Study On Hot Deformation Behavior Of Low Density Automobile Steel Containing Medium Manganese And High Aluminum

With the rapid development of Chinese automobile industry,energy crisis and environmental pollution become more and more serious.Vehicle lightweight has become an effective way to solve this problem.Fe-Mn-Al-C steel has high strength,high toughness,low density and good corrosion resistance.Under the premise of ensuring excellent formability and impact resistance,the effect of weight reduction is obvious,which is the development direction of automotive steel in the future.Metal and alloy are usually used after hot processing.To understand the deformation behavior under different deformation conditions is very important for formulating the forming processes.At present,there are few studies on the hot deformation behavior of low density automobile steel containing medium manganese and high aluminum.Therefore,it is of great significance to study the hot deformation behavior of low density automobile steel containing medium manganese and high aluminum and control its deformed microstructures and properties.In this paper,an experimental steel with a composition of Fe-11Mn-10Al-0.9C is designed,which is composed of austenite and ferrite at high temperature.The thermal deformation behavior of the experimental steel are studied by single-pass compression experiment with Gleeble-1500 at 800?1050?and 0.001?1s-1.On the basis of the true stress-strain curved,the influence of deformation degree,deformation temperature and strain rate on the deformation resistance of experimental steel is analyzed.The Z parameter is determined and the constitutive equation of the experimental steel is established.The activation energy of the experimental steel is calculated to be 485kJ·mol-1.The critical stress value of dynamic recrystallization is obtained by fitting the relation curves of ?-?by cubic polynomial,and the relationship between the critical stress and the peak stress is obtained.The effect of different deformation conditions on microstructure is investigated by observing the metallography of the specimens.With the decrease of strain rate and the increase of deformation temperature,the austenite volume fraction and the recrystallization degree increases.The equiaxed grain size increases,and a large number of coarse annealing twins appear in austenite.The deformation of austenite is dominated by dynamic recrystallization and the deformation of ferrite is dominated by dynamic recovery.The deformation process is more sufficient with the increase of the deformation temperature and the decrease of the strain rate.At low temperature and low strain rate,the original deformated austenite is decomposed into ferrite and ?-carbide.It is more beneficial to the formation and growth of ?-carbide at lower deformation temperature and strain rate.The ?-carbide is brittle and hard,which can increase the hardness of the material.However,the large size of ?-carbide leads to the formation of microcracks at the grain boundary.According to the dynamic material model,the hot processing maps of the experimental steel are drawn.By combining the processing maps with the microstructures,the reasons of the instability during the deformation processes are analyzed.The best process area of heat processing is 925?1050? and 0.1?s-1.