A device and method for preparing high-quality special steel by using a magnetron vacuum self-consumption remelting

Abstract

The application belongs to the technical field of vacuum self-consumption remelting, and particularly relates to a device and method for preparing high-quality special steel by using magnetic control vacuum self-consumption remelting. The hollow cylindrical support ring of the vertical sliding rail stand is fixedly connected through the end rings at the upper and lower ends of the vertical electric arc furnace body, and the coil arrangement frame is sleeved on the outer side of the sliding rail stand; the double-layer lifting coil is fixedly installed on the upper and lower ends of the coil arrangement frame, and is connected with the actuator of the automatic lifting traction platform through the support, and during work, the coil arrangement frame is synchronously lifted to realize dynamic adjustment of the magnetic field generation area. The application establishes a vacuum self-consumption remelting process model, including a thermal-magnetic flow-solidification-solute redistribution coupling model and an inclusion motion trajectory prediction model, carries out multi-field coupling simulation calculation of the magnetic control VAR process, obtains the influence law of alternating magnetic field strength and frequency and other parameters on composition segregation and inclusion migration, and guides accurate setting of the magnetic field parameters in the actual device.

Description

Technical Field

[0001] This invention belongs to the field of vacuum arc remelting (VAR) technology, specifically relating to an apparatus and method for preparing high-quality special steel using magnetically controlled vacuum arc remelting, which is particularly suitable for the industrial production of ultra-pure, low-segregation special steel. Background Technology

[0002] As the final stage of the high-end special steel vacuum induction melting-vacuum arc remelting (VIM-VAR) dual-vacuum process, the VAR process uses a DC arc as a heat source to perform secondary refining of the alloy under vacuum conditions. The molten droplets formed at the tip of the arc remelting electrode pass through the arc gap and fall into a water-cooled copper crucible, gradually solidifying into ingots, playing a decisive role in the quality of the ingot. However, the inherent solute redistribution behavior during VAR solidification leads to significant compositional segregation, severely disrupting the homogeneity of the steel matrix. Furthermore, non-metallic inclusions that enter the molten pool with the droplets from the arc remelting electrode tip cannot be completely removed through conventional flotation separation and wall adsorption; some residual inclusions are captured by the solidification front, resulting in a significant deterioration in steel purity. Both of these metallurgical defects are difficult to eliminate through subsequent forging and heat treatment, easily causing stress concentration and leading to the initiation and propagation of fatigue cracks.

[0003] Due to the limitations of the harsh environment and high cost of the smelting process in experimental research, modeling the transport phenomena in the VAR process based on actual processes has become an efficient and economical method for elucidating its underlying mechanisms. Current VAR solidification simulations mainly rely on early continuous medium models, which lack sufficient ability to accurately predict multi-field coupling and segregation defects. To accurately quantify solute redistribution and inclusion movement behavior, it is urgent to develop an Eulerian solid-liquid two-phase flow model that integrates electromagnetic-flow-solidification synergistic effects.

[0004] Patent CN105132705A discloses a method and apparatus for refining metals using vacuum magnetic arc remelting. This method employs a static magnetic field (fixed installation of permanent magnets / electromagnetic coils), which cannot dynamically adjust the magnetic field position as the molten pool grows, causing the arc zone to deviate from the optimal range of action within the molten pool. Furthermore, the magnetic field effect is only focused on arc stability and grain refinement, failing to address the migration problem of small inclusions. Patent CN118563052A discloses a method for improving the cleanliness of bearing steel vacuum consumable remelting ingots. This method involves adding a horizontal coil outside the crucible and manually adjusting the current after observing the molten pool to counteract the self-induced magnetic field, causing inclusions to accumulate at the edges for subsequent machining removal. However, because the magnetic field direction is horizontal, the stirring efficiency is low. Additionally, because the coil position is fixed, it cannot be adjusted as the ingot grows, and the magnetic field's effective area easily deviates from the molten pool. The patent with publication number CN117947276A proposes an external electromagnetic stirring device for electroslag remelting. The external electromagnetic stirring device for electroslag remelting includes a rotating magnetic field and a traveling wave magnetic field. It adopts a layered fixed magnetic field (upper / middle / lower layer coils), which cannot track the movement of the solid-liquid interface of the molten pool in real time. The stirring force is unidirectional (the traveling wave magnetic field flows longitudinally), and it cannot suppress VAR solute segregation.

[0005] Current VAR technology has very limited ability to remove small inclusions with slow flotation speed and low wall adsorption efficiency, requiring targeted measures to improve inclusion removal efficiency. Magnetic control VAR technology using alternating magnetic fields has been shown to have the potential to improve ingot quality, but its underlying mechanism and specific control strategies based on process characteristics are still unclear, and it faces prominent problems in practical applications such as poor process portability, insufficient control precision and stability. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide an apparatus and method for preparing high-quality special steel using magnetron vacuum arc remelting (VAR), which solves the problems of magnetic field shift, difficulty in removing small-sized inclusions, and severe macroscopic segregation in traditional VAR processes, providing a new technical path for the industrial preparation of ultrapure and highly homogeneous special steel.

[0007] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0008] A device for preparing high-quality special steel using magnetron vacuum arc remelting includes an axial alternating magnetic field generating coil, a coil arrangement frame, a double-layer lifting spiral, an automatic lifting traction platform, and a slide rail column. The specific structure is as follows:

[0009] Vertical slide rail columns evenly distributed along the circumference are fixed to the upper and lower end rings to form a hollow cylindrical support frame surrounding the vertical electric arc furnace body. The coil arrangement frame is fitted onto the outside of the slide rail columns, and the magnetic field generating coil is wound circumferentially and evenly distributed on the coil arrangement frame. A high-temperature resistant gasket is provided between the magnetic field generating coil and the coil arrangement frame. The upper and lower ends of the magnetic field generating coil are connected to a square wave AC power supply. The double-layer lifting solenoid includes two solenoids of the same specification, arranged coaxially. The double-layer lifting solenoid is fixedly installed at the upper and lower ends of the coil arrangement frame. The double-layer lifting solenoid is connected to the actuator of the automatic lifting traction platform through the bracket. When the double-layer lifting solenoid is working, it will drive the coil arrangement frame to rise and fall synchronously to realize the dynamic adjustment of the magnetic field generating area.

