1. A preparation method of an ultra-low sulfur high-temperature alloy is characterized in that a VIM-ESR-VIM-VAR quadruple process is adopted in the preparation process, and specifically comprises the following steps:

the method comprises the following steps: a first vacuum induction VIM process, preparing metal raw materials according to requirements, selecting the metal raw materials with the sulfur content of more than 25ppm, putting the raw materials except aluminum and titanium into a vacuum induction furnace, adding CaO with the weight of 0.5-1% of the raw materials at the upper part of the raw materials, filling argon to be not less than 25000Pa after refining is finished, and adding Ni-Ca with the weight of 2-4% of the raw materials; after refining is finished for 30 minutes, optionally adding aluminum and titanium, and preserving heat for 1-2 hours at 1300-; after sampling, argon is filled again to be not less than 25000Pa, Ni-Mg with the weight being 2-4% of the weight of the materials in the vacuum induction furnace is added, and the materials are fully stirred and poured to obtain an electrode E1;

step two: ESR (electroslag remelting) process, wherein an electrode E1 is subjected to electroslag remelting after shot blasting and rust removal, and in the ESR process: the adopted slag system comprises CaF as the component and the weight ratio thereof₂：Al₂O₃: CaO = 20: 40: 40; controlling the electrode insertion depth to be less than 3mm by setting the slew value to 0.55-0.6 milliohms; setting a melting speed V (kg/min) = 2-4 times of the diameter (dm) of the crystallizer to obtain an electrode E2;

step three: performing a second vacuum induction melting VIM process, namely performing shot blasting on an electrode E2 to remove surface oxide skin, taking the electrode E2 as a raw material of the second vacuum induction melting VIM process, filling argon to a pressure not less than 25000Pa before casting, adding Ni-Mg accounting for 0.1-0.2% of the weight of the electrode E2, fully stirring, and then casting to obtain an electrode E3;

step four: and a vacuum arc remelting VAR process, wherein the electrode E3 is subjected to vacuum arc remelting VAR process after shot blasting or grinding by a grinding wheel, and a final target product is obtained.

2. The method for preparing an ultra-low sulfur superalloy according to claim 1, wherein Ni-Ca and Ni-Mg are stored in a Ni box and inserted into the molten pool through the CaO layer using a sampling rod, and stirred at 50-60Hz after being inserted into the molten pool.

3. The method according to claim 1, wherein the CaO is roasted at 850 ℃ or higher for 6 hours or more before being charged into the furnace, and the CaO is removed from the furnace before charging.

4. The method for preparing an ultra-low sulfur superalloy as in claim 1, wherein a diameter of a runner bottom nozzle selected in a VIM process is not less than 40 mm.

Background

S is an impurity element in high-performance metal, can form a eutectic substance with low melting point, and easily forms a liquid film in the crystallization process, thereby reducing the plasticity of the material. Sulfur also belongs to easily segregated elements, the range of the brittleness temperature range of the alloy is enlarged, and the crack sensitivity is increased. As a high-temperature alloy material used in the key fields of aerospace, nuclear power and the like, the requirement on the S content is continuously increased, the S content is even required to be not more than 2ppm in a part of advanced rotary parts for aero-engines and key nuclear power parts, in order to realize good purity and solidification quality of the material, the manufacturing process of the advanced high-temperature alloy material usually requires VIM-VAR (commonly called double vacuum process) or VIM-ESR-VAR (commonly called triple process), and the process can hardly realize the control of the ultralow S content on the premise of ensuring the solidification quality (without metallurgical defects).

The current literature and patent technologies mainly focus on the development and application of single-process desulfurization technologies. For example, the raw material part, taking GH4169 with the largest dosage as an example, involves selecting nearly ten alloy elements such as selected pure nickel, pure Cr, pure iron, pure Nb and the like with ultra-low S content, and the optimization can cause the raw material cost to increase by multiple and is extremely unfavorable for the economic benefit of enterprises.

