Electroslag smelting method of low-si low-al b-containing heat-resistant stainless steel

Abstract

The application discloses a kind of low Si low Al B-containing heat-resistant stainless steel electric slag refining methods, the electric slag refining method is by quaternary slag system to make electric furnace cast bar after electric slag remelting The component qualification rate of ingot head and tail reaches 100%, and the sum of non-metallic inclusion fine system / coarse system meets the requirement of not higher than 3 levels;Through ingot stress relief annealing to prevent ingot thermal stress and phase transformation stress cracking, by low temperature annealing process to eliminate the tensile stress generated by thermal expansion and contraction during cooling and the phase transformation stress generated by structure transformation, prevent ingot cracking during long time storage or sawing, solve many defects of prior art, with significant industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to an electroslag smelting method for low-Si, low-Al, B-containing heat-resistant stainless steel. Background Technology

[0002] In recent years, nationwide power shortages have been caused by drought and high temperatures. Therefore, the government has launched three 80 million kilowatt projects, which will be put into operation successively. Thus, in terms of both installed capacity and power generation, coal-fired power units remain the main source of power supply in my country, playing a regulatory and safety net role in the power supply. The coal-fired steam turbine is the core device for converting coal into electricity; the higher the steam temperature, the higher the conversion efficiency. Therefore, the requirements for key materials of the steam turbine, such as rotors, blades, and cylinders, are becoming increasingly stringent. From the initial 12Cr heat-resistant steel, various elements that improve high-temperature strength, such as Nb, W, Co, and B, are added to improve the material's temperature performance limits.

[0003] Low-Si, low-Al, B-containing heat-resistant stainless steels (such as FB2 and Co3W3) are key components for ultra-supercritical thermal power generation. Previously, they were entirely dependent on imports, but domestic production is gradually being achieved. However, domestic manufacturers' processes for developing FB2 materials are not yet perfect, particularly regarding the unstable yield of B. Some manufacturers have even used electric furnace steel to replace electroslag steel to circumvent the Al, Si, and B yield issues encountered during the electroslag process, but this introduces quality risks such as non-metallic inclusions and uneven composition.

[0004] Low-Si, low-Al, and boron-containing heat-resistant stainless steels (such as FB2 and Co3W3) are often produced using electric furnace ingots, which frequently results in non-metallic inclusions that fail to meet standards. To improve material purity, electroslag remelting (ESR) ingots are used. Because of its low Si and low Al content, FB2 material is prone to uneven boron loss during ESR remelting, and the ESR slag system also leads to an increase in Si and Al content, ultimately resulting in Si, Al, and B composition that does not meet standard requirements. Furthermore, the ingots face a risk of cracking during cooling due to thermal and structural stresses after ESR.

[0005] Therefore, it is necessary to propose an electroslag remelting method for low-Si, low-Al, B-containing heat-resistant stainless steel to solve the problems mentioned above in the prior art. Summary of the Invention

[0006] The purpose of this invention is to provide an electroslag remelting method for low-Si, low-Al, B-containing heat-resistant stainless steel, so as to at least solve one of the above-mentioned problems in the prior art.

[0007] Specifically, the solution of the present invention is as follows: An electroslag remelting method for low-Si, low-Al, B-containing heat-resistant stainless steel, comprising the following steps: S1. By refining and controlling the mass percentage of each chemical component in the casting rod, internal control is exercised over the elements Si, Al, and B. S2. Peel off the surface of the casting rod to remove oxide scale and oil stains; S3. The cast rod is used as an electrode for electroslag remelting. The electroslag material used has the following composition by mass percentage: CaF2: 70~72%, Al2O3: 24~26%, CaO: 2~4%, FeB: 0.3~0.6%; S4. The steel ingot obtained by electroslag remelting is cooled in the crystallizer for ≥60 min; S5. After holding the steel ingot at 700-750℃ for more than 15 hours, furnace cooling is used to obtain low-Si, low-Al, B-containing heat-resistant stainless steel.