[0010] The aforementioned device for preparing high-quality special steel using magnetically controlled vacuum self-consumable remelting comprises a double-layer lifting screw ring encircled on a slide rail column via a sliding self-locking element. The sliding self-locking element is installed between the double-layer lifting screw ring and the slide rail column, with sliding self-locking elements evenly arranged on the inner side of each layer of screw ring. The sliding self-locking element is a concave block structure, with the concave block having a semi-cylindrical notch that encircles the corresponding slide rail column. A ball spring assembly structure is provided on the inner side of the notch, and the ball is pushed to abut against the slide rail column by the spring. The back of each sliding self-locking element is fixedly connected to the double-layer lifting screw ring.

[0011] The device for preparing high-quality special steel using magnetically controlled vacuum self-consumable remelting has an automatic lifting traction platform with a hydraulic cylinder, a support, and a control unit. The control unit includes a PLC controller and a hydraulic control circuit. The control signal output by the PLC controller is sent to the solenoid valve in the hydraulic control circuit. The solenoid valve in the hydraulic control circuit is installed in the hydraulic cylinder oil supply line. The hydraulic cylinder serves as the actuator, and its piston rod is connected to the double-layer lifting screw ring through the support.

[0012] The device for preparing high-quality special steel using magnetically controlled vacuum consumable remelting has thermocouples arranged longitudinally on the outer wall of the electric arc furnace. By referring to the thermocouple readings at different heights, the longitudinal position of the double-layer lifting spiral is adjusted by an automatic lifting traction platform to achieve positioning control of the coil arrangement frame, ensuring that the electric arc area and the molten metal pool are always within the optimal range of action of the magnetic field generating coil.

[0013] A method for preparing high-quality special steel using magnetron vacuum arc remelting includes the following steps:

[0014] Step 1): Establish a VAR process model, including a coupled thermomagnetic flow-solidification-solid redistribution model based on the Euler solid-liquid two-phase flow method, an inclusion trajectory prediction model, and a dynamic computational domain based on dynamic mesh technology;

[0015] Step 2): Determine the physical properties and VAR process parameters of the special steel;

[0016] Step 3): Use the VAR process model to perform multi-field coupling simulation calculations for the preparation of special steel by magnetic control VAR, and obtain the influence of alternating magnetic field strength and frequency parameters on compositional segregation and inclusion migration.

[0017] The method for preparing high-quality special steel using magnetron vacuum arc remelting utilizes a VAR process model for multi-physics coupled simulation calculations. The physical fields include the electromagnetic field, flow field, temperature, and solute distribution of the continuous phase melt, as well as the motion trajectory of the discrete phase inclusion particles. The electromagnetic field distribution is calculated using the following formula:

[0018] Electric potential equation: Current density: Magnetic vector potential equation:

[0019] Self-induced magnetic field strength: Self-induced electromagnetic force: Electromagnetic stirring force caused by external field: Joule fever: Q Joule =J 2 / σ;

[0020] Where σ is the electrical conductivity; It is the electric potential; is the magnetic vector potential; μ0 is the magnetic permeability; The applied axial alternating magnetic field strength.

[0021] The method for preparing high-quality special steel using magneto-controlled vacuum arc remelting, specifically the Euler solid-liquid two-phase flow method in step 1), involves establishing a set of mass, momentum, energy, and solute conservation equations for both the solid and liquid phases, and utilizing the solid-liquid phase transition rate M... ls Connect the two sets of equations, M ls We obtain it from the following formula:

[0022]

[0023] Among them, the dendrite tip growth rate: Radius of the primary dendrite trunk: Far-field radius of the primary dendrite trunk: Dendrite surface concentration: Dendrite growth surface collision:

[0024] Among them, D l The diffusion coefficient of the solute in the liquid phase; and The concentrations of the solute in the liquid and solid phases at the interface equilibrium; λ1 is the primary dendrite spacing; f l f s These represent the liquid phase and solid phase fractions, respectively.

[0025] The flow field distribution in a molten metal pool is calculated using the following formula:

[0026]

[0027]

[0028]

[0029] in, p is the melt velocity; ρ is the pressure. It is the stress-strain tensor; It is the vector of gravitational acceleration; This is the momentum exchange caused by the phase transition; For solid-liquid phase drag force;

[0030] The temperature distribution of the melt is determined by solving the energy conservation equation in enthalpy form:

[0031]

[0032]

[0033] Among them, h l h s These are the liquid phase enthalpy and the solid phase enthalpy, respectively; T l T s For the liquid and solid phase temperatures; k l k s Thermal conductivity; and This refers to the energy source term caused by the phase transition; For energy exchange between solid and liquid phases;

[0034] The solute distribution in the melt is obtained by solving the solute conservation equation:

[0035]

[0036]

[0037] Among them, c l c s These represent the solute concentrations in the liquid and solid phases, respectively; D s The solid-phase solute diffusion coefficient; Solute exchange between solid and liquid phases;

[0038] The volume average concentration c of the solid-liquid two-phase mixture mix Characterizing local solute concentration:

[0039] c mix =(ρ s f s cs +ρ l f l c l ) / (ρ s f s +ρ l f l )

[0040] The equations for the trajectory prediction model of the inclusions in step 1) are as follows:

[0041]

[0042] Where, m p The mass of the inclusion particles; Particle velocity; These are the buoyancy force, interphase drag force, lift force, virtual mass force, pressure gradient force, and electromagnetic pressure acting on the particles, respectively.

[0043] The method for preparing high-quality special steel using magnetically controlled vacuum self-consuming remelting, in step 1), is based on a dynamic computational domain using dynamic mesh technology. Specifically, the molten metal dripping from the electrode continuously enters the computational domain through the top boundary. In each time step, an equivalent mass corresponding to the melting rate is added to the surface of the melt, and the top boundary moves upward in real time accordingly, thus equivalent to the continuous growth process of the ingot.