There are also a number of desulfurization techniques and methods in vacuum induction melting. At present, in the industrial production practice, several hundred Pa of argon is filled before casting, and then a premelted NiMg or NiCa alloy block is added for desulfurization, because the adverse effect of the subsequent VAR process on the arc stability is feared, the adding amount of the NiMg or NiCa alloy is generally strictly limited, so that the S content is difficult to be reduced to below 8 ppm. CN1137275C mentions that CaO is used as a crucible material and can be effectively desulfurized, but the CaO material has insufficient strength and is easily corroded, and is difficult to be applied industrially. CN103276231B, CN102776378B, CN102199683B, CN106544532A and the like all mention methods of adding a desulfurizing agent to desulfurize, and the methods comprise CaO, metal Ca, Mg, a rare earth element Y and the like. Because slagging-off is inconvenient in a vacuum environment, CaO serving as slag must be strictly limited in use in vacuum induction melting, and the related invention does not mention how to control CaO slag, therefore, under the current process flow and technical conditions, the difficulty in really adding CaO for desulfurization in the production of the high-temperature alloy needs to be overcome.

In the electroslag remelting (ESR) process, a high-alkalinity slag system containing higher CaO components is generally adopted for desulfurization, but the use of the high-alkalinity slag system is also limited in the current high-temperature alloy production process in consideration of the quality requirement of the electrode surface and the risks of the CaO components on aspects of hydrogen increment, brittle inclusions and the like, and the CaO content in the slag system for producing high-grade high-temperature alloy at present is usually not more than 25 wt%.

From the foregoing analysis, it can be seen that, in the dual vacuum (VIM-VAR) and triple vacuum (VIM-ESR-VAR) processes corresponding to the development and production of high-quality high-temperature alloys, it is difficult for the current technology to stably achieve an ultra-low sulfur content level with an S content of less than 2ppm at a controllable cost while ensuring solidification quality.

Disclosure of Invention

The invention aims to solve the technical problems that the desulfurization cost is high, the purity and the solidification quality cannot be considered simultaneously, and the control of ultralow S content is stably realized through the innovation of a process flow in the prior art. The invention aims at a high-quality high-temperature alloy manufacturing technology which is used for key components in the fields of advanced aerospace, nuclear power and the like and has ultralow S content and no solidification related metallurgical defects.

The invention adopts the following technical scheme: a preparation method of an ultra-low sulfur high-temperature alloy adopts a VIM-ESR-VIM-VAR four-in-one process, and specifically comprises the following steps:

the method comprises the following steps: a first vacuum induction VIM process, preparing metal raw materials according to requirements, selecting the metal raw materials with the sulfur content of more than 25ppm, putting the raw materials except aluminum and titanium into a vacuum induction furnace, adding CaO with the weight of 0.5-1% of the raw materials at the upper part of the raw materials for desulfurization treatment, filling argon to be not less than 25000Pa after the refining period is finished, and adding Ni-Ca with the weight of 2-4% of the raw materials; optionally adding aluminum and titanium 30 minutes after refining, and preserving heat at 1300-; and after sampling, argon is filled again to be not less than 25000Pa, Ni-Mg accounting for 2-4% of the weight of the materials in the vacuum induction furnace is added, and the materials are fully stirred and poured to obtain an electrode E1. In the step, conventional metal raw materials with high S content, including Cr, Fe, Ni, Nb and the like, can be selected, and in the step, the metal raw materials, namely aluminum and titanium, are added after refining is finished instead of being added together with other metal raw materials, so that oxygen and nitrogen in the aluminum and titanium and other metal raw materials can be prevented from being combined into impurities, such as aluminum oxide and titanium nitride, the alkalinity of calcium oxide is reduced, and the diffusion desulfurization effect is influenced. The method is characterized in that 0.5-1% of CaO by weight of the raw materials is added to the upper part of the raw materials for diffusion desulfurization, conventional slag skimming or reverse dumping operation is not needed in the follow-up process, the high-temperature alloy containing CaO slag can be directly poured into an electrode without worrying about the influence of the high-temperature alloy on the last vacuum arc remelting VAR process, the technical problem that CaO cannot be actually and really used for desulfurization in the vacuum induction melting VIM process in the prior art is solved, and partial sulfur can be effectively removed in the step.

