Method for smelting nickel-based superalloys

Abstract

The present application relates to a kind of nickel-based superalloy smelting method, belong to metallurgical technical field.The mass percentage component of the nickel-based superalloy described in the application is as follows:C≤0.06%, Si≤0.50%, Mn≤0.50%, P≤0.015%, S≤0.015%, Ni=60~70%, Cr=20~23%, Mo=8~10%, Nb=3~4%, Fe≤5%, B≤0.005%, Co≤1.0%, Al≤0.40%, Ti≤0.40%, O≤0.01%, N≤0.02%.The method of the present application can make full use of electric arc furnace and refining furnace and other traditional equipment, improve the yield and large-scale of nickel-based superalloy.Solve the difficulty of impurity element and gas content control in the traditional production process of heavy machinery industry, which cannot be large-scale production in vacuum induction furnace of nickel-based superalloy.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for smelting nickel-based superalloy, belonging to the technical field of metallurgy. BACKGROUND

[0002] Nickel-based superalloy is a high-temperature alloy with nickel as the matrix, generally with a nickel content of more than 50%, and has high strength and good oxidation resistance and gas corrosion resistance in the range of 650-1000℃. In view of the demand of ultra-supercritical coal-fired power generation technology, developing a new type of nickel-based heat-resistant alloy for ultra-supercritical steam turbine cylinder is an alloy of interest to many metallurgical workers. High-temperature nickel-based alloy generally requires low C, Si and Mn content, generally ultra-low carbon C≤0.06%, Fe element is an impurity element, gas elements O and N≤100PPm, so the chemical composition control is very difficult. In order to obtain pure and extremely high molten steel, reduce the content of gas and residual harmful elements; at the same time, due to the existence of some alloying elements such as Al and Ti which are easy to oxidize, it is difficult to control the smelting in a non-vacuum way; in order to obtain better performance of nickel-based heat-resistant alloy, vacuum induction furnace is usually used for smelting, or even vacuum induction smelting plus vacuum consumable furnace or electroslag furnace remelting method is used for production below 10 tons, which has high production cost and cannot be produced in large scale. At present, the production is mostly below 10 tons. For example, CN 115125339 A discloses an ultra-high temperature nickel-based alloy and a preparation method thereof, and the smelting method comprises: sending nickel-chromium electric heating alloy powder to the air brick at the bottom of the vacuum induction smelting furnace through high pressure for smelting. Vacuum induction smelting is required.

[0003] At present, only the traditional heavy machinery industry of electric arc furnace, ladle furnace and the like cannot effectively control the impurity elements and gas content in the production of nickel-based superalloy, which limits the production of nickel-based superalloy in the heavy machinery industry, and it is difficult to produce high-temperature alloy with extremely high purity. SUMMARY

[0004] The purpose of the present application is to provide a new method for smelting nickel-based superalloy.

[0005] In order to achieve the purpose of the present application, the mass percentage composition of the nickel-based superalloy is:

[0006] C≤0.06%, Si≤0.50%, Mn≤0.50%, P≤0.015%, S≤0.015%, Ni=60-70%, Cr=20-23%, Mo=8-10%, Nb=3-4%, Fe≤5%, B≤0.005%, Co≤1.0%, Al≤0.40%, Ti≤0.40%, O≤0.01%, N≤0.02%;

[0007] The method for smelting the nickel-based superalloy comprises:

[0008] Electric arc furnace melting alloy roughening→ladle furnace slag refining→ladle furnace VOD refining→ladle furnace adjusting composition, temperature, final deoxidation→pouring;

[0009] The raw materials of Ni, Cr, Mo, Nb used in the electric arc furnace melting alloy roughening are metal grade alloys or nickel-based high-temperature alloy return materials with purity≥99%.

[0010] The ladle furnace slag refining includes: pouring the alloy melted in the electric arc furnace into the ladle furnace to re-create refining slag, diffusion deoxidation, and adjusting the alloy composition to mass percentage Cr=22-23%, Mo=8-10%, Ni=63-68%.

