultimate tensile strength of 707 MPa,total elongation of 64%and product of strength and elongation of 45 GPa·%.after annealing at 850? for 5 min.Besides,the influence of cooling ways on mechanical properties was investigated.The results showed that compared with the hot rolled and air cooled steels,the hot rolled and water cooled steels presented better ultimate tensile strength and total elongation.(2)After the same heat treatment,the tensile strength and elongation of hot rolled water-quenching experimental steel were lower than that of the air-cooled experimental steel.(3)The microstructure before/after tensile test and fracture morphology of the investigated steels were characterized.The results showed that a large amount of mechanical twins and a little martensite transformation were found during tensile deformation indicting the occurrence of TWIP effect and TRIP effect.(4)The impact toughness of the investigated steels was examined under various temperatures.The result shows that The impact toughness of the test steel at room temperature is maintained at around 180 J/cm2,the impact toughness was little affected by temperature,When the temperature ranges from-50?75?,the impact toughness of air-cooled experimental steel increases from 160J/cm2 to 180J/cm2,which is largely affected by temperature.When the temperature is in the range of 25?-75?,the impact toughness of water-quenching experimental steel increases from 150 J/cm2 to 180 J/cm2.(5)The microstructure after impact test and fracture morphology of the investigated steels were characterized.The results revealed that the investigated steels presented ductile fracture under different impacting temperature.A large amount of mechanical twins and a little martensite transformation were observed after impacting test indicting the occurrence of TWIP effect and TRIP effect.