Tensile Properties And Fracture Mechanism Of Cold Rolled Low Carbon Martensite Steel At Different Strain Rates And Temperatures

The mechanical properties of metal materials measured by tensile test are the important basis for their production and practical application.It is found that the tensile test results vary with the change of tensile temperature or strain rate.To study the effect of strain rate and temperature on the properties of materials and to determine the true properties of materials is a basic research topic of metallurgy,which is very important for the actual production and application of materials.In this paper,low-carbon steel with quenched cold-rolled and fully annealed state is selected as experimental material.Tensile tests were carried out at different tensile temperatures and strain rates to analyze the effects of tensile conditions on the mechanical properties of the material.The effects of temperature and strain rate on the microstructures and atomic segregation behavior of materials after tensile deformation were studied by means of metallographic microscope,scanning electron microscopy and transmission electron microscopy,and the fracture mechanism under different tensile conditions was analyzed.The results show that the properties of the same structure of the tested steel are different at the same temperature and different tensile rates,that is,there is uncertainty in testing the tensile rate of mechanical properties.When stretching at 85?at the same rate,strength rebound occurs,that is,there is uncertainty in testing the tensile temperature of mechanical properties.When quenched and cold-rolled specimens are stretched at high strain rates from room temperature to 200?,the microstructure of the material is still deformed lath martensite.The number of dislocation channels available for C atom segregation increases,and the degree of segregation at weak interface increases,so the strength is greater than that at low strain rate.When tension is carried out at high strain rate at 600?,the strength of high strain rate is higher than that of low strain rate because of insufficient recrystallization.When specimens were stretched at 3×10^-1 s^-1/85?,the solute atoms segregated most at the weak interface,and the maximum strength appeared.When the tensile temperature of annealed samples is constant,compared with low strain rate,dislocation slip is hindered at high strain rate,the strength increases,the elongation decreases,and the deformation degree of ferrite and pearlite near the fracture surface is small.At the same rate,with the increase of temperature,the resistance of lattice to dislocation motion decreases,which promotes dislocation slip and grain boundary diffusion.The dislocation density decreases,the strength decreases,and the ferrite elongation near the fracture increases.There are obvious delamination cracks on the fracture surface of quenched and cold rolled specimens when they are stretched at room temperature to 200?,and there are more delamination cracks and stronger strength at high strain rate.The inner side of delamination cracks is cleavage fracture,and the morphology of elongated dimples is between delamination cracks.At high temperature,the weak interface decomposes and the delamination crack disappears,and the fracture surface is dimple morphology.The tensile fracture morphology of annealed specimens is equiaxed dimple.With the increase of temperature or the decrease of strain rate,the dimple diameter increases and the dimple depth increases.