Refining process for vacuum induction melting of 3J468 alloy

Abstract

The invention discloses a refining process for vacuum induction melting of 3J468 alloy, which adopts high and low temperature double refining under high vacuum degree, that is, first high temperature and high vacuum degree refining is carried out under the conditions of 1665 DEG C and vacuum degree superior to 1Pa, and then second low temperature and high vacuum degree refining is carried out under the conditions of 1450 DEG C and vacuum degree superior to 0.8 Pa, according to the technology, harmful elements which cause serious hot working cracking of the alloy ingot or the alloy blank can be reduced or removed from the source, the hot working cracking problem in the production process of the high-crack-tendency difficult-to-machine alloy material is remarkably solved, the cracking proportion of a hot working single procedure is reduced to be only smaller than or equal to 20%, the yield is increased to be larger than or equal to 80%, and the production cost is reduced to be smaller than or equal to 20%. And the potential risk of the finished product quality is eliminated, the very remarkable effect is achieved, and a good solution is provided for normal manufacturing of the alloy material.

Description

Technical Field

[0001] This invention belongs to the field of special alloy smelting and relates to a high vacuum degree high and low temperature dual refining process for vacuum induction melting of 3J468 alloy. Background Technology

[0002] Special alloys mainly include high-temperature alloys, corrosion-resistant alloys, functional metallic materials, and special stainless steels. Special alloy materials typically include bars, strips, wires, plates, strips, and tubes. Special alloys are usually produced by hot forging, hot rolling, and other hot working processes to create the final product and meet technical performance requirements.

[0003] However, some special grades of special alloys (especially high-temperature alloys) are prone to problems during hot working. Currently, the 3J468 high-temperature, high-elasticity alloy (hereinafter referred to as 3J468 alloy), which is highly prone to cracking and difficult to machine, has the following chemical composition by mass percentage: C≤0.05%, Si≤0.4%, Mn≤0.4%, S≤0.010%, P≤0.015%, Cr 18~20%, Ti 2.7~3.2%, Al 1.3~1.8%, Co 5.5~6.7%, W 9.0~10.5%, Ce≤0.05%, B≤0.003%, Nb≤0.2%, V≤0.2%, Cu≤0.07%, Fe≤1.0%, and Ni balance. This alloy is prone to cracking in multiple hot working processes, especially during the hot forging of alloy ingots, where severe internal core cracking makes it almost impossible to produce usable material, and even obtaining a small amount of experimental material is difficult. The same situation occurs during the subsequent hot rolling of alloy billets. The cracking rate during the hot working process is as high as ≥60%, and the yield is ≤40%, making it practically impossible to produce and supply normally.

[0004] The main reasons for the above problems are: 1. The inherent characteristics of the alloy that cannot be changed: The alloy contains very high levels of alloying elements such as carbon, tungsten, cobalt, titanium, and aluminum, which have significant characteristics of high cracking tendency and difficulty in processing; 2. The vacuum induction melting process is inadequate, resulting in low achievement of the smelting objectives and poor metallurgical effect and quality. The reason is that if the conventional vacuum induction melting process is used, the requirements for reducing or removing harmful elements such as low-melting-point fusible impurities (such as As, Sn, Sb, Pb, Bi, Zn, Cu, S, P elements) and gaseous elements (such as N, H, O elements) are not met, resulting in low achievement of the smelting objectives and poor metallurgical effect and quality. Subsequent processes are unable to effectively reduce or remove harmful elements, as these residual harmful elements are characterized by either low melting points or low intercrystalline bonding. During hot working, the working temperature reaches 1165℃~1180℃, which is higher than the melting point of harmful elements. This causes the melting of harmful elements with low melting points in the alloy, and the low intergranular bonding strength significantly reduces grain boundary strength, leading to hot working cracks. Conversely, if the hot working temperature is lowered below the melting point of harmful elements, the thermal strength becomes too high, preventing thermoplastic deformation and failing to achieve the basic purpose of hot working. Therefore, when the hot working temperature is high (e.g., the normal hot working temperature is 1165℃~1180℃), hot working cracks will occur; when the hot working temperature is low (e.g., below the melting point of harmful elements), the thermal strength is too high and the thermoplasticity is too low, making hot working impossible. Both cannot be achieved simultaneously. 3. The original chemical composition of the alloy contains few microalloying elements that can reduce or remove low-melting-point fusible impurities; only one element, Ce, is present.

[0005] How to reduce or remove harmful elements in alloys that cause severe hot working cracking of alloy ingots or billets during the initial smelting process, and improve or solve the problem of hot working cracking, is a concern for those skilled in the art. Summary of the Invention

[0006] In response to the problems described in the background art, this invention provides a high-vacuum, high-temperature and low-temperature dual refining process for vacuum induction melting of 3J468 alloy. This process reduces or removes harmful elements in the alloy that cause severe hot working cracking of alloy ingots or billets during the initial smelting process, and can significantly improve the cracking problem during hot working.

