Fast-reaching heat treatment process for preventing heat treatment cracks of special alloy

Abstract

The invention relates to a fast-reaching heat treatment process for preventing special alloy heat treatment cracks. According to the process, fast-reaching heat treatment is carried out on large-specification blanks by adopting a direct electrifying method, and fast-reaching heat treatment is carried out on small-specification blanks by adopting a salt bath method. The process disclosed by the invention is suitable for a small amount of relatively special marks in the special alloy (especially in high-temperature alloy), and solves the problem that cracks are generated during annealing softening heat treatment after cold machining in the production process of the high-crack-tendency and difficult-to-process special alloy, so that the special alloy can be manufactured into an alloy material; and a solution is provided for normal manufacturing of the alloy material. The process can be used as pretreatment before formal heat treatment and can also be used as formal heat treatment, and the purposes of annealing, softening and crack prevention are achieved at the same time. The method has the advantages that the obtained alloy material is free of cracks and good in quality, the yield is 100%, and the method has remarkable effects in the aspects of feasibility, reliability, yield, quality and the like.

Description

Technical Field

[0001] The present invention belongs to the field of heat treatment in the production of special alloys, and relates to a quick-reaching heat treatment process for preventing cracks from being generated during annealing and softening heat treatment after cold processing in the production process of special alloys with high crack tendency and difficult to process. Background Art

[0002] Special alloys mainly include high-temperature alloys, corrosion-resistant alloys, metal functional materials, special stainless steels, etc. Special alloy material varieties usually include bars, strips, wires, plates, strips, pipes, etc. In the production process from billet to material, hot deformation processing and continuous hot deformation processing are rarely adopted or purchased due to the reasons of failing to meet performance requirements, low process stability, large equipment investment, low equipment adaptability, and low equipment utilization rate. Cold deformation processing (referred to as cold processing, such as cold drawing, cold drawing, cold rolling, etc.) combined with annealing and softening heat treatment are the main process methods; after cold processing, the billet will produce cold work hardening, its strength and hardness will increase, and its plasticity will be significantly reduced. After a certain degree, it will lose its plastic deformation ability and can no longer continue cold processing. Annealing and softening heat treatment must be performed to restore the plasticity of the billet before cold processing can continue.

[0003] However, a small number of special grades in special alloys (especially high-temperature alloys) have some problems in heat treatment, which are manifested as follows: when the alloy is annealed and softened after cold working, if the usual heating method is used, that is, the heating time in the heating stage is as long as several hours or as short as several minutes (usually called slow heating, slow reaching temperature, etc.), whether it is a box-type furnace for periodic heat treatment or a continuous heat treatment furnace for continuous heat treatment, whether it is a cold-charged furnace, a hot-charged furnace, or a warm-charged furnace, the alloy material will have cracks, including longitudinal cracks, oblique cracks, and transverse cracks, and the alloy material may even break completely due to cracks. Moreover, the possibility of this problem occurring is almost 100%. When the furnace is cold-charged, the crackling sound of the billet after cracking can be heard during the heat treatment heating process. The cracks can be directly observed with the naked eye after the heat treatment is completed, and the alloy material may even be completely broken. When the furnace is hot-charged or warm-charged, the crackling sound of the billet after cracking can be heard during the charging process. The cracks can be directly observed with the naked eye after the heat treatment is completed, and the alloy material may even be completely broken. This problem exists in a small number of special alloys such as 68NiCrWCoTiAl alloy, GH4049 alloy, and GH4099 alloy. These alloys have very high content of alloying elements such as carbon, tungsten, molybdenum, cobalt, titanium, and aluminum, and thus have the significant characteristics of high crack tendency and difficulty in processing, making the alloy basically impossible to be made into materials. Even if it is made into materials, its quality has serious uncertainty problems and the risk of serious quality problems, which has become a technical obstacle for the production of alloy materials. How to achieve annealing, softening, and prevent cracks at the same time is a problem that must be solved. Through research, it is found that when a fast heating method with a heating time of ≤30 seconds is adopted (i.e. the core technical point of the present invention), the problem can be perfectly solved. Summary of the invention