[0044] The method for preparing high-quality special steel using magnetically controlled vacuum consumable remelting requires the following boundary conditions to be set before simulation calculations in step 3):

[0045] 1) Apply no-slip boundary conditions to both the sidewalls and bottom boundary of the ingot;

[0046] 2) The current density at the top of the molten pool follows a Gaussian distribution:

[0047] Where β1 and β2 are shape factors describing the Gaussian distribution characteristics; r is the distance from each position on the top of the ingot to the center of the electric arc; R a The radius of the electric arc;

[0048] 3) Ignoring thermal radiation from the molten pool surface during the melting of the consumable electrode, the falling metal droplets are continuously heated as they pass through the plasma arc region, and their temperature upon reaching the molten pool surface is:

[0049] Among them, T liq D is the liquidus temperature of the steel grade; i The diameter of the ingot;

[0050] 4) After the electrode melts, the top of the molten pool begins to radiate heat outwards, with a heat flux density of:

[0051] Where ε is the emissivity at the top of the ingot; σ s T is the Stefan-Boltzmann constant; e The ambient temperature;

[0052] 5) The sides and bottom of the ingot are equivalent to convective heat transfer, with a heat flux density of: q conv =h(T)·(T) ingot -T wall );

[0053] Where h(T) is the equivalent convective heat transfer coefficient; T ingot and T wall These are the surface temperature of the ingot and the wall temperature of the crucible, respectively.

[0054] The method for preparing high-quality special steel using magnetron vacuum arc remelting includes the following steps in step 3): establishing a calculation baseline through parameter initialization; using the phase-coupled SIMPLE algorithm to discretize and solve the continuous phase equation and the discrete phase equation; using an axisymmetric mesh for discretization, where the main mesh stores scalar parameters and the staggered mesh records the current density and velocity vector; dynamically adjusting the time step during the calculation, performing a maximum of 60 iterations in each time step to reduce the normalization residual; updating the position and velocity of inclusions in real time based on the Lagrange method, and outputting the calculation results for each iteration; and obtaining the compositional segregation and inclusion distribution patterns under different alternating magnetic field strengths and frequencies through calculation.

[0055] The design concept of this invention is:

[0056] This invention proposes an apparatus and method for preparing high-quality special steel using magnetron vacuum arc remelting (VAR). Through the synergistic effect of a dynamic magnetic field tracking device and a multi-field coupling model, it solves the problems of macroscopic segregation caused by solute redistribution, low flotation / removal efficiency of small inclusions, and deviation of the effective magnetic field area as melting progresses in existing VAR processes. This significantly improves the compositional uniformity and cleanliness of the special steel. The specific design is as follows:

[0057] (1) Dynamic Magnetic Field Tracking: Through a double-layer lifting spiral coil, thermocouple feedback, and PLC control, the magnetic field generating coil follows the position of the electric arc zone and the molten pool in real time, ensuring that the magnetic field always acts on the key areas. The axial alternating magnetic field generating coil arrangement frame is fitted onto the outside of the electric arc furnace body, and its longitudinal position is precisely adjusted through a double-layer lifting spiral coil and an automatic lifting traction platform. The double-layer lifting spiral coil consists of two identical spiral coils, fixed to the upper and lower ends of the coil arrangement frame, connected to a hydraulic cylinder via a bracket, and controlled by a PLC controller using PID control based on temperature data fed back from the thermocouples. Thermocouples are arranged longitudinally on the outer wall of the furnace body to monitor the temperature in real time and provide feedback to the PLC controller to adjust the coil position.

[0058] (2) Multi-field coupling simulation: Establish an Eulerian solid-liquid two-phase flow model, integrate electromagnetic field, flow field, temperature field, solute distribution and inclusion trajectory prediction, quantify the influence of magnetic field parameters (intensity, frequency) on segregation and inclusion migration, and achieve precise parameter optimization.

[0059] (3) Axial alternating magnetic field enhancement: The electromagnetic stirring force generated by the axial alternating magnetic field breaks the flow mode of the molten pool dominated by the self-induced electromagnetic force, and promotes the uniform distribution of solute and the floating of inclusions.

[0060] The present invention has the following beneficial effects and advantages:

[0061] 1. This invention establishes a vacuum arc remelting (VAR) process model, including a coupled thermomagnetic flow-solidification-solidification model and an inclusion trajectory prediction model. Multi-field coupled simulation calculations of the magnetically controlled VAR process are performed to obtain the influence of parameters such as alternating magnetic field strength and frequency on compositional segregation and inclusion migration. This guides the precise setting of magnetic field parameters in actual equipment. This invention utilizes precise electromagnetic control to effectively suppress segregation and efficiently remove inclusions, significantly improving the internal quality of special steels prepared by the VAR process.

[0062] 2. The device of the present invention achieves automated and precise positioning of the magnetic field coil through the combination of mechanical structure (double-layer spiral ring, slide rail column), control system (PLC, hydraulic circuit) and thermocouple, solving the problem of fixed magnetic field action area and inability to adapt to changes in process conditions in the prior art.

[0063] 3. The method of this invention, through the close integration of theoretical models and process practice, not only proposes an innovative physical model, but also uses it to guide the optimization of actual process parameters, and establishes a quantitative relationship between magnetic field parameters and metallurgical quality through statistical methods.

[0064] 4. The "special steel" of this invention mainly includes high-end steel grades with strict requirements for purity, composition uniformity and microstructure, such as bearing steel, heat-resistant steel, stainless steel, tool steel and high-temperature alloys. Attached Figure Description

[0065] Figure 1 This is a schematic diagram of the apparatus for preparing high-quality special steel using magnetically controlled vacuum arc remelting according to the present invention. In the figure, 1 is the cooling water inlet, 2 is the thermocouple, 3 is the sliding self-locking element, 4 is the coil arrangement frame, 5 is the electric arc furnace body, 6 is the double-layer lifting screw, 7 is the square wave AC power supply, 8 is the magnetic field generating coil, 9 is the slide rail column, 10 is the PLC controller, 11 is the piston rod, 12 is the hydraulic cylinder, 13 is the cooling water outlet, 14 is the support, 15 is the upper ring, and 16 is the lower ring.