[0008] Further, the chemical composition of the cast rod, by mass percentage, includes: C: 0.12~0.15%, Si: ≤0.10%, Mn: 0.30~0.45%, P: ≤0.010%, S: ≤0.005%, Cr: 9.00~9.50%, Mo: 1.40~1.60%, Co: 1.10~1.30%, Ni: 0.10~0.20%, V: 0.15~0.25%, Nb: 0.040~0.060%, N: 0.015~0.030%, B: 0.008~0.011%, Cu: ≤0.15%, As: ≤0.020%, Sn: ≤0.015%, Al: ≤0.010%, Sb: ≤0.0015%.

[0009] Furthermore, in step S1, the internal control requirements for Si, Al, and B are as follows: Si: 0.06~0.09%, Al: ≤0.010%, B: 0.010~0.011%.

[0010] Furthermore, in step S2, the electroslag material is mixed according to the specified ratio and then baked in a heating furnace at 700°C for 6-8 hours or more.

[0011] Preferably, the electroslag material is lifted out of the heating furnace and put into use within 10 minutes, and is uniformly added using a high-temperature slag feeder, so that the slag material continuously melts in the crystallizer at a high temperature.

[0012] Preferably, FeB is added to the electroslag material after all other components have been added and the material is in a liquid molten state.

[0013] Furthermore, in step S2, an arc is initiated using a base pad of the same steel grade with a thickness of 30-50 mm during electroslag remelting.

[0014] Further, in step S2, the electrode melting rate during the electroslag remelting process is (0.6~0.8)D. kg / h, where D is the diameter of the electroslag steel ingot.

[0015] Furthermore, in step S2, an inert gas, such as argon, is used for protection during the electroslag remelting process.

[0016] Another objective of this invention is to provide a low-Si, low-Al, B-containing heat-resistant stainless steel material obtained by the electroslag smelting method described above. Through the electroslag smelting method, the head and tail component qualification rate reaches 100%, and the non-metallic inclusions fine / coarse series A+B+C+D ≤ 3.0 grade.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The electroslag remelting method provided by this invention achieves a 100% qualified rate of the head and tail components of the electric furnace casting rod after electroslag remelting through a quaternary slag system, and the fine / coarse non-metallic inclusions meet the requirement of being below level 3. Through stress-relief annealing of steel ingots, cracking caused by thermal stress and phase transformation stress of steel ingots is prevented. Through low-temperature annealing, tensile stress caused by thermal expansion and contraction and phase transformation stress caused by microstructure transformation of steel ingots during cooling are eliminated, preventing cracking of steel ingots during long-term storage or sawing. This method solves many defects of the prior art and has significant prospects for industrial application. Detailed Implementation

[0018] The technical solution of the present invention will now be clearly and completely described in conjunction with preferred embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] In one embodiment, an electroslag remelting method for low-Si, low-Al, B-containing heat-resistant stainless steel is proposed, wherein the chemical composition of the heat-resistant stainless steel is shown in Table 1.

[0020] The balance in Table 1 is Fe.

[0021] The electroslag remelting method for low-Si, low-Al, B-containing heat-resistant stainless steel includes the following steps: production process flow: electric furnace casting of ingots—scraping of ingots with grinding wheel—slag and electroslag preparation—electroslag remelting—ingot cooling—ingot annealing—ingot composition sampling—ingot composition testing. Details are as follows: 1. Electric furnace casting: The process employs an electric furnace combined with ladle refining to ensure the composition meets the internal control requirements for casting. Difficult-to-control elements are required to be: Si: 0.06~0.09%, Al: ≤0.010%, B: 0.010-0.011%.

[0022] 2. Removing the outer layer of the cast rod grinding wheel: Remove the outer layer of the grinding wheel surface, ensuring that there is no oxide scale or oil stains.

[0023] 3. Slag and Electroslag Remelting Preparation: Use a base pad of the same steel grade for arc initiation, 30-50mm thick, to reduce the oxidation loss of Si, B, and other components at the bottom of the steel ingot. After mixing the slag according to the formula, bake it in a heating furnace at 700℃ for 6-8 hours or more to fully dry it and reduce the moisture content. The electroslag remelting uses a mixed quaternary slag system, with the main components being CaF2: 70-72%, Al2O3: 24-26%, CaO: 2-4%, and FeB: 0.3-0.6%.

