Method for preparing high-nitrogen steel by applying pressurized electroslag remelting of carbon-containing nitrogen-increasing slag system

Abstract

The invention relates to a method for preparing high-nitrogen steel by applying pressurized electroslag remelting of a carbon-containing nitrogen-increasing slag system, which comprises the following steps of: uniformly mixing high-purity fluorite, lime, industrial aluminum oxide and fused magnesia, and preparing pre-melted slag through high-temperature smelting of a three-phase slagging furnace; crushing the pre-melted slag, and mixing the crushed pre-melted slag with graphite powder to prepare carbon-containing nitrogen-increasing slag; and after slagging is completed, the nitrogen filling pressure is controlled according to the target nitrogen content, meanwhile, graphite particles are added at a constant speed, and the nitrogen content of the high-nitrogen steel reaches the target range through pressurized gas-phase nitriding. The novel carbon-containing nitrogen-increasing slag system for pressurized electroslag remelting is developed on the basis of the technology for preparing the high-nitrogen steel through pressurized electroslag remelting and gas-phase nitriding, the nitrogen capacity of the slag system is remarkably improved, gas-phase nitriding is effectively promoted, nitrogen distribution is uniform, the nitrogen content in the steel is easily controlled by adjusting the nitrogen pressure, and the nitrogen-containing nitrogen-increasing slag system is suitable for large-scale production. And on the premise that the components and performance of the high-nitrogen steel are guaranteed, the production efficiency is improved, and the production cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of high nitrogen steel preparation, and in particular to a method for preparing high nitrogen steel by pressurized electroslag remelting using a carbon-containing nitrogen-enhanced slag system. Background Art

[0002] In high nitrogen steel, nitrogen is dissolved in the matrix in the form of interstitial atoms and distributed in the form of nitrides at the grain boundaries and inside the matrix. Therefore, nitrogen as an alloying element can not only replace expensive nickel alloys, but also improve the strength and hardness of steel through solid solution strengthening, dispersion strengthening and fine grain strengthening, while promoting the formation of a dense oxide film on the surface of steel, significantly enhancing its corrosion resistance. Therefore, as an important engineering material, high nitrogen steel has broad application prospects in aerospace, marine engineering, petrochemicals, atomic energy and other fields.

[0003] Pressurized electroslag remelting technology is an effective method for preparing high nitrogen steel. Among them, the nitrogen addition of nitrided alloy particles (such as Si3N4, Fe-Cr-N and Cr-N, etc.) is adopted in the process of pressurized electroslag remelting to achieve nitrogen addition in molten steel. However, not only the high cost of nitrided alloy particles will increase the preparation cost of high nitrogen steel, but also improper addition will easily lead to the formation of nitrogen bubbles, thereby affecting the internal quality of steel. At the same time, it is difficult to accurately control the amount and timing of nitrided alloy particles, and it is difficult to achieve uniform distribution of nitrogen. The nitrogen addition of molten steel is carried out by pressurized gas phase nitriding. The high nitrogen pressure atmosphere in the pressurized electroslag furnace is used to continuously add nitrogen to the molten pool through the slag pool. It has the advantages of continuous and stable nitrogen addition, uniform nitrogen distribution, easy to control the nitrogen content in steel by pressure regulation, and low cost. It is currently a very potential nitrogen alloying technology for preparing high nitrogen steel by pressurized electroslag remelting.

[0004] The nitrogen capacity of the slag system can accurately reflect its ability to dissolve and fix nitrogen. Therefore, in the process of pressurized electroslag remelting vapor nitriding, the nitrogen capacity of the slag system directly affects the vapor nitriding rate and efficiency of the molten pool. At present, the nitrogen capacity of the slag system used for pressurized electroslag remelting is generally low, which limits the efficiency of pressurized electroslag remelting vapor nitriding to prepare high nitrogen steel. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] The present invention aims to develop a carbon-containing nitrogen-enhanced slag system for preparing high nitrogen steel by pressurized electroslag remelting, so as to realize the efficient preparation of high nitrogen steel by pressurized vapor phase nitriding in the process of pressurized electroslag remelting.

[0007] (II) Technical solution

[0008] To this end, the present application mentions a method for preparing high nitrogen steel by pressurized electroslag remelting using a carbon-containing nitrogen-enhanced slag system, comprising:

[0009] Step 1: High-purity fluorite, lime, industrial alumina and fused magnesia are uniformly mixed, smelted in a three-phase slag furnace at a temperature range of 1200-1500°C until completely melted, poured into a steel tank, and cooled to room temperature to obtain pre-melted slag;

[0010] Step 2: crush the pre-melted slag to a particle size of 1 to 10 mm, then bake it at 400 to 600° C. for 8 to 10 hours, and then evenly mix it with graphite powder to prepare carbon-containing nitrogen-enriched slag;

[0011] Step 3: Load the electrode, add the carbon-containing nitrogen-enriched slag into the crystallizer of the pressurized electroslag furnace, introduce high-purity nitrogen into the smelting chamber of the pressurized electroslag furnace to remove the air in the smelting chamber, and seal the smelting chamber;

[0012] Step 4: After slag making is completed, the nitrogen pressure is controlled according to the target nitrogen content, and the smelting temperature is controlled. At the same time, graphite particles are added at a uniform speed using a stepping feeder. Pressurized gas nitriding is performed while the electrode is remelted to ensure that the nitrogen content of the electroslag ingot of high nitrogen steel reaches the target range.