[0066] Figure 2This figure shows the changes in the molten pool and solute distribution during the VAR process of special steel without an external field, according to an embodiment of the present invention. In the figure, Liquid fraction represents the volume fraction of the liquid phase, and C concentration represents the mass fraction of carbon.

[0067] Figure 3 This figure shows the changes in the molten pool and solute distribution during the VAR process of special steel under an axial alternating magnetic field of 15G strength and 0.1Hz frequency, according to an embodiment of the present invention. In the figure, Liquid fraction is the volume fraction of the liquid phase, C concentration represents the mass fraction of carbon, and Sum velocity is the total velocity (m / s) weighted by radial, axial, and circumferential velocities.

[0068] Figure 4 This figure illustrates the effect of external field application on the distribution of inclusions in a special steel VAR ingot according to an embodiment of the present invention. In the figure, Ingotgrowth represents the ingot growth direction, and Particlediameter represents the diameter of the inclusion particles.

[0069] Figure 5 for Figure 1 A partial cross-sectional view at point A in the figure. In the figure, 3 is a sliding self-locking element, 6 is a double-layer lifting screw, 9 is a slide rail column, 17 is a ball bearing, and 18 is a spring. Detailed Implementation

[0070] The present invention will now be further described in conjunction with the accompanying drawings and embodiments.

[0071] like Figure 1 As shown, this invention provides an apparatus for preparing high-quality special steel using magnetically controlled vacuum arc remelting, comprising an axial alternating magnetic field generating coil 8, a coil arrangement frame 4, a double-layer lifting screw coil 6, an automatic lifting traction platform, a thermocouple 2, and a slide rail column 9, the specific structure of which is as follows:

[0072] In this embodiment, eight slide rail columns 9 are used. The vertical slide rail columns 9 are evenly distributed along the circumference and are fixed to the outside of the vertical electric arc furnace body 5 by the end rings (upper end ring 15 and lower end ring 16) at both ends. The support is set around the outside of the vertical electric arc furnace body 5 and has a specified gap with the outside of the electric arc furnace body 5. The double-layer lifting screw ring 6 is set around the slide rail column 9 by the sliding self-locking element 3. The coil arrangement frame 4 is mounted on the outside of the slide rail column 9. A multi-turn magnetic field generating coil 8 is wound circumferentially and evenly distributed on the coil arrangement frame 4. A high-temperature resistant gasket is provided between the magnetic field generating coil 8 and the coil arrangement frame 4. The upper and lower ends of the magnetic field generating coil 8 are connected to a square wave AC power supply 7. The double-layer lifting screw 6 consists of two identical screws arranged coaxially. The double-layer lifting screw 6 is fixedly installed at the upper and lower ends of the coil arrangement frame 4. The double-layer lifting screw 6 is connected to the actuator of the automatic lifting traction platform via a bracket 14. When the double-layer lifting screw 6 is working, it drives the coil arrangement frame 4 to move up and down synchronously, thereby achieving dynamic adjustment of the magnetic field generating area. The longitudinal position of the double-layer lifting screw 6 is adjusted by the automatic lifting traction platform to ensure that the arc area and the molten metal pool are always within the optimal range of action of the magnetic field generating coil. In addition, a water-cooled circulation channel is provided inside the side wall of the electric arc furnace body 5. The upper part of the water-cooled circulation channel has a cooling water inlet 1, and the lower part of the water-cooled circulation channel has a cooling water outlet 13.

[0073] like Figure 5 As shown, the sliding self-locking element 3 is installed between the double-layer lifting screw ring 6 and the slide rail column 9. In this embodiment, there are 8 sliding self-locking elements 3, with 4 evenly distributed on the inner side of each layer of screw ring, and they are concave block structures. The concave block has a semi-cylindrical notch that surrounds the corresponding slide rail column 9. A ball spring assembly structure is provided on the inner side of the notch, and the ball 17 is pushed by the spring 18 to abut against the slide rail column 9. The back of each sliding self-locking element 3 is fixedly connected to the double-layer lifting screw ring 6.

[0074] The automatic lifting traction platform includes a hydraulic cylinder 12, a support 14, and a control unit. The control unit includes a PLC controller 10 and a hydraulic control circuit. The control signal output by the PLC controller 10 is sent to the solenoid valve in the hydraulic control circuit. The solenoid valve in the hydraulic control circuit is installed in the oil supply line of the hydraulic cylinder 12. The hydraulic cylinder 12 is the actuator in this invention, and its piston rod 11 is connected to the double-layer lifting screw ring 6 through the support 14. Under the control of the hydraulic cylinder 12, the double-layer lifting screw ring 6 slides on the slide rail column 9 through the sliding self-locking element 3.

[0075] In this embodiment, 15 thermocouples 2 are arranged longitudinally on the outer wall of the electric arc furnace body 5. The measurement data of the thermocouples 2 is wirelessly transmitted to the PLC controller 10 in real time. The automatic lifting traction platform adopts PID control technology. It finds the area with the highest temperature through the temperature data fed back by the thermocouples 2 in real time, calculates the displacement to be adjusted according to the current height of the double-layer lifting screw 6, controls the movement stroke of the piston rod 11, and adjusts the longitudinal position of the double-layer lifting screw 6 to realize the positioning control of the coil arrangement frame 4, ensuring that the electric arc area and the molten metal pool are always within the optimal range of action of the magnetic field generating coil 8.

[0076] In its specific implementation, this invention also provides a method for preparing high-quality special steel using magnetically controlled vacuum arc remelting, which is described below from two parts: VAR model assumptions and simulation calculations.

[0077] 1. VAR Model Assumptions

[0078] The VAR process involves highly complex physicochemical phenomena, making its modeling quite challenging. To improve simulation feasibility while ensuring solution stability, appropriate assumptions and simplifications need to be made to the actual VAR process, mainly as follows:

[0079] (1) Considering the symmetry of actual physical phenomena, in order to improve computational efficiency, a two-dimensional axisymmetric vortex computational domain is used to simulate the formation of the molten pool and the solidification of the ingot in the VAR process under the external field.

