Smelting method of clean high-chromium martensitic stainless steel

Abstract

The invention provides a smelting method of clean high-chromium martensitic stainless steel, silicon, aluminum and oxygen are controlled in the whole process, and clean smelting of the high-chromium martensitic stainless steel containing less than or equal to 0.05% of Si, less than or equal to 0.01% of Al and easy-to-oxidize elements such as B / Nb is realized, and the smelting method comprises the following steps: putting raw materials into an electric furnace for crude smelting according to main components of the high-chromium martensitic stainless steel; the produced steel material enters an AOD furnace to be subjected to oxidation period treatment and reduction period treatment; lime and chromium are added in the oxidation period according to the lower limit of stainless steel components; an aluminum ingot is used as a deoxidizer in the reduction period, and Si is controlled to be smaller than or equal to 0.05% in The steel material produced by reduction is put in an LF furnace for refining, and Al is controlled in the process; obtained refining slag, auxiliary materials containing lime and alloy and steel slag friends are mixed for slagging, and Al in outbound molten steel is 0.02-0.03%; produced molten steel enters a VD furnace for refining, and is kept at a certain ultimate vacuum degree; and the produced molten steel is poured, and the electrode bar is subjected to electroslag ingot remelting in a protective atmosphere electroslag furnace. The method is simple in process and low in cost.

Description

Technical Field

[0001] The invention belongs to the technical field of high chromium martensitic stainless steel, and in particular relates to a smelting method of clean high chromium martensitic stainless steel with Si≤0.05% and Al≤0.01%, which is suitable for industrial smelting of high chromium martensitic stainless steel with [Si]≤0.05% and [Al]≤0.01% and high chromium martensitic stainless steel with high cleanliness requirements, strict non-metallic inclusion requirements and low oxygen content requirements. Background Art

[0002] With the development of the energy industry, materials are constantly updated and the industry's demand for materials is getting higher and higher. Materials that add cobalt (Co), tungsten (W), vanadium (V), niobium (Nb), nitrogen (N), boron (B) and other elements to the traditional Cr12 martensitic steel are widely used in ultra-supercritical steam turbine units because of their good thermal strength, high creep strength and excellent high-temperature corrosion resistance. The typical use is the last stage blades of the steam turbine. Among them, typical materials include high-purity 2Cr12Ni4Mo3VNbN steel for the last stage large blade steel, 10Cr11Co3W3NiMoVNbNB steel for ultra-supercritical steam turbines, 13Cr9Mo1Co1NiVNbNB (or 13Cr9Mo2Co1NiVNbNB or FB2) steel, etc.

[0003] Silicon (Si) and aluminum (Al) are commonly used deoxidizers in the steelmaking process. Si≤0.05%, Al≤0.01%. In order to ensure the purity of the steel, the content of Si and Al elements must be ensured. This process is very difficult. The traditional smelting process uses "vacuum induction furnace + electroslag", and the ingredients of this process use precious metals and pure iron to ensure the content of Si and Al and the purity of the material. This smelting method has high ingredient costs, strict requirements on the purity of raw materials, and slow production rhythm, which restricts the development of such high-end materials. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a method for smelting clean high chromium martensitic stainless steel, which smelts clean high chromium martensitic stainless steel with [Si]≤0.05%, [Al]≤0.01%, and the finished product can achieve composition control of [Si]≤0.05%, [Al]≤0.01% and high purity control of molten steel, and the cost is low.

