A method for preparing constantan alloy by vacuum melting

Abstract

The invention discloses a method for preparing a constantan alloy by vacuum melting, comprising the following steps: S1, weighing raw materials, S2, charging and preheating in a furnace, S3, vacuum melting, S4, casting, and S5, unmolding. The preparation method of the invention can effectively solve the problem of a large number of pores and defects in the ingot caused by the material being extremely easy to absorb air during the melting and casting process of the prior art, and can also effectively solve the processing defects existing in the ingot during subsequent processing. Impurity elements such as oxygen and sulfur can be reduced by a deoxidizer, thereby further improving the performance of the constantan alloy.

Description

Technical Field

[0001] The present invention relates to the technical field of nonferrous metal alloys, and in particular to a method for preparing a constantan alloy by vacuum melting. Background Art

[0002] Constantan is a resistance alloy primarily composed of copper and nickel (40% nickel and 1.5% manganese). It is suitable for manufacturing variable resistors and strain gauge resistors used in AC instruments. It features a low temperature coefficient of resistance, a wide operating temperature range (below 480°C), excellent machinability, corrosion resistance, and ease of brazing. It can be used to manufacture resistors and components for instrumentation, electronics, and industrial equipment. It is suitable for use in AC circuits as precision resistors, sliding resistors, and resistance strain gauges. It can also be used in thermocouples and thermocouple extension wire.

[0003] Currently, most Constantan alloys are smelted in non-vacuum conditions, and the resulting ingots often contain high levels of sulfide inclusions, which can affect the processing and application of the material. Furthermore, the ingots contain central shrinkage cavities and subcutaneous pores that are difficult to remove, resulting in a low material utilization rate.

[0004] Using a non-vacuum smelting method, electrolytic copper plates, nickel plates and electrolytic manganese are added to a medium-frequency furnace for smelting to remove impurities. However, the electrolytic manganese is burned too much during the smelting process. At the same time, the cast ingots have deep central shrinkage holes and more subcutaneous pores, resulting in low material utilization and excessive waste. At the same time, the constantan material is more sensitive to impurity elements, and the high sulfur content in the material will affect subsequent processing. Summary of the Invention

[0005] Therefore, the present invention provides a method for preparing a constantan alloy by vacuum melting, comprising the following steps:

[0006] S1. Raw material weighing:

[0007] In the form of nickel plate, electrolytic manganese and copper plate, 39.5-40.5% Ni, 1.8-2.2% Mn and the balance Cu are mixed as raw materials;

[0008] S2. Furnace preheating:

[0009] The raw materials of step S1 are loaded into a graphite crucible, and the graphite crucible is then placed in a vacuum melting furnace, the furnace cover is closed, and the vent valve is closed; the vacuum melting furnace is first evacuated to a pressure of less than or equal to -0.09 MPa, and then the temperature is increased at a power of 20 to 30 kW. When the temperature reaches 600°C, the temperature is kept preheated for 20 to 30 minutes;

[0010] S3. Vacuum melting:

[0011] Perform heating and smelting at 95-105kw. When the temperature reaches 1360℃, add 0.1% deoxidizer to the raw materials and smelt for 1 hour to clear the raw materials. Then gradually reduce the equipment power to 80kw, and then fill the furnace with argon. When the pressure in the furnace rises to -0.08Mpa, refining is carried out at constant pressure for 15-20 minutes.

[0012] The deoxidizer is a modified copper-magnesium alloy with a magnesium content of 15%, and the modified copper-magnesium alloy consists of 15% magnesium, 3-6% graphene powder, 1-3% calcium hexaboride powder, 0.1-0.2% rhenium, and the balance is copper.

[0013] S4. Casting:

[0014] At 1490-1510°C, casting is carried out using a steel mold with an insulated riser. At the same time, the equipment power is gradually reduced to 30 kW, and the casting time is 7-8 minutes. First, 70% of the mold body is cast in 2-3 minutes, and then feeding is performed 3-5 times in the remaining time until the steel mold is filled.

[0015] S5, released:

[0016] The ingot is then taken out of the furnace after cooling for 30 to 40 minutes.

[0017] Description: The above-mentioned smelting method can effectively solve the problem of a large number of pores and defects inside the ingot due to the material's easy absorption of air during the smelting and casting process. At the same time, it can effectively solve the processing defects of the ingot in the subsequent processing process, reduce impurity elements such as oxygen and sulfur, and further improve the performance of the constantan material. The above-mentioned problems can be better solved by setting the smelting and casting steps.