[0080] (2) The computational domain includes only the ingot portion and does not consider the consumable electrode and the arc region. The mass, momentum, and energy of the molten droplets generated at the electrode tip and carried into the molten pool, as well as the effect of the arc region on the molten pool, are all modeled in the form of source terms or boundary conditions.

[0081] (3) The movement of inclusions is controlled by the melt flow, but since the number of inclusions is small and their size is relatively small, it is believed that the presence of inclusions will not affect the melt flow in turn.

[0082] (4) Assume that the inclusions are regular spherical and in thermal equilibrium with the surrounding melt.

[0083] 2. VAR process simulation calculation

[0084] Based on the above model assumptions, the relevant simulation calculations are performed through the following steps:

[0085] Step 1: Establish a VAR process model, including a coupled thermomagnetic flow-solidification-solidification redistribution model based on the Euler solid-liquid two-phase flow method, an inclusion trajectory prediction model, and a dynamic computational domain based on dynamic mesh technology. Multiphysics coupled simulation calculations are performed using the process model. The physical fields include the electromagnetic field, flow field, temperature, and solute distribution of the continuous phase melt, as well as the motion trajectory of the discrete phase inclusion particles. Details are as follows:

[0086] In actual VAR processes, the self-induced electromagnetic force and stirring electromagnetic force generated by the interaction of the smelting current with its self-induced magnetic field and the applied axial magnetic field respectively affect the melt flow. Simultaneously, the Joule heat generated by the current flowing through the ingot alters the temperature distribution within the ingot. (Based on the potential method) Solving Maxwell's equations to describe the above electromagnetic behavior, and then incorporating the resulting electromagnetic force and Joule heat as source terms into the momentum and energy conservation equations, respectively. The electromagnetic field distribution of the VAR process is calculated by the following formula:

[0087] Electric potential equation:

[0088] The current density is calculated from the potential gradient:

[0089] Magnetic vector potential equation:

[0090] The self-induced magnetic field strength is the curl of the magnetic vector potential:

[0091] Self-induced electromagnetic force:

[0092] Electromagnetic stirring force caused by external field:

[0093] Joule fever: Q Joule =J 2 / σ(7)

[0094] Where σ is the electrical conductivity (S / m); Current density (A / m) 2 ); Electric potential (V); λ is the magnetic vector potential (Wb / m); μ0 is the magnetic permeability (H / m); The self-induced magnetic field strength (T); Self-induced electromagnetic force (N / m) 3 ); Electromagnetic force for stirring (N / m) 3 ); The applied axial alternating magnetic field strength (T); Q Joule Joule heat (W / m 3 J is the current density (A / m³). 2 ).

[0095] The Euler solid-liquid two-phase flow method establishes separate mass, momentum, energy, and solute conservation equations for the solid and liquid phases, and utilizes the solid-liquid phase transition rate M. ls Connect the two sets of equations. M ls It can be obtained from the following formula:

[0096]

[0097] Among them, the dendrite tip growth rate:

[0098] Radius of the primary dendrite trunk:

[0099] Far-field radius of the primary dendrite trunk:

[0100] Dendrite surface concentration:

[0101] Dendrite growth surface collision:

[0102] Among them, M ls Solid-liquid phase transition rate (kg / (m)) 3 ·s));v Rc S is the dendrite tip growth rate (m / s); A Dendrite surface concentration (m -1 );ρ s Solid density (kg / m³) 3 );φ imp R represents the volume fraction of solute involved in surface collisions during dendrite growth. c R is the radius of the primary dendrite trunk (m); f D is the far-field radius (m) of the primary dendrite trunk; l The diffusion coefficient of the solute in the liquid phase (m) 2 / s); and These represent the solute concentrations (wt.%) in the liquid and solid phases at interfacial equilibrium, respectively; c l λ is the solute concentration in the liquid phase (wt.%); λ1 is the primary dendrite spacing (m); f l f s These represent the liquid volume fraction and the solid volume fraction, respectively.

[0103] The flow field distribution in a molten metal pool is calculated using the following formula:

[0104] mass conservation equation:

[0105]

[0106] Momentum conservation equation:

[0107]

[0108] Among them, the momentum exchange caused by phase transition:

[0109] Solid-liquid phase drag:

[0110] Among them, M ls Solid-liquid phase transition rate (kg / (m)) 3 ·s));ρ l Liquid phase density (kg / m³) 3 );f l ρ is the liquid volume fraction; s Solid density (kg / m³) 3 );f s It represents the volume fraction of the solid phase. ρ is the melt velocity (m / s); p is the pressure (Pa); The stress-strain tensor (kg / (m·s)) 2 )); The liquid phase gravitational acceleration vector (m / s²) 2 ); Self-induced electromagnetic force (N / m) 3 ); Electromagnetic force for stirring (N / m) 3 ); The momentum exchange caused by phase transition (kg / (m)) 2 ·s 2 )); The interphase drag force (kg / (m)) 2 ·s 2 )); The solid-phase velocity (m / s); μ l K is the viscosity of the liquid phase (Pa·s); K is the permeability of the paste region (m³). 2 ).

[0111] The temperature distribution of the melt is determined by solving the energy conservation equation in enthalpy form:

[0112]

[0113]

[0114] Among them, the energy source term caused by the phase transition:

[0115]

[0116] Solid-liquid phase energy exchange:

[0117] Where, ρ l Liquid phase density (kg / m³) 3 );f l ρ is the liquid volume fraction; s Solid density (kg / m³) 3 );fs It represents the volume fraction of the solid phase. h is the melt velocity (m / s). l h s These are the liquid phase enthalpy and solid phase enthalpy (J / kg), respectively; T l T s These represent the liquid and solid phase temperatures (K), respectively; k l k s The values ​​are the thermal conductivity (W / (m·K)) of the liquid phase and the solid phase, respectively. Energy source term caused by liquid phase transition (W / m) 3 ); Energy source term caused by solid-state phase transition (W / m) 3 ); For solid-liquid phase energy exchange (W / m 3 );Q Joule Joule heat (W / m 3 );Δh f The latent heat of phase change (J / kg); M ls Solid-liquid phase transition rate (kg / (m)) 3 ·s));H * The volumetric heat transfer coefficient (W / (m)) 3 ·K)).

