Process for refining solidification structure of metal by multi-frequency complex pulse magnetic field

Abstract

The present application belongs to the technical field of metal solidification structure refinement, and particularly relates to a process for refining metal solidification structure by using a multi-frequency combined pulse magnetic field, which comprises the following steps: sleeving an electromagnetic coil outside a crystallizer, a secondary cooling zone or a solidification end of a continuous casting billet; and applying a multi-frequency pulse magnetic field to the crystallizer, the secondary cooling zone or the solidification end of the continuous casting billet by using the electromagnetic coil; wherein the multi-frequency pulse magnetic field is generated by a multi-frequency pulse current; and wherein the multi-frequency pulse current comprises a plurality of main pulses, each of which is composed of a plurality of sub-pulses, and the peak magnetic field strength of the magnetic field generated by the sub-pulses is taken as the magnetic field strength of the multi-frequency pulse magnetic field. The process allows a higher-intensity magnetic field to be applied while suppressing melt splashing, so that the dendrites can be broken more effectively and the solidification structure can be refined more effectively. The present application also covers various optional embodiments of the magnetic field parameter range, waveform, polarity and coil type, and a static magnetic field can be superimposed, so that the process has good flexibility.

Description

Technical Field

[0001] This invention belongs to the field of metal solidification structure refinement technology, and particularly relates to a process for refining metal solidification structure using a multi-frequency composite pulsed magnetic field. Background Technology

[0002] In the solidification process of metallic materials, compositional inhomogeneity is a common and unavoidable phenomenon, directly affecting the mechanical properties and service life of the final product. To address this issue, refining the solidification microstructure is considered an effective technical approach. Currently, the main refining methods in the industry can be divided into two categories: physical methods and chemical methods. Among them, physical methods have received widespread attention due to their advantages such as being environmentally friendly and pollution-free, specifically including mechanical stirring, ultrasonic treatment, electromagnetic stirring, and pulsed magnetostrictive oscillation. However, these existing technologies all have their own limitations. For example, mechanical stirring and ultrasonic treatment are difficult to implement in high-temperature molten environments and are inefficient; electromagnetic stirring easily induces macroscopic segregation of the melt composition.

[0003] Pulsed magnetostrictive oscillation technology uses pulsed magnetic fields to generate electromagnetic force to break dendrites, making them free nucleation sites, thereby refining the microstructure and showing certain application potential.

[0004] Nevertheless, existing pulsed magnetostrictive oscillation (PMO) techniques typically employ a single-frequency, narrow-pulse magnetic field mode. This mode has a significant drawback: when attempting to enhance the refining effect by increasing the magnetic field strength, excessively strong electromagnetic forces can cause violent agitation and even splashing of the molten metal, posing a threat to equipment and process safety. Therefore, in practical applications, the magnetic field strength is often limited to a low level to suppress splashing. This strength limitation results in insufficient ability to break up columnar crystals, reaching a bottleneck in the refining effect and failing to meet the stringent requirements for uniform microstructure in the large-scale industrial production of high-performance metallic materials. The field strength values ​​recorded in existing technical literature and patents also confirm this, becoming a key bottleneck restricting the further promotion and application of this technology.

[0005] Therefore, there is an urgent need for a new technology that can achieve higher magnetic field strength and thus obtain better solidification structure refinement while avoiding molten metal splashing, in order to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a process for refining the solidified metal structure using a multi-frequency composite pulsed magnetic field, in order to solve the above-mentioned problems.

[0007] To achieve the above objectives, the present invention provides the following solution: A process for refining the solidified structure of metal using a multi-frequency composite pulsed magnetic field includes: An electromagnetic coil is installed on the outside of the crystallizer, secondary cooling zone, or solidification end of the continuously cast billet. A multi-frequency pulsed magnetic field is applied to the crystallizer, secondary cooling zone, or solidification end of the continuously cast billet through the electromagnetic coil; The multi-frequency pulsed magnetic field is generated by a multi-frequency pulsed current; The multi-frequency pulsed current includes multiple main pulses, each main pulse is composed of multiple sub-pulses, and the peak magnetic field strength of the magnetic field generated by the sub-pulses is used as the magnetic field strength of the multi-frequency pulsed magnetic field.

[0008] Optionally, the magnetic field strength range of the multi-frequency pulsed magnetic field is 100Gs-30T.

[0009] Optionally, the frequency of the sub-pulse is 10-10 GHz, and the duty cycle is 1-99%.

[0010] Optionally, the frequency of the main pulse is 0.01-100KHz, and the duty cycle is 0.1%-50%.

[0011] Optionally, the shape of the multi-frequency pulsed magnetic field is one of square, rectangular, sine wave, triangular wave, or trapezoid.