[0024] 4. Electroslag remelting: 1) Before smelting, place the electrode casting rod into the crystallizer, seal it, and then fill the crystallizer with argon gas to isolate it from air. 2) Good slag-forming operation is the primary condition for ensuring uniform composition at the bottom of the steel ingot. The slag material is lifted out of the heating furnace and put into use within 10 minutes. It is added evenly using a high-temperature slag feeder, so that the slag material is continuously melted in the crystallizer at high temperature, reducing the risk of moisture absorption. After other slag materials are added, FeB is added separately in a special way. FeB slag is uniformly melted in the liquid molten slag material, so that all components of slag material can be completely melted and uniformly melted. 3) Based on the diameter of each ingot, match appropriate electroslag remelting process parameters, with a melting rate of 0.6-0.8 kg / h as a reference, and optimize control according to actual conditions. Electroslag steel ingot diameter range 500- 1200mm.

[0025] 5. Ingot cooling: The ingot is cooled in the crystallizer for ≥60 minutes.

[0026] 6. Ingot annealing: The ingot is held at a low temperature of 700-750℃ for more than 15 hours and then furnace cooled.

[0027] 7. Steel Ingot Composition Sampling: A full elemental analysis was performed on samples from both the head and tail of the steel ingot. Iron filings were taken from a depth of 20mm using a 20mm diameter drill bit. Samples were taken from the larger end at the 7% mark and from the smaller end at the 6% mark.

[0028] 8. Steel ingot acceptance: The surface quality and chemical composition of the steel ingots are judged to ensure they meet the standard requirements.

[0029] In the above embodiments, the composition of the head and tail sections after electroslag remelting meets the requirements of Si: ≤0.1%, Al: ≤0.010%, and B: 0.008-0.011%, with the recovery rate of easily burnable elements controlled above 80%. The qualified rate of the head and tail components reaches 100%, and the non-metallic inclusions (fine / coarse series A+B+C+D) are ≤3.0 grade. Stress-relief annealing is performed on the steel ingot to prevent cracking due to thermal stress and phase transformation stress. Low-temperature annealing (700-750℃) eliminates the tensile stress generated by thermal expansion and contraction and the phase transformation stress generated by microstructure transformation during the cooling process, preventing cracking of the steel ingot during long-term storage or sawing.

[0030] Example 1

[0031] An electroslag remelting method for low-Si, low-Al, B-containing heat-resistant stainless steel includes the following steps: 1. Electric furnace cast rod: produced using an electric furnace + ladle refining process. The 400mm casting rod has a composition that meets the internal control requirements for casting rods. The specific chemical composition is as follows:

[0032] 2. Removing the outer layer of the cast rod grinding wheel: Remove the outer layer of the grinding wheel surface, ensuring that there is no oxide scale or oil stains.

[0033] 3. Slag and Electroslag Preparation: Use a base pad of the same steel grade for arc initiation, 50mm thick, to reduce the oxidation loss of Si, B, and other components at the bottom of the steel ingot. After mixing the slag according to the formula, bake it in a heating furnace at 700℃ for 8 hours to fully dry it and reduce the moisture content. The electroslag uses a mixed quaternary slag system with the composition in the mass ratio of CaF2, Al2O3, CaO, FeB = 71.6:25:3:0.4.

[0034] 4. Electroslag remelting: 1) Before smelting, place the electrode rod into the crystallizer, seal it, and fill the crystallizer with argon gas to isolate it from air.

[0035] 2) The slag material is controlled to be added within 10 minutes of being hoisted from the heating furnace and put into use. A high-temperature slag feeder is used for uniform addition, ensuring the slag material continuously melts at high temperatures within the crystallizer. After other slag materials are added, FeB is added separately. The FeB slag melts uniformly within the liquid molten slag material, ensuring complete and uniform melting of all slag components. The electrode melting rate during the electroslag remelting process is 300 kg / h.

