Study On The Performance Control And Strengthening And Toughening Mechanism Of Hot-rolled And As-cast Low Density Steel

Aging-strengthened austenitic Fe-Mn-Al-C low-density steel has characteristics of high manganese,high aluminumand high carbon,which always cause problem such as significant structural defects and difficult of processing.In order to achieve the successful application of this type of steel in automobile manufacturing and other fields,this article takes the aging strengthened austenitic low-density steel Fe-30Mn-9Al-1C-1Si-0.5Mo as the research object.From the aspects of processing strategy selection and heat treatment process optimization,the high-temperature deformation behavior of the steel was studied and thethermal processing map was constructed.The relationship between the structure and properties of Mn30Al9Si steel and heat treatment process and its strengthening and toughening mechanism were studied.The structure,properties and strengthening and toughening mechanism of low-density steel obtained by different processing strategies were compared and analyzed.The main research contents and conclusions of the paper are as follows:(1)The hot deformation behavior of Mn30Al9Si steel was studied by Gleeble simulation compression experiment,and thethermal processing map based on Prasad instability criterion was constructed.The results show that the deformation resistance increases with the increase of strain rate and decreases with the increase of deformation temperature.In addition,according to the hot working diagram,the best hot working window is the parameter area of deformation temperature 1000??1050?,strain rate0.1s^-1?1s^-1.(2)Taking the hot rolled Mn30Al9Sisteel as the object,the relationship between heat treatment process and microstructure and properties and the mechanism of strengthening and toughening were studied.The results show that with the increase of solution temperature and solution time,the grains grow up and the volume fraction of annealing twins increases.After aging treatment at 450?and 500?,the?-carbides dispersed in austenite,which endows Mn30Al9Sisteel with excellent strength and toughness.After aging at 550?,the?-carbide in the matrix disappears,and the continuous transformation of??B2?DO3 takes place in the ferrite.The yield strength of the material increases and the plasticity decreases greatly.The strengthening and toughening mechanism of hot rolled Mn30Al9Si steel is dominated by the microstrip induced plasticity(MBIP)effect.(3)Taking as-cast Mn30Al9Si low-density steel as the object,the relationship between heat treatment process and microstructure and properties,as well as the strengthening and toughening mechanism were studied.The results show that the carbide in the original structure dissolves and the grain grows gradually with the process of solid solution.The distribution of?-carbides in the matrix after aging at 450?gives the as cast Mn30Al9Si steel good ductility.With the increase of aging temperature,?-Mn precipitates in the matrix,and its content increases with the increase of aging temperature.The strengthening and toughening mechanism of as cast Mn30Al9Si steel is dominated by the microstrip induced plasticity(MBIP)effect.(4)The relationship between the microstructure,properties and heat treatment process of Mn30Al9Si steel under different processing strategies was compared and analyzed.The properties of hot rolled and cast Mn30Al9Si steels and the reasons for the similarities and differences in strengthening and toughening mechanisms were analyzed,the results are as follows.Unlike cast Mn30Al9Si steel,a large number of annealed twins are generated in the hot-rolled specimen during solution treatment.The existence of twin boundaries hinders the movement of dislocations and the generation of slip,making it strong plastic due to as-cast Mn30Al9Si steel.After high temperature aging,different types of brittle phases were precipitated in the hot-rolled and cast steel substrates,respectively DO3 and?-Mn,which greatly reduced the elongation of Mn30Al9Si material.