Electroslag smelting method of low-Si low-Al B-containing heat-resistant stainless steel

Abstract

The invention discloses an electroslag smelting method of low-Si low-Al B-containing heat-resistant stainless steel. According to the electroslag smelting method, the qualification rate of head and tail components of a steel ingot of an electric furnace casting rod after electroslag remelting reaches 100% through a quaternary slag system, and the sum of a fine system and a coarse system of non-metallic inclusions meets the requirement of not higher than grade 3; the thermal stress and phase change stress cracking of the steel ingot is prevented through stress relief annealing of the steel ingot, the tensile stress generated due to thermal expansion and cold contraction in the cooling process of the steel ingot and the phase change stress generated due to structural transformation are eliminated through the low-temperature annealing process, the steel ingot is prevented from cracking during long-time storage or saw cutting, many defects in the prior art are overcome, and the quality of the steel ingot is improved. The method has a remarkable industrial application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to an electroslag smelting method of low-Si low-Al B-containing heat-resistant stainless steel. BACKGROUND

[0002] In recent years, the nationwide power shortage caused by drought and high temperature. Therefore, the country will start three 8000 million kilowatt plans to be put into gradually, therefore no matter from the installed capacity and power generation, coal power unit is still the main power source of current China's power supply, plays a role in regulating, bottom protection in power supply. Coal power turbine is the core device of coal to electricity conversion, the higher the steam temperature, the higher the conversion efficiency. Therefore, the key materials of the turbine rotor, blade, cylinder and other materials are increasingly high. From the initial 12Cr heat-resistant steel, by adding various high-temperature strength elements such as Nb, W, Co, B to improve the temperature use limit of the material.

[0003] Low-Si low-Al B-containing heat-resistant stainless steel (such as FB2, Co3W3 and other materials) belongs to supercritical power generation key component steel, which was previously entirely dependent on imports, and now gradually realizes the production of domestic products. The process of domestic manufacturers in the development of FB2 material is not perfect, especially the yield of B is unstable, and some manufacturers even use electric furnace steel to replace electroslag steel to avoid the yield problem of Al, Si and B in the electroslag process, but also brings the quality risks of non-metallic inclusions and uneven composition.

[0004] Low-Si low-Al B-containing heat-resistant stainless steel (such as FB2, Co3W3 and other materials) adopts electric furnace steel ingot production, which often leads to unqualified non-metallic inclusions, and the use of electroslag steel ingot production is adopted to improve the purity of the material. FB2 material is prone to uneven B burning loss in the electroslag remelting process due to low Si and low Al, and the Si content and Al content will also rise due to the electroslag slag system, and finally the composition of Si, Al and B does not meet the standard requirements. After the electroslag of the steel ingot is completed, the risk of steel ingot burst will be caused by thermal stress and organizational stress in the cooling process.

[0005] Therefore, it is necessary to propose an electroslag smelting method of low-Si low-Al B-containing heat-resistant stainless steel to solve the problems in the prior art. SUMMARY

[0006] The purpose of the present application is to provide an electroslag smelting method of low-Si low-Al B-containing heat-resistant stainless steel to at least solve one of the above problems in the prior art.

[0007] Specifically, the scheme of the present application is as follows: An electroslag smelting method of low-Si low-Al B-containing heat-resistant stainless steel, comprising the following steps: S1. Controlling the mass percentage of each chemical component of the casting rod to internally control the elements Si, Al and B; S2. Scraping the surface of the casting rod to remove the oxide scale and oil stains; S3. Using the casting rod as an electrode for electroslag remelting, and the electroslag material used is composed of CaF2: 70-72%, Al2O3: 24-26%, CaO: 2-4%, and FeB: 0.3-0.6% by mass percentage; S4. Cooling the steel ingot obtained by electroslag remelting in the crystallizer for ≥60 min; S5. Furnace cooling the steel ingot after holding at 700-750°C for 15 h or more to obtain low-Si and low-Al B-containing heat-resistant stainless steel.

[0008] Further, the chemical components of the casting rod include, by mass percentage: 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%, and Sb: ≤0.0015%.

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

[0010] Further, in step S2, the electroslag material is baked in a heating furnace at 700°C for 6-8 h or more after being mixed according to the ratio.

[0011] Preferably, the electroslag material is lifted out of the heating furnace and used within 10 min, and is uniformly added by using a high-temperature slag adding machine, so that the slag material continuously melts in the crystallizer in a high-temperature state.

