Study On Solidification And Thermal Deformation Of Large Size Die Steel Ingot

Die steel is a kind of common alloy tool steel,which is mainly used in the manufacture of various molds.Large size die steel is mostly formed into ingot by die casting,and then formed into module by forging.The mold of required size can be obtained by cutting module.Domestic steel mills usually cast polygonal ingot for module production,flat ingot began to rise in recent years,many steel mills choose to make module with flat ingot.In order to explore the influence of flat ingot and polygonal ingot on the quality of die steel,the solidification and thermal deformation processes of flat ingot and polygonal ingot with the same tonnage were studied in this paper.Numerical simulation and industrial test were combined.The temperature field,flow field,carbon segregation distribution during solidification of ingot,as well as the temperature,equivalent stress and equivalent strain during forging process are studied.It is concluded that under the condition of the same ingot weight,the quality of properly designed flat ingot is better than that of polygonal ingot.In the process of solidification,the flat ingot of the same solid phase rate is reduced by the volume of the same solid,and the air gap is thinner than the multi-angle ingot,the time is short,the fluid is large in the radial space,and the transfer of heat and the diffusion of the solute.The flow field distribution and solidification time are closely related to segregation defects.The longer solidification time is,the more serious positive segregation is at riser.The higher the temperature of liquid steel,the smaller the viscosity,the faster the flow rate,so the flow field distribution of high velocity is more dispersed,conducive to heat and mass transfer,the lighter the segregation degree.By comparing the segregation between 28 t flat ingot and polygonal ingot,it is found that the segregation degree of flat ingot is light,and the carbon segregation range of the ingot body is 18.56% lighter than that of polygonal ingot.Field test results also show that under the same tonnage condition,the segregation degree of flat ingot is light,and the carbon segregation range of the ingot tail and riser section is improved by 36.05% compared with that of the polygonal ingot.When the finished product is a module,the shape of the flat ingot is similar to the module,and the edge and Angle of the polygonal ingot are less,there is no need to give priority to "chamfering" treatment,so under the condition of the same ingot weight,the forging process of the flat ingot is short,the temperature loss at the edge and Angle is less,the deformation resistance is small,the internal deformation is uniform,the surface quality is better;The cutting rates of flat ingot and polygonal ingot are 9.21% and 12.36% respectively,so the metal utilization rate of flat ingot is high,which avoids material loss and reduces cost loss.The cutting rates of 28 t flat ingot and polygonal ingot were 19.75% and 23.49%,respectively,which also confirmed the high metal utilization rate of flat ingot with the same tonnage.The final results show that: when the forging product is module,whether in the solidification process or the forging process,under the condition of the same ingot weight,the reasonably designed flat ingot has light segregation degree,good surface quality,uniform internal deformation and high material utilization rate due to the advantages of its ingot structure.