[0118] The solute distribution in a melt can be obtained by solving the solute conservation equation:

[0119]

[0120]

[0121] Among them, solute exchange between solid and liquid phases:

[0122] Where, ρ l Liquid phase density (kg / m³) 3 );f l ρ is the liquid volume fraction; s Solid density (kg / m³) 3 );f s c is the solid volume fraction; l c s These represent the solute concentrations (wt.%) in the liquid and solid phases, respectively; D l The diffusion coefficient of the solute in the liquid phase (m) 2 / s); D s The solid solute diffusion coefficient (m) 2 / s); Solid-liquid interphase solute exchange (kg / (m 3 ·s));k is the equilibrium distribution coefficient; M represents the solute concentration (wt.%) in the interfacial equilibrium liquid phase; ls Solid-liquid phase transition rate (kg / (m)) 3 ·s)). The volume average concentration c of the solid-liquid two-phase mixture. mix Characterizing local solute concentration:

[0123] c mix =(ρ s f s c s +ρ l f l c l ) / (ρ s f s +ρ l f l (27)

[0124] The motion of the inclusion is governed by Newton's second law, and its trajectory prediction equation is as follows:

[0125]

[0126] Among them, c mix ρ represents the volume average concentration (%) of the solid-liquid two-phase mixture. l Liquid phase density (kg / m³) 3 );f l ρ is the liquid volume fraction; s Solid density (kg / m³) 3 );f s c is the solid volume fraction; l c s These represent the solute concentrations (wt.%) in the liquid and solid phases, respectively; m p Mass of the inclusion particles (kg); Particle velocity (m / s); These are the buoyancy force, interphase drag force, lift force, virtual mass force, pressure gradient force, and electromagnetic pressure (N) acting on the particles, respectively.

[0127] The dynamic computational domain based on the dynamic mesh technology is specifically the molten metal melted by the electrode continuously entering the computational domain through the top boundary. In each time step, an equivalent mass corresponding to the melting rate is added to the surface of the melt, and the top boundary moves upward in real time accordingly, thus equivalent to the continuous growth process of the ingot.

[0128] Step 2: Before the simulation calculation, electromagnetic boundary conditions, velocity boundary conditions, and thermal boundary conditions need to be set, mainly as follows:

[0129] 1) Apply no-slip boundary conditions to both the sidewalls and bottom boundary of the ingot;

[0130] 2) The current density at the top of the molten metal pool follows a Gaussian distribution:

[0131]

[0132] Among them, J top Current density at the top of the molten metal pool (A / m) 2 σ is the electrical conductivity (S / m); Electric potential (V); η is the normal unit vector; I is the efficiency; β1 and β2 are the shape factors describing the Gaussian distribution characteristics; r is the distance (m) between each position on the top of the ingot and the center of the arc; R a The radius of the electric arc is (m).

[0133] 3) During the melting of the consumable electrode, the thermal radiation on the surface of the molten pool is ignored. The dripping metal droplets are continuously heated as they pass through the plasma arc region, and have a certain degree of superheat when they reach the surface of the molten pool:

[0134]

[0135] Among them, T top T represents the temperature at the top of the molten metal pool (K); liq D is the liquidus temperature (K) of the steel grade; i I represents the ingot diameter (m); I represents the current (A).

[0136] 3) After the electrodes have melted, the top of the molten pool begins to radiate heat outwards until the ingot completely solidifies. The radiative heat flux density is:

[0137]

[0138] Where, q rad Radiative heat flux density (W / m 2 ); ε is the emissivity at the top of the ingot; σ s Stefan-Boltzmann constant (W / (m)) 2 ·K 4 ));T e Ambient temperature (K); T top The temperature at the top of the molten metal pool is (K).

[0139] 4) The sides and bottom of the ingot can be equivalent to convective heat transfer, with a heat flux density of:

[0140] q conv =h(T)·(T) ingot -T wall (32)

[0141] Where, q conv For convective heat transfer heat flux density (W / m³) 2h(T) is the equivalent convective heat transfer coefficient (W / (m³)). 2 ·K));T ingot and T wall These are the surface temperature of the ingot and the wall temperature of the crucible (K), respectively.

[0142] Step 3: Determine the physical properties and VAR process parameters of the special steel. This invention selects high-carbon bearing steel M50 as an example; its chemical composition is shown in Table 1 below, and its physical properties and process parameters are shown in Table 2 below.

[0143] Table 1. Chemical composition (wt.%) of the steel in the examples

[0144] C Cr Mo V Mn Ni Fe 0.80 4.14 4.72 0.98 0.24 0.08 margin

[0145] Table 2. Physical properties and process parameters of the steel in the examples.

[0146] Physical properties value parameter value <![CDATA[Density / kg·m -3 > 7796 Stable smelting period current / A 4000 <![CDATA[Specific heat capacity / J·kg -1 ·K -1 > 750 <![CDATA[Melting rate during stable melting period / kg·min -1 > 2.35 <![CDATA[Thermal conductivity / W·m -1 ·K -1 > 30.5 Consumable electrode diameter / m 0.224 <![CDATA[Viscosity / kg·m -1 ·s -1 > <![CDATA[5.0×10 -3 ]]> crucible diameter / m 0.28 <![CDATA[Latent heat of phase change / J·kg -1 > <![CDATA[1.9×10 5 ]]> Ingot length / m 0.83

[0147] Step 4: Establish the calculation baseline through parameter initialization, and use the phase-coupled SIMPLE algorithm to discretize and solve the continuous phase equation (electromagnetic field-flow field-temperature-solute distribution equation) and the discrete phase equation (inclusion motion).

[0148] Step 5: Discretize the data using an axisymmetric grid, where the main grid stores scalar parameters and the staggered grid records current density and velocity vectors; dynamically adjust the time step during the calculation, performing a maximum of 60 iterations in each time step to reduce normalized residuals.

[0149] Step 6: Update the position and velocity of inclusions in real time based on the Lagrange method, and output the calculation results for each iteration.