[0012] Preferably, FeB is added after the addition of other components in the electroslag material is completed and the electroslag material is in a liquid molten state.

[0013] Further, in step S2, an arc is started using a bottom pad of the same steel grade during electroslag remelting, and the thickness is 30-50 mm.

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

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

[0016] Another object of the present application is to provide a low-Si low-Al B-containing heat-resistant stainless steel material obtained by the electroslag refining method described above, and the head and tail composition qualification rate reaches 100% by the electroslag refining method, and the non-metallic inclusion fine / coarse system A+B+C+D is ≤3.0 level.

[0017] Compared with the prior art, the present application has the following beneficial effects: The electroslag refining method provided by the present application makes the head and tail composition qualification rate of the electroslag remelted electroslag ingot reach 100% by using a four-component slag system, and the non-metallic inclusion fine / coarse system meets the requirement of being less than 3 levels; stress relief annealing of the ingot prevents cracking of the ingot due to thermal stress and phase transformation stress, and eliminates the tensile stress generated by thermal expansion and contraction and the phase transformation stress generated by microstructure transformation during the cooling process of the ingot, thereby preventing cracking of the ingot during long-term storage or sawing, and solving many defects of the prior art, and having a significant industrial application prospect. DETAILED DESCRIPTION

[0018] The technical solutions of the present application will be described below in conjunction with preferred embodiments, obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0019] In one embodiment, an electroslag refining method of a low-Si low-Al B-containing heat-resistant stainless steel is provided, and the heat-resistant stainless steel contains the chemical components shown in Table 1:

[0020] The balance in Table 1 is Fe.

[0021] The electroslag refining method of the low-Si low-Al B-containing heat-resistant stainless steel includes the following production process flow: electroslag ingot - electroslag ingot sand wheel skinning - slag and electroslag preparation - electroslag remelting - electroslag ingot mold cooling - electroslag ingot annealing - electroslag ingot composition sampling - electroslag ingot composition inspection. Specifically as follows: 1. Electroslag ingot: electroslag ingot + secondary refining smelting process is adopted, and the composition meets the requirements of the electroslag ingot internal control range. The difficult-to-control elements require Si: 0.06-0.09%, Al: ≤0.010%, and B: 0.010-0.011%.

[0022] 2. Electroslag ingot sand wheel skinning: surface sand wheel skinning is not allowed to have oxide scale and oil stains.

[0023] 3. Slag and electroslag preparation: use the same steel grade bottom pad to start the arc, thickness 30-50mm, reduce the oxidation loss of Si, B and other components at the bottom of the ingot. After mixing according to the ratio, bake in the heating furnace for 700℃ for 6-8h or more, dry thoroughly to reduce the moisture in the slag. The electroslag adopts a mixed four-component slag system, the main components are CaF2: 70~72%, Al2O3: 24~26%, CaO: 2~4%, FeB: 0.3~0.6%.

[0024] 4. Electroslag remelting: 1) Put the electrode casting rod into the crystallizer before smelting, seal it well, and fill argon gas in the crystallizer to isolate air; 2) Good slag operation is the primary condition to ensure the uniformity of the composition at the bottom of the ingot. The slag is lifted out of the heating furnace and used within 10 minutes, and the high-temperature slag feeder is used to add it evenly, so that the slag can be continuously melted in the crystallizer at high temperature, reducing the risk of moisture absorption. After adding other slag, FeB is added separately in a special way. The FeB slag is evenly melted in the liquid molten slag, so that the components of the slag can be completely melted and evenly distributed; 3) According to the diameter of each ingot type, match the reasonable electroslag remelting process parameters, the melting speed is 0.6-0.8Dkg / h, and the actual situation is optimized and controlled. The diameter range of electroslag ingot 500- 1200mm.

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

[0026] 6. Ingot annealing: anneal at 700-750℃ for 15h or more in the low temperature section, and then cool in the furnace.

[0027] 7. Ingot composition sampling: drill samples at the head and tail of the ingot for full element analysis, use a 20mm diameter drill bit to take 20mm deep iron filings for detection. The large head is sampled at 7% position, and the small head is sampled at 6% position.

[0028] 8. Ingot acceptance: judge the surface quality and chemical composition of the ingot, and meet the standard requirements.