Step two: ESR (electroslag remelting) process, wherein an electrode E1 is subjected to shot blasting rust removal and then electroslag remelting smelting, and in the ESR process, a slag system with ultrahigh alkalinity and high resistance is adopted, and the composition and mass ratio of the slag system are CaF₂:Al₂O₃CaO = 20: 40: 40, controlling the insertion depth of the electrode by high swing, wherein the corresponding process parameter is that the electrode insertion depth is controlled to be less than 3mm by setting the pressure swing value to be 0.55-0.6 milliohm; and (3) obtaining an electrode E2 with a high melting speed V (kg/min) = 2-4 times of the diameter (dm) of the crystallizer. In particular, 3-5wt% of TiO is not required to be added into premelting slag in the procedure like the conventional triple process₂So as to adjust the Ti and Al component deviation of the head and the tail of the electroslag ingot. After the process, the desulfurization rate exceeds 80%, and the power consumption of each ton of steel is reduced by more than 50% compared with the conventional process, so that the rapid electroslag production with high desulfurization rate and low cost is realized. The conductivity of the slag system with ultrahigh alkalinity and high resistance is not more than 1.45 omega at 1600 DEG C^-1•cm^-1Light ofThe chemical alkalinity is not lower than 0.85, the high resistance slag system brings low conductivity, the slag system conductivity is lower, and the reduction of power consumption is facilitated; the high alkalinity is to ensure good desulfurization during the remelting process.

Step three: removing surface oxide skin of the electrode E2 by shot blasting, using the electrode E2 as a raw material of a second vacuum induction melting VIM process, filling argon to a pressure not less than 25000Pa before casting, adding Ni-Mg with the weight of 0.1-0.2% of that of the electrode E2, stirring for 3-5 minutes at 50-60Hz, and then casting to obtain an electrode E3. And (3) removing the surface oxide skin of the electrode E2 obtained in the step two by shot blasting, wherein the loss of the yield of the electrode E2 serving as a raw material in the step is less than 0.5%. In the step, slagging is not needed, and the S content is lower than 2ppm only by filling argon before casting and adding Ni-Mg with the weight of 0.1-0.2% of that of the electrode E2. Meanwhile, CaO, Ni-Ca and Ni-Mg added in the first vacuum induction melting VIM process are effectively removed through the second step and the first step, and the stability of the vacuum arc remelting VAR process in the next step cannot be affected.

Step four: and performing a VAR (vacuum arc remelting) process according to the existing production process to obtain a finished product.

And (3) storing the Ni-Ca and the Ni-Mg in the step one by adopting a nickel box, inserting the Ni-Ca and the Ni-Mg into a molten pool through a CaO layer by utilizing a sampling rod, and stirring at 50-60Hz after inserting the Ni-Ca and the Ni-Mg into the molten pool.

Further, in the first step, before adding CaO, the CaO is baked at 850 ℃ or higher for 6 hours or more, and before charging, the CaO can be taken out of the heating furnace to avoid moisture absorption, and preferably, before adding CaO, the metal raw material is preheated to promote the molten slag to be rapidly melted.

In the second step, in the high-melting-speed rapid electroslag process, the melting speed V (kg/min) is set to be 2-4 times of that of the crystallizer (dm).

And in the second step, the insertion depth of the electrode is less than 3 mm.

In order to avoid the accretion of a molten pool containing more slag at the lower sprue gate of the launder, the diameter of the lower sprue gate of the launder selected in the step I of vacuum induction melting VIM is not less than 40 mm.