[0013] Furthermore, in step 4, the calculation formula for the nitrogen capacity of the carbon-containing nitrogen-enriched slag is:

[0014]

[0015] in, is the nitrogen content of carbon-enriched nitrogen slag, (%CN - ) is the mass percentage of cyanide ions in the slag, is the pressure of oxygen, P N2 is the nitrogen pressure for pressurized vapor nitriding, K1 is the reaction equilibrium constant, is the activity of oxygen ions in the slag, a C is the carbon activity in the slag, is the activity coefficient of cyanide ions in the slag.

[0016] Furthermore, the target carbon content of the electroslag ingot is calculated as follows:

[0017]

[0018] in, is the target carbon content of electroslag ingot, is the upper limit of carbon content of target steel grade, It is the lower limit of carbon content of the target steel grade.

[0019] Furthermore, in step 3, the carbon content of the electrode is calculated as:

[0020]

[0021] Where, [%C] 电极is the carbon content of the electrode, is the target carbon content of electroslag ingot.

[0022] Furthermore, in step 2, the calculation formula for the carbon content in the carbon-containing nitrogen-enriched slag is:

[0023]

[0024] Where, [%C] 渣 is the carbon content in the carbon-containing nitrogen-enriched slag, is the target carbon content of electroslag ingot.

[0025] Furthermore, in step 4, the calculation formula for the mass of graphite particles is:

[0026]

[0027] Among them, m 石墨粒 is the total mass of graphite particles added, is the target carbon content of electroslag ingot, [%C] 电极 is the carbon content of the electrode, m 电极 is the mass of the electrode.

[0028] Furthermore, in step 4, the calculation formula for the speed of adding graphite particles is:

[0029]

[0030] Where, v is the speed of adding graphite particles, m 石墨粒 is the total mass of graphite particles added, and t is the pressurized gas phase nitriding time.

[0031] Further, in step 4, the nitrogen pressure for pressurized gas phase nitriding is:

[0032]

[0033] Among them, P N2 P is the nitrogen pressure for pressurized gas phase nitriding. 0 is the standard atmospheric pressure, [%N] is the target nitrogen content of the steel grade, T is the smelting temperature, The first-order interaction coefficient of element j on N, is the second-order interaction coefficient of element j on N, and [% j] is the content of element j in steel.

[0034] Furthermore, the chemical composition of the prepared high nitrogen steel electroslag ingot includes, by mass percentage: C: 0.10-1.50%, Si: ≤1.00%, Mn: ≤1.00%, Cr: 12.00-18.00%, Mo: ≤1.20%, Ni: ≤1.00%, N: 0.10-1.00%, V: ≤1.00%, S: ≤0.05%, P: ≤0.06% and the balance Fe.

[0035] Furthermore, the chemical composition of the carbon-containing nitrogen-enriched slag includes, by mass percentage, CaF2: 52-57%, CaO: 25-29%, Al2O3: 13-17%, MgO: 2-5%, and C: 0.4-1.5%.

[0036] (III) Beneficial effects

[0037] The beneficial effects of the present invention are as follows: the present invention discloses a method for preparing high nitrogen steel by pressurized electroslag remelting using a carbon-containing nitrogen-enriched slag system, wherein the method comprises: uniformly mixing high-purity fluorite, lime, industrial alumina, and fused magnesia, smelting them at a temperature range of 1200 to 1500° C. in a three-phase slag furnace until they are completely melted, pouring them into a steel tank, cooling them to room temperature, and obtaining pre-melted slag; crushing the pre-melted slag to a particle size of 1 to 10 mm, and then baking them at a temperature of 400 to 600° C. for 8 to 10 minutes; 0h, and then evenly mix it with graphite powder to make carbon-containing nitrogen-enriched slag; load the electrode, add the carbon-containing nitrogen-enriched slag into the crystallizer of the pressurized electric slag furnace, introduce high-purity nitrogen into the smelting chamber of the pressurized electric slag furnace to expel the air in the smelting chamber, and seal the smelting chamber; after slag making is completed, control the nitrogen pressure according to the target nitrogen content, control the smelting temperature, and use a stepping feeder to uniformly add graphite particles, and perform pressurized gas phase nitriding while remelting the electrode, so that the nitrogen content of the electric slag ingot of high nitrogen steel reaches the target range.

[0038] In the process of pressurized electroslag remelting, the present application adopts a carbon-containing nitrogen-enhanced slag system, which fundamentally changes the way nitrogen is dissolved in the slag. The nitrogen capacity is much higher than that of carbon-free slag of similar composition, which significantly increases the nitriding rate between slag and steel. Carbon-containing nitrogen-enhanced slag and electrodes with matching carbon content are configured, and graphite particles are added at a uniform speed using a stepping feeder during the pressurized electroslag remelting process to maintain the carbon content in the slag and ensure that the carbon content of the molten steel is within the target range. The high nitrogen capacity of the slag can be maintained throughout the pressurized electroslag remelting process, significantly enhancing the nitriding efficiency of the molten pool under high nitrogen pressure, and the preparation cost is low and easy to operate. Based on this, the pressurized gas phase nitriding preparation of electroslag ingots of high nitrogen stainless steel is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic flow chart of a method for preparing high nitrogen steel by pressurized electroslag remelting using a carbon-containing nitrogen-enhanced slag system as mentioned in the present application. DETAILED DESCRIPTION

[0040] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0041] When amount, concentration or other value or parameter is represented by range, preferred range or a series of upper preferred value and lower preferred value, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when disclosing range "1-5", described range should be interpreted as including range "1-4", "1-3", "1-2", "1-2 and 4-5", "1-3 and 5" etc. When numerical range is described in this article, unless otherwise stated, the range is intended to include its end value and all integers and fractions within the range.