[0012] Optionally, the magnetic field generated by the main pulse is unipolar or bipolar; When the magnetic field generated by the main pulse is bipolar, the positive and negative shapes of the magnetic field generated by the main pulse are either symmetrical or asymmetrical.

[0013] Optionally, the magnetic field generated by the sub-pulse is unipolar or bipolar. When the magnetic field generated by the sub-pulse is bipolar, the positive and negative shapes of the magnetic field generated by the sub-pulse are symmetrical or asymmetrical.

[0014] Optionally, the electromagnetic coil is a solenoid coil or a bamboo-shaped coil.

[0015] Optionally, the cross-sectional area of ​​the electromagnetic coil is 1-10000 mm2.

[0016] Optionally, a static magnetic field and a multi-frequency pulsed magnetic field are simultaneously applied to the electromagnetic coil to form a static magnetic field superimposed with a pulsed magnetic field mode.

[0017] Compared with the prior art, the present invention has the following advantages and technical effects: This invention employs a magnetic field design that nests multiple high-frequency sub-pulses within a low-frequency main pulse. This allows the high-frequency sub-pulses to complete their cycle just before the molten metal is about to splash due to electromagnetic disturbances, thus enabling the peak intensity of the pulsed magnetic field to be significantly higher than that of traditional single-frequency wide-pulse magnetic fields. The higher magnetic field intensity generates a stronger electromagnetic force, which more effectively breaks up columnar dendrites at the solidification front, making them more heterogeneous nucleation sites. This significantly promotes grain refinement, expands the equiaxed grain region, and results in a more uniform and dense metal solidification structure. Furthermore, by dividing the process into multiple segments and independently controlling the magnetic field parameters of each segment, this method possesses excellent process adaptability and flexibility, allowing for precise control and optimization of processing effects for different metal materials, billet specifications, and process conditions. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a schematic diagram illustrating the implementation stages of the present invention.

[0019] Figure 2 This is a waveform diagram of the multi-frequency pulsed magnetic field of the present invention.

[0020] Figure 3 This is a waveform diagram of the conventional pulsed magnetic field of the present invention.

[0021] Figure 4 This is a schematic diagram of the bamboo-shaped coil of the present invention.

[0022] Figure 5 This is a schematic diagram of the solenoid coil of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] Reference Figures 1 to 5This invention discloses a process for refining the solidified structure of metal using a multi-frequency composite pulsed magnetic field, comprising: An electromagnetic coil is installed on the outside of the crystallizer, secondary cooling zone, or solidification end of the continuously cast billet. A multi-frequency pulsed magnetic field is applied to the crystallizer, secondary cooling zone, or solidification end of the continuously cast billet using an electromagnetic coil. The multi-frequency pulsed magnetic field is generated by the multi-frequency pulsed current. The multi-frequency pulsed current contains multiple main pulses, each of which consists of multiple sub-pulses. The peak magnetic field strength of the magnetic field generated by the sub-pulses is used as the magnetic field strength of the multi-frequency pulsed magnetic field.

[0026] The purpose of this invention is to provide a process for refining the solidified metal structure using a multi-frequency composite pulsed magnetic field. The magnetic field has a low-frequency main frequency and a high-frequency sub-frequency. A low-frequency main pulse contains several high-frequency sub-pulses, which can improve the magnetic field strength, reduce splashing of molten metal, and obtain a better homogenized metal structure.

[0027] Among them, the multi-frequency pulse magnetic field refers to the composite magnetic field generated by the different frequencies and duty cycles of the main pulse and the sub-pulse; the main pulse is a low-frequency narrow pulse, and the sub-pulse is a high-frequency pulse.

[0028] The specific method involves first placing an electromagnetic coil around the outside of the crystallizer, secondary cooling zone, or solidification end region of the continuously cast billet; then, a multi-frequency pulsed current composed of multiple sub-pulse currents is passed through the electromagnetic coil, thereby exciting a multi-frequency pulsed magnetic field in the coil, which is then applied to the crystallizer, secondary cooling zone, or solidification end region of the continuously cast billet. The technical effect is that, through the action of this composite pulsed magnetic field, columnar dendrites at the solidification front can be more effectively broken up, prompting them to become heterogeneous nucleation sites, thus significantly refining the solidification structure of the metal, expanding the equiaxed grain region, and making the billet structure more uniform.

[0029] As can be seen, the specific solution of this invention is: when metal solidifies in a strong magnetic field and a wide pulse, it will cause the molten metal to splash. In use, the magnetic field strength can only be reduced to about 1000Gs to prevent splashing. Therefore, multiple high-frequency sub-pulse magnetic fields are designed within the original wide pulse magnetic field to form the main magnetic field frequency and the sub-magnetic field frequency.