[0007] The present invention adopts the following technical solution: The refining process for vacuum induction melting of 3J468 alloy employs a dual refining method under high vacuum conditions, using both high-temperature and low-temperature methods. First, high-temperature refining is performed at 1665℃±10℃, followed by low-temperature refining at 1450℃±10℃. Specifically, the process includes the following steps: S1. Ingredients: Weigh each component according to the chemical composition of 3J468 alloy; S2. Loading and melting: Take the components Ni, Cr, Co, and W, and heat them under a vacuum of ≤10 Pa to melt all of them into molten steel. S3. First stage of refining (high temperature and high vacuum refining): Under vacuum conditions ≤1Pa, the temperature of the molten steel is reached and maintained at 1665℃±10℃, and the steel is refined with intermittent stirring. The refining time is determined according to the furnace type. If the vacuum induction melting furnace is a small furnace, such as a 50 kg furnace, the refining time for the first refining is 28±1 minutes; if the vacuum induction melting furnace is a large furnace, such as a 500 kg furnace, the refining time for the first refining is 80±1 minutes. S4. Second Refining (Low Temperature High Vacuum Refining): Under vacuum conditions ≤0.8Pa, the temperature of the molten steel is reduced and maintained at 1450℃±10℃, and the steel is refined with intermittent stirring. The refining time is determined according to the furnace type. If the vacuum induction melting furnace is a small furnace type, such as a 50 kg furnace type, the refining time of the second refining is 20±1 minutes; if the vacuum induction melting furnace is a large furnace type, such as a 500 kg furnace type, the refining time of the second refining is 60±1 minutes. S5. Alloying and settling: Add C, Si, Mn, Ti, Al, Ce, and B to the molten steel, stir thoroughly, raise and maintain the temperature of the molten steel at 1540℃±10℃, and let it stand. The settling time is determined according to the furnace type. If the vacuum induction melting furnace is a small furnace, such as a 50 kg furnace, the settling time is 10±1 minutes; if the vacuum induction melting furnace is a large furnace, such as a 500 kg furnace, the settling time is 30±1 minutes.

[0008] S6. Casting: After the settling period, molten steel is poured in and cooled to obtain 3J468 master alloy steel bar.

[0009] The intermittent stirring described in steps S3 and S4 includes electromagnetic stirring and mechanical stirring. After the first stirring, stirring is performed every 8 to 10 minutes, with each stirring session lasting 1 to 3 minutes. The number of stirrings depends on the type of vacuum induction melting furnace. For example, when using a 50 kg furnace, the first refining process involves 4 stirrings, and the second refining process involves 3 stirrings. When using a 500 kg furnace, the first refining process involves 11 stirrings, and the second refining process involves 8 stirrings. This process ensures that the chemical composition of the molten steel is uniform and that harmful elements float to the surface of the molten steel, where they are then adsorbed by the crucible wall and attached to the vicinity of the molten steel surface, or are removed to the outside by the vacuum system.

[0010] The intermittent stirring is an energized operation, meaning that the induction coil of the crucible in the vacuum induction melting furnace is continuously energized during electromagnetic and mechanical stirring.

[0011] The core of the previous refining process for 3J468 alloy was single-stage medium-temperature refining (e.g., under vacuum conditions better than 3Pa, the refining temperature was 1560℃±10℃, the refining time for small furnaces was 30 minutes, and the refining time for large furnaces was 90 minutes). This process focused on reducing the burning loss of the main alloying elements to increase the yield and save costs, as well as minimizing the impact of medium-temperature refining on the crucible. However, the master alloy steel bars produced by this process cracked severely during the subsequent hot working of the alloy ingots or billets obtained by remelting. The cracking rate in a single hot working process was as high as ≥60%, and the yield was ≤40%. The reason is that in vacuum induction melting, previous refining processes did not focus on reducing or removing harmful elements such as low-melting-point fusible impurities and gaseous elements, resulting in low achievement of smelting objectives and poor metallurgical effects and quality. Subsequent processes could no longer effectively reduce or remove harmful elements. These residual harmful elements, due to their low melting points or low intercrystalline bonding, melt during hot working because the hot working temperature (normal hot working temperature is 1165℃~1180℃) is higher than the melting point of the harmful elements. This further weakens the intercrystalline bonding and significantly reduces the grain boundary strength, leading to hot working cracks.