[0011] The ladle furnace VOD refining includes: pouring the molten steel after the ladle furnace slag refining into the VOD ladle for oxygen blowing decarburization operation to remove carbon and gas elements H, N in the steel, and then performing secondary carbon deoxidation operation and high vacuum operation to further remove oxygen and gas element content in the steel, so that C≤0.06% and N≤0.02%, if C>0.06% and / or N>0.02%, then repeat the ladle furnace VOD refining to make C≤0.06% and N≤0.02%.

[0012] The vacuum degree of the carbon deoxidation operation and the first high vacuum operation are both below 133 Pa.

[0013] The ladle furnace composition adjustment includes fine-tuning the composition to adjust the alloy composition to mass percentage Nb=3-4%.

[0014] The deoxidation material used in the final deoxidation is a material without carbon and silicon.

[0015] The pouring also takes anti-oxidation measures.

[0016] The pouring conditions can affect the oxygen content, and the casting pouring is carried out in an air environment, so secondary anti-oxidation measures need to be taken during pouring, such as pre-argon replacement of the cavity, ring argon and protective cover protection during pouring, and other conventional pouring anti-oxidation measures.

[0017] The raw materials of Ni, Cr, Mo, Nb used in the electric arc furnace melting alloy roughening are metal grade alloys with purity≥99%, such as electrolytic plate, metallic chromium, molybdenum strip, niobium strip, or smelted niobium.

[0018] The return material refers to the material block formed by pouring the excess molten steel after the ladle furnace refining, which fully meets the standard requirements, the residual steel in the steel pouring channel, and the riser material discarded after product cutting, etc.

[0019] The carbon deoxidation operation is VCD.

[0020] Generally, alloy steel only needs to undergo one VOD refining operation in a ladle furnace. If the C and N content of the alloy steel is too high, or due to improper operation, the C content of the alloy steel may still be >0.06% and the N content may still be >0.02% after one operation. In this case, repeat the VOD refining operation until C ≤0.06% and N ≤0.02%.

[0021] In one specific embodiment, when the raw material is a metallic alloy with a purity ≥99%, the method for rough refining the alloy using an electric arc furnace is a method of melting the alloy with minimal oxygen blowing in the electric furnace; when the raw material is a nickel-based high-temperature alloy return material, the method for rough refining the alloy using an electric arc furnace is a method of melting the return alloy material with minimal oxygen blowing in the electric furnace. There is no difference in operation between the "electric furnace with minimal oxygen blowing and alloy melting method" and the "electric furnace with minimal oxygen blowing and return alloy material melting method"; both aim to melt the alloy or return material with as little oxygen as possible to reduce burn-off.

[0022] In one specific embodiment, the refractory material used in the ladle furnace for slag refining in the electric arc furnace and ladle furnace is magnesia-carbon brick or magnesia brick.

[0023] In one specific embodiment, the furnace body of the electric arc furnace is a newly constructed furnace body. If the continuous production of this type of material or materials with similar composition can guarantee that the element content, especially the impurity elements, in the molten steel after ladle refining does not exceed the standard, then it is not necessary to use a newly constructed furnace body. However, if the electric arc furnace produces other materials or materials with significantly different compositions, and cannot guarantee that the element content, especially the impurity elements, in the molten steel after ladle refining exceeds the standard, then it is necessary to use a newly constructed furnace body.

[0024] In one specific embodiment, the electric arc furnace is further cleaned of residual steel and slag before use.

[0025] The residual steel slag is the residual steel slag after the previous furnace was used.

[0026] In one specific embodiment, the refractory material used in the ladle furnace VOD refining is carbon-free, corrosion-resistant, and high-temperature resistant.

[0027] In one specific embodiment, the refractory materials used in the ladle furnace VOD refining are magnesia-chrome bricks and magnesia-alumina spinel bricks.

[0028] In one specific embodiment, the diffusion deoxidizing material is at least one of carbon powder and aluminum granules, and the final deoxidizing material is at least one of aluminum wire, aluminum block, and sponge titanium; the preferred frequency of adding the diffusion deoxidizing material is 5-20 kg / time and 5-20 min / time.

[0029] In one specific embodiment, the H content in the composition of the nickel-based superalloy is ≤1ppm.

[0030] In one specific embodiment, the nickel-based superalloy has an O content of ≤0.002% and an N content of ≤0.004%.