[0018] Furthermore, the speed of reducing the equipment power in steps S3 and S4 is 5 to 8 kw / min.

[0019] Note: By setting the above speed, the impact of reducing equipment power on the material can be reduced. At the same time, reducing equipment power during smelting can save equipment power consumption under constant temperature conditions. Reducing equipment power during casting can promote the realization of the casting process.

[0020] Note: By setting the composition of the modified copper-magnesium alloy, the refining effect can be enhanced, and impurity elements such as sulfur, carbon, and nitrogen can be removed while removing oxygen.

[0021] Furthermore, the preparation method of the modified copper-magnesium alloy is:

[0022] 1) Take 50% of the total amount of dried industrial pure magnesium and copper, add them into a vacuum non-consumable electrode arc melting furnace, heat and melt them, raise the temperature to 1110-1120℃, stir for 20 minutes, and melt for 0.5-1 hour;

[0023] 2) Grind the graphene powder, calcium hexaboride powder, rhenium and the remaining 50% of copper in a ball mill for 20 to 30 minutes; then add them to the furnace of step 1) for smelting, control the smelting temperature to 1240 to 1270° C., smelt for 1 to 2 hours, and then refine and cool to obtain a modified copper-magnesium alloy ingot.

[0024] Description: The modified copper-magnesium alloy obtained by the above method has a good impurity removal effect and is effective in the refining process of constantan alloy. By adding the copper-magnesium intermediate alloy and the other raw materials in steps, the utilization effect of graphene powder, calcium hexaboride powder and rhenium can be maximized, so that the obtained modified copper-magnesium alloy has a good impurity removal effect. The addition of the rare earth element rhenium can not only change the processability of the alloy, but also facilitate refining and degassing, and at the same time improve the tensile strength, hardness and other properties of the alloy.

[0025] Furthermore, the smelting step in step 1) is as follows: first, vacuum the furnace to a pressure of 5×10 -2 Pa, then fill with argon until the pressure in the furnace is 0.05MPa, and then melt.

[0026] Note: The above parameter settings are the most commonly used and optimal parameters for copper-magnesium master alloys.

[0027] Furthermore, the refining and cooling method in step 2) is to reduce the temperature to 1110-1120°C after smelting, refine under a nitrogen atmosphere for 15-20 minutes; then cool to 990-1000°C for slag removal, casting, and then cool at a rate of 15°C / min to obtain a modified copper-magnesium alloy ingot.

[0028] Description: The modified copper-magnesium alloy ingot obtained by the above refining and cooling method has high purity and good properties such as strength and pressure resistance.

[0029] Furthermore, the refining step in step S3 is:

[0030] S3-1. Take three-quarters of the total amount of the modified copper-magnesium alloy ingot, crush it, grind it into 1-3 mm modified copper-magnesium alloy powder, and set aside;

[0031] S3-2, taking one-quarter of the total amount of the modified copper-magnesium alloy ingot, and melting it into a molten state to obtain a liquid modified copper-magnesium alloy for later use;

[0032] S3-3. Add the modified copper-magnesium alloy powder obtained in step S3-1 at 1360°C, stir, and remove the surface slag; then blow argon mixed with the liquid modified copper-magnesium alloy obtained in step S3-2 into the smelted raw materials in a graphite crucible for 7 to 10 minutes; then let it stand for 5 minutes, remove the slag, and then cast.

[0033] Note: The above refining method can achieve the best refining effect. By adding the modified copper-magnesium alloy powder and the liquid alloy in different forms and conditions, the impurity removal performance of the modified copper-magnesium alloy can be more fully utilized. The addition of powder can increase the contact area. By adding it by blowing, the impurity elements in the molten constantan can be further combined with the liquid alloy, thereby enhancing the refining effect.

[0034] Furthermore, the stirring parameters are: stirring at 1500 r / min for 8 to 10 minutes.

[0035] Note: By setting the stirring parameters, the stirring and refining effects can be optimized.

[0036] Furthermore, in step S4, after the casting is started, ultrasound is applied to the upper part of the liquid surface at an ultrasonic frequency of 34 to 42 kHz for 2 to 3 minutes. At the same time, the power of the equipment is reduced from 80 kW at a rate of 5 to 8 kW / min. After it is reduced to 50 kW, the ultrasonic frequency is decreased at 10 kHz / min until it reaches zero.