[0150] Step 7: The effects of axial alternating magnetic field strength and frequency on melt flow heat transfer, solute redistribution, and inclusion migration behavior are investigated using the controlled variable method. Numerical simulation experiments with diverse parameter combinations are constructed, and statistical methods are used to extract the synergistic effects of each parameter on component segregation and inclusion distribution. Multiple regression analysis is used to accurately fit the data, establishing a quantitative relationship between each magnetic field parameter and the degree of component segregation and inclusion characteristics, guiding the precise setting of magnetic field parameters in actual equipment.

[0151] like Figure 2As shown, the changes in the molten pool and solute distribution during the VAR process of the steel in the example without an external field are: (a) 10 min; (b) 60 min; (c) 100 min; (d) 150 min; (e) solidification complete. During the initial arc phase of the VAR process, the molten pool of the steel in the example gradually deepens. During the stable melting period, the shape of the molten pool remains basically unchanged, and it gradually becomes shallower after the hot capping begins. After the electrode melting is complete, the top of the ingot begins to radiate heat outward until solidification is complete. Two opposing flows exist in the molten pool: counterclockwise flow caused by the buoyancy of the hot solute and clockwise flow caused by the self-induced electromagnetic force. Ultimately, the center of the ingot exhibits obvious positive segregation, while the sides exhibit negative segregation.

[0152] like Figure 3 As shown, the changes in the molten pool and solute distribution during the VAR process of the steel in Example 1 under an axial alternating magnetic field of intensity 15G and frequency 0.1Hz are: (a) 10 min; (b) 60 min; (c) 100 min; (d) 150 min; (e) solidification complete. The flow field distribution is characterized by the total velocity weighted by radial, axial, and circumferential velocities, compared with the attached... Figure 2 It was found that after applying an axial magnetic field, the flow in most areas of the molten pool (excluding those marked) was dominated by the stirring electromagnetic force, with the stirring intensity being greatest near the mid-radius region. The application of the external field significantly reduced the positive segregation region in the ingot, effectively suppressing the macroscopic segregation of solute elements, confirming that the external field control employed in this invention can improve the compositional uniformity within the ingot.

[0153] like Figure 4 As shown, the effect of external field application on the distribution of inclusions in the VAR ingot of the example steel is illustrated in (a) without external field and (b) under an axial alternating magnetic field with an intensity of 15G and a frequency of 0.1Hz. Inclusions of different sizes, ranging from 1 to 7 μm, were injected into the ingot at a height of approximately 0.2 m (marked position). Without an external field, the inclusions were mainly distributed in the lower part of the ingot, and larger inclusions tended to sink and accumulate near the sides of the ingot. After applying an external field, the upward movement of inclusions was significantly enhanced, with the vast majority of inclusions migrating to the vicinity of the top of the ingot, greatly facilitating subsequent machining removal. This fully demonstrates that the external field has a significant enhancing effect on inclusion removal.

[0154] The results show that, through innovative mechanical and control combination design, the present invention achieves automated and precise positioning of the magnetic field generating coil in terms of device structure; and through a complete multi-physics coupling model and parameter optimization based on numerical simulation, the present invention significantly improves the quality of special steel prepared by VAR process in terms of method flow.

[0155] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and technical principles of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An apparatus for preparing high-quality special steel using magnetically controlled vacuum arc remelting, characterized in that, It includes an axial alternating magnetic field generating coil, a coil arrangement frame, a double-layer lifting solenoid, an automatic lifting traction platform, and a slide rail column. The specific structure is as follows: Vertical slide rail columns evenly distributed along the circumference are fixed to the upper and lower end rings to form a hollow cylindrical support frame surrounding the vertical electric arc furnace body. The coil arrangement frame is fitted onto the outside of the slide rail columns, and the magnetic field generating coil is wound circumferentially and evenly distributed on the coil arrangement frame. A high-temperature resistant gasket is provided between the magnetic field generating coil and the coil arrangement frame. The upper and lower ends of the magnetic field generating coil are connected to a square wave AC power supply. The double-layer lifting solenoid includes two solenoids of the same specification, arranged coaxially. The double-layer lifting solenoid is fixedly installed at the upper and lower ends of the coil arrangement frame. The double-layer lifting solenoid is connected to the actuator of the automatic lifting traction platform through the bracket. When the double-layer lifting solenoid is working, it will drive the coil arrangement frame to rise and fall synchronously to realize the dynamic adjustment of the magnetic field generating area.

2. The apparatus for preparing high-quality special steel using magnetically controlled vacuum arc remelting according to claim 1, characterized in that, The double-layer lifting screw ring is encircled on the slide rail column by a sliding self-locking element. The sliding self-locking element is installed between the double-layer lifting screw ring and the slide rail column. The sliding self-locking element is evenly arranged on the inner side of each layer of screw ring. The sliding self-locking element is a concave block structure. The notch of the concave block is semi-cylindrical and surrounds the corresponding slide rail column. The inner side of the notch is equipped with a ball spring combination structure, and the ball is pushed to abut against the slide rail column by the spring. The back of each sliding self-locking element is fixedly connected to the double-layer lifting screw ring.

3. The apparatus for preparing high-quality special steel using magnetically controlled vacuum arc remelting according to claim 1, characterized in that, The automatic lifting traction platform has a hydraulic cylinder, a support frame, and a control unit. The control unit includes a PLC controller and a hydraulic control circuit. The control signal output by the PLC controller is sent to the solenoid valve in the hydraulic control circuit. The solenoid valve in the hydraulic control circuit is installed in the hydraulic cylinder oil supply line. The hydraulic cylinder acts as the actuator, and its piston rod is connected to the double-layer lifting screw ring through the support frame.

4. The apparatus for preparing high-quality special steel using magnetically controlled vacuum arc remelting according to claim 1, characterized in that, Thermocouples are arranged longitudinally on the outer wall of the electric arc furnace. By referring to the thermocouple readings at different heights, the longitudinal position of the double-layer lifting screw is adjusted by the automatic lifting traction platform to achieve the positioning control of the coil arrangement frame, ensuring that the electric arc area and the molten metal pool are always within the optimal range of action of the magnetic field generating coil.