[0031] Beneficial effects:

[0032] This invention allows for full utilization of traditional equipment such as electric arc furnaces and refining furnaces, increasing the yield and scale of nickel-based superalloy production. It solves the problems of the inability to scale up production in vacuum induction furnaces for nickel-based superalloys and the difficulties in controlling impurity elements and gas content in traditional heavy machinery production processes.

[0033] The method of this invention can produce high-purity nickel-based superalloys.

[0034] The raw materials of this invention can be recycled nickel-based high-temperature alloys whose alloy composition meets the requirements for residual elements, which can significantly reduce production costs.

[0035] The furnace gas content of the nickel-based high-temperature alloy smelted by this invention can reach: H≤1.0ppm, O≤20ppm, N≤40ppm. Attached Figure Description

[0036] Figure 1 The example illustrates the addition of a deoxidizer.

[0037] Figure 2 The slag in the example;

[0038] Figure 3 The pouring operation is shown in the example. Detailed Implementation

[0039] To achieve the objective of this invention, the nickel-based superalloy has the following mass percentage composition:

[0040] C≤0.06%, Si≤0.50%, Mn≤0.50%, P≤0.015%, S≤0.015%, Ni=60~70%, Cr=20~23%, Mo=8~ 10%, Nb=3~4%, Fe≤5%, B≤0.005%, Co≤1.0%, Al≤0.40%, Ti≤0.40%, O≤0.01%, N≤0.02%;

[0041] The method for smelting the nickel-based superalloy includes:

[0042] Electric arc furnace melting of alloy roughing → ladle furnace slag refining → ladle furnace VOD refining → ladle furnace adjustment of composition, temperature and final deoxidation → casting;

[0043] The raw materials used for alloy roughing in the electric arc furnace melting process are metal-grade alloys or nickel-based high-temperature alloy recycled materials with a purity of ≥99%.

[0044] The ladle furnace slag refining process includes: pouring the alloy melted in the electric arc furnace into the ladle furnace to re-form refining slag, performing diffusion deoxidation, and adjusting the alloy composition to a mass percentage of Cr=22-23%, Mo=8-10%, and Ni=63-68%.

[0045] The ladle furnace VOD refining process includes: pouring the molten steel refined by the ladle furnace slag into a VOD ladle for oxygen blowing and decarburization to remove carbon, gaseous elements H and N from the steel; then performing a carbon deoxidation operation and a high-vacuum operation to further remove oxygen and gaseous element content from the steel, so that C ≤ 0.06% and N ≤ 0.02%. If C > 0.06% and / or N > 0.02%, the ladle furnace VOD refining process is repeated until C ≤ 0.06% and N ≤ 0.02%.

[0046] The vacuum levels of both the carbon deoxidation operation and the first high vacuum were below 133 Pa.

[0047] The ladle furnace adjustment composition includes fine-tuning the composition, adjusting the alloy composition to a mass percentage Nb of 3-4%;

[0048] The deoxidizing material used for final deoxidation is a carbon-free and silicon-free material;

[0049] Anti-oxidation measures were also taken during the casting process.

[0050] Pouring conditions affect oxygen content. Since casting is done in an air environment, secondary anti-oxidation measures are required during pouring, such as argon replacement of the mold cavity in advance, and the use of ring argon and protective shields to protect the pouring flow, etc., which are conventional anti-oxidation measures for pouring.

[0051] The raw materials used in the electric arc furnace for alloy refining are metallic alloys with a purity of ≥99%, such as electrolytic plates, metallic chromium, molybdenum bars, niobium bars, or smelted niobium.

[0052] The returned material refers to recyclable waste materials such as lumps of excess molten steel formed after ladle furnace refining, which fully meet the standard requirements and are used for casting products, residual steel in the casting channel, and riser material discarded after product cutting.

[0053] Carbon deoxidation operation, i.e., VCD.

[0054] Generally, alloy steel only needs to undergo one VOD refining operation in a ladle furnace. If the C and N content of the alloy steel is too high, or due to improper operation, the C content of the alloy steel may still be >0.06% and the N content may still be >0.02% after one operation. In this case, repeat the VOD refining operation to make C ≤0.06% and N ≤0.02%.