[0004] The present invention provides a quick-heat treatment process for preventing cracks from being generated during annealing and softening heat treatment after cold working in the production process of special alloys with high crack tendency and difficult to process. The process is suitable for a small number of relatively special grades in special alloys (especially high-temperature alloys), and solves the problem of cracks being generated during annealing and softening heat treatment after cold working in the production process of these special alloys with high crack tendency and difficult to process, so that they can be manufactured into alloy materials, providing a solution for the normal manufacturing of such alloy materials. The process can be used as a pretreatment before formal heat treatment, and can also be used as formal heat treatment, and can achieve multiple purposes of annealing, softening, and preventing cracks at the same time. The alloy material obtained has the advantages of no cracks, good quality, and a yield rate of 100%.

[0005] The technical scheme of the process of the present invention is as follows:

[0006] The Cryo-Temperature heat treatment process to prevent heat treatment cracks in specialty alloys includes the following steps:

[0007] 1) Cleaning large-sized blanks;

[0008] Clean the lubricant, oil, sand and other dirt on the surface of the blank to avoid chemical element infiltration and other effects on the blank; if it is determined that the surface dirt has no effect on the blank, it is not necessary to clean the blank. It can be cleaned with tap water, alkaline water, acid solution and other appropriate methods, without special requirements.

[0009] 2) Unwinding of blank;

[0010] 3) Direct electric annealing softening heat treatment of large-sized billets;

[0011] Electrodes are connected at both ends of the blank to be heat treated, and the blank is heated by direct current, so that the blank is quickly heated to a holding temperature of 900-1100°C within ≤30 seconds, and the holding time at this temperature is 30-60 seconds.

[0012] 4) Remove the current applied to the blank, air cool it to room temperature, and coil the blank to complete the first direct electric annealing softening heat treatment;

[0013] 5) The blank after the first direct electric annealing softening heat treatment is subjected to the first cold working to reduce the cross-sectional area of ​​the blank, that is, to reduce the diameter, thickness, etc.;

[0014] Repeat steps 1) to 5) to perform the second, third, and other multiple "direct electrical annealing softening heat treatment + cold working" process cycles on the large-sized billet until a small-sized billet is obtained.

[0015] When annealing and softening heat treatment is required for small-sized billets, the following steps are included:

[0016] 1) Cleaning small-sized blanks;

[0017] 2) The billet is loosely rolled to make the billet as loose as possible to facilitate the entry of heat treatment medium during salt bath annealing and softening heat treatment;

[0018] 3) Salt bath annealing and softening heat treatment of small size billets;

[0019] Prepare the salt bath heat treatment furnace. There should be enough heat treatment medium in the furnace to ensure sufficient heat capacity. When the heat treatment medium in the salt bath heat treatment furnace reaches the required insulation temperature, place the billet in the material frame, and then quickly immerse the billet in the material frame in the heat treatment medium with an insulation temperature of 900-1100°C within ≤5 seconds. The insulation time at this insulation temperature is 60-180 seconds. Then take out the billet and air cool it to room temperature.

[0020] 4) Cleaning the blank, washing off the salt heat treatment medium adhering to the blank in water, and then rolling the blank to complete the first salt bath annealing softening heat treatment;

[0021] 5) The blank after the first salt bath annealing softening heat treatment is subjected to the first cold working to reduce the cross-sectional area of ​​the blank, that is, to reduce the diameter, thickness, etc.;

[0022] Repeat steps 1) to 5) to perform the second, third, and other multiple "salt bath annealing softening heat treatment + cold working" process cycles on the small-sized billet until the finished alloy material is obtained.

[0023] The cross-sectional area of ​​the large-size blank is greater than 6.8 mm 2 .