[0042] In these embodiments, unless otherwise specified, the parts and percentages are all measured by mass. "Parts by mass" refers to the basic unit of measurement representing the mass ratio relationship of multiple components. 1 part can represent any unit mass, such as 1g, 3.527g, etc. If we say that the mass parts of component A are a parts and the mass parts of component B are b parts, it means the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it means that the mass of component A is aK and the mass of component B is bK (K is an arbitrary number, indicating a multiple factor). It should not be misunderstood that, unlike the mass parts, the sum of the mass parts of all components is not limited to 100 parts. "And / or" is used to indicate that one or both of the situations described may occur, for example, A and / or B include (A and B) and (A or B).

[0043] refer to Figure 1 The present application discloses a method for preparing high nitrogen steel by pressurized electroslag remelting using a carbon-containing nitrogen-enriched slag system, comprising:

[0044] Step 1: Evenly mix high-purity fluorite, lime, industrial alumina and fused magnesia. By mixing these specific raw materials, the basic components can be provided for the subsequent preparation of carbon-containing nitrogen-enhanced slag system. Smelt them in a three-phase slag furnace at a temperature range of 1200-1500°C until they are completely melted, and pour them into a steel tank and cool them to room temperature to obtain pre-melted slag.

[0045] Among them, smelting at a specific high temperature for a sufficient time can make various raw materials fully mixed to form a uniform slag system.

[0046] Step 2: crush the pre-melted slag into a particle size of 1 to 10 mm, and then bake it at a temperature of 400 to 600° C. for 8 to 10 hours, and then evenly mix it with graphite powder to prepare carbon-containing nitrogen-enriched slag.

[0047] Among them, baking at a specific temperature can remove moisture and impurities in the slag and improve the quality and stability of the slag.

[0048] In the present technical solution, in step 2, the calculation formula for the carbon content in the carbon-containing nitrogen-enriched slag is:

[0049]

[0050] In formula [1], [%C] 渣 is the carbon content in the carbon-containing nitrogen-enriched slag, is the target carbon content of the electroslag ingot. Exemplarily, the mass of the slag is about 4% to 8% of the mass of the electrode.

[0051] Formula [1] is used to determine the carbon content in carbon-containing nitrogen-enhanced slag. The carbon content of the slag is designed by the target carbon content of the electroslag ingot, the coefficient and the percentage of the mass of the slag to the mass of the electrode (4% to 8%). Graphite powder is added to increase the carbon content in the slag system, which significantly improves the gas phase nitriding efficiency of the molten steel. Among them, the calculation formula for the target carbon content of the electroslag ingot is:

[0052]

[0053] In formula [2], is the target carbon content of electroslag ingot, is the upper limit of carbon content of target steel grade, It is the lower limit of carbon content of the target steel grade.

[0054] Step 3: Load the electrode, add the carbon-containing nitrogen-enriched slag into the crystallizer of the pressurized electroslag furnace, introduce high-purity nitrogen into the smelting chamber of the pressurized electroslag furnace to remove the air in the smelting chamber, and seal the smelting chamber.

[0055] Carbon-containing nitrogen-enhanced slag can absorb inclusions, deoxidize, desulfurize, improve purity, adjust the composition of molten steel, etc. during the remelting process, and significantly improve the nitrogen content of the slag and enhance the gas phase nitriding efficiency of the molten steel. The introduction of high-purity nitrogen to remove air can prevent the molten steel from being oxidized, and at the same time create a nitrogen atmosphere for gas phase nitriding. The sealed smelting chamber can prevent air from entering and keep the pressure stable, which is conducive to gas phase nitriding. Exemplarily, in the present application, the carbon content of the electrode is 80% to 95% of the target carbon content of the electroslag ingot. During the electroslag remelting process, the carbon in the carbon-containing nitrogen-enhanced slag system will partially enter the molten steel. If the carbon content of the electrode is equal to or higher than the upper limit of the carbon content of the steel grade, the carbon content in the obtained electroslag ingot exceeds the target range of the carbon content of the steel grade. Therefore, the electrode carbon content is set to 80% to 95% of the target carbon content of the electroslag ingot. The carbon content of the molten steel can be increased by the carbon-containing slag system and the subsequent addition of graphite particles, thereby controlling the carbon content of the molten steel to meet the requirements of the steel grade.

[0056] In step 3, the calculation formula for the electrode carbon content is:

[0057]

[0058] In formula [3], [%C] 电极 is the carbon content of the electrode, is the target carbon content of electroslag ingot.

[0059] Step 4: After slag making is completed, the nitrogen pressure is controlled according to the target nitrogen content, and the smelting temperature is controlled. At the same time, graphite particles are added at a uniform speed using a stepping feeder to balance the carbon content in the slag to maintain a high nitrogen capacity of the slag and maintain efficient nitriding of the molten steel. Pressurized gas phase nitriding is performed while the electrode is remelted to ensure that the nitrogen content is within the target range.

[0060] Specifically, controlling the nitrogen pressure according to the target nitrogen content can accurately adjust the dissolved nitrogen content in the molten steel to meet the requirements of different steel grades. Gas phase nitriding under pressurized nitrogen conditions can improve the nitrogen addition speed and efficiency. Controlling the smelting temperature can ensure the fluidity and reactivity of the molten steel and promote the absorption of nitrogen. During the pressurized gas phase nitriding process, the carbon-containing nitrogen-increasing slag significantly increases the nitrogen capacity of the slag system due to the presence of carbon, but during the electroslag remelting process, the carbon content in the slag system will gradually decrease and penetrate into the molten steel. Therefore, the use of a step-by-step feeder to uniformly add graphite particles can effectively adjust the carbon content in the slag system and the molten steel, maintain the high nitrogen capacity of the slag system, and maintain efficient gas phase nitriding.