[0005] The present invention provides a method for smelting clean high-chromium martensitic stainless steel, comprising the following steps:

[0006] S1. According to the main components of high chromium martensitic stainless steel, the raw materials are placed in an electric furnace for rough refining, and the silicon content in the output steel is controlled to be ≤0.20%;

[0007] S2, the steel produced by the electric furnace is put into the AOD furnace for oxidation treatment and reduction treatment; in the oxidation treatment, lime is added into the furnace, the chromium content is added according to the lower limit of the stainless steel composition, and the content of other elements is added according to the upper limit of the stainless steel composition, and the amount of lime added is controlled according to the ternary basicity of the slag being 2.0-3.0; the reduction treatment includes the first reduction and the second reduction in sequence, and aluminum ingots are used as deoxidizers for all of them, and the silicon content is controlled to be ≤0.05%;

[0008] S3, placing the steel produced by the second reduction in an LF furnace, heating and refining, removing slag, and the steel liquid level is 1 / 2 of the ladle; mixing the obtained refined slag, auxiliary materials including lime and alloy, and steel slag to make slag, wherein the amount of lime is controlled according to the ternary basicity of the slag being 3.0-4.0, and the content of the obtained slag components is controlled to be CaO55%-65%, Al2O3 25%-35%, SiO2≤8%, and the aluminum content in the outgoing steel liquid is 0.02-0.03%;

[0009] S4, the molten steel produced by the LF furnace is put into a VD furnace for refining, and maintained under the condition of ultimate vacuum degree ≤ 67Pa for a time ≥ 25 minutes;

[0010] S5, pouring the molten steel produced by the VD furnace, remelting the obtained electrode rod in an electroslag ingot in a protective atmosphere electroslag furnace to obtain clean high-chromium martensitic stainless steel with Si≤0.05% and Al≤0.01%.

[0011] According to an embodiment of the smelting method of the present invention, a 40-ton electric furnace is used in step S1; and / or a 40-ton AOD furnace is used in step S2.

[0012] According to an embodiment of the smelting method of the present invention, in the step S2, the first reduction includes: adding aluminum ingots according to the ternary basicity of the slag of 2.0-3.0, and when the composition meets the requirements of Al≤0.01% and Si≤0.05%, removing 1 / 3 of the slag to see the steel liquid surface.

[0013] According to an embodiment of the smelting method of the present invention, in the step S2, the second reduction includes: adding lime and aluminum ingots, the amounts of the lime and aluminum ingots are controlled according to the ternary basicity of the slag of 3.0-5.0, and the aluminum content in the output steel is controlled to be ≤0.015%.

[0014] According to an embodiment of the smelting method of the present invention, in step S2, fluorite is further added in both the first reduction and the second reduction.

[0015] According to an embodiment of the smelting method of the present invention, a 40-ton LF furnace is used in step S3; the alloy includes nickel plate, ferroniobium, ferrovanadium, ferromolybdenum and metallic manganese.

[0016] According to an embodiment of the smelting method of the present invention, a 40-ton VD furnace is used in step S4.

[0017] According to an embodiment of the smelting method of the present invention, in the step S5, the calming time of the pouring is 30 minutes of soft argon blowing time.

[0018] According to an embodiment of the smelting method of the present invention, a 3.0-ton protective atmosphere electric slag furnace is used in step S5; the remelting slag system is CaF2 55-65%, Al2O3 20-30%, and CaO 8-18%.

[0019] According to an embodiment of the smelting method of the present invention, the lime in the raw materials and auxiliary materials is 95% CaO; the steel slag contains 15% Al2O3 and 55% Al; and the purity of the aluminum ingot is 98%.

[0020] Compared with the prior art, the smelting method of clean high chromium martensitic stainless steel with Si≤0.05% and Al≤0.01% provided by the present invention mainly adopts a specific electric furnace roughing, AOD furnace oxidation and reduction treatment, LF furnace refining and VD furnace refining, and protective atmosphere electric slag furnace remelting smelting process. The present invention realizes the control of Si and Al components and high purity of molten steel through certain oxygen control, silicon control, aluminum control and slag control technologies. The embodiment of the present invention realizes the control of finished product [Si]≤0.05%, [Al]≤0.01%, and the molten steel is of high purity ([O]≤0.0025%, non-metallic inclusions A coarse system≤0.5 level, B coarse system≤0.5 level, C coarse system≤0.5 level, D coarse system≤0.5 level, A fine system≤0.5 level, B fine system≤1.0 level, C fine system≤0.5 level, D fine system≤1.0 level, Ds class≤1.0 level, A coarse