[0012] The process described in this invention involves refining at high temperature and high vacuum, where the temperature exceeds the boiling points of harmful elements such as As, Sb, Bi, Zn, S, and P. These harmful elements are vaporized and then extracted to the outside by the vacuum system, thus reducing or removing them. However, because the solubility of gases in the molten steel increases significantly at very high refining temperatures, the content of saturated gases in the molten steel is high and needs to be reduced or removed. Therefore, low temperature and high vacuum refining (with the refining temperature close to the alloy solidification temperature) is subsequently used. This significantly reduces the solubility of gases in the molten steel, and the N, H, and O saturated gases dissolved during high-temperature refining escape from the molten steel and are extracted to the outside by the vacuum system. Because the molten steel is in a vacuum environment, the escape of gases from the molten steel becomes very easy, and the escape extraction and removal process is very rapid and thorough.

[0013] Therefore, this application adopts a process of first refining at high temperature and high vacuum (first refining) and then refining at low temperature and high vacuum (second refining), which ingeniously combines the beneficial effects of each refining process on the alloy. The two processes are matched and matched in stages to achieve the two important objectives of reducing or removing low-melting-point fusible impurity elements and gaseous elements. This solves the contradiction that a single medium-temperature refining process cannot simultaneously achieve the two important objectives of reducing or removing low-melting-point fusible impurity elements and gaseous elements, and obtains good metallurgical effect and quality.

[0014] Practical application verification shows that when using the process described in this invention, due to the reduction or removal of harmful elements, the single-process cracking ratio of the alloy ingots or billets obtained by subsequent remelting is only ≤20% and the yield is ≥80% during hot processing, which significantly improves the previous hot processing cracking problem and eliminates serious quality risks; and since those harmful elements are also harmful to the alloy properties, reducing or removing harmful elements also ensures the good stability of the alloy properties.

[0015] The process described in this invention is applicable to 3J468 alloy. The process significantly improves the problem of hot working cracking in the production of 3J468 alloy materials with high cracking tendency and difficult processing. The cracking rate of a single hot working process is reduced to only ≤20%, and the yield is increased to ≥80%. It eliminates serious uncertainty and risk of serious quality problems in the finished product, and the yield, performance and quality are all guaranteed, providing a better solution for the normal manufacturing of this alloy material.

[0016] The process described in this invention is applicable to the mass production of products and has significant effects in terms of feasibility, reliability, yield, performance, and quality. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0018] The process flow described in this invention is described in [reference]. Figure 1 . Example 1

[0019] A 50 kg vacuum induction melting furnace was used to prepare 3J468 alloy master alloy steel bars. The mass percentage of each component in its chemical composition was as follows: C, 0.01; Si, 0.3; Mn, 0.3; Cr, 19; Ti, 3.0; Al, 1.6; Co, 6.2; W, 9.6; Ce, 0.05; B, 0.002, with the balance being Ni and unavoidable impurities.

[0020] The preparation process includes the following steps: S1. Ingredients: Weigh each component according to the chemical composition table of 3J468 alloy; S2. Loading and melting: Load the raw materials of Ni, Cr, Co and W into the crucible and melt them into molten steel under a vacuum of better than 10 Pa; load the raw materials of C, Si, Mn, Ti, Al, Ce and B into the alloying charging bucket for later use.

[0021] S3. First refining: Using a high-power 45±3kW power supply, under a vacuum degree better than 1Pa, the temperature of the molten steel is reached and maintained at 1665℃±10℃, and the refining time is 28±1 minutes. The first stirring is carried out at the beginning of the refining, followed by electromagnetic stirring and mechanical stirring every 8 to 10 minutes. Each stirring lasts for 1 to 3 minutes, for a total of 4 stirrings. All stirring operations are carried out under power.

[0022] S4. Second refining: Using a low-power power supply of 16±3kW, under the condition of vacuum degree better than 0.8Pa, the temperature of the molten steel is reduced and maintained at 1450℃±10℃, and the refining time is 20±1 minutes; the first stirring is carried out at the beginning of refining, and then electromagnetic stirring and mechanical stirring are carried out every 8 to 10 minutes thereafter, with each stirring time being 1 to 3 minutes, for a total of 3 stirrings, and all stirring is carried out under power.

[0023] S5. Alloying and settling: Add C, Si, Mn, Ti, Al, Ce and B alloying elements to the molten steel and stir thoroughly. Then, use a medium power supply of 20±3kW to moderately increase and maintain the temperature of the molten steel at 1540℃±10℃, and settling time is 10±1 minutes.

[0024] S6. Casting: After the settling period, the molten steel is slowly and continuously poured into the steel bar mold, and then the vacuum is broken and the furnace is removed to complete the vacuum induction melting and obtain the master alloy steel bar.

[0025] The remaining processes are then carried out, and the master alloy steel bar is remelted to obtain an alloy ingot, which is then hot-forged at 1165°C.