[0055] In one specific embodiment, the method specifically includes: material preparation → electric furnace with reduced oxygen blowing and electric furnace alloy melting to smelt crude water → pouring into a magnesia-carbon ladle → LF (slag) → slag formation and power supply to raise the temperature → alloying to adjust the composition and temperature of Cr, Mo, Ni, etc. → ladle pouring → ladle furnace VOD refining (VOD + VCD + one-time high vacuum) → sampling → power supply to raise the temperature → fine-tuning the composition, adjusting the composition of Nb, Al, Ti, etc. → sampling → after the composition and temperature are qualified, tapping the steel → casting;

[0056] The ladle furnace VOD refining process is as follows: First, oxygen is blown to remove carbon content (VOD) from the molten steel; second, after the oxygen blowing is completed, the molten steel is in a peroxidized state, and carbon deoxidation is performed under vacuum conditions to reduce the oxygen content (VCD) of the molten steel; finally, after the vacuum is completed, the vacuum cover is opened to add slag, deoxidizer, alloys, etc. (this operation is slag making, deoxidation and composition adjustment), and then the vacuum cover is closed again to perform a high vacuum to remove the gas content in the molten steel (first high vacuum).

[0057] In one specific embodiment, the method specifically includes: material preparation → electric furnace with reduced oxygen blowing, electric furnace melting and return of alloy material to smelting crude water → pouring into a magnesia-carbon ladle → LF (slag) → slag formation, power supply and heating → alloying and adjustment of Cr, Mo, Ni and other components and temperature → ladle pouring, ladle furnace VOD refining (VOD + VCD + one-time high vacuum) → sampling → power supply and heating → fine-tuning of composition, adjusting Nb, Al, Ti and other components → sampling → after the composition and temperature are qualified, tapping the steel → casting.

[0058] In one specific embodiment, the method specifically includes: pouring the ladle, VOD refining in the ladle furnace (VOD+VCD+one high vacuum) → sampling. If C>0.06% and / or N>0.02% occurs during this process, the process of "VOD refining in the ladle furnace (VOD+VCD+one high vacuum) → sampling" can be repeated again.

[0059] The methods for adjusting the chemical composition, such as adjusting the alloy composition and adjusting the composition of the ladle furnace, as described in this invention can be conventional artificial methods, such as adding high-purity alloys such as aluminum blocks, metallic chromium, nickel plates, molybdenum bars, and niobium bars.

[0060] In one specific embodiment, the ladle furnace VOD refining includes: LF, VOD+VCD+one high vacuum.

[0061] In one specific embodiment, when the raw material is a metallic alloy with a purity ≥99%, the method for rough refining the alloy using an electric arc furnace is a method of melting the alloy with minimal oxygen blowing in the electric furnace; when the raw material is a nickel-based high-temperature alloy return material, the method for rough refining the alloy using an electric arc furnace is a method of melting the return alloy material with minimal oxygen blowing in the electric furnace. There is no difference in operation between the "electric furnace with minimal oxygen blowing and alloy melting method" and the "electric furnace with minimal oxygen blowing and return alloy material melting method"; both aim to melt the alloy or return material with as little oxygen as possible to reduce burn-off.

[0062] In one specific embodiment, the refractory material used in the ladle furnace for slag refining in the electric arc furnace and ladle furnace is magnesia-carbon brick or magnesia brick.

[0063] In one specific embodiment, the furnace body of the electric arc furnace is a newly constructed furnace body. If the continuous production of this type of material or materials with similar composition can guarantee that the element content, especially the impurity elements, in the molten steel after ladle refining does not exceed the standard, then it is not necessary to use a newly constructed furnace body. However, if the electric arc furnace produces other materials or materials with significantly different compositions, and cannot guarantee that the element content, especially the impurity elements, in the molten steel after ladle refining exceeds the standard, then it is necessary to use a newly constructed furnace body.

[0064] In one specific embodiment, the electric arc furnace is further cleaned of residual steel and slag before use.

[0065] The residual steel slag is the residual steel slag after the previous furnace was used.

[0066] In one specific embodiment, the refractory material used in the ladle furnace VOD refining is carbon-free, corrosion-resistant, and high-temperature resistant.

