A method for controlling shrinkage cavity defects in vacuum arc casting of titanium and titanium alloys

Abstract

This invention relates to a method for controlling shrinkage cavity defects in vacuum arc furnace ingots of titanium and titanium alloys, comprising the following steps: S1, raw material preparation; S2, vacuuming; S3, melting; S4, determining the weight and time of the feeding electrode according to the feeding requirements of the titanium alloy; S5, ingot feeding; S6, cooling. This invention effectively solves the problem of shrinkage cavity defects in titanium and titanium alloy ingots smelted in a vacuum arc furnace, thereby significantly improving the internal quality of the ingots and laying a solid foundation for the smelting and development of titanium and titanium alloy products.

Description

Technical Field

[0001] This invention relates to the field of titanium metallurgy, and in particular to a method for controlling shrinkage defects in vacuum consumable ingots of titanium and titanium alloys. Background Technology

[0002] Titanium and titanium alloys possess advantages such as high specific strength, good corrosion resistance, and excellent high-temperature performance, low-temperature toughness, and low-temperature superconductivity, making them widely used in aerospace, military industry, and civilian fields. Currently, the smelting of titanium and titanium alloys mainly employs the vacuum arc remelting process. However, ingots smelted using this process are prone to internal defects such as shrinkage cavities and segregation. This is because gases are not promptly removed during the later stages of smelting, and the shrinkage cavities caused by the solidification of the molten metal are not effectively replenished by the liquid metal, thus forming shrinkage cavities inside the ingot. This not only affects the internal crystal structure but also reduces the cleanliness of the ingot and lowers the yield. Therefore, ingot feeding is a crucial step in the vacuum arc remelting process for titanium and titanium alloys.

[0003] For a long time, many metallurgists have been engaged in research on titanium and titanium alloys. There are numerous patents and documents on vacuum arc remelting of titanium and titanium alloys, but most focus on smelting processes and product development, with very few documents addressing the control of shrinkage defects in vacuum arc remelting ingots. An article published in *Special Steel Technology*, Issue 3, 2009, entitled "Research on Feeding Process for Vacuum Arc Remelting of Titanium and Titanium Alloys," points out that Chen Xin et al. conducted experimental research on the feeding process for titanium and titanium alloy smelting in a 3-ton vacuum arc remelting furnace. The feeding weight was 150 kg, the current was reduced from 20,000 amperes to 3,000 amperes, and the feeding time adopted a pattern of short initial and later stages and a longer middle stage. The shrinkage depth after ingot head cutting was 40 mm. This feeding method has the following problems: First, the feeding weight is too small, accounting for only 5% of the total ingot weight. Changes in current, voltage, and molten metal pool temperature have a certain reaction time. If the feeding weight is too small, the feeding will be insufficient and the effect will be unsatisfactory. Secondly, the current drop gradient in the early stage of feeding is too large, reaching 25%, which leads to a sharp drop in molten pool temperature and a significant reduction in molten pool stirring intensity, which will aggravate element segregation and reduce the internal quality of the ingot. Thirdly, the low current duration in the later stage of feeding is too short, which will cause the upper molten metal to solidify too quickly and cannot fill the shrinkage cavities generated in the lower part in time, resulting in poor feeding effect. Fourthly, after using this method for feeding, the shrinkage cavity depth of the ingot reached 40 mm, and the feeding effect was not ideal. Summary of the Invention

[0004] The purpose of this invention is to provide a method for controlling shrinkage defects in vacuum consumable ingots of titanium and titanium alloys, which can effectively solve problems such as shrinkage defects in ingots generated during the smelting of titanium and titanium alloys in a vacuum consumable furnace.

[0005] The technical solution adopted in this invention is as follows:

[0006] The present invention proposes a method for controlling shrinkage defects in vacuum consumable ingots of titanium and titanium alloys, comprising the following steps: S1, raw material preparation; S2, vacuuming; S3, smelting;

[0007] S4. Determine the weight and time of the feeding electrode according to the feeding requirements of the titanium alloy; S5. Feeding of the ingot; S6. Cooling.

[0008] Furthermore, step S1 specifically includes: using a vacuum arc furnace of corresponding capacity for melting, preparing the electrode to be melted, and loading it into a copper crucible.

[0009] Furthermore, step S2 specifically includes: starting the mechanical pump of the vacuum arc furnace, starting the Roots pump when the vacuum degree reaches 700Pa, and starting the booster pump when the vacuum degree reaches 5Pa.