[0024] The cross-sectional area of ​​the small-sized blank is ≤6.8mm 2 .

[0025] The direct power supply adopts direct current or alternating current.

[0026] Directly applying power to make the billet quickly reach the required insulation temperature and maintain the electrical parameters such as current and voltage required should change accordingly with the changes in the cross-sectional area and length of the billet, and need to be determined based on the billet specifications (such as wire diameter, plate and strip thickness and width, etc.) and length.

[0027] The method of direct current annealing softening heat treatment is to apply a voltage V1 of 72V and a current I1 of 800A to an alloy billet with a diameter D1 of φ9mm and a length L1 of 16m as a basis. When the cross-sectional area and length of the billet change, the applied voltage V2 remains unchanged at 72V. The direct current I2 is estimated according to the formula I1×((D2÷D1)^2×(L1÷L2))^0.5, and a correction of ±15% is required to determine the current, voltage and other electrical parameters required to enable the billet to quickly reach the required insulation temperature and maintain the insulation temperature.

[0028] The salt bath annealing and softening heat treatment adopts a salt bath heat treatment furnace, and the heat treatment medium is BaCl2 and NaCl.

[0029] The weight ratio of BaCl2 to NaCl is 85:15.

[0030] The volume of the heat treatment medium is ≥100 times the net volume of the processed blank.

[0031] The principle of the process of the present invention is:

[0032] After cold processing, the blank will produce cold work hardening, its strength and hardness will increase, and its plasticity will significantly decrease. After a certain degree, it will lose its plastic deformation ability and can no longer continue to be cold processed. It must be annealed and softened by heat treatment to restore the plasticity of the blank before it can continue to be cold processed.

[0033] After cold working, the inside of the billet is in a high stress state, but this high stress is lower than its tensile strength, so no cracks are generated. When the conventional heat treatment process is used for heat treatment, during the heating process of the billet, the heat in the heat treatment medium air in the heat treatment furnace is transferred from the outer surface of the billet to the inside, and both the outer surface and the inside gradually heat up, but this process is relatively slow, and there is a temperature difference between the outer surface and the inside, resulting in a difference in internal and external stress. The newly generated stress is superimposed on the high stress that already exists due to cold working, exceeding the tensile strength of the billet, and cracks are generated.

[0034] According to the direct current supply method of the present invention, on the one hand, when the blank is heated and the temperature is raised, the heat is generated in the bulk, both inside and outside, and as a whole. The temperature from the outer surface to the inside is basically raised at the same time and is the same. There is basically no new stress difference, and the high stress already existing due to cold working will not be superimposed on it, and the tensile strength of the blank will not be exceeded, so cracks will not be generated. On the other hand, even if new stress is superimposed on the high stress already existing due to cold working, leading to a trend of crack initiation, the blank reaches the insulation temperature very quickly, both inside and outside, and as a whole. When the insulation temperature is reached, the blank is immediately in an annealing low stress state, loses elasticity and softens, and new stress superposition cannot be caused. That is, the speed at which the blank is in an annealing low stress state, loses elasticity and softens is far faster than the speed at which cracks are initiated, which is equivalent to only speed without cracks, and cracks have no time to be generated, and there is no subsequent crack expansion or cracking.

[0035] The salt bath method of the present invention is that heat is conducted from the outer surface of the blank to the inside, generating external and internal stress difference, generating new stress superposition, and leading to the trend of crack initiation. However, during the heat treatment process, the blank is quickly immersed in the heat treatment medium, and the heat treatment medium conducts heat to the blank. The heat conduction efficiency is very high, and the instantaneous heat capacity is sufficient, and the total heat capacity is sufficient to continuously supply heat to ensure the temperature. Therefore, the inside and outside of the blank instantly reach the insulation temperature almost simultaneously and as a whole. When the insulation temperature is reached, the blank is immediately in an annealing low stress state, loses elasticity and softens, and cannot cause new stress superposition, that is, the speed at which the blank is in an annealing low stress state, loses elasticity and softens is far faster than the speed at which cracks are initiated, which is equivalent to only speed without breaking, and cracks have no time to be generated, let alone subsequent crack expansion and cracking.