[0061] In step 4, nitrogen in the carbon-containing nitrogen-enriched slag system reacts with carbon and oxygen ions in the slag through the reaction of equation [4] to easily form cyanide ions (CN - ) is dissolved in the slag in the form of:

[0062] 1 / 2N2+C+1 / 2(O 2- )=(CN - )+1 / 4O2[4];

[0063] The calculation formula of nitrogen capacity of carbon-containing nitrogen-enriched slag is:

[0064]

[0065] In formula [5], is the nitrogen content of carbon-enriched nitrogen slag, (%CN - ) is the mass percentage of cyanide ions in the slag, is the pressure of oxygen, P N2 is the nitrogen pressure for pressurized vapor nitriding, K1 is the reaction equilibrium constant, is the activity of oxygen ions in the slag, a C is the carbon activity in the slag, It is the activity coefficient of cyanide ions in the slag. The nitrogen capacity calculation formula of carbon-containing nitrogen-enhanced slag is used to calculate the capacity of carbon-containing nitrogen-enhanced slag to accommodate nitrogen.

[0066] For carbon-free slag system, nitrogen reacts with oxygen ions in the slag to form nitrogen ions (N 3- ) is dissolved in the slag in the form of:

[0067] 1 / 2N2+3 / 2(O 2- )=(N 3- )+3 / 4O2[6];

[0068] The calculation formula of nitrogen capacity of carbon-free nitrogen-enriched slag is:

[0069]

[0070] In formula [7], is the nitrogen capacity of the carbon-free slag system, K2 is the reaction equilibrium constant of equation [6], is the activity coefficient of nitrogen ions in the slag, (%N 3- ) is the mass percentage of nitrogen ions in the slag.

[0071] Specifically, in the method mentioned in the present application, nitrogen in the carbon-containing nitrogen-enriched slag system is dissolved in the slag through the reaction of equation [4], and it is very easy to form cyanide ions (CN - ), equation [5] is the definition of nitrogen capacity. Compared with the carbon-free slag system (the nitrogen dissolution reaction in the slag system is equation [6], and the nitrogen capacity definition is equation [7]), its nitrogen capacity is much higher than that of the carbon-free slag system with similar composition.

[0072] In the technical solution, in step 4, graphite particles are added at a uniform speed using a stepping feeder, and the graphite particles are high-purity graphite. Specifically, the mass of the graphite particles is calculated as follows:

[0073]

[0074] In formula [8], m 石墨粒 is the mass of graphite particles, is the target carbon content of electroslag ingot, [%C] 电极 is the carbon content of the electrode, m 电极 is the mass of the electrode.

[0075] By combining the target carbon content of the electroslag ingot, the carbon content of the electrode and the mass of the electrode, equation [9] can be used to calculate the mass of graphite particles required to be added.

[0076] In this technical solution, in step 4, the calculation formula for the speed of adding graphite particles is:

[0077]

[0078] In formula [9], v is the speed of adding graphite particles, m 石墨粒 is the mass of graphite particles, and t is the pressurized gas phase nitriding time.

[0079] Formula [9] is used to determine the speed of adding graphite particles. The addition rate is calculated based on the total mass of graphite particles and the pressurized gas phase nitriding time, which can ensure that during the electroslag remelting process, graphite particles can be added to the slag at an appropriate rate to compensate for the carbon loss caused by the transfer of carbon from the slag to the molten steel, maintain the high nitrogen capacity of the slag, and maintain an efficient gas phase nitriding rate.

[0080] In the technical solution, in step 4, the nitrogen pressure for pressurized gas phase nitriding is:

[0081]

[0082] In formula

[10] , P N2 P is the nitrogen pressure for pressurized gas phase nitriding. 0 is the standard atmospheric pressure, [%N] is the target nitrogen content of the steel grade, T is the smelting temperature, The first-order interaction coefficient of element j on N, is the second-order interaction coefficient of element j on N, and [% j] is the content of element j in steel.

[0083] Formula

[10] is used to calculate the nitrogen pressure required for pressurized vapor nitriding. The required nitrogen pressure is determined by factors such as the target nitrogen content of the steel grade, the smelting temperature, and the interaction coefficients of various elements in the steel with nitrogen. By accurately calculating the nitrogen pressure, the amount of nitrogen dissolved in the molten steel can be effectively controlled to meet the nitrogen content requirements of high nitrogen steel. Table 1 provides the interaction coefficients of various alloying elements with nitrogen.

[0084] Table 1 Interaction coefficients of various alloy elements with nitrogen

[0085]

[0086] In the present technical scheme, the chemical composition of the prepared high nitrogen steel includes: C: 0.10-1.50%, Si: ≤1.00%, Mn: ≤1.00%, Cr: 12.00-18.00%, Mo: ≤1.20%, Ni: ≤1.00%, N: 0.10-1.00%, V: ≤1.00%, S: ≤0.05%, P: ≤0.06% and the balance of Fe.

[0087] Calculated by mass percentage, the chemical composition of the carbon-containing nitrogen-enriched slag includes: CaF2: 52-57%, CaO: 25-29%, Al2O3: 13-17%, MgO: 2-5%, and C: 0.4-1.5%.