[0067] In one specific embodiment, the refractory materials used in the ladle furnace VOD refining are magnesia-chrome bricks and magnesia-alumina spinel bricks.

[0068] In one specific embodiment, the diffusion deoxidizing material is at least one of carbon powder and aluminum granules, and the final deoxidizing material is at least one of aluminum wire, aluminum block, and sponge titanium; the preferred frequency of adding the diffusion deoxidizing material is 5-20 kg / time and 5-20 min / time.

[0069] In one specific embodiment, the H content in the composition of the nickel-based superalloy is ≤1ppm.

[0070] In one specific embodiment, the nickel-based superalloy has an O content of ≤0.002% and an N content of ≤0.004%.

[0071] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0072] Example 1

[0073] Clean the residual steel and slag from the electric arc furnace thoroughly. When using high-purity alloys with the content listed in Table 1 as raw materials or when the raw materials are recycled nickel-based high-temperature alloys, the method for smelting the raw water in the electric arc furnace is to use a method of minimal oxygen blowing and melting alloy materials. After the raw water in the electric arc furnace is added to the magnesium-carbon ladle, it is directly hoisted to the LF station for slag formation and heating. Then, alloying is performed to adjust the composition of Cr, Mo, Ni, etc.: Cr=22-23%, Mo=8-10%, Ni=63-68%. The molten steel is then poured into the magnesium-chromium ladle and hoisted to the VOD station for vacuum oxygen blowing and decarburization to remove carbon, gaseous elements H, and N from the steel. The vacuum degree during the oxygen blowing process reaches a minimum of 23 Pa. Then, a carbon deoxidation operation and a high vacuum operation are performed to further remove oxygen and gaseous element content from the steel. The vacuum degree of the carbon deoxidation operation and the first high vacuum operation are both below 133 Pa, and C and N are blown to below C≤0.06% and N≤0.02%. After the VOD operation is completed (VOD operation includes VCD + one high vacuum), the ladle is hoisted back to the LF station for operation. The ladle furnace is then re-slag-forming, reduction, diffusion deoxidation to produce white slag, refined steel sampling, and then the composition is fine-tuned and other normal refining operations are performed. After fine-tuning, Nb=3~4%.

[0074] The specific process flow for the first furnace is as follows: material preparation → electric furnace with reduced oxygen blowing and alloy material melting to smelt crude water → pouring in magnesia-carbon bag → LF (slag) → slag formation and power supply for heating → alloying to adjust the composition and temperature of Cr, Mo, Ni, etc. → pouring in magnesia-chromium bag, LF (VOD + VCD + one-time high vacuum) → sampling → fine-tuning the composition, adjusting the composition of Nb, Al, Ti, etc. → sampling → after the composition and temperature are qualified → casting. In this example, the minimum vacuum level of the high vacuum reached 10 Pa. The diffusion deoxidation process involved adding carbon powder and / or aluminum granules in loose, small, and multiple batches, without detailed specifications for the amount and frequency of addition; sometimes it was added only after half an hour. Final deoxidation was carried out using aluminum blocks and sponge titanium.

[0075] The specific process flow for the second furnace is as follows: Material preparation → Electric furnace with reduced oxygen blowing, melting and returning to alloy material smelting of crude molten steel → Pouring into a magnesia-carbon ladle → LF (slag flux) → Slag formation, power supply and heating → Alloying to adjust Cr, Mo, Ni, and other compositions and temperature → Pouring into a magnesia-chromium ladle, LF (VOD + VCD + one high vacuum) → Sampling. When C > 0.06% and N > 0.02%, the process of "LF (VOD + VCD + one high vacuum) → sampling" is repeated. The diffusion deoxidation process uses carbon powder and / or aluminum granules added in loose form, added every 5-20 minutes, with each addition being 5-20 kg, depending on the steel deoxidation status. Final deoxidation is performed using aluminum blocks and sponge titanium.

[0076] Table 1 Specifications of Some Raw Material Alloys

[0077]

[0078] Two ultra-supercritical steam turbine high-temperature cylinders were produced using the above smelting method. The composition of the high-temperature alloy before the furnace is shown in Table 2.