[0037] Description: Through the setting of the above-mentioned casting method, the ingot produced by casting will not have the problem of uneven solidification. By carrying out the casting speed and ultrasonic treatment at the same time, the problem of central shrinkage cavity and subcutaneous pores in the ingot being difficult to remove can be solved. By introducing ultrasonic waves into the metal melt during casting, the problem of low utilization efficiency caused by the reflection of ultrasonic waves at the interface between air and metal can be solved. Applying ultrasonic waves to metal in liquid or solidification process can achieve the effects of degassing the metal liquid, removing inclusions, increasing the reaction speed, and promoting the refinement of solidification structure.

[0038] Furthermore, the cooling step in step S5 is as follows: after reducing the power of the equipment from 30 kW to 15 kW at a reduction rate of 8 kW / min, maintaining it for 10 to 20 minutes, then shutting down the equipment, cooling it for 20 minutes and then taking it out of the furnace.

[0039] Note: By setting the above cooling parameters, the occurrence of central shrinkage cavities during the cooling process can be avoided, so that the obtained Constantan alloy ingot has better properties.

[0040] The beneficial effects of the present invention are:

[0041] (1) The present invention, through the setting of the constantan alloy preparation method, can effectively solve the problem of a large number of pores and defects in the ingot due to the material's easy absorption of air during the smelting and casting process. At the same time, it can effectively solve the processing defects of the ingot in the subsequent processing process, reduce impurity elements such as oxygen and sulfur, and further improve the performance of the constantan material. By setting the smelting and casting steps, the above problems can be better solved.

[0042] (2) The modified copper-magnesium alloy obtained by the above method has a good impurity removal effect and is used in the refining process of constantan alloy. By adding the copper-magnesium intermediate alloy and the other raw materials in steps, the utilization effect of graphene powder, calcium hexaboride powder and rhenium can be maximized, so that the obtained modified copper-magnesium alloy has a good impurity removal effect. The addition of the rare earth element rhenium can not only change the processability of the alloy, but also facilitate refining and degassing, and at the same time improve the tensile strength, hardness and other properties of the alloy. By setting the above speed, the reduction of equipment power can have less impact on the material. At the same time, by reducing the equipment power during smelting, the power consumption of the equipment can be saved under a constant temperature state. The equipment power can be reduced during the casting process, which promotes the realization of the casting process.

[0043] (3) The present invention performs refining by the above method, which can achieve the best refining effect. By adding the modified copper-magnesium alloy powder and the liquid alloy in different forms and conditions, the impurity removal performance of the modified copper-magnesium alloy can be more fully utilized. The contact area can be increased by adding the powder. By adding it by blowing, the impurity elements in the molten constantan can be further combined with the liquid alloy, thereby enhancing the refining effect.

[0044] (4) The present invention can prevent the ingot produced by casting from having uneven solidification problems by setting the above-mentioned casting method. By carrying out the casting speed and ultrasonic treatment at the same time, the problem of central shrinkage holes and subcutaneous pores in the ingot being difficult to remove can be solved. By introducing ultrasonic waves into the metal melt during casting, the problem of low utilization efficiency caused by the reflection of ultrasonic waves at the interface between air and metal can be solved. Applying ultrasonic waves to metal in liquid or solidifying process can achieve the effects of degassing the metal liquid, removing inclusions, increasing the reaction speed, and promoting the refinement of solidification structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is the cast metallographic structure diagram of CuNi40 100X of the present invention;

[0046] Figure 2 This is the as-cast metallographic structure of CuNi40 200X of the present invention; DETAILED DESCRIPTION

[0047] The present invention will be further described in detail below in conjunction with specific implementation methods to better demonstrate the advantages of the present invention.

[0048] Example 1:

[0049] A method for preparing a constantan alloy by vacuum melting comprises the following steps:

[0050] S1. Raw material weighing:

[0051] Nickel plates, electrolytic manganese plates, and copper plates are prepared with a weight percentage of 39.6% Ni, 2.0% Mn, and the balance Cu as raw materials;

[0052] S2. Furnace preheating:

[0053] The raw materials of step S1 were loaded into a graphite crucible, and the graphite crucible was then placed in a vacuum melting furnace, the furnace cover was closed, and the vent valve was closed; the vacuum melting furnace was first evacuated to a pressure of -0.1 MPa, and then the temperature was increased at a power of 25 kW. When the temperature reached 600°C, the temperature was kept and preheated for 25 minutes;

[0054] S3. Vacuum melting:

[0055] The furnace is heated at 100 kW and heated to 1360°C. A deoxidizer accounting for 0.1% of the raw material is added, and the furnace is smelted for 1 hour to clear the raw material. The power of the equipment is then gradually reduced to 80 kW. Argon is then introduced into the furnace. When the pressure in the furnace rises to -0.08 MPa, refining is performed at a constant pressure for 18 minutes. The deoxidizer is a copper-magnesium alloy with a magnesium content of 15%.