[0026] The results of the hot forging process inspection and statistics show that the cracking rate of a single process is only ≤20% and the yield is ≥80%, which can meet the needs of scientific research and production, and the effect is good. Example 2

[0027] A 500 kg vacuum induction melting furnace was used to prepare 3J468 alloy master alloy steel bars. The mass percentage of each component in its chemical composition was as follows: C, 0.01; Si, 0.3; Mn, 0.3; Cr, 19; Ti, 3.0; Al, 1.6; Co, 6.2; W, 9.6; Ce, 0.05; B, 0.002, with the balance being Ni and unavoidable impurities.

[0028] The preparation process includes the following steps: S1 and S2 are the same as in Example 1.

[0029] S3. First refining: Using a high-power supply of 290±8kW, under a vacuum degree better than 1Pa, the temperature of the molten steel is reached and maintained at 1665℃±10℃, and the refining time is 80±1 minutes. The first stirring is carried out at the beginning of the refining process, followed by electromagnetic stirring and mechanical stirring every 8 to 10 minutes. Each stirring lasts for 1 to 3 minutes, for a total of 11 stirrings. All stirring operations are carried out while the power is on.

[0030] S4. Second refining: Using a low-power power supply of 110±8kW, under the condition of a vacuum degree better than 0.8Pa, the temperature of the molten steel is reduced and maintained at 1450℃±10℃, and the refining time is 60±1 minutes; the first stirring is performed at the beginning of the refining, and then electromagnetic stirring and mechanical stirring are performed every 8 to 10 minutes thereafter, with each stirring time being 1 to 3 minutes, for a total of 8 stirrings, and all stirring is performed under power.

[0031] S5. Alloying and settling: Add C, Si, Mn, Ti, Al, Ce and B alloying elements to the molten steel and stir thoroughly. Then, use a medium power supply of 130±8kW to moderately increase and maintain the temperature of the molten steel at 1540℃±10℃, and settling time is 30±1 minutes.

[0032] S6 is the same as in Example 1.

[0033] The results of the hot forging process inspection and statistics show that the cracking rate of a single process is only ≤20% and the yield is ≥80%, which can meet the needs of scientific research and production, and the effect is good.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A refining process for vacuum induction melting of 3J468 alloy, characterized in that, The high-low temperature dual refining method under high vacuum includes the following steps: S1. Ingredients: Weigh each component according to the chemical composition of 3J468 alloy; S2. Loading and melting: Take the components Ni, Cr, Co, and W, and heat them under a vacuum of ≤10 Pa to melt all of them into molten steel. S3. First Refinement Stage: Under vacuum conditions ≤1Pa, the temperature of the molten steel is reached and maintained at 1665℃±10℃, and the steel is refined with intermittent stirring. S4. Second Refinement: Under vacuum conditions ≤0.8Pa, the temperature of the molten steel is reduced and maintained at 1450℃±10℃, and the steel is refined with intermittent stirring. S5. Alloying and settling: Add C, Si, Mn, Ti, Al, Ce, and B to the molten steel, stir thoroughly, raise and maintain the temperature of the molten steel at 1540℃±10℃, and let it stand. S6. Casting: After the settling period, molten steel is poured in and cooled to obtain 3J468 master alloy steel bar.

2. The process according to claim 1, characterized in that, The refining time for the first and second refining stages is determined based on the furnace type.

3. The process according to claim 2, characterized in that, If the vacuum induction melting furnace is a 50 kg furnace type, the refining time for the first refining stage is 28±1 minutes and the refining time for the second refining stage is 20±1 minutes; if the vacuum induction melting furnace is a 500 kg furnace type, the refining time for the first refining stage is 80±1 minutes and the refining time for the second refining stage is 60±1 minutes.

4. The process according to claim 1, characterized in that, The settling time mentioned in step S5 is determined according to the furnace type.

5. The process according to claim 4, characterized in that, If the vacuum induction melting furnace is a 50 kg furnace type, the settling time is 10±1 minutes; if the vacuum induction melting furnace is a 500 kg furnace type, the settling time is 30±1 minutes.

6. The process according to claim 1, characterized in that, The intermittent stirring described in steps S3 and S4 is electromagnetic stirring and mechanical stirring. After the first stirring, stirring is performed once every 8 to 10 minutes, and each stirring lasts for 1 to 3 minutes.

7. The process according to claim 1, characterized in that, The number of intermittent stirrings is determined according to the type of vacuum induction melting furnace. If the vacuum induction melting furnace is a 50 kg furnace, the first refining stirring is performed 4 times and the second refining stirring is performed 3 times. If the vacuum induction melting furnace is a 500 kg furnace, the first refining stirring is performed 11 times and the second refining stirring is performed 8 times.

8. The process according to claim 1, characterized in that, The intermittent stirring is performed under electrical conditions.

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