5. A method for preparing high-quality special steel using the apparatus described in any one of claims 1 to 4 via magnetically controlled vacuum arc remelting, characterized in that, Includes the following steps: Step 1): Establish a VAR process model, including a coupled thermomagnetic flow-solidification-solid redistribution model based on the Euler solid-liquid two-phase flow method, an inclusion trajectory prediction model, and a dynamic computational domain based on dynamic mesh technology; Step 2): Determine the physical properties and VAR process parameters of the special steel; Step 3): Use the VAR process model to perform multi-field coupling simulation calculations for the preparation of special steel by magnetic control VAR, and obtain the influence of alternating magnetic field strength and frequency parameters on compositional segregation and inclusion migration.

6. The method for preparing high-quality special steel using magnetically controlled vacuum arc remelting according to claim 5, characterized in that, Multiphysics coupling simulation calculations were performed using a VAR process model. The physical fields included the electromagnetic field, flow field, temperature, and solute distribution of the continuous phase melt, as well as the motion trajectory of the discrete phase inclusion particles. The electromagnetic field distribution was calculated using the following formula: Electric potential equation: Current density: Magnetic vector potential equation: Self-induced magnetic field strength: Self-induced electromagnetic force: Electromagnetic stirring force caused by external field: Joule fever: Q Joule =J 2 / σ; Where σ is the electrical conductivity; It is the electric potential; is the magnetic vector potential; μ0 is the magnetic permeability; The applied axial alternating magnetic field strength.

7. The method for preparing high-quality special steel using magnetically controlled vacuum arc remelting according to claim 5, characterized in that, Step 1) uses the Euler solid-liquid two-phase flow method, specifically establishing a set of mass, momentum, energy, and solute conservation equations for both the solid and liquid phases, and utilizing the solid-liquid phase transition rate M. ls Connect the two sets of equations, M ls We obtain it from the following formula: Among them, the dendrite tip growth rate: Radius of the primary dendrite trunk: Far-field radius of the primary dendrite trunk: Dendrite surface concentration: Dendrite growth surface collision: Among them, D l The diffusion coefficient of the solute in the liquid phase; and The concentrations of the solute in the liquid and solid phases at the interface equilibrium; λ1 is the primary dendrite spacing; f l f s These represent the liquid phase and solid phase fractions, respectively. The flow field distribution in a molten metal pool is calculated using the following formula: in, p is the melt velocity; ρ is the pressure. It is the stress-strain tensor; It is the vector of gravitational acceleration; This is the momentum exchange caused by the phase transition; For solid-liquid phase drag force; The temperature distribution of the melt is determined by solving the energy conservation equation in enthalpy form: Among them, h l h s These are the liquid phase enthalpy and the solid phase enthalpy, respectively; T l T s For the liquid and solid phase temperatures; k l k s Thermal conductivity; and This refers to the energy source term caused by the phase transition; For energy exchange between solid and liquid phases; The solute distribution in the melt is obtained by solving the solute conservation equation: Among them, c l c s These represent the solute concentrations in the liquid and solid phases, respectively; D s The solid-phase solute diffusion coefficient; For solute exchange between solid and liquid phases; The volume average concentration c of the solid-liquid two-phase mixture mix Characterizing local solute concentration: c mix =(ρ s f s c s +r l f l c l ) / (ρ s f s +r l f l ) The equations for the trajectory prediction model of the inclusions in step 1) are as follows: Where, m p The mass of the inclusion particles; Particle velocity; These are the buoyancy force, interphase drag force, lift force, virtual mass force, pressure gradient force, and electromagnetic pressure acting on the particles, respectively.

8. The method for preparing high-quality special steel using magnetically controlled vacuum arc remelting according to claim 5, characterized in that, In step 1), the dynamic computational domain based on the moving mesh technology is specifically the molten metal dripping from the electrode continuously entering the computational domain through the top boundary. In each time step, an equivalent mass corresponding to the melting rate is added to the surface of the melt, and the top boundary moves upward in real time accordingly, thus equivalent to the continuous growth process of the ingot.

9. The method for preparing high-quality special steel using magnetically controlled vacuum arc remelting according to claim 5, characterized in that, Before performing the simulation calculation in step 3), the following boundary conditions need to be set: 1) Apply no-slip boundary conditions to both the sidewalls and bottom boundary of the ingot; 2) The current density at the top of the molten pool follows a Gaussian distribution: Where β1 and β2 are shape factors describing the Gaussian distribution characteristics; r is the distance from each position on the top of the ingot to the center of the electric arc; R a The radius of the electric arc; 3) Ignoring thermal radiation from the molten pool surface during the melting of the consumable electrode, the falling metal droplets are continuously heated as they pass through the plasma arc region, and their temperature upon reaching the molten pool surface is: Among them, T liq D is the liquidus temperature of the steel grade; i The diameter of the ingot; 4) After the electrode melts, the top of the molten pool begins to radiate heat outwards, with a heat flux density of: Where ε is the emissivity at the top of the ingot; σ s T is the Stefan-Boltzmann constant; e The ambient temperature; 5) The sides and bottom of the ingot are equivalent to convective heat transfer, with a heat flux density of: q conv =h(T)·(T) ingot -T wall ); Where h(T) is the equivalent convective heat transfer coefficient; T ingot and T wall These are the surface temperature of the ingot and the wall temperature of the crucible, respectively.

10. The method for preparing high-quality special steel using magnetically controlled vacuum arc remelting according to claim 5, characterized in that, Step 3) includes the following simulation calculations: establishing a calculation baseline through parameter initialization; using the phase-coupled SIMPLE algorithm to discretize and solve the continuous phase equation and the discrete phase equation; using an axisymmetric mesh for discretization, where the main mesh stores scalar parameters and the staggered mesh records the current density and velocity vector; dynamically adjusting the time step during the calculation, performing a maximum of 60 iterations in each time step to reduce normalization residuals; updating the position and velocity of inclusions in real time based on the Lagrange method, and outputting the calculation results for each iteration; and obtaining the compositional segregation and inclusion distribution patterns under different alternating magnetic field strengths and frequencies through calculation.

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