[0036] The process of the present invention adopts a direct electrification method in the large-size billet stage and a salt bath method in the small-size billet stage. The two-stage methods can be used separately or in combination.

[0037] The main features of the process of the present invention and the conventional heat treatment process are compared in Table 1. This comparison is based only on the case where the heat-treated material is a special alloy that is difficult to process and has a high crack tendency.

[0038] Table 1 Comparison of the process of the present invention with conventional heat treatment process

[0039]

[0040]

[0041] The process described in the present invention is suitable for a small amount of relatively special grades in special alloys (especially high-temperature alloys), and can prevent cracks from occurring during the annealing and softening heat treatment after cold processing in the production process of these high-crack-prone and difficult-to-process special alloys. It is a fast-reaching warm heat treatment process that can be suitable for mass production of products and has exclusive advantages in terms of feasibility, reliability, yield rate, quality, etc.

[0042] Beneficial effects of the present invention

[0043] The process of the present invention solves the problem of cracks generated during annealing, softening and heat treatment after cold processing in the production process of special alloys with high crack tendency and difficult to process, and achieves multiple purposes of annealing, softening and preventing cracks, so that this type of special alloy can be transformed from being basically unable to be produced (even if it is produced, its quality is subject to serious uncertainty problems and risks of serious poor quality) to being able to be produced normally with guaranteed production rate and quality, thus achieving a breakthrough in the manufacture of this type of alloy and providing a solution for the normal manufacture of this type of alloy.

[0044] The process of the present invention is mainly suitable for special alloys with high crack tendency and difficult to process, especially a small amount of relatively special grades in high-temperature alloys, such as 68NiCrWCoTiAl alloy, GH4049 alloy, GH4099 alloy, etc., and can be suitable for mass production of products. The obtained alloy has no cracks, good quality, and a yield rate of 100%. It has the advantages of feasibility, reliability, high yield rate, good quality, etc.

[0045] This process can be used as a pretreatment before formal heat treatment or as formal heat treatment. DETAILED DESCRIPTION

[0046] Requirements for the process of the present invention:

[0047] 1) Requirements for unwinding and rewinding:

[0048] Unwinding and rewinding can be performed by using an unwinding device and a rewinding device.

[0049] During or after the direct electric annealing and softening heat treatment of the billet, the billet should be coiled into a suitable coil diameter while it is in a red-hot state to facilitate subsequent loading into the furnace for solution treatment.

[0050] After the temperature of the billet drops to room temperature, cold bending and other cold working operations shall not be performed. Bending and other operations should be performed when the billet is in a red-hot state at a high temperature, otherwise new internal stress will be generated.

[0051] 2) Requirements for direct electrical annealing and softening heat treatment:

[0052] a) It must be ensured that the heating stage can reach the required temperature quickly, that is, the billet must quickly reach the required insulation temperature within ≤15 to 30 seconds.

[0053] b) The insulation temperature required to be reached after the billet is heated is within a relatively wide range, which is 250℃ lower than the solution treatment temperature corresponding to the alloy and the solution treatment temperature. Usually, 900℃ to 1100℃ can meet the requirements. The insulation temperature reached is directly tested on the billet using an infrared temperature measuring gun.

[0054] c) After the blank reaches the holding temperature, it should be kept at the holding temperature for 30 to 60 seconds until the blank loses its elasticity after cold processing and softens. The specific judgment method is that the blank appears to be hanging due to its own weight, falling over due to its own weight, collapsing due to its own weight, or rolling without twisting.

[0055] d) Directly apply power to make the billet quickly reach the required insulation temperature and maintain the required electrical parameters such as current and voltage. They should change accordingly with the changes in the cross-sectional area and length of the billet, and need to be determined based on the billet specifications (such as wire diameter, plate and strip thickness and width, etc.) and length.