[0030] The sub-magnetic field has a higher frequency and a shorter pulse width. The pulse has already completed a pulse cycle before the liquid metal is splashed due to electromagnetic agitation. Therefore, the peak magnetic field strength can be designed to be very high, which can more effectively break columnar crystal dendrites and obtain a better homogenized metal structure.

[0031] Furthermore, the multi-frequency pulsed magnetic field can be divided into multiple segments according to the time length within a single process. The frequency, duty cycle, polarity, and shape parameters of each segment of the multi-frequency pulsed magnetic field can be adjusted individually, and each segment can be the same or different.

[0032] By dividing a process into multiple segments based on time length and allowing for individual parameter adjustments, process flexibility is effectively increased.

[0033] As an optional implementation, the magnetic field strength range of the multi-frequency pulsed magnetic field is 100Gs-30T.

[0034] As an optional implementation, the frequency of the sub-pulse is 10-10 GHz, and the duty cycle is 1-99%.

[0035] As an optional implementation, the frequency of the main pulse is 0.01-100KHz, and the duty cycle is 0.1%-50%.

[0036] As an optional implementation method, the shape of the multi-frequency pulsed magnetic field can be one of square, rectangular, sine wave, triangular wave, or trapezoid.

[0037] As an optional implementation, the magnetic field generated by the main pulse is unipolar or bipolar; When the magnetic field generated by the main pulse is bipolar, the positive and negative shapes of the magnetic field generated by the main pulse are either symmetrical or asymmetrical.

[0038] As an optional implementation, the magnetic field generated by the sub-pulse is unipolar or bipolar. When the magnetic field generated by the sub-pulse is bipolar, the positive and negative shapes of the magnetic field generated by the sub-pulse are symmetrical or asymmetrical.

[0039] As an alternative implementation, the electromagnetic coil is a solenoid coil or a bamboo-shaped coil.

[0040] As an optional implementation, the cross-sectional area of ​​the electromagnetic coil is 1-10000 mm². 2 .

[0041] As an optional implementation, a static magnetic field and a multi-frequency pulsed magnetic field are simultaneously applied to the electromagnetic coil to form a static magnetic field superimposed with a pulsed magnetic field mode.

[0042] Pulsed magnetic fields are typically achieved using solenoids or bamboo-shaped coils, with a pulsed power supply used to generate the magnetic field.

[0043] The coil can be circular, rectangular, triangular, or trapezoidal; the material is usually a conductive metal such as copper or aluminum, and the cross-sectional area ranges from 1 to 10,000 mm². 2 between.

[0044] The pulse power supply has a peak current of 50-10000A, a peak voltage of 20-6000V, a frequency of 0.01-10GHz, and a duty cycle of 0.1-99%. It can be unipolar or bipolar, and when bipolar, it can be symmetrical or asymmetrical. The pulse power supply operates in constant current, constant voltage, or constant power mode.

[0045] The static magnetic field is generated by driving the coil with a DC power supply. The DC power supply is superimposed on the pulse power supply to form a static magnetic field superimposed on the pulse magnetic field mode. The DC power supply can be superimposed on either the positive pulse or the negative pulse of the pulse power supply.

[0046] The DC power supply has a current of 10-3000A and a peak voltage of 20-6000V.

[0047] This invention can be implemented in the following specific ways.

[0048] First, the magnetic field generating components are constructed, taking a bamboo-joint type coil structure as an example. A copper tube with an outer diameter of 10mm and an inner diameter of 8mm is selected as the conductor to prepare the bamboo-joint type coil. The copper tube is wound into a coil with a diameter of 15cm and two turns to form a single coil unit. A cable connection terminal is welded to the end of the copper tube for electrical connection, and a water pipe connection port is welded for water cooling. This process is repeated to prepare three identical coil units.

[0049] The three sets of coils are evenly arranged at a distance of 3cm and fixed and encapsulated with insulating epoxy resin material, thus integrating them into a whole bamboo-shaped pulse magnetic field generator.

[0050] In application, the bamboo-shaped pulse magnetic field generator is placed over the GCr15 bearing steel billet to be processed. The water pipe connections of each coil are connected to the cooling water circulation system via plastic insulated hoses to ensure controlled temperature rise during operation. For electrical connections, the cable terminals of the three coils are connected in series to ensure they are in phase, simplifying drive requirements. The start and end cables of the series circuit are connected to the output of the pulse power supply.

[0051] Next, the process parameters are set. The pulse power supply is set to bipolar, square wave operating mode. Specific parameters are: constant current control during the positive pulse phase, with a peak current of 2000A, a pulse frequency of 100Hz, and a duty cycle of 14%. After the positive pulse ends, a reverse voltage is applied with constant voltage control, set to 5V. This design decelerates and reverses the movement of charged particles in the melt, thus causing secondary breakage of the dendrites. Simultaneously, the casting speed of the continuous casting machine is set to 0.5m / min. The pulse power supply and cooling system are started, and the device begins operation, processing the solidified molten metal under the action of a multi-frequency composite pulse magnetic field.