[0036] 5. Ingot cooling: The ingot is cooled in the crystallizer for 60 minutes.

[0037] 6. Ingot annealing: After holding at 730℃ for 15 hours in a low-temperature section, the ingot is furnace cooled to obtain a diameter of [missing information]. 500mm electroslag steel ingot.

[0038] Example 2

[0039] An electroslag remelting method for low-Si, low-Al, B-containing heat-resistant stainless steel includes the following steps: 1. Electric furnace cast rod: produced using an electric furnace + ladle refining process. The 575mm casting rod has a composition that meets the internal control requirements for casting rods. The specific chemical composition is as follows:

[0040] 2. Removing the outer layer of the cast rod grinding wheel: Remove the outer layer of the grinding wheel surface, ensuring that there is no oxide scale or oil stains.

[0041] 3. Slag and Electroslag Preparation: Use a base pad of the same steel grade for arc initiation, 40mm thick, to reduce the oxidation loss of Si, B, and other components at the bottom of the steel ingot. After mixing the slag according to the formula, bake it in a heating furnace at 700℃ for 8 hours to fully dry it and reduce the moisture content. The electroslag uses a mixed quaternary slag system with the following composition by mass ratio: CaF2, Al2O3, CaO, FeB = 70.5: 25.5: 3.4: 0.5.

[0042] 4. Electroslag remelting: 1) Before smelting, place the electrode rod into the crystallizer, seal it, and fill the crystallizer with argon gas to isolate it from air.

[0043] 2) The slag material is controlled to be added within 10 minutes of being hoisted from the heating furnace and put into use. A high-temperature slag feeder is used for uniform addition, ensuring the slag material continuously melts at high temperatures within the crystallizer. After other slag materials are added, FeB is added separately. The FeB slag melts uniformly within the liquid molten slag material, ensuring complete and uniform melting of all slag components. The electrode melting rate during the electroslag remelting process is 520 kg / h.

[0044] 5. Ingot cooling: The ingot is cooled in the crystallizer for 100 minutes.

[0045] 6. Ingot annealing: After holding at 720℃ for 20 hours in a low-temperature section, the ingot is furnace cooled to obtain a diameter of [missing information]. 740mm steel ingot.

[0046] Example 3

[0047] An electroslag remelting method for low-Si, low-Al, B-containing heat-resistant stainless steel includes the following steps: 1. Electric furnace cast rod: produced using an electric furnace + ladle refining process. The 950mm casting rod has a composition that meets the internal control requirements for casting rods. The specific chemical composition is as follows:

[0048] 2. Removing the outer layer of the cast rod grinding wheel: Remove the outer layer of the grinding wheel surface, ensuring that there is no oxide scale or oil stains.

[0049] 3. Slag and Electroslag Preparation: Use a base pad of the same steel grade for arc initiation, 40mm thick, to reduce the oxidation loss of Si, B, and other components at the bottom of the steel ingot. After mixing the slag according to the formula, bake it in a heating furnace at 700℃ for 8 hours to fully dry it and reduce the moisture content. The electroslag uses a mixed quaternary slag system with the following composition by mass ratio: CaF2, Al2O3, CaO, FeB = 72:24.6:2.8:0.6.

[0050] 4. Electroslag remelting: 1) Before smelting, place the electrode rod into the crystallizer, seal it, and fill the crystallizer with argon gas to isolate it from air.

[0051] 2) The slag material is controlled to be added within 10 minutes of being hoisted from the heating furnace and put into use. A high-temperature slag feeder is used for uniform addition, ensuring the slag material continuously melts at high temperatures within the crystallizer. After other slag materials are added, FeB is added separately. The FeB slag melts uniformly within the liquid molten slag material, ensuring complete and uniform melting of all slag components. The electrode melting rate during the electroslag remelting process is 850 kg / h.

[0052] 5. Ingot cooling: The ingot is cooled in the crystallizer for 240 minutes.

[0053] 6. Ingot annealing: After holding at 700℃ for 18 hours in a low-temperature section, the ingot is furnace cooled to obtain a diameter of [missing information]. 1185mm steel ingot.