[0056] e) The power source required for direct power supply can be either direct current or alternating current.

[0057] f) The direct annealing and softening heat treatment of the billet by power-on can be carried out in a periodic or continuous manner. In the periodic method, the billet is divided into several sections of the same length, and electrodes are connected to both ends of each section of the billet. After the first section of annealing and softening heat treatment is completed, the second section of annealing and softening heat treatment is carried out, and after the second section of annealing and softening heat treatment is completed, the third section of annealing and softening heat treatment is carried out, and so on. In the continuous method, the billet passes continuously between two conductive wheels as electrodes at an appropriate distance in the continuous power-on annealing equipment, and the billet is kept in contact with the conductive wheels, and the billet between the two conductive wheels is annealed and softened. During the direct power-on process, it is necessary to ensure that the billet is in good contact with the conductive head or conductive wheel, and the operating process of "power can be turned on only after good contact with the conductive head or conductive wheel, and the contact with the conductive head or conductive wheel can be removed only after power is turned off" must be strictly followed to avoid arcing due to poor contact, resulting in welding scars and new defects.

[0058] g) During direct power-on annealing and softening heat treatment, the billet coils must not touch each other, otherwise it will cause a short circuit and fuse.

[0059] h) Necessary direct power supply and current, voltage and other electrical parameter control and adjustment devices should be equipped.

[0060] i) The specifications applicable to the direct current method are generally not restricted, and the cross-sectional area of ​​the billet can be large or small. However, small-sized billets are prone to arc damage at the conductive contact points that affect quality, difficulty in temperature control leading to over-temperature melting and fracture, cumbersome operation, and relatively low efficiency. The actual use effect is poor, so it is only used for rapid heat treatment at the large-sized billet stage. For rapid heat treatment at the small-sized billet stage, the salt bath method needs to be used.

[0061] 3) Requirements for salt bath annealing and softening heat treatment:

[0062] a) A salt bath heat treatment furnace is used (the high temperature salt bath heat treatment furnace used in the tool manufacturing industry can be used), wherein the heat treatment medium contains two salts, BaCl2 and NaCl, and the weight ratio of BaCl2 to NaCl is 85:15.

[0063] b) The volume of the heat treatment medium in the salt bath heat treatment furnace is 100 times or more of the net volume of the treated billet to ensure that the heat treatment medium has sufficient heat capacity to achieve rapid temperature reach and maintain insulation temperature.

[0064] c) It must be ensured that the temperature is reached quickly, that is, all the blanks in the basket must be immersed in the heat treatment medium in the salt bath heat treatment furnace within ≤5 seconds so that all the blanks can quickly reach the required insulation temperature.

[0065] d) The insulation temperature required to be reached after the billet is heated is within a relatively wide range, which is 250°C lower than the corresponding solution treatment temperature of the alloy and the solution treatment temperature. Usually, 900-1100°C can meet the requirements. The insulation temperature reached is detected by thermocouples for the heat treatment medium in the salt bath heat treatment furnace.

[0066] e) After the blank reaches the holding temperature, it should be kept in the heat treatment medium in the salt bath heat treatment furnace for 60 to 180 seconds so that the blank loses its elasticity after cold working and softens.

[0067] f) The applicable specifications of the salt bath method are limited and are only applicable to blanks with a cross-sectional area of ​​≤6.8mm 2 Small-sized billets (such as wires with a diameter ≤φ2.94mm) are not suitable for large-sized billets (because it is difficult to ensure that the core of the large-sized billets reaches temperature quickly).