[0056] S4. Casting:

[0057] At 1500°C, casting was performed using a steel mold with an insulated riser. At the same time, the equipment power was gradually reduced to 30 kW, and the casting time was 7 minutes. First, 70% of the mold body was cast within 2 minutes, and then feeding was performed 4 times in the remaining time until the steel mold was filled. The equipment power was reduced at a rate of 7 kW / min in both steps S3 and S4.

[0058] S5, released:

[0059] The temperature is then lowered and cooled, and after cooling in the furnace for 35 minutes, the Constantan alloy ingot is taken out of the furnace.

[0060] Example 2

[0061] The difference between this embodiment and embodiment 1 is that the raw material components in step S1 are different, and 40.5% by weight of Ni, 2.2% by weight of Mn, and the balance of Cu are used as the raw materials.

[0062] Example 3

[0063] The difference between this embodiment and embodiment 1 is that the condition parameters of step S2 and step S3 are different. In step S2, preheating is performed at 30 kW for 20 minutes; in step S3, heating is performed at 105 kW and refining is performed for 20 minutes.

[0064] Example 4

[0065] The difference between this embodiment and embodiment 1 is that the condition parameters of step S2 and step S3 are different. In step S2, preheating is performed at 20 kW for 30 minutes; in step S3, heating is performed at 95 kW and refining is performed for 15 minutes.

[0066] Example 5

[0067] The difference between this embodiment and embodiment 1 is that the condition parameters in step S4 are different. The casting is performed at 1490°C and the casting time is 8 minutes. Among them, 70% of the casting of the mold body is completed within 3 minutes, and then the shrinkage is performed 3 times in the remaining time until the steel mold is filled. The speed of reducing the equipment power in steps S3 and S4 is both 8kw / min.

[0068] Example 6

[0069] The difference between this embodiment and embodiment 1 is that the condition parameters in step S4 are different. The casting is performed at 1510°C and the casting time is 8 minutes. Among them, 70% of the casting of the mold body is completed within 3 minutes, and then the shrinkage is performed 5 times in the remaining time until the steel mold is filled. The speed of reducing the equipment power in steps S3 and S4 is 5kw / min.

[0070] Example 7

[0071] The difference between this embodiment and embodiment 1 is that in step S5, the product is cooled in the furnace for 40 minutes before being taken out of the furnace.

[0072] Example 8

[0073] The difference between this embodiment and embodiment 1 is that in step S5, the product is cooled in the furnace for 30 minutes before being taken out of the furnace.

[0074] Example 9

[0075] The modified copper-magnesium alloy is composed of 15% magnesium, 5% graphene powder, 2% calcium hexaboride powder, 0.15% rhenium, and the balance copper;

[0076] The preparation method of the modified copper-magnesium alloy is:

[0077] 1) Take 50% of the total amount of dried industrial pure magnesium and copper and add them into a vacuum non-consumable electrode arc melting furnace. First, evacuate the furnace to a pressure of 5×10-2 Pa, then fill with argon until the pressure in the furnace is 0.05MPa, then melt at 1115℃ for 0.8h, stir for 20min, and melt for 0.5~1h;

[0078] 2) Put the graphene powder, calcium hexaboride powder, rhenium and the remaining 50% of copper into a ball mill and grind them at a speed of 600 r / min for 30 min; then add them to the furnace of step 1) for smelting, control the smelting temperature to 1260°C, and then refine and cool. The refining and cooling method is as follows: after smelting, reduce the temperature to 1115°C, refine under a nitrogen atmosphere for 18 min; then cool to 995°C for slagging, cast, and then cool at a rate of 15°C / min to obtain a modified copper-magnesium alloy ingot.

[0079] Example 10

[0080] The difference between this embodiment and embodiment 9 is that the modified copper-magnesium alloy has different components, consisting of 15% magnesium, 6% graphene powder, 1% calcium hexaboride powder, 0.1% rhenium, and the balance is copper.