[0029] In the above examples, the head and tail components after electroslag remelting meet the requirements of Si: ≤0.1%, Al: ≤0.010%, B: 0.008-0.011%, and the yield of easily burned elements is controlled at more than 80%. The head and tail component qualification rate reaches 100%, and the non-metallic inclusion fine system / coarse system A+B+C+D is ≤3.0 level. The ingot is stress relieved by annealing to prevent cracking of the ingot due to thermal stress and phase transformation stress, and the tensile stress and phase transformation stress generated by thermal expansion and cold contraction during cooling of the ingot are eliminated by low temperature annealing (700-750°C) to prevent cracking of the ingot during long-term storage or sawing.

[0030] Example 1

[0031] An electroslag smelting method of a low-Si low-Al B-containing heat-resistant stainless steel includes the following steps: 1. Electrode furnace cast bar: prepared by using an electrode furnace + secondary refining smelting process 400mm cast bar, the composition meets the cast bar internal control range requirements. The specific chemical composition is as follows:

[0032] 2. Cast bar grinding wheel skinning: surface grinding wheel skinning, no oxide scale and oil stains are allowed.

[0033] 3. Slag and electroslag preparation: use the same steel grade bottom pad to start arcing, thickness 50mm, reduce the oxidation loss of Si, B and other components at the bottom of the ingot. After mixing the slag according to the proportion, bake it in the heating furnace for 8h at 700°C, dry it thoroughly to reduce the moisture in the slag. The electroslag adopts a mixed four-component slag system, and the composition is CaF2, Al2O3, CaO, FeB=71.6:25:3:0.4 by mass ratio.

[0034] 4. Electroslag remelting: 1) Before smelting, put the electrode cast bar into the crystallizer, seal it well, and fill argon gas in the crystallizer to isolate air.

[0035] 2) The slag is lifted out of the heating furnace and added uniformly within 10min, so that the slag continuously melts in the crystallizer at high temperature. After the addition of other slag is completed, FeB is added separately, and FeB slag is uniformly melted in liquid state, so that each component of the slag can be completely melted and uniformly distributed. The electrode melting speed during electroslag remelting is 300kg / h.

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

[0037] 6. Ingot annealing: annealing at a low temperature of 730°C for 15h and furnace cooling to obtain an electroslag ingot with a diameter of 500mm.

[0038] Example 2

[0039] The ESR method for smelting a low-Si low-Al B-containing heat-resistant stainless steel includes the following steps: 1. Electrode furnace casting rod: prepared by using an electrode furnace + secondary refining smelting process to obtain a 575 mm casting rod, the composition of which meets the internal control range requirements. The specific chemical composition is as follows:

[0040] 2. Casting rod grinding wheel skinning: surface grinding wheel skinning, and no oxide scale and oil stains are allowed.

[0041] 3. Slag and ESR preparation: the same steel grade bottom pad is used to start the arc, and the thickness is 40 mm, which reduces the oxidation loss of Si, B and other components at the bottom of the ingot. After the slag is mixed according to the ratio, it is baked in a heating furnace at 700°C for 8h to fully dry and reduce the moisture content of the slag. The ESR uses a mixed four-component slag system, and the composition is CaF2, Al2O3, CaO, FeB = 70.5:25.5:3.4:0.5 by mass ratio.

[0042] 4. ESR remelting: 1) Before smelting, the electrode casting rod is placed in the crystallizer, and after sealing, argon is filled in the crystallizer to isolate air.

[0043] 2) The slag is lifted out of the heating furnace and added uniformly within 10 min, so that the slag continuously melts in the crystallizer at high temperature. After the addition of other slag is completed, FeB is added separately, and the FeB slag is uniformly melted in the liquid molten slag, so that each component of the slag can be completely melted and uniformly distributed. The electrode melting speed during the ESR remelting process is 520 kg / h.

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

[0045] 6. Ingot annealing: a 740 mm diameter ingot is obtained by furnace cooling after annealing at 720°C for 20h in the low temperature section.

[0046] Example 3

[0047] The ESR method for smelting a low-Si low-Al B-containing heat-resistant stainless steel includes the following steps: 1. Electrode furnace casting rod: prepared by using an electrode furnace + secondary refining smelting process to obtain a 950 mm casting rod, the composition of which meets the internal control range requirements. The specific chemical composition is as follows:

[0048] 2. Casting rod grinding wheel skinning: surface grinding wheel skinning, and no oxide scale and oil stains are allowed.​

[0049] 3. Slag and ESR preparation: using the same steel grade bottom pad to start the arc, thickness 40 mm, reducing the oxidation loss of Si, B and other elements at the bottom of the ingot. After mixing the slag according to the ratio, bake it in the heating furnace at 700°C for 8h, dry it thoroughly to reduce the moisture in the slag. The ESR uses a mixed four-component slag system, with a composition of CaF2, Al2O3, CaO, FeB = 72:24.6:2.8:0.6 by mass.