The technical principle of the invention is as follows: the technological characteristics of VIM, ESR and VAR procedures are comprehensively utilized, and the brand new quadruple technology is formed by optimized combination. The method is characterized in that CaO and Ni-Ca or/and Ni-Mg, especially the addition of CaO, are added in the first vacuum induction VIM smelting process, so that better desulfurization can be realized compared with the prior art, in order to overcome the influence of CaO added in the first vacuum induction VIM smelting process on the subsequent smelting process of the high-temperature alloy and solve the problem that the prior art cannot practically desulfurize by CaO, the third vacuum induction VIM smelting process is added, CaO added in the first vacuum induction VIM smelting process can be effectively removed through the treatment of the second vacuum induction VIM smelting process and the third vacuum arc remelting VAR process, and the fourth vacuum arc remelting VAR process cannot be influenced.

In the ESR procedure of electroslag remelting and smelting in the second step, a slag system with high content of CaO is adopted, the technical limitation that the addition amount of CaO in the slag system in the prior art is usually not more than 25% of the total mass of the slag system is broken, and better desulfurization is realized. Aiming at new technical requirements under the condition of the quadruple process, high-level desulfurization, inclusion and slag inclusion removal, production cost control and the like are realized by controlling the electrode insertion depth, the melting speed and the like.

The beneficial technical effects of the invention are as follows: the technical problems that the desulfurization cost is high, the purity and the solidification quality cannot be considered, and the control of the ultralow S content is stably realized in the prior art are solved through the innovation of the process flow, and the sulfur content in the alloy is reduced to be below 0.5 ppm. The invention can be used for the manufacturing technology of the high-quality high-temperature alloy with ultralow S content and no solidification related metallurgical defects for key parts in the fields of advanced aerospace, nuclear power and the like.

Detailed Description

Example 1

Production of ultralow S content high-temperature alloy GH4169 for aviation rotor parts

Firstly, the raw materials are selected from the conventional domestic No. 1 nickel, metal Cr, Nb blocks, industrial pure iron and the like, the addition amount of each metal raw material is 530 Kg of the domestic No. 1 nickel, 180 Kg of the metal Cr, 5 Kg of the Nb blocks, 20 Kg of the industrial pure iron, 5 Kg of aluminum, 1 Kg of pure titanium and 3 Kg of molybdenum, and the S content in the metal raw materials is 30 ppm. Charging other raw materials except Al and Ti into the furnace, spreading CaO with 1% of the weight of the raw materials on the upper part of the raw materials, baking at 900 ℃ for 6h before adding the CaO, and taking out from the heating furnace before charging. The first vacuum induction melting VIM process is carried out, the process comprises the conventional steps of full melting, refining, sampling and the like, part of parameters are the same as those of the prior art, and the difference is that: after the refining period is finished, argon is filled until the pressure is 25000Pa, 4% of Ni-Ca of the weight of the raw materials is added, the Ni-Ca is welded by a Ni box, a sampling rod penetrates through a CaO layer and is inserted into a molten pool, and the mixture is stirred by 60Hz after being inserted into the molten pool; after refining is finished for 30 minutes, adding aluminum and titanium, and preserving heat for 1-2 hours at 1300-; and after sampling, argon is filled to 25000Pa again, Ni-Mg with the weight of 4% of the material in the vacuum induction furnace is added, the mixture is stirred for 3min by adopting 60Hz and then is directly poured, and in order to avoid the nodulation of a molten pool containing more slag at the lower pouring opening of the launder, the diameter of the lower pouring opening of the launder selected in the first vacuum induction smelting VIM procedure is 40 mm. Electrode E1 analyzed for sulfur content to be 4 ppm.

Step two, performing electroslag remelting smelting on the electrode E1 after shot blasting and rust removal, wherein in the process, a slag system adopts a high-alkalinity and high-resistance slag system CaF₂：Al₂O₃: CaO = 20: 40: 40 (weight ratio), the slag system weight is: 37Kg, the melting speed of electroslag remelting is set to be 2 times of the diameter (dm) of the crystallizer, and the insertion depth of the electrode is controlled to be 2 mm. And filling argon for 30-50L/min according to a conventional process to form atmosphere protection. The S content analysis result of the electrode E2 obtained in this step was 0.5 to 1.5 ppm.