[0010] Furthermore, step S3 specifically includes: starting melting when the vacuum level reaches below 0.1 Pa and the leakage rate reaches below 1 Pa / min, and entering the normal melting stage after the arc ignition stage. The current in the normal melting stage is 7000-7200A and the voltage is 31-32V.

[0011] Furthermore, in step S4, the weight of the feeding electrode is 10%-20% of the total weight of the melting electrode; the feeding time is 25%-35% of the total melting time.

[0012] Furthermore, step S5 specifically includes: after melting for 60-66 minutes, when the remaining electrode weight reaches a certain weight, feeding begins; in the early stage of feeding, the current decrease gradient is 5%-15% of the normal melting current, and the time is 15%-25% of the total feeding time; in the middle stage of feeding, the current decrease gradient is 2%-10% of the normal melting current, and the time is 35%-55% of the total feeding time; in the later stage of feeding, the current is 15%-25% of the normal melting current, and the time is 30%-40% of the total feeding time; in the early stage of feeding, the voltage decrease gradient is 1%-2% of the normal melting voltage; and in the middle and later stages of feeding, the voltage decrease gradient is 0.5%-1.5% of the normal melting voltage.

[0013] Furthermore, step S6 specifically includes: after the feeding is completed, the ingot is cooled in a copper crucible, and the vacuum degree is controlled below 1 Pa, with a cooling time of 3-8 hours.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] This invention proposes a method for controlling shrinkage cavity defects in vacuum arc remelting furnace ingots of titanium and titanium alloys. When melting titanium and titanium alloys in a vacuum arc remelting furnace, sufficient weight of the feeding electrode is reserved in the later stages of melting to fully feed the ingot. The magnitude of the current and voltage drop in the early stages of feeding is controlled to avoid affecting the internal quality of the ingot due to a significant drop in current. In the later stages of feeding, the duration of the low current is appropriately extended to ensure that the upper metal remains liquid while the lower metal solidifies, allowing the gas inside the ingot to escape completely. Furthermore, the shrinkage cavity caused by the solidification and shrinkage of the lower metal can be effectively filled by the upper metal liquid, thus completing the feeding of the ingot. The method provided by this invention can completely solve the problem of shrinkage cavity defects in titanium and titanium alloy ingots, and is simple to operate, easy to implement, and poses no safety hazards. Detailed Implementation

[0016] The present invention proposes a method for controlling shrinkage defects in vacuum consumable ingots of titanium and titanium alloys, which specifically includes the following steps:

[0017] S1. Raw material preparation;

[0018] The electrodes to be melted are prepared by using a vacuum arc furnace of appropriate capacity and then placed into a copper crucible.

[0019] S2, Vacuuming;

[0020] Start the mechanical pump of the vacuum arc furnace. When the vacuum degree reaches 700 Pa, start the Roots pump of the vacuum arc furnace. When the vacuum degree reaches 5 Pa, start the booster pump of the vacuum arc furnace.

[0021] S3, Smelting;

[0022] Melting begins when the vacuum level reaches below 0.1 Pa and the leakage rate reaches below 1 Pa / min. After the arc ignition stage, the normal melting stage begins. The current during the normal melting stage is 7000-7200 A and the voltage is 31-32 V.

[0023] S4. Determine the weight and time of the feeding electrode according to the feeding requirements of the titanium alloy;

[0024] The weight of the feeding electrode is 10%-20% of the total weight of the melting electrode; the feeding time is 25%-35% of the total melting time.

[0025] S5, Ingot feeding;

[0026] After 60-66 minutes of melting, when the remaining electrode weight reaches a certain value, feeding begins. In the early feeding stage, the current decrease gradient is 5%-15% of the normal melting current, lasting for 15%-25% of the total feeding time. In the middle feeding stage, the current decrease gradient is 2%-10% of the normal melting current, lasting for 35%-55% of the total feeding time. In the later feeding stage, the current decrease gradient is 15%-25% of the normal melting current, lasting for 30%-40% of the total feeding time. In the early feeding stage, the voltage decrease gradient is 1%-2% of the normal melting voltage. In the middle and later feeding stages, the voltage decrease gradient is 0.5%-1.5% of the normal melting voltage.

[0027] S6, Cooling;

[0028] After feeding is completed, the ingot is cooled in a copper crucible with the vacuum level controlled below 1 Pa for 3-8 hours.