[0081] Example 11

[0082] The difference between this embodiment and embodiment 9 is that the modified copper-magnesium alloy has different components, consisting of 15% magnesium, 3% graphene powder, 3% calcium hexaboride powder, 0.2% rhenium, and the balance copper.

[0083] Example 12

[0084] The difference between this embodiment and embodiment 9 is that the field parameters in the preparation of the modified copper-magnesium alloy are different. In step 1), the alloy is smelted at 1110°C for 1 hour, and in step 2), the smelting temperature is 1240°C. After smelting, the temperature is lowered to 1120°C and refined under a nitrogen atmosphere for 15 minutes. The alloy is then cooled to 1000°C for slagging.

[0085] Example 13

[0086] The difference between this embodiment and Example 9 is that the field parameters in the preparation of the modified copper-magnesium alloy are different. In step 1), the alloy is smelted at 1120°C for 0.5h, and in step 2), the smelting temperature is 1270°C; after smelting, the temperature is lowered to 1110°C and refined under a nitrogen atmosphere for 20min; and then the temperature is lowered to 990°C for slagging.

[0087] Example 14

[0088] This embodiment differs from embodiment 1 in that the refining steps are different:

[0089] S3-1. Take three-quarters of the total amount of the modified copper-magnesium alloy ingot, crush it, grind it into 1-3 mm modified copper-magnesium alloy powder, and set aside;

[0090] S3-2, taking one-quarter of the total amount of the modified copper-magnesium alloy ingot, and melting it into a molten state to obtain a liquid modified copper-magnesium alloy for later use;

[0091] S3-3. Add the modified copper-magnesium alloy powder obtained in step S3-1 at 1360°C, stir for 9 minutes, and then remove the surface slag; then blow argon mixed with the liquid modified copper-magnesium alloy obtained in step S3-2 into the smelted raw materials in the graphite crucible for 8 minutes; then let it stand for 5 minutes, remove the slag, and then cast.

[0092] Example 15

[0093] The difference between this embodiment and embodiment 14 is that the time parameters in step S3-3 are different. After stirring at 1500 r / min for 8 minutes, the surface slag is removed; the blowing is continued for 7 minutes and then the mixture is allowed to stand.

[0094] Example 16

[0095] The difference between this embodiment and embodiment 14 is that the time parameters in step S3-3 are different. After stirring at 1500 r / min for 10 minutes, the surface slag is removed; the blowing is continued for 10 minutes and then the mixture is allowed to stand.

[0096] Example 17

[0097] The difference between this embodiment and embodiment 14 is that in step S4, after the casting is started, ultrasound is applied to the upper part of the liquid surface at an ultrasonic frequency of 38 kHz for 2.5 minutes. At the same time, the power of the equipment is reduced from 80 kW at a rate of 7 kW / min. After it is reduced to 50 kW, the ultrasonic frequency is reduced at a rate of 10 kHz / min until it reaches zero.

[0098] Example 18

[0099] The difference between this embodiment and embodiment 17 is that the sound wave frequency is 34 kHz, the treatment is 3 minutes, and the equipment power is reduced from 80 kW to 8 kW / min.

[0100] Example 19

[0101] The difference between this embodiment and embodiment 17 is that the sonic wave frequency is 42 kHz, the treatment is performed for 2 minutes, and the equipment power is reduced from 80 kW to 5 kW / min.

[0102] Example 20

[0103] The difference between this embodiment and embodiment 17 is that in step S5, the reduction speed is maintained at 8 kW / min for 15 minutes, and then the equipment is turned off and the product is taken out of the furnace after cooling for 20 minutes.

[0104] Example 21

[0105] The difference between this embodiment and embodiment 17 is that in step S5, the reduction speed is maintained at 8 kW / min for 20 minutes, then the equipment is turned off, and the product is taken out of the furnace after cooling for 20 minutes.

[0106] Example 22

[0107] The difference between this embodiment and embodiment 17 is that in step S5, the reduction speed is maintained at 8 kW / min for 10 minutes, then the equipment is turned off, and the product is taken out of the furnace after cooling for 20 minutes.

