Investigation On Preparation Of Two Alloys Turbine Rotor And Microstructure Simulation By Electroslag Remelting Process

Electroslag remelting(ESR)is a complex refining technology,which contains many physical phenomenons and chemical reactions such as flow,heat transfer,mass transfer,solidification,electromagnetic induction.Because of its unique advantages in improving the molten steel purity,reduce segregation and so on,the ESR technology has been widely researched and applied in the field of special metallurgy and fine metallurgy.With the development of the national economy,the industry increases the demand for high quality steel.So the ESR technology is continuously booming.With advantages of a narrow translation zone and consecutive microstructure,the sequence preparation of the turbine rotor by ESR process is an important innovation.In the actual production process,the operating parameters,such as melting current,fill ration and slag thickness,play an important role in the quality of the ESR ingot.My study respectively research the effect of melting current,slag thickness and consumable electrode fill ratio on the remelting of two alloys electrode in ESR by experiment.Then,by means of numerical simulation,the melting current and electromagnetic stirring's impacts on microstructure of the ESR ingot are studied.The main research topics:(1)In the ESR experiment,two kinds of cylinder alloys with different Ni concentration are welded into a consumable electrode.Research of different melting current,slag thickness and fill ratio on the depth of molten pool,melt rate,slag pool temperature,microstructure,transition zone morphology and Ni element segregation in the electroslag remelting process is applied.By comparing different experimental results,optimize operating parameters will be concluded.(2)In the numerical simulation part,a transient two-dimensional(2D)axsymmetric model is developed to understand the effect of the melting current and electromagnetic stirring(EMS)on the depth of molten pool,temperature field,solidification filed and the grain morphology of the ESR ingot.The finite element method is used to simulate the ESR process,and the cellular automaton-finite element technique is employed to describe the nucleation and growth of the grain.The research concluded:(1)In the ESR process,melting current density has an important effect on remelting and solidification process.With the increase of melting current,the consumable electrode melting ratio and slag pool temperature rising,which makes smelt efficiently.And dendrite morphology showed a trend of refining and the melting quality is better.But the metal pool is deeper,melting rate and slag pool temperature rises,the segregation of Ni elements becomes graveness and the translation zone changes from a uniform line to a blurry shape.Comparing with the numerical simulation result,there will be a critical melting current where the grain is finest and secondary dendrite arm spacing(SDAS)is minimal.(2)The amount of slag in the water cooling mold is another element which effects the remelting process.The melting rate of consumable electrode,the thickness of the transition zone,the degree of Ni element segregation and the grain size show a decline after the first rising trend with the increase of slag thickness.But the slag pool temperature still drops.In the two of experiments,the spot segregation is found in the ESR ingot macrostructure.So the relation among spot segregation,macro segregation and bubble inclusion is analyzed.(3)Contrasting three different filling ratio groups of ESR experiments,it is found that,with the increase of filling ratio,the melting rate of electrode increases,Ni elements segregation continuously highs,the grain size rises,the translation zone expands and the slag pool temperature rises.At the same time,in the longitudinal cross-section profile center of two groups of large fill ratio ingots,some equiaxed grains are discovered,which can influence the mechanical and processing properties of the ingot and it should be avoid.(4)In the 200kg ESR furnace,whose mold size is ?120×600mm,it can be determined that when remelt the AISI 202 alloy with an electrode diameter of 55 mm,choose the slag thickness 60 mm,melting current 1800A can smelt a ingot in high quality.(5)Electromagnetic stirring technique can significantly improve the quality of esr melting ingot.After loading the electromagnetic stirring,the growth direction of the grain at the bottom is the same as usual,while changes to the radial as the ingot grow and the number of equiaxed grain in the chilling layer by the ingot has a huge increase.The grain is significantly refined by the EMS.Both the local solidification time and SDAS decreases with the increasing stirring intensity.But the deeper metal pool favors macro-segregation formation.