[0050] 4. ESR remelting: 1) Before smelting, put the electrode casting rod into the crystallizer and seal it. Then fill argon gas into the crystallizer to isolate air.

[0051] 2) The slag is lifted out of the heating furnace and added uniformly within 10 minutes using a high-temperature slag adding machine, so that the slag continuously melts in the crystallizer at high temperature. After the addition of other slag, FeB is added separately. The FeB slag is uniformly melted in the liquid molten slag, so that each component of the slag can be completely melted and uniformly distributed. The electrode melting speed during ESR remelting is 850 kg / h.

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

[0053] 6. Ingot annealing: after annealing at 700°C for 18h in the low temperature section, the furnace is cooled to obtain an ingot with a diameter of 1185 mm.

[0054] Test Example

[0055] Sampling of the ingot composition obtained in Examples 1-3: full element analysis was performed on the samples drilled from the head and tail of the ingot, using a 20mm diameter drill bit to take a 20mm deep iron chip for testing. The sample was taken at the 7% position for the large head and at the 6% position for the small head.

[0056] The Si, Al, B content in the head and tail is as follows (%):

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

[0058] After ESR remelting, the head and tail composition meets the requirements of Si: ≤0.1%, Al: ≤0.010%, B: 0.008-0.011%, and the yield of easy loss elements is more than 80%. The non-metallic inclusion fine system / coarse system A + B + C + D is ≤3.0 grade. In addition, the ingots obtained in Examples 1-3 do not crack after 30 days of storage, and do not crack after sawing.

[0059] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. An electroslag refining method of a low Si low Al B-containing heat-resistant stainless steel, characterized by steps of The application relates to a heat-resistant stainless steel material and a preparation method thereof. S1. Controlling the mass percentage of each chemical component of the casting rod by electric furnace smelting, and internally controlling elements Si, Al and B; S2. Peeling the surface of the casting rod to remove the oxide skin and oil stains; S3. Taking the casting rod as an electrode to perform electroslag remelting, and adopting electroslag material with a composition of CaF2: 70-72%, Al2O3: 24-26%, CaO: 2-4% and FeB: 0.3-0.6% in percentage by mass; S4. Cooling the steel ingot obtained through electroslag remelting in a crystallizer for more than or equal to 60 min; The chemical components of the casting rod include the following in percentage by mass: 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 refining method according to claim 1, characterized in that, In step S1, the internal control requirements of Si, Al and B are as follows: Si: 0.06-0.09%, Al: <=0.010% and B: 0.010-0.011%.

3. The electroslag refining method according to claim 1, characterized by, In step S2, the electroslag material is mixed according to the proportion and baked in a heating furnace for more than or equal to 6-8 h at 700 DEG C.

4. The electroslag refining method according to claim 1, characterized by, The electroslag material is hoisted out from the heating furnace and used within 10 min, and is uniformly added by using a high-temperature slag adding machine, so that the slag material is continuously melted in the crystallizer in a high-temperature state.

5. The electroslag refining method according to claim 4, characterized in that, FeB in the electroslag material is added after other components are added and in a liquid molten state.

6. The electroslag refining method according to claim 4, characterized in that, In step S2, the same steel type bottom pad is used to start the arc during the electroslag remelting, and the thickness is 30-50 mm.

7. The electroslag refining method of claim 1, wherein, In step S2, inert gas protection is used during the electroslag remelting process.

8. The electroslag refining method of claim 1, wherein, In step S2, the electrode melting speed in the electroslag remelting process is (0.6-0.8)D kg / h, and D is the diameter of the electroslag ingot.

9. The electroslag refining method of claim 1, wherein, The heat-resistant stainless steel material obtained through the electroslag smelting method in any one of claims 1-9 has a 100% qualified rate of head and tail components, and non-metallic inclusion fine systems / coarse systems A+B+C+D are <=3.0 levels.

10. A low-Si low-Al B-containing heat-resistant stainless steel material characterized by comprising, in mass %, ​

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