[0108] Experimental example

[0109] 1. Composition tests were performed on the Constantan alloy ingots obtained in Examples 1 to 2, Example 9, Example 14, Example 17, and Example 20, and the test results are as follows:

[0110] 1. Explore the effects of different treatment methods on the composition and impurities of Constantan alloy ingots;

[0111] Comparative Example 1: The same raw material components as in Example 1 were taken and smelted using conventional non-vacuum smelting, which is Comparative Example 1;

[0112] Examples 1 to 2, Example 9, Example 14, Example 17, Example 20 and Comparative Example 1 were compared, as shown in Table 1;

[0113] Table 1 Effects of different treatment methods on the composition and impurity composition of Constantan alloy ingots

[0114]

[0115]

[0116] As can be seen from Table 1, the constantan alloy ingots obtained in Example 17 and Example 20 have the least impurity components and are more preferred. Comparing Example 1 with Comparative Example 1, it can be seen that the impurity components in Comparative Example 1 are relatively large, and the loss of manganese and nickel is relatively high. Therefore, the vacuum melting method in Example 1 is more preferred; comparing Example 1 with Example 2, it can be seen that slight changes in composition have little effect on the impurity components; comparing Example 1 with Example 9, it can be seen that the modified magnesium-copper alloy using Example 9 has a good impurity removal effect; comparing Example 9 with Example 14, it can be concluded that the refining effect of the method using Example 14 is better, and the impurities are further reduced; comparing Example 14 with Example 17, it can be seen that the ultrasonic treatment in Example 17 can further reduce impurities. Comparing Example 17 with Example 20, it can be found that the change in cooling method has little effect on the various components.

[0117] 2. The metal hardness test was performed on the Constantan alloy ingots obtained in Examples 1 to 22, and the bulk density test was performed on Example 1 and Comparative Example 1. The test results are as follows:

[0118] The bulk density of Example 1 is 9.0 g / cm 3 The bulk density of Comparative Example 1 is 8.6 g / cm 3 ; It can be seen that the porosity can be reduced by adopting the method of Example 1;

[0119] The metal hardness of Examples 1 to 8 and Comparative Example 1 was compared, as shown in Table 2.

[0120] Table 2 Influence of Constantan alloy ingot properties under different conditions and parameters

[0121]

[0122]

[0123] As can be seen from Table 2, by comparing Example 1 with Examples 2 to 8, it can be found that there is little difference between Example 2 and Example 1, and the performance of the Constantan alloy ingots obtained by the condition parameters of Examples 3 to 8 is not as good as that of Example 1.

[0124] 3. Explore the effects of different deoxidizers on the properties of Constantan alloy ingots;

[0125] Examples 9 to 13 were compared, as shown in Table 3.

[0126] Table 3 Effect of different deoxidizers on the properties of Constantan alloy ingots

[0127] parameter Vickers hardness / Hv Example 9 128 Example 10 127 Example 11 126 Example 12 127 Example 13 128

[0128] As can be seen from Table 3, by comparing Example 9, Example 10 and Example 11, it can be found that the deoxidizer component of Example 9 is more preferred, and by comparing Example 9, Example 12 and Example 13, it can be found that the parameters of Example 9 are more preferred.

[0129] 4. Explore the effects of different refining treatments on the properties of Constantan alloy ingots;

[0130] Examples 14 to 16 were compared, as shown in Table 4.

[0131] Table 4 Effects of different refining treatments on the properties of Constantan alloy ingots

[0132] parameter Vickers hardness / Hv Example 14 129 Example 15 128 Example 16 128

[0133] It can be seen from Table 4 that different refining treatment parameters have little effect on the properties of Constantan alloy ingots, and the Constantan alloy ingot obtained by using the parameters of Example 14 is more preferred.

[0134] 5. Explore the effects of different casting treatments on the properties of Constantan alloy ingots;

[0135] Examples 17 to 19 were compared, as shown in Table 5.

[0136] Table 5 Effects of different casting treatments on the properties of Constantan alloy ingots

[0137] parameter Vickers hardness / Hv Example 17 130 Example 18 129 Example 19 128

[0138] It can be seen from Table 5 that different casting processing parameters have little effect on the properties of the Constantan alloy ingot, and the Constantan alloy ingot obtained by using the parameters of Example 17 is more preferred.

[0139] 6. Explore the effects of different cooling treatments on the properties of Constantan alloy ingots;

[0140] Examples 20 to 22 were compared, as shown in Table 6.

[0141] Table 6 Effects of different cooling treatments on the properties of Constantan alloy ingots

[0142] parameter Vickers hardness / Hv Example 20 131 Example 21 129 Example 22 130

[0143] It can be seen from Table 6 that different cooling treatment parameters have little effect on the properties of the Constantan alloy ingot, and the Constantan alloy ingot obtained by using the parameters of Example 20 is more preferred.