[0068] Example 1

[0069] Take 68NiCrWCoTiAl alloy as an example

[0070] 1. Annealing and softening heat treatment and cold processing of large-sized billets are carried out by direct power-on method:

[0071] Take a 68NiCrWCoTiAl alloy billet with a diameter of φ9mm and a length of 16m, rinse it with tap water and release the coil; use a periodic treatment, connect electrodes at both ends of the section to be heat treated and power on, reach the required insulation temperature within 20 to 28 seconds, the insulation temperature is 1050℃, and maintain the insulation time for 58 to 60 seconds, during which the direct current is 800A and the voltage is 72V, and a DC power supply is used to smoothly achieve annealing and softening heat treatment, then remove the applied current, and then coil it; then cold draw it into an alloy billet with a diameter of φ6.8mm.

[0072] Repeat the above steps to anneal and soften the alloy billet with a diameter of φ6.8mm and a length of 20m, during which the direct current is 550A and the voltage is 72V; then cold draw the alloy billet with a diameter of φ5.2mm.

[0073] Repeat the above steps to anneal and soften the alloy billet with a diameter of φ5.2mm and a length of 25m, during which the direct current is 360A and the voltage is 72V; then cold draw the alloy billet with a diameter of φ4mm.

[0074] Repeat the above steps to anneal and soften the alloy billet with a diameter of φ4mm and a length of 30m, during which the direct current is 250A and the voltage is 72V; then cold draw the alloy billet with a diameter of φ2.8m to make it a small-sized billet.

[0075] 2. If the small-sized billet is to be subjected to annealing and softening heat treatment and cold processing, the salt bath method is used for annealing and softening heat treatment:

[0076] Take an alloy billet with a diameter of φ2.8mm, rinse it with tap water, and then spread out the coil; prepare a salt bath heat treatment furnace with a sufficient amount of heat treatment medium in the furnace, the volume of the heat treatment medium is about 160 times the net volume of the treated billet, and the weight ratio of BaCl2 to NaCl in the heat treatment medium is 85:15; when the heat treatment medium reaches the required insulation temperature of 1100°C, place the billet in a basket, and then quickly immerse the billet in the basket in the heat treatment medium within about 3 seconds, and after keeping the insulation temperature for about 150 seconds, take the billet in the basket out of the heat treatment medium and let the billet cool naturally in the air; then rinse the billet with tap water, and then roll it, that is, complete the salt bath annealing softening heat treatment; then cold draw it into an alloy billet with a diameter of φ2.1mm.

[0077] Repeat the above steps to anneal and soften the alloy billet with a diameter of φ2.1 mm; then cold draw it into an alloy billet with a diameter of φ1.6 mm.

[0078] Repeat the above steps to anneal and soften the alloy billet with a diameter of φ1.6 mm; then cold draw it into a cold-deformed alloy material with a diameter of φ1.2 mm to obtain an alloy product.

[0079] Results: The success rate of annealing and softening heat treatment increased from ≤20% to almost 100%, and the yield rate of annealing and softening heat treatment increased from ≤10% to almost 100%. The alloy material has good quality and no cracks, which fully meets the needs of scientific research and production, and the effect is very good.

[0080] Example 2

[0081] Take GH4049 alloy as an example

[0082] For large-size billets, annealing and softening heat treatment and cold processing are carried out by direct power-on method:

[0083] Take a GH4049 alloy billet with a diameter of φ10mm and a length of 18m, rinse it with tap water and release the coil; use a periodic treatment, connect electrodes at both ends of the section to be heat treated and power on, reach the required insulation temperature within 20 to 28 seconds, the insulation temperature is 1100℃, and maintain the insulation time for 58 to 60 seconds, during which the direct current is 850A and the voltage is 72V, and a DC power supply is used to smoothly achieve annealing and softening heat treatment, then remove the applied current, and then coil it; then cold draw it into an alloy billet with a diameter of φ7.8mm.

[0084] Repeat the above steps to anneal and soften the alloy billet with a diameter of φ7.8mm and a length of 23m, during which the direct current is 590A and the voltage is 72V; then cold draw the alloy billet with a diameter of φ6mm.