[0088] The present application adopts a carbon-containing nitrogen-enriched slag system to prepare high-nitrogen steel, which fundamentally changes the way the slag system dissolves nitrogen. Compared with ordinary slag systems, it significantly increases the nitrogen capacity, thereby greatly improving the nitriding rate and significantly promoting the gas-phase nitrogen enrichment of molten steel during pressurized electroslag remelting.

[0089] In the present application, in order to control the carbon content in the electroslag ingot, the carbon content of the electrode is designed to be 80% to 95% of the target carbon content of the electroslag ingot, and the carbon content of the appropriate carbon-containing nitrogen-enhanced slag system and the mass of the graphite particles added at a uniform rate during the pressurized electroslag remelting process are matched. Among them, the carbon content of the slag is designed by the target carbon content, coefficient and percentage of the slag mass to the electrode mass (4% to 8%) of the electroslag ingot. At the same time, the total mass of the graphite particles required to be added is matched by combining the target carbon content of the electroslag ingot, the carbon content of the electrode and the mass of the electrode. After calculating the total mass of the graphite particles, the addition rate of the graphite particles is determined according to the pressurized gas phase nitriding time. In this way, it can be ensured that during the electroslag remelting process, the graphite particles can be added to the slag at a suitable rate to compensate for the carbon loss caused by the transfer of carbon from the slag to the molten steel, maintain the high nitrogen capacity of the slag system, and maintain the efficient gas phase nitriding rate. The nitrogen pressure required for pressurized gas phase nitriding is further calculated according to the target nitrogen content, and the nitrogen pressure directly affects the ability of the molten steel to dissolve nitrogen.

[0090] This application mentions a method for preparing high nitrogen steel by pressurized electroslag remelting of a carbon-containing nitrogen-enriched slag system. Based on the technology of preparing high nitrogen steel by pressurized electroslag remelting and vapor phase nitriding, a new type of carbon-containing nitrogen-enriched electroslag remelting slag system has been developed, which significantly improves the nitrogen capacity of the slag system and effectively promotes the vapor phase nitriding. At the same time, the nitrogen is evenly distributed and the nitrogen content in the steel can be easily controlled by adjusting the nitrogen pressure. Under the premise of ensuring the composition and performance of high nitrogen steel, the production efficiency is improved and the production cost is reduced.

[0091] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0092] Example 1

[0093] The smelting equipment used is a 100kg pressurized electroslag remelting furnace with a maximum operating pressure of 2.0MPa and a furnace load of 100kg.

[0094] The following two electrodes with basically the same composition were obtained by smelting in a vacuum induction furnace protected by argon gas, and were respectively applied to smelting methods 1 and 2, and their compositions are as follows.

[0095] Electrode 1: C: 0.25%, Si: 0.55%, Mn: 0.81%, Cr: 15.50%, Mo: 0.92%, Ni: 0.43%, N: 0.0021% and Fe (balance);

[0096] Electrode 2: C: 0.25%, Si: 0.53%, Mn: 0.80%, Cr: 15.60%, Mo: 0.90%, Ni: 0.43%, N: 0.0035% and Fe (balance).

[0097] Reasonably match the slag carbon content, electrode carbon content, smelting temperature, nitrogen pressure, nitriding time, graphite particle mass added during the smelting process and uniform feeding rate: the slag carbon content is 0.6%, the electrode carbon content is 0.25%, the smelting temperature is about 1600℃, the nitrogen pressure during the smelting process is 1.23MPa, the time is about 110min, the mass of graphite particles added during the smelting process is 50g, and the uniform feeding rate is 0.45g / min.

[0098] The target composition of 30Cr15Mo1N high nitrogen stainless steel is: C: 0.25~0.35%, Si: ≤1.00%, Mn: ≤1.00%, Cr: 14.00~16.00%, Mo: 0.85~1.10%, Ni: ≤0.50%, N: 0.30~0.50% and Fe (balance).

[0099] Smelting method 1: This method uses pressurized electroslag remelting vapor nitriding technology to smelt 30Cr15Mo1N steel. The chemical composition mass percentage of the slag system used is: CaF2: 54.2%, CaO: 26.2%, A12O3: 15.5%, MgO: 3.5% and C: 0.6%. The specific steps include:

[0100] Step 1: Use high-purity fluorite, lime, industrial alumina, fused magnesia and graphite powder as raw materials, accurately weigh the above ingredients according to the target mass percentage, and evenly mix all the components except graphite powder. Smelt them in a three-phase slag furnace at a temperature of 1500°C until they are completely melted, pour them into a steel tank, and cool them to room temperature to obtain pre-molten slag.

[0101] Step 2: crush the pre-melted slag into a particle size of 1 to 10 mm, bake it at 500°C for 10 hours before use, and then mix the graphite powder with it to make a carbon-containing nitrogen-enriched slag.

[0102] Step 3: After other preparatory operations for pressurized electroslag remelting are completed, electrodes (C: 0.25%) are loaded, and the prepared slag is added to the pressurized electroslag furnace crystallizer, high-purity nitrogen is introduced into the pressurized electroslag furnace melting chamber to expel the air in the melting chamber, and the melting chamber is sealed.

[0103] Step 4: After slag making is completed, fill with 1.23MPa nitrogen pressure, control the smelting temperature to about 1600°C, and use a stepping feeder to add graphite particles at a uniform speed (0.45g / min) to balance the carbon content of the slag steel to maintain a high nitrogen capacity of the slag and maintain efficient nitriding of the molten steel. Pressurized gas phase nitriding is carried out while the electrode is remelted. The smelting is completed in about 110min, and the nitrogen content reaches 0.3986%, which is within the target nitrogen content range.

