A Study On Microtructure And Mechanical Properties Of A Kind Of Martensite High Strength Low Carbon Steel

After stepping into the 21th century,the global steel industry has entered a new stage.A new generation of iron and steel materials is heavily used,and the strength of steel has increased one times,the service life of steel member is longer,the safety of steel structure and equipment are greatly increased,the author hopes to optimize the consumption of steel,steel production and use to achieve the purpose of reduction.This thesis uses low carbon martensite high strength steel BS960 as research object,studying the samples along the width of the raw materials of different position of steel to solve the deformed problems Analyze the microstructure with optical microscope,SEM,TEM and so on.Test the physical properties of samples with tensile testing machine,thermal expansion instrument,internal friction instrument and the method of specific volume.And the untreated samples were analyzed by different temperature quenching and tempering testing,finally through a series of experimental data to determine the cause of the deformation.The research results turn out as follows:the deformation of BS960 steel is mainly due to the different microstructures.Through metallographic observation that steel plate during quenching cooling rates were inhomogeneous so that microstructure were inhomogeneous,and the TEM had confirmed that the core of quenching steel had the presence of carbides.The internal friction peak of edge samples and core samples were:4.801*10-3,3.593*10-3,the peak edge higher than the core 25.16%.Under conditions of the same dislocation density,this difference is due to interstitial carbon atoms of the edge are higher than the core.This was a strong evidence to prove the existence of a certain amount of core non-quenched martensite structure.Thermal expansion experiment indicates that the martensite content of the core was less than the edge,and the method of specific volume measure the volume of martensite of different positions of steel plate along the direction of the plate width.Comparing with the thermal expansion method,the method of specific volume was higher precision.For the sample without heat treatment were tested with the following processing:different final quenching temperature,different cooling rates and different tempering temperatures.When the final quenching temperature was 50?,martensite was appeared obviously,and the hardness of samples was increased to HV356,the mechanical properties were improved greatly.And when the cooling rate increased to 40?/s,martensite was appeared obviously.The faster the cooling rate,the better the mechanical properties.At the same time,the method of specific volume was used to analysis the samples of quenched,20?,300?,400?,500? along the direction of the plate width of different position,and the combination of internal friction experimental analysis to ultimately determine the 300? was the optimum tempering temperature.