[0085] Repeat the above steps to anneal and soften the alloy billet with a diameter of φ6mm and a length of 28m, during which the direct current is 410A and the voltage is 72V; then cold-draw it into a cold-deformed alloy material with a diameter of φ4.5mm to obtain an alloy product.

[0086] Results: The success rate of annealing and softening heat treatment increased from ≤30% to almost 100%, and the yield rate of annealing and softening heat treatment increased from ≤20% to almost 100%. The alloy material has good quality and no cracks, which fully meets the needs of scientific research and production, and the effect is very good.

Claims

1. A fast heat treatment process for preventing heat treatment cracks in special alloys, characterized in that: The following steps are involved: 1) Cleaning large-sized blanks; 2) Unwinding of blank; 3) Direct electric annealing softening heat treatment of large-sized billets; Electrodes are connected at both ends of the heat treatment section of the billet, and the billet is heated by direct current, so that the billet is quickly heated to a holding temperature of 900-1100°C within ≤30 seconds, and the holding time at this temperature is 30-60 seconds; 4) Remove the current applied to the blank, air cool it to room temperature, and coil the blank to complete the first direct electric annealing softening heat treatment; 5) The blank after the first direct electric annealing softening heat treatment is subjected to the first cold working to reduce the cross-sectional area of ​​the blank (i.e., reduce the diameter, thickness, etc.); Repeat steps 1) to 5) to obtain small-sized billets.

2. The process according to claim 1, characterized in that When annealing and softening heat treatment is required for small-sized billets, the following steps are included: 1) Cleaning small-sized blanks; 2) Loose coils of blanks; 3) Salt bath annealing and softening heat treatment of small size billets; The blank is placed in a material frame, and the blank is quickly immersed in a heat treatment medium with a holding temperature of 900 to 1100°C within ≤5 seconds. The holding time at this temperature is 60 to 180 seconds, and then the blank is taken out and air-cooled to room temperature; 4) Cleaning the blank, then rolling the blank to complete the first salt bath annealing softening heat treatment; 5) The blank after the first salt bath annealing softening heat treatment is subjected to the first cold working to reduce the cross-sectional area of ​​the blank (i.e., reduce the diameter, thickness, etc.); Repeat steps 1) to 5) until the finished alloy material is obtained.

3. The process according to claim 1, characterized in that: The cross-sectional area of ​​the large-size blank is greater than 6.8 mm 2 .

4. The process according to claim 1, characterized in that: The cross-sectional area of ​​the small-sized blank is ≤6.8mm 2 .

5. The process according to claim 1, characterized in that: The power source for direct power supply adopts direct current or alternating current; Directly applying power to make the billet quickly reach the required insulation temperature and maintain the electrical parameters such as current and voltage required should change accordingly with the changes in the cross-sectional area and length of the billet, and need to be determined based on the billet specifications (such as wire diameter, plate and strip thickness and width, etc.) and length.

6. The process according to claim 1, characterized in that: The method of direct current annealing softening heat treatment is to apply a voltage V1 of 72V and a current I1 of 800A to an alloy billet with a diameter D1 of φ9mm and a length L1 of 16m as a basis. When the cross-sectional area and length of the billet change, the applied voltage V2 remains unchanged at 72V. The direct current I2 is estimated according to the formula I1×((D2÷D1)^2×(L1÷L2))^0.5, and a correction of ±15% is required to determine the current, voltage and other electrical parameters required to enable the billet to quickly reach the required insulation temperature and maintain the insulation temperature.

7. The process according to claim 2, characterized in that: The salt bath annealing and softening heat treatment adopts a salt bath heat treatment furnace, and the heat treatment medium is BaCl2 and NaCl.

8. The process according to claim 7, characterized in that: The weight ratio of BaCl2 to NaCl is 85:

15.

9. The process according to claim 2, characterized in that: The volume of the heat treatment medium is ≥100 times the net volume of the processed blank.

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