[0029] The working principle of this invention is as follows: During the vacuum arc remelting process, the molten metal cools and solidifies sequentially from bottom to top. During solidification, volume shrinkage creates shrinkage cavities in the center. The unsolidified molten metal at the top flows into these cavities to fill and replenish the shrinkage. However, if the shrinkage cavities formed by the last solidified molten metal at the top are not effectively replenished by the liquid metal, they will form persistent shrinkage defects in the ingot, accompanied by internal defects such as porosity and segregation, which will adversely affect subsequent rolling processes. Therefore, the later-stage shrinkage replenishment in vacuum arc remelting is a crucial step. The replenishment current and voltage must be gradually reduced according to a certain gradient while maintaining a liquid state to ensure that the liquid metal can flow into the shrinkage cavities for replenishment.

[0030] The present invention will be further illustrated below through specific embodiments:

[0031] Example 1

[0032] This embodiment proposes a method for controlling shrinkage cavities in vacuum consumable ingots of titanium and titanium alloys. The specific implementation process for smelting titanium alloy TA18 is as follows:

[0033] S1. Raw material preparation

[0034] A vacuum arc furnace with a capacity of 150 kg was used for melting. The TA18 electrode to be melted was prepared, weighing 132 kg, and placed in a copper crucible with a diameter of 310 mm.

[0035] S2, Vacuuming

[0036] Start the mechanical pump, start the Roots pump when the vacuum reaches 700Pa, and start the booster pump when the vacuum reaches 5Pa.

[0037] S3, Smelting

[0038] When the vacuum level reaches below 0.1 Pa and the leakage rate reaches below 1 Pa / min, melting begins. After the arc ignition stage, the normal melting stage begins. The normal melting current is 7000 A and the voltage is 31 V.

[0039] S4. Determine the weight and time of the feeding electrode.

[0040] Based on the feeding requirements of titanium alloy, the weight of the feeding electrode was determined to be 25 kg, and the feeding time was determined to be 31 min.

[0041] S5, Ingot Feeding

[0042] After 60 minutes of melting, when the remaining electrode weight reaches 25 kg, feeding begins. In the early feeding stage, the current decreases at a gradient of 500 A with intervals of 1 min, for a total of 6 min. In the middle feeding stage, the current decreases at a gradient of 200-300 A with intervals of 1.5-2 min, for a total of 13 min. In the later feeding stage, the current decreases to 1700 A for 12 min. The feeding voltage decreases at a gradient of 0.5 V in the early stage and 0.25 V in the middle and later stages.

[0043] S6, Cooling

[0044] After the feeding is completed, stop melting, maintain the vacuum degree below 1 Pa, keep the outer wall of the crucible cooled by circulating water, and demold after cooling for 300 minutes.

[0045] Ten furnaces of TA18 titanium alloy ingots were smelted using the method of this invention, and no shrinkage defects were found in any of them after inspection.

[0046] Example 2

[0047] This embodiment proposes a method for controlling shrinkage defects in vacuum consumable ingots of titanium and titanium alloys. The specific implementation process for smelting titanium alloy TB5 is as follows:

[0048] S1. Raw material preparation

[0049] A vacuum arc furnace with a capacity of 150 kg was used for melting. The TB5 electrode to be melted was prepared, weighing 134 kg, and placed in a copper crucible with a diameter of 310 mm.

[0050] S2, Vacuuming

[0051] Start the mechanical pump, start the Roots pump when the vacuum reaches 700Pa, and start the booster pump when the vacuum reaches 5Pa.

[0052] S3, Smelting

[0053] When the vacuum level reaches below 0.1 Pa and the leakage rate reaches below 1 Pa / min, melting begins. After the arc ignition stage, the normal melting stage begins. The normal melting current is 7100 A and the voltage is 32 V.

[0054] S4. Determine the weight and time of the feeding electrode.

[0055] Based on the feeding requirements of titanium alloy, the weight of the feeding electrode was determined to be 26 kg, and the feeding time was determined to be 32 min.

[0056] S5, Ingot Feeding

[0057] After 64 minutes of melting, when the remaining electrode weight reached 26 kg, feeding began. In the early feeding stage, the current decrease gradient was 500 A at 1-minute intervals, for a total of 7 minutes. In the middle feeding stage, the current decrease gradient was 200-300 A at 1.5-2-minute intervals, for a total of 13 minutes. In the later feeding stage, the current decreased to 1600 A for 12 minutes. The feeding voltage decrease gradient was 0.5 V in the early stage and 0.25 V in the middle and later stages.

[0058] S6, Cooling

[0059] After the feeding is completed, stop melting, maintain the vacuum degree below 1 Pa, keep the outer wall of the crucible cooled by circulating water, and demold after cooling for 320 minutes.

[0060] Eleven furnaces of TB5 titanium alloy ingots were smelted using the method of this invention, and no shrinkage defects were found after inspection.