[0104] Table 2 Composition (%) of 30Cr15Mo1N high nitrogen stainless steel electroslag ingot prepared by smelting method 1

[0105]

[0106] Smelting method 2: This method uses pressurized electroslag remelting vapor nitriding technology to smelt 30Cr15Mo1N steel. The chemical composition mass percentage of the slag system used is: CaF2: 54.5%, CaO: 26.5%, A12O3: 15.5% and MgO: 3.5%. The specific steps include:

[0107] Step 1: Use high-purity fluorite, lime, industrial alumina and fused magnesia as raw materials, accurately weigh the above ingredients according to the target mass percentage, mix the components evenly, smelt them in a three-phase slag furnace at a temperature of 1500°C until they are completely melted, pour them into a steel tank, cool and solidify them to room temperature, and obtain pre-molten slag.

[0108] Step 2: crush the pre-melted slag into a particle size of 1 to 10 mm, and bake it at 500°C for 10 hours before use to form slag.

[0109] Step 3: After other preparatory operations for pressurized electroslag remelting are completed, electrodes (C: 0.25%) are loaded, and the prepared slag is added to the pressurized electroslag furnace crystallizer, high-purity nitrogen is introduced into the pressurized electroslag furnace melting chamber to expel the air in the melting chamber, and the melting chamber is sealed.

[0110] Step 4: After slag making is completed, fill with 1.23MPa nitrogen pressure to remelt the electrode and perform vapor nitriding under pressurized nitrogen conditions. The smelting temperature is controlled to be about 1600°C. The smelting time is about 110min. The nitrogen content reaches 0.2165%, which does not reach the target nitrogen content.

[0111] Table 3 Composition (%) of 30Cr15Mo1N high nitrogen stainless steel electroslag ingot prepared by smelting method 2

[0112] C Si Mn Cr Mo Ni N S P Fe 0.25 0.53 0.80 15.50 0.89 0.42 0.2165 0.004 0.005 margin

[0113] It can be seen from the test results of the electroslag ingots shown in Tables 1 and 2 that the nitrogen content in the electroslag ingots prepared by method 1 using the carbon-containing nitrogen-increasing slag system reaches 0.3986%, while the method 2 (carbon-free slag system) only increases by 0.2130%. The carbon-containing nitrogen-increasing slag system of the present invention can meet the needs of gas phase nitrogen increase during electroslag remelting, and the nitrogen content meets the content requirements of the steel grade; the carbon content in the electroslag ingots prepared by method 1 increases slightly to 0.30%, and the carbon content of the electroslag ingots prepared by method 2 has no obvious change (0.25%). The method of using the carbon-containing nitrogen-increasing slag system of the present invention can realize the control of the carbon content in the electroslag ingot, and the carbon content meets the content requirements of the steel grade.

[0114] Example 2

[0115] The smelting equipment used is a 100kg pressurized electroslag remelting furnace with a maximum operating pressure of 2.0MPa and a furnace load of 100kg.

[0116] The electrode is obtained by smelting in a vacuum induction furnace protected by argon gas, and its composition is as follows.

[0117] Electrode 3: C: 0.25%, Si: 0.65%, Mn: 0.50%, Cr: 15.00%, Mo: 0.95%, Ni: 0.25%, N: 0.0031% and Fe (balance);

[0118] Reasonably match the slag carbon content, electrode carbon content, smelting temperature, nitrogen pressure, nitriding time, the mass of graphite particles added during the smelting process and the uniform feeding rate: the slag carbon content is 0.6%, the electrode carbon content is 0.25%, the smelting temperature is about 1650℃, the nitrogen pressure during the smelting process is 1.38MPa, the time is about 100min, the mass of graphite particles added during the smelting process is 50g, and the uniform feeding rate is 0.50g / min.

[0119] The target composition of 30Cr15Mo1N high nitrogen stainless steel is: C: 0.25~0.35%, Si: ≤1.00%, Mn: ≤1.00%, Cr: 14.00~16.00%, Mo: 0.85~1.10%, Ni: ≤0.50%, N: 0.30~0.50% and Fe (balance).

[0120] The 30Cr15Mo1N steel is smelted by the pressurized electroslag remelting vapor nitriding technology, and the chemical composition mass percentage of the slag system used is: CaF2: 54.0%, CaO: 26.4%, A12O3: 15.2%, MgO: 3.8% and C: 0.6%. The specific steps include:

[0121] Step 1: Use high-purity fluorite, lime, industrial alumina, fused magnesia and graphite powder as raw materials, accurately weigh the above ingredients according to the target mass percentage, and evenly mix all the components except graphite powder. Smelt them in a three-phase slag furnace at a temperature of 1550°C until they are completely melted, pour them into a steel tank, and cool them to room temperature to obtain pre-molten slag.

[0122] Step 2: crush the pre-melted slag into a particle size of 1 to 10 mm, bake it at 500°C for 10 hours before use, and then mix the graphite powder with it to make a carbon-containing nitrogen-enriched slag.

[0123] Step 3: After other preparatory operations for pressurized electroslag remelting are completed, electrodes (C: 0.25%) are loaded, and the prepared slag is added to the pressurized electroslag furnace crystallizer, high-purity nitrogen is introduced into the pressurized electroslag furnace melting chamber to expel the air in the melting chamber, and the melting chamber is sealed.

[0124] Step 4: After slag making is completed, fill with 1.38MPa nitrogen pressure, control the smelting temperature to be about 1650℃, and use a stepping feeder to add graphite particles at a uniform speed (0.50g / min) to balance the carbon content of the slag steel to maintain the high nitrogen capacity of the slag and maintain the efficient nitriding of the molten steel. Pressurized gas phase nitriding is carried out while the electrode is remelted. The smelting time is about 100min, and the nitrogen content reaches 0.4048%, which is within the target nitrogen content range.