Claims

1. A method for preparing constantan alloy by vacuum melting, characterized in that: The following steps are involved: S1. Raw material weighing: In the form of nickel plate, electrolytic manganese and copper plate, 39.6-40.5% Ni, 2.0-2.2% Mn and the balance Cu are mixed as raw materials; S2. Furnace preheating: The raw materials of step S1 are loaded into a graphite crucible, and the graphite crucible is then placed in a vacuum melting furnace, the furnace cover is closed, and the vent valve is closed; the vacuum melting furnace is first evacuated to a pressure of less than or equal to -0.09 MPa, and then the temperature is increased at a power of 20 to 30 kW. When the temperature reaches 600°C, the temperature is kept preheated for 20 to 30 minutes; S3. Vacuum melting: Perform heating and smelting at 95-105kW. When the temperature reaches 1360℃, add 0.1% deoxidizer to the raw materials and smelt for 1 hour to clear the raw materials. Then gradually reduce the equipment power to 80kW, and then fill the furnace with argon. When the pressure in the furnace rises to -0.08MPa, refining is carried out at constant pressure for 15-20 minutes. The deoxidizer is a modified copper-magnesium alloy with a magnesium content of 15%, and the modified copper-magnesium alloy is composed of 15% magnesium, 3-6% graphene powder, 1-3% calcium hexaboride powder, 0.1-0.2% rhenium, and the balance is copper. The preparation method of the modified copper-magnesium alloy is as follows: 1) Take 50% of the total amount of dried industrial pure magnesium and copper, add them into a vacuum non-consumable electrode arc melting furnace, heat and melt them, raise the temperature to 1110-1120°C, stir for 20 minutes, and melt for 0.5-1 hour; 2) placing graphene powder, calcium hexaboride powder, rhenium and the remaining 50% of copper into a ball mill and grinding them at a speed of 600 r / min for 30 minutes; then adding them into the furnace of step 1) for smelting, controlling the smelting temperature to 1240-1270° C., smelting for 1-2 hours, and then refining and cooling to obtain a modified copper-magnesium alloy ingot; S4. Casting: Casting is performed at 1490-1510°C using a steel mold with an insulated riser. At the same time, the equipment power is gradually reduced to 30kW, and the casting time is 7-8 minutes. First, 70% of the mold body is cast in 2-3 minutes, and then feeding is performed 3-5 times in the remaining time until the steel mold is filled. S5, released: The temperature is then lowered and cooled, and after cooling in the furnace for 30 to 40 minutes, the Constantan alloy ingot is taken out of the furnace to obtain.

2. The method for preparing constantan alloy by vacuum melting according to claim 1, characterized in that: The speed of reducing the equipment power in steps S3 and S4 is 5 to 8 kW / min.

3. The method for preparing constantan alloy by vacuum melting according to claim 1, characterized in that: The smelting step in step 1) is as follows: first, vacuum the furnace to a pressure of 5×10 -2 Pa, and then fill with argon until the pressure in the furnace is 0.05MPa, and then carry out smelting.

4. The method for preparing constantan alloy by vacuum melting according to claim 1, characterized in that: The refining and cooling method in step 2) is as follows: after smelting, the temperature is lowered to 1110-1120°C, and refined under a nitrogen atmosphere for 15-20 minutes; then the temperature is lowered to 990-1000°C for slagging, casting, and then cooling at a rate of 15°C / min to obtain a modified copper-magnesium alloy ingot.

5. The method for preparing constantan alloy by vacuum melting according to claim 1, characterized in that: In step S4, after the casting is started, ultrasound is applied to the upper part of the liquid surface at a frequency of 34 to 42 kHz for 2 to 3 minutes. At the same time, the power of the equipment is reduced from 80 kW at a rate of 5 to 8 kW / min. After it is reduced to 50 kW, the ultrasound frequency is decreased at a rate of 10 kHz / min until it reaches zero.

6. The method for preparing constantan alloy by vacuum melting according to claim 1, characterized in that: The cooling step in step S5 is as follows: reduce the power of the equipment from 30 kW to 15 kW at a reduction rate of 8 kW / min, maintain the power for 10 to 20 minutes, then turn off the equipment, cool for 20 minutes and then take out of the furnace.

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