[0052] After treatment with the aforementioned bamboo-shaped pulsed magnetic field, metallographic analysis was performed on samples of bearing steel billets, and the microstructure was compared with that of untreated samples (see Table 1). The results show that the proportion of columnar dendritic regions in the treated samples was significantly reduced, while the proportions of coarse and fine equiaxed crystal regions were significantly increased. This demonstrates that the multi-frequency composite pulsed magnetic field can effectively inhibit columnar crystal growth and promote equiaxed crystal formation, achieving significant refinement and homogenization of the solidification microstructure.

[0053] Table 1. Sample Comparison Chart Besides the bamboo-shaped coil, the magnetic field can also be generated by a solenoid coil. The pulsed magnetic field is composed of a low-frequency main pulse and several nested high-frequency sub-pulses. The main pulse frequency ranges from 0.01 to 10 kHz, and the sub-pulse frequency ranges from 100 to 10 GHz. The overall peak magnetic field strength can be adjusted between 100 Gs and 30 T. The pulse shape can be one of square, rectangular, sine wave, triangular wave, or trapezoidal; the polarity can be unipolar or bipolar. Within a complete process, both the main pulse and sub-pulses can be divided into multiple segments according to time. The frequency, duty cycle, polarity, and waveform parameters of each segment can be independently set and adjusted, thereby providing high process flexibility. Optionally, a DC power supply can be superimposed on the pulse power supply to generate a static magnetic field in the coil, which, combined with the pulsed magnetic field, forms a "static magnetic field superimposed on pulsed magnetic field" working mode. The current of the DC power supply can be superimposed on the positive or negative portion of the pulse.

[0054] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0055] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A process for refining the solidified structure of metal using a multi-frequency composite pulsed magnetic field, characterized in that, include: An electromagnetic coil is installed on the outside of the crystallizer, secondary cooling zone, or solidification end of the continuously cast billet. A multi-frequency pulsed magnetic field is applied to the crystallizer, secondary cooling zone, or solidification end of the continuously cast billet through the electromagnetic coil; The multi-frequency pulsed magnetic field is generated by a multi-frequency pulsed current; The multi-frequency pulsed current includes multiple main pulses, each of which consists of multiple sub-pulses. The peak magnetic field strength of the magnetic field generated by the sub-pulses is used as the magnetic field strength of the multi-frequency pulsed magnetic field.

2. The process for refining metal solidification structures using a multi-frequency composite pulsed magnetic field according to claim 1, characterized in that, The magnetic field strength range of the multi-frequency pulsed magnetic field is 100 Gs-30 T.

3. The process for refining metal solidification structures using a multi-frequency composite pulsed magnetic field according to claim 1, characterized in that, The frequency of the sub-pulse is 10-10 GHz, and the duty cycle is 1-99%.

4. The process for refining metal solidification structures using a multi-frequency composite pulsed magnetic field according to claim 1, characterized in that, The frequency of the main pulse is 0.01-100KHz, and the duty cycle is 0.1%-50%.

5. The process for refining metal solidification structures using a multi-frequency composite pulsed magnetic field according to claim 1, characterized in that, The shape of the multi-frequency pulsed magnetic field is one of square, rectangular, sine wave, triangular wave, or trapezoid.

6. The process for refining metal solidification structures using a multi-frequency composite pulsed magnetic field according to claim 1, characterized in that, The magnetic field generated by the main pulse is unipolar or bipolar; When the magnetic field generated by the main pulse is bipolar, the positive and negative shapes of the magnetic field generated by the main pulse are either symmetrical or asymmetrical.

7. The process for refining metal solidification structures using a multi-frequency composite pulsed magnetic field according to claim 1, characterized in that, The magnetic field generated by the sub-pulse is unipolar or bipolar. When the magnetic field generated by the sub-pulse is bipolar, the positive and negative shapes of the magnetic field generated by the sub-pulse are symmetrical or asymmetrical.

8. The process for refining metal solidification structure using a multi-frequency composite pulsed magnetic field according to claim 1, characterized in that, The electromagnetic coil is a solenoid coil or a bamboo-shaped coil.

9. The process for refining metal solidification structure using a multi-frequency composite pulsed magnetic field according to claim 1, characterized in that, The cross-sectional area of ​​the electromagnetic coil is 1-10000 mm². 2 .

10. The process for refining metal solidification structure using a multi-frequency composite pulsed magnetic field according to claim 1, characterized in that, A static magnetic field and a multi-frequency pulsed magnetic field are simultaneously applied to the electromagnetic coil, forming a static magnetic field superimposed with a pulsed magnetic field mode.

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