Study On Microstructure And Properties Of High Strength And Toughness Cold Stamping Tool Steel

With the transformation and upgrading of the automobile and product iteration cycle continues to shorten,higher requirements are put forward for the die processing level and speed of automobile parts.In the next few years,precision and complex cold stamping dies will become the focus of the development of the die industry.The basic research of China's tool steel industry is weak,and the steel in the high-end market is heavily dependent on imports.Therefore,the research on the strengthening and toughening of cold stamping tool steel has important theoretical and practical value.In order to explore the difference mechanism of microstructure and properties of tool steel products at home and abroad and improve the quality of domestic tool steel,three typical cold stamping tool steels,domestic Cr8Mo2 Si V,Datong DC53 and ASSAB Calmax,numbered 1#,2#,3#,were studied by means of DSC,TMA,SEM,XRD,hardness test,impact toughness test and other analysis methods,systematically study the phase transformation characteristics,microstructure,mechanical properties,corrosion resistance and dimensional stability of the test steel,and explore the heat treatment process to improve the annealing structure of domestic Cr8Mo2 Si V steel,so as to provide data reference for the selection of steel type and heat treatment process.The main research contents are as follows:Firstly,through the comparative analysis of the microstructure and properties of the three test steels,the difference mechanism is deeply discussed.The results show that: the unevenness grades of eutectic carbides in annealing structures of 1# steel,2# steel and 3# steel are grade 2,grade 1 and less than grade 1 respectively,and the annealing hardness is 255 HB,240HB and185 HB respectively,the difference of hardness is caused by the joint action of alloy composition and carbide morphology;After conventional quenching process,the residual austenite content(volume fraction)of 1# steel,2# steel and 3# steel are 12.61%,14.15% and 7.57% respectively,and their quenching hardness are 62.3HRC,62.6HRC and 58.3HRC respectively,2# steel has strong solid solution strengthening effect during quenching;After two tempering treatments at520?×2h,it was found that 1# steel and 2# steel have obvious secondary hardening phenomenon,and their tempering hardness is significantly higher than that of 3# steel,but the impact toughness of 3# steel is more excellent;The high content of Cr,Mo and other elements in1# steel and 2# steel is the key to ensure the corrosion resistance,but the higher content of residual austenite also makes its dimensional stability inferior to that of 3# steel.At the same time,the effect of stabilization with additional tempering on the properties of the test steel was also investigated.It was found that the stabilization with additional tempering at 400°C did not cause a significant decrease in the hardness value of the test steel and no significant change in its corrosion resistance,but the impact toughness and dimensional stability of the material were effectively improved.In addition,for the problem of uneven distribution of annealed microstructure in domestic1# steel,a new process of rapid pre-cooling isothermal spheroidizing annealing is used,and combined with the principle of orthogonal test,range and variance analysis,the best combination of process parameters is sought.The results show that: the rapid precooling isothermal spheroidizing annealing process with heating temperature of 840?,heating time of 0.5h,isothermal temperature of 740? and isothermal time of 1H is selected to improve the cutting performance and obtain fine and uniform spherical pearlite structure of carbide,and after the same quenching and tempering treatment,its impact toughness is 56.6% higher than that of the original annealing process,can be compared with imported 2# steel.At the same time,the annealing process only takes 1.5h,which greatly shortens the delivery cycle and reduces meaningless energy consumption.It not only meets the requirements of enterprises for steel quality,but also conforms to the manufacturing concept of energy conservation,emission reduction,consumption reduction and efficiency enhancement in China.