[0061] Example 3

[0062] This embodiment proposes a method for controlling shrinkage cavities in vacuum consumable ingots of titanium and titanium alloys. The specific implementation process for smelting Ti80 titanium alloy is as follows:

[0063] S1. Raw material preparation

[0064] A vacuum arc furnace with a capacity of 150 kg was used for melting. The Ti80 electrode to be melted was prepared, weighing 136 kg, and placed in a copper crucible with a diameter of 310 mm.

[0065] S2, Vacuuming

[0066] Start the mechanical pump, start the Roots pump when the vacuum reaches 700Pa, and start the booster pump when the vacuum reaches 5Pa.

[0067] S3, Smelting

[0068] When the vacuum level reaches below 0.1 Pa and the leakage rate reaches below 1 Pa / min, melting begins. After the arc ignition stage, the normal melting stage begins. The normal melting current is 7200 A and the voltage is 32 V.

[0069] S4 determines the weight and time of the feeding electrode.

[0070] Based on the feeding requirements of titanium alloy, the weight of the feeding electrode was determined to be 27 kg, and the feeding time was determined to be 34 min.

[0071] S5, Ingot Feeding

[0072] After 66 minutes of melting, when the remaining electrode weight reached 27 kg, feeding began. In the early feeding stage, the current decrease gradient was 500 A at 1-minute intervals, for a total of 7 minutes. In the middle feeding stage, the current decrease gradient was 200-400 A at 1.5-2-minute intervals, for a total of 14 minutes. In the later feeding stage, the current decreased to 1600 A for 13 minutes. The feeding voltage decrease gradient was 0.5 V in the early stage and 0.25 V in the middle and later stages.

[0073] S6, Cooling

[0074] After the feeding is completed, stop melting, maintain the vacuum degree below 1 Pa, keep the outer wall of the crucible cooled by circulating water, and demold after cooling for 360 minutes.

[0075] Ten furnaces of Ti80 titanium alloy ingots were smelted using the method of this invention, and no shrinkage defects were found in any of them after inspection.

[0076] All matters not covered in this invention are common knowledge.

[0077] 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 method for controlling shrinkage defects in vacuum consumable ingots of titanium and titanium alloys, characterized in that: Includes the following steps: S1. Raw material preparation; S2. Vacuuming; S3. Melting; S4. Determine the weight and time of the feeding electrode according to the feeding requirements of the titanium alloy; S5. Ingot feeding; S6. Cooling; In step S4, the weight of the feeding electrode is 10%-20% of the total weight of the melting electrode; the feeding time is 25%-35% of the total melting time. Step S5 specifically includes: after melting for 60-66 minutes, when the remaining electrode weight reaches a certain weight, the feeding process begins; in the early stage of feeding, the current decrease gradient is 5%-15% of the normal melting current, and the time is 15%-25% of the total feeding time; in the middle stage of feeding, the current decrease gradient is 2%-10% of the normal melting current, and the time is 35%-55% of the total feeding time; in the later stage of feeding, the current is 15%-25% of the normal melting current, and the time is 30%-40% of the total feeding time; in the early stage of feeding, the voltage decrease gradient is 1%-2% of the normal melting voltage; and in the middle and later stages of feeding, the voltage decrease gradient is 0.5%-1.5% of the normal melting voltage.

2. The method for controlling shrinkage defects in vacuum consumable ingots of titanium and titanium alloys according to claim 1, characterized in that, Step S1 specifically includes: using a vacuum arc furnace of corresponding capacity for melting, preparing the electrode to be melted, and loading it into a copper crucible.

3. The method for controlling shrinkage cavity defects in vacuum consumable ingots of titanium and titanium alloys according to claim 2, characterized in that, Step S2 specifically includes: starting the mechanical pump of the vacuum self-consuming furnace, starting the Roots pump when the vacuum degree reaches 700Pa, and starting the booster pump when the vacuum degree reaches 5Pa.

4. The method for controlling shrinkage defects in vacuum consumable ingots of titanium and titanium alloys according to claim 3, characterized in that, Step S3 specifically includes: when the vacuum degree reaches below 0.1 Pa and the leakage rate reaches below 1 Pa / min, the melting begins. After the arc ignition stage, the normal melting stage begins. The current in the normal melting stage is 7000-7200A and the voltage is 31-32V.

5. The method for controlling shrinkage cavity defects in vacuum consumable ingots of titanium and titanium alloys according to claim 1, characterized in that, Step S6 specifically includes: after the feeding is completed, the ingot is cooled in a copper crucible, and the vacuum degree is controlled below 1 Pa, and the cooling time is 3-8 hours.