[0125] Table 4 Composition of prepared 30Cr15Mo1N high nitrogen stainless steel electroslag ingot (%)

[0126]

[0127]

[0128] It can be seen from the test results of the electroslag ingot shown in Table 4 that the nitrogen content in the electroslag ingot prepared by using the carbon-containing nitrogen-increased slag system reaches 0.4048%. The carbon-containing nitrogen-increased slag system of the present invention can meet the needs of gas phase nitrogen increase in the process of electroslag remelting, and the nitrogen content meets the content requirements of the steel grade; the carbon content in the electroslag ingot prepared by using the carbon-containing nitrogen-increased slag system increases slightly to 0.30%. The use method of the carbon-containing nitrogen-increased slag system of the present invention can realize the control of the carbon content in the electroslag ingot, and the carbon content meets the content requirements of the steel grade.

[0129] Example 3

[0130] The smelting equipment used is a 100kg pressurized electroslag remelting furnace with a maximum operating pressure of 2.0MPa and a furnace load of 100kg.

[0131] The electrode is obtained by smelting in a vacuum induction furnace protected by argon gas, and its composition is as follows.

[0132] Electrode 4: C: 1.00%, Si: 0.50%, Mn: 0.20%, Cr: 4.00%, Mo: 9.50%, V: 1.20%, W: 1.55%, Co: 8.00%, N: 0.0021% and Fe (balance);

[0133] Reasonably match the slag carbon content, electrode carbon content, smelting temperature, nitrogen pressure, nitriding time, the mass of graphite particles added during the smelting process and the uniform feeding rate: the slag carbon content is 0.9%, the electrode carbon content is 1.00%, the smelting temperature is about 1650℃, the nitrogen pressure during the smelting process is 1.27MPa, the time is about 100min, the mass of graphite particles added during the smelting process is 75g, and the uniform feeding rate is 0.75g / min.

[0134] The target composition of W2Mo9Cr4VCo8 high nitrogen stainless steel is: C: 1.00-1.15%, Si: ≤0.65%, Mn: ≤0.40%, Cr: 3.50-4.50%, Mo: 9.00-10.00%, V: 0.95-1.35%, W: 1.15-1.85%, Co: 7.50-8.50%, N: 0.10-0.20% and Fe (balance).

[0135] The W2Mo9Cr4VCo8 steel is smelted by the pressurized electroslag remelting vapor nitriding technology, and the chemical composition mass percentage of the slag system used is: CaF2: 54.0%, CaO: 26.1%, A12O3: 15.5%, MgO: 3.5% and C: 0.9%. The specific steps include:

[0136] Step 1: Use high-purity fluorite, lime, industrial alumina, fused magnesia and graphite powder as raw materials, accurately weigh the above ingredients according to the target mass percentage, and evenly mix all the components except graphite powder. Smelt them in a three-phase slag furnace at a temperature of 1550°C until they are completely melted, pour them into a steel tank, and cool them to room temperature to obtain pre-molten slag.

[0137] Step 2: crush the pre-melted slag into a particle size of 1 to 10 mm, bake it at 500°C for 10 hours before use, and then mix the graphite powder with it to make a carbon-containing high-efficiency nitrogen-enriched slag.

[0138] Step 3: After other preparatory operations for pressurized electroslag remelting are completed, electrodes (C: 1.00%) are loaded, and the prepared slag is added to the pressurized electroslag furnace crystallizer; high-purity nitrogen is introduced into the pressurized electroslag furnace melting chamber to expel the air in the melting chamber, and the melting chamber is sealed.

[0139] Step 4: After slag making is completed, fill with 1.27MPa nitrogen pressure, control the smelting temperature to about 1650°C, and use a stepping feeder to add graphite particles at a uniform speed (0.75g / min) to balance the carbon content of the slag steel to maintain a high nitrogen capacity of the slag and maintain efficient nitriding of the molten steel. The smelting is completed in about 100min, and the nitrogen content reaches 0.1551%, which is within the target nitrogen content range.

[0140] Table 5 Composition of prepared W2Mo9Cr4VCo8 high nitrogen stainless steel electroslag ingot (%)

[0141] C Si Mn Cr Mo V W Co N S P Fe 1.08 0.49 0.20 3.98 9.49 1.18 1.55 8.00 0.1551 0.005 0.006 margin

[0142] From the test results of the electroslag ingot shown in Table 5, it can be seen that the nitrogen content in the electroslag ingot prepared by using the carbon-containing nitrogen-increased slag system reaches 0.1551%. The carbon-containing nitrogen-increased slag system of the present invention can meet the needs of gas phase nitrogen increase in the process of electroslag remelting, and the nitrogen content meets the content requirements of the steel grade; the carbon content in the electroslag ingot prepared by using the carbon-containing nitrogen-increased slag system increases slightly to 1.08%. The use method of the carbon-containing nitrogen-increased slag system of the present invention can realize the control of the carbon content in the electroslag ingot, and the carbon content meets the content requirements of the steel grade.

[0143] In the description of the present invention, each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0144] In the description of the present invention, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically limited. Moreover, the term "includes", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment including a series of elements not only includes those elements, but also includes other elements not clearly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of more restrictions, the elements limited by the sentence "comprising one..." do not exclude the existence of other identical elements in the process, method, article or equipment including the elements.

