The Influence Of Alloying Elements On The Temperature And Kinetics Of The Solid State Phase Transformation Of The Casting Cold Work Die Steel

Cold work die steel is an important mold,and occupies a pivotal position in the industrial production.Thus,the cold work die steel is required to have high hardness and strength,good toughness,excellent wear resistance and so on.The heat treatment is the most important way to obtain these properties for the cold work die steel,The performance potential is fully exploited,the mold quality and service life are improved when the reasonable heat treatment process is performed for the cold work die steel,and improved the economic benefits.Normally,heat treatment heating process has been based on the Fe-Fe3 C equilibrium phase diagram,but the Fe-Fe3 C equilibrium phase diagram is just a binary equilibrium phase diagram,there are some limitations in the actual production process for the multielement alloy,the temperature can only be estimated.Thus,it is very important significance to find a new method,establish the corresponding relation between the composition and the temperature,to determine the heating temperature of the heat treatment process of the alloy steel.In this paper,the effects of alloying elements(Cr,Mn,Mo and V)on the starting temperature and kinetics of austenite phase transition of Fe-M-C ternary alloy steels were studied,established the relationship between alloying elements(Cr,Mn,Mo and V)and the starting temperature,and the regression equation between the composition and the starting temperature was obtained.Moreover,the practicality of the regression equation was verified by using the casting alloy die steel YBD-3 and DSC99 as the experimental object.The main results are as follows:(1)The phase transition kinetic process of Fe-M-C ternary alloy steel(M = Cr,Mn,Mo and V)from pearlite to austenite can be described in three overlapping steps: site saturation nucleation,diffusion-controlled growth,and impingement correction.The phase transition process is affected by the original organization,alloy content and superheat.The more dense the original organization,which can provide more nucleation position at the same time,but also can shorten the effective diffusion distance of the elements;the more the alloy content,the more restricted the carbon element,and the carbides will play a pinning effect in the growth process of austenite;the greater the degree of superheat,the greater the phase transition driving force,the more conducive to the formation and growth of the austenite phase.(2)There is a linear relationship between the starting temperature of austenitizing phase transition of Fe-M-C ternary alloy steels(M = Cr,Mn,Mo and V)and the alloying elements(Cr,Mn,Mo and V).Among them,in addition to the Mn element,the starting temperature increases with the Cr,Mo and V element contents,and the linear regression equation is as follows: a.Fe-Cr-C ternary alloy steels: (K)= 1037.427+6.420×Cr element contents(wt.%)b.Fe-Mn-C ternary alloy steels: (K)= 1016.823-6.593×Mn element contents(wt.%)c.Fe-Mo-C ternary alloy steels: (K)= 1009.918+11.233×Mo element contents(wt.%)d.Fe-V-C ternary alloy steels: (K)= 1023.706+3.707×V element contents(wt.%)(3)The multivariate regression analysis was performed between the composition of the casting alloy die steel and the starting temperature of the austenitic phase transition.The results show that there is a linear relationship between the starting temperature of the phase transition and the alloying elements contents(Cr,Mn,Mo and V),which can meet demand that the starting temperature of the austenite phase transition is predicted by the regression equation using the alloy steel composition.And the regression equation is as follows:(K)= 1017.960+8.606×Cr element contents(wt.%)-6.863×Mn element contents(wt.%)+5.304×Mo element contents(wt.%)+12.892×V element contents(wt.%)(4)The practicality of the regression equation between the alloying elements contents(Cr,Mn,Mo and V)and the starting temperature of the austenitic phase transition was verified by using the casting alloy die steel YBD-3 and DSC99 as the experimental object.The results show that the organization of the casting alloy die steel YBD-3 and DSC99 are finer,the carbides is smaller and the distribution is more uniform when the second case is used as the heat treatment process,which is based on the predicted value of the starting temperature calculated by the regression equation.Moreover,the tempering hardness is significantly better than the first case(The heat treatment process is designed based on the experimental value of the starting temperature).Besides,the performance test results show that the tensile strength and impact toughness is significantly higher than the first case when the casting alloy die steel YBD-3 and DSC99 using the second case as the heat treatment process.In summary,the influence of alloying elements(Cr,Mn,Mo and V)on the starting temperature and kinetics of austenite phase transition was studied,the regression equation between the alloying element contents and the starting temperature was established,and the practicality of the regression equation was verified by experimental comparison.The purpose was implemented that the starting temperature of the austenite phase transition was predicted by the regression equation using the alloy steel composition,and as a basis to design the parameters of heat treatment process.