Step three, a second vacuum induction melting VIM procedure, removing surface oxide skin by adopting a shot blasting mode after demoulding an electrode E2, and directly loading the electrode E2 into a vacuum induction melting crucible, wherein CaO is not added in the procedure. Sampling the finished product, filling argon to 25000Pa, adding Ni-Mg with the weight of 0.2 percent of that of the electrode E2, stirring at 60Hz for 3min, and directly casting. The analysis result of the S content in the electrode E3 obtained in this step was 0.5ppm, and the electrode had no cluster-like inclusions such as CaO and MgO, and had a Ca content of less than 1ppm and a Mg content of less than 2 ppm.

And step four, performing vacuum arc remelting VAR (vacuum arc remelting) process, namely performing vacuum arc remelting on the electrode E3 after shot blasting or grinding by using a grinding wheel, and finally obtaining a finished product ingot with the S content of less than 0.2ppm and without metallurgical defects such as black spots, white spots and the like.

Example 2

Special smelting production of high-temperature alloy 690 with ultralow S content requirement for nuclear power

Firstly, a vacuum induction melting process, wherein the raw materials are conventional domestic No. 1 nickel, metal Cr, industrial pure iron and the like, the adding amount of each metal raw material is 620 Kg of domestic No. 1 nickel, 280 Kg of metal Cr and 100 Kg of industrial pure iron, and the S content in the metal raw materials is 25 ppm. CaO with the weight of 0.5 percent of the weight of the raw materials is spread on the upper part of the raw materials, the raw materials are roasted for 7 hours at the temperature of 850 ℃ before being added, and the raw materials are taken out of the heating furnace before being charged. After the refining period is finished, argon is filled to 25000Pa, Ni-Ca with 2 percent of the weight of the raw materials is added, the Ni-Ca is welded by a Ni box, a sampling rod penetrates through a CaO layer and is inserted into a molten pool, and the mixture is stirred by 60Hz after being inserted into the molten pool. And after sampling, argon is filled again until the pressure is not less than 26000Pa, Ni-Mg with the weight of 2 percent of the material in the vacuum induction furnace is added, and the mixture is stirred for 5min at 60Hz and then is directly poured to obtain an electrode E1. The diameter of a lower sprue gate of a launder selected in the first vacuum induction VIM smelting process is 50 mm. The S content in the electrode E1 was analyzed to be 4 ppm.

Step two, performing an electroslag remelting smelting process after the electrode E1 is subjected to shot blasting and rust removal, wherein a slag system adopts a high-alkalinity and high-resistance slag system CaF₂：Al₂O₃: CaO = 20: 40: 40 (weight ratio), and the weight of the slag system is 50 Kg. The melt rate was set to 3 times the diameter (dm) of the mold, and the electrode insertion depth was controlled to 2.8 mm. And filling argon for 30-50L/min according to a conventional process to form atmosphere protection. The S content of the electrode E2 was analyzed to be 1 ppm.

Step three, a second vacuum induction melting VIM process, removing surface oxide skin by adopting a shot blasting mode after demoulding of an electrode E2, directly putting the electrode E2 into a vacuum induction melting crucible, filling argon to 26000Pa after sampling a finished product, adding Ni-Mg with the weight of 0.2 percent of that of the electrode E2, stirring for 3-5min at 60Hz, and directly pouring to obtain an electrode E3. The analysis result of the S content in the electrode E3 was 0.5ppm, and the electrode had no cluster-like inclusions such as CaO and MgO, and had a Ca content of less than 1ppm and a Mg content of less than 2 ppm.

And step four, performing vacuum arc remelting VAR (vacuum arc remelting) process, wherein the electrode E3 is subjected to vacuum arc remelting after shot blasting or grinding by using a grinding wheel, and the S content in the finished product ingot is 0.3ppm finally.