Research Of Bonded Interface Of High-Speed Steel Composite Roll

The bonded interface is an important part of the composite roll.And the properties of the composite roll are closely related with the nature of bonded interface.Firstly,according to the solidification temperature field simulation results of composite roll produced by compound casting,the curve of temperature changing with solidification time was fitted in interface.Then,taking the element concentrations on the roll core and work layer and temperatures in interface as initial conditions,this paper used the Dictra software to calculate and analyze the diffusion behavior of interface elements.Then,based on the element concentrations in interface calculated above,the carbides precipitation laws influenced by different element with different concentration were reseached using Thermo-Calc software.Finally,the microstructure and components of bonded interface of present high speed steel composite roll were analyzed.The conclusions could be obtained as following:The elements in interface diffuse from high concentration area to low concentration area,and the diffusion rate and distance decrease with the temperature reduce in the interface.The C and Si diffuse full out,and C also presents uphill diffusion.The Cr,W,V and Mo diffuse gently with no mutation.The diffusion distance of elements in interface increase firstly and then trend to steady with the temperatures and time.In this calculation conditions,the diffusion distance of Cr,V,Mo and W is 14 μm,16 μm,18 μm and 16.5 μm respectively.The carbides precipitation laws influenced by alloy elements in interface were reseached and detected that the W influences the precipitation temperatures of M6C and MC_SHP,but a little influence on the precipitation temperatures of M23C6 and M3C2.The maximum precipitation of M23C6,MC_SHP and M6C influenced greatly by W,but the maximum precipitation of M7C3 and M3C2 were influenced a little by W.At the same time,the starting transition temperatures from M23C6 to M7C3 reduce with the increase of W.The precipitation temperatures of M23C6 and M6C increase with the increase of Mo and the precipitation temperatures of other carbides decrease.With the increase of Mo,the maximum precipitation of M23C6 and M6C increase,but that of M7C3 decrease and other carbides were influence a little.With the increase of Cr,only the precipitation temperatures decrease and precipitation amounts nearly stay the same,but the precipitation temperatures and precipitation amounts of other carbides increase.The starting transition temperatures from M23C6 to M7C3 go up.With increase of V,the precipitation temperatures of M7C3 and MC_SHP go up firstly and then reduce.The precipitation temperatures of M23C6 decrease firstly,then increase and finally decreased with the influence of V.The precipitation temperatures and precipitation amounts were greatly influenced by V.The maximum precipitation of M23C6 decrease.The starting transition temperatures from M23C6 to M7C3 were 820 to 880 K.The macroscopic detection of the bonded interface of high speed composite roll has found that the bonding line is distinct and keeps circular,fully indicating that the uniformity of the composite process between the working layer and the roll core.The matrix microstructural of high speed steel side is martensite and various carbides distribute in matrix which made work roll high hardness and abrasive resistance.The matrix microstructural of alloy steel is lath martensite.Through the scanning electron microscope(SEM)and energy dispersion spectroscopy(EDS)analysis,it can be found that some inclusions and small carbides exist in interface.The results of line scanning show that alloy elements distribution trend in interface,which diffuse from high concentration to law concentration,is similar to that distribution trend calculated by Dictra software.Based on the studies above,this paper argues that the liquid-solid bonding mechanisms of bimetal composite roll contain two stages which are mechanical contact and diffusion bonding.