[0079] Table 2. Main steel composition (%) at the actual furnace tapping site

[0080]

[0081] Table 2 shows that the high-temperature nickel-based alloy compositions of both the first and second heats meet the relevant standards. The oxygen content of the steel from the second heat is particularly low because the diffusion deoxidation process was enhanced in the second heat, with detailed specifications for the amount and frequency of deoxidizer use. A comparison of the gas contents of the two heats is shown in Table 3.

[0082] Table 3 Gas content (ppm)

[0083]

Claims

1. A method for smelting nickel-based superalloys, characterized in that, The mass percentage composition of the nickel-based superalloy is as follows: C≤0.06%, Si≤0.50%, Mn≤0.50%, P≤0.015%, S≤0.015%, Ni=60~70%, Cr=20~23%, Mo=8~10%, Nb=3~4%, Fe≤5%, B≤0.005%, Co≤1.0%, Al≤0.40%, Ti≤0.40%, O≤0.002%, N≤0.004%, H content≤1ppm; The method for smelting the nickel-based superalloy includes: Electric arc furnace melting of alloy roughing → ladle furnace slag refining → ladle furnace VOD refining → ladle furnace adjustment of composition, temperature and final deoxidation → casting; The raw materials used for alloy roughing in the electric arc furnace melting process are metal-grade alloys or nickel-based high-temperature alloy recycled materials with a purity of ≥99%. The ladle furnace slag refining process includes: pouring the alloy melted in the electric arc furnace into the ladle furnace to re-form refining slag, performing diffusion deoxidation, and adjusting the alloy composition to a mass percentage of Cr=22-23%, Mo=8-10%, and Ni=63-68%. The ladle furnace VOD refining process includes: pouring the molten steel refined by the ladle furnace slag into a VOD ladle for oxygen blowing and decarburization to remove carbon, gaseous elements H and N from the steel; then performing a carbon deoxidation operation and a high-vacuum operation to further remove oxygen and gaseous element content from the steel, so that C ≤ 0.06% and N ≤ 0.02%. If C > 0.06% or N > 0.02%, the ladle furnace VOD refining process is repeated until C ≤ 0.06% and N ≤ 0.004%. The vacuum levels of both the carbon deoxidation operation and the first high vacuum were below 133 Pa. The ladle furnace adjustment composition includes fine-tuning the composition, adjusting the alloy composition to a mass percentage Nb of 3-4%; The deoxidizing material used for final deoxidation is a carbon-free and silicon-free material; Anti-oxidation measures were also taken during the casting process; The diffusion deoxidizing material is at least one of carbon powder and aluminum granules, and the final deoxidizing material is at least one of aluminum wire, aluminum block, and sponge titanium; the frequency of adding the diffusion deoxidizing material is 5-20 kg / time and 5-20 min / time.

2. The method for smelting nickel-based superalloys according to claim 1, characterized in that, When the raw material is a metallic alloy with a purity of ≥99%, the method for rough refining the alloy by melting the alloy in an electric arc furnace is to use an electric furnace with less oxygen blowing and the alloy melting method; when the raw material is a nickel-based high-temperature alloy return material, the method for rough refining the alloy by melting the alloy in an electric arc furnace is to use an electric furnace with less oxygen blowing and the return alloy material melting method.

3. The method for smelting nickel-based superalloys according to claim 1 or 2, characterized in that, The refractory material used in the ladle furnace for slag refining in the electric arc furnace and ladle furnace is magnesia-carbon brick or magnesia brick.

4. The method for smelting nickel-based superalloys according to claim 1 or 2, characterized in that, The furnace body of the electric arc furnace is a newly constructed furnace body.

5. The method for smelting nickel-based superalloys according to claim 1 or 2, characterized in that, Before using the electric arc furnace, residual steel and slag must be thoroughly cleaned.

6. The method for smelting nickel-based superalloys according to claim 1 or 2, characterized in that, The refractory materials used in the VOD refining process of the ladle furnace are carbon-free, corrosion-resistant, and high-temperature resistant.

7. The method for smelting nickel-based superalloys according to claim 1 or 2, characterized in that, The refractory materials used in the VOD refining process of the ladle furnace are magnesia-chrome bricks and magnesia-alumina spinel bricks.

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