[0145] In the present invention, unless otherwise clearly specified and limited, when a first feature is “on” or “below” a second feature, it may be that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Moreover, when a first feature is “above”, “above” or “above” a second feature, it may be that the first feature is directly above or obliquely above the second feature, or it may simply mean that the first feature is higher in level than the second feature. When a first feature is “below”, “below” or “below” a second feature, it may be that the first feature is directly below or obliquely below the second feature, or it may simply mean that the first feature is lower in level than the second feature.

[0146] In the description of this specification, the description of the terms "one embodiment", "some embodiments", "embodiment", "example", "specific example" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0147] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing high nitrogen steel by pressurized electroslag remelting using a carbon-containing nitrogen-enriched slag system, characterized in that: include: Step 1: High-purity fluorite, lime, industrial alumina and fused magnesia are uniformly mixed, smelted in a three-phase slag furnace at a temperature range of 1200-1500°C until completely melted, poured into a steel tank, and cooled to room temperature to obtain pre-melted slag; Step 2: crush the pre-melted slag to a particle size of 1 to 10 mm, then bake it at 400 to 600° C. for 8 to 10 hours, and then evenly mix it with graphite powder to prepare carbon-containing nitrogen-enriched slag; Step 3: Load the electrode, add the carbon-containing nitrogen-enriched slag into the crystallizer of the pressurized electroslag furnace, introduce high-purity nitrogen into the smelting chamber of the pressurized electroslag furnace to remove the air in the smelting chamber, and seal the smelting chamber; Step 4: After slag making is completed, the nitrogen pressure is controlled according to the target nitrogen content, and the smelting temperature is controlled. At the same time, graphite particles are added at a uniform speed using a stepping feeder. Pressurized gas nitriding is performed while the electrode is remelted to ensure that the nitrogen content of the electroslag ingot of high nitrogen steel reaches the target range.

2. The method for preparing high nitrogen steel by pressurized electroslag remelting using carbon-containing nitrogen-enhanced slag system according to claim 1, characterized in that: In step 4, the calculation formula for the nitrogen capacity of the carbon-containing nitrogen-enriched slag is: in, is the nitrogen content of carbon-enriched nitrogen slag, (%CN - ) is the mass percentage of cyanide ions in the slag, is the pressure of oxygen, P N2 is the nitrogen pressure for pressurized vapor nitriding, K1 is the reaction equilibrium constant, is the activity of oxygen ions in the slag, a C is the carbon activity in the slag, is the activity coefficient of cyanide ions in the slag.

3. The method for preparing high nitrogen steel using carbon-containing nitrogen-enhanced slag system according to claim 1, characterized in that: The calculation formula for the target carbon content of electroslag ingot is: in, is the target carbon content of electroslag ingot, is the upper limit of carbon content of target steel grade, It is the lower limit of carbon content of the target steel grade.

4. The method for preparing high nitrogen steel using carbon-containing nitrogen-enhanced slag system according to claim 1, characterized in that: In step 3, the carbon content of the electrode is calculated as: Where, [%C] 电极 is the carbon content of the electrode, is the target carbon content of electroslag ingot.

5. The method for preparing high nitrogen steel by pressurized electroslag remelting using carbon-containing nitrogen-enhanced slag system according to claim 1, characterized in that: In step 2, the calculation formula for the carbon content in the carbon-containing nitrogen-enriched slag is: Where, [%C] 渣 is the carbon content in the carbon-containing nitrogen-enriched slag, is the target carbon content of electroslag ingot.

6. The method for preparing high nitrogen steel by pressurized electroslag remelting using carbon-containing nitrogen-enhanced slag system according to claim 1, characterized in that: In step 4, the calculation formula for the mass of graphite particles is: Among them, m 石墨粒 is the total mass of graphite particles added, is the target carbon content of electroslag ingot, [%C] 电极 is the carbon content of the electrode, m 电极 is the mass of the electrode.

7. The method for preparing high nitrogen steel by pressurized electroslag remelting using carbon-containing nitrogen-enhanced slag system according to claim 1, characterized in that: In step 4, the speed of adding graphite particles is calculated as follows: Where, v is the speed of adding graphite particles, m 石墨粒 is the total mass of graphite particles added, and t is the pressurized gas phase nitriding time.

8. The method for preparing high nitrogen steel by pressurized electroslag remelting using carbon-containing nitrogen-enhanced slag system according to claim 1, characterized in that: In step 4, the nitrogen pressure for pressurized gas phase nitriding is: Among them, P N2 P is the nitrogen pressure for pressurized gas phase nitriding. 0 is the standard atmospheric pressure, [%N] is the target nitrogen content of the steel grade, T is the smelting temperature, The first-order interaction coefficient of element j on N, is the second-order interaction coefficient of element j on N, and [% j] is the content of element j in steel.

9. The method for preparing high nitrogen steel by pressurized electroslag remelting using carbon-containing nitrogen-enhanced slag system according to claim 1, characterized in that: The chemical composition of the high nitrogen steel electroslag ingot includes, by mass percentage, C: 0.10-1.50%, Si: ≤1.00%, Mn: ≤1.00%, Cr: 12.00-18.00%, Mo: ≤1.20%, Ni: ≤1.00%, N: 0.10-1.00%, V: ≤1.00%, S: ≤0.05%, P: ≤0.06% and the balance of Fe.

10. The method for preparing high nitrogen steel by pressurized electroslag remelting using carbon-containing nitrogen-enhanced slag system according to claim 1, characterized in that: Calculated by mass percentage, the chemical components of the carbon-containing and nitrogen-enriched slag include: CaF2: 52-57%, CaO: 25-29%, Al2O3: 13-17%, MgO: 2-5%, and C: 0.4-1.5%.

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