[0054] Test case

[0055] Sampling of the steel ingot composition obtained in Examples 1-3 above: Full elemental analysis was performed on drill samples from both the head and tail of the steel ingot. Iron filings were taken from a depth of 20mm using a 20mm diameter drill bit. Samples were taken from the larger end at the 7% position and from the smaller end at the 6% position.

[0056] The percentages (%) of Si, Al, and B at the head and tail ends are as follows:

[0057] The quality level (grade) of non-metallic inclusions is tested as follows:

[0058] After electroslag remelting, the composition of the head and tail sections meets the requirements of Si: ≤0.1%, Al: ≤0.010%, and B: 0.008-0.011%, with a recovery rate of over 80% for easily burnable elements. The non-metallic inclusions (fine / coarse series A+B+C+D) are ≤3.0 grade. Furthermore, the steel ingots obtained in Examples 1-3 do not crack after 30 days of storage, nor do they crack after sawing.

[0059] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for electroslag refining of low-Si, low-Al, B-containing heat-resistant stainless steel, characterized in that the steps include... include: S1. Control the mass percentage of each chemical component in the cast rod through electric furnace smelting, and internally control the elements Si, Al, and B. S2. Peel off the surface of the casting rod to remove oxide scale and oil stains; S3. The cast rod is used as an electrode for electroslag remelting. The electroslag material used has the following composition by mass percentage: CaF2: 70~72%, Al2O3: 24~26%, CaO: 2~4%, FeB: 0.3~0.6%; S4. The steel ingot obtained by electroslag remelting is cooled in the crystallizer for ≥60 min; S5. After holding the steel ingot at 700-750℃ for more than 15 hours, it is then furnace cooled and removed from the furnace. The chemical composition of the cast rod, by mass percentage, includes: C: 0.12~0.15%, Si: ≤0.10%, Mn: 0.30~0.45%, P: ≤0.010%, S: ≤0.005%, Cr: 9.00~9.50%, Mo: 1.40~1.60%, Co: 1.10~1.30%, Ni: 0.10~0.20%, V : 0.15~0.25%, Nb: 0.040~0.060%, N: 0.015~0.030%, B: 0.008~0.011%, Cu: ≤0.15%, As: ≤0.020%, Sn: ≤0.015%, Al: ≤0.010%, Sb: ≤0.0015%.

2. The electroslag remelting method according to claim 1, characterized in that, In step S1, the internal control requirements for Si, Al, and B are as follows: Si: 0.06~0.09%, Al: ≤0.010%, B: 0.010~0.011%.

3. The electroslag remelting method according to claim 1, characterized in that, In step S3, the electroslag material is mixed according to the formula and then baked in a heating furnace at 700°C for 6-8 hours or more.

4. The electroslag remelting method according to claim 3, characterized in that, The electroslag material is lifted out of the heating furnace and put into use within 10 minutes. It is added evenly using a high-temperature slag feeder so that the electroslag material continuously melts in the crystallizer at a high temperature.

5. The electroslag remelting method according to claim 3, characterized in that, FeB is added to the electroslag material after all other components have been added and the material is in a liquid molten state.

6. The electroslag remelting method according to claim 1, characterized in that, In step S3, an arc is initiated using a base pad of the same steel grade with a thickness of 30-50 mm during electroslag remelting.

7. The electroslag remelting method according to claim 1, characterized in that, In step S3, the electrode melting rate during electroslag remelting is (0.6~0.8)D*kg / h, where D is the diameter of the electroslag steel ingot.

8. The electroslag remelting method according to claim 1, characterized in that, In step S3, an inert gas is used for protection during the electroslag remelting.

9. A low-Si, low-Al, B-containing heat-resistant stainless steel material, characterized in that, Obtained by the electroslag smelting method according to any one of claims 1-8, the heat-resistant stainless steel material has a head and tail composition qualification rate of 100%, and the non-metallic inclusions fine / coarse series A+B+C+D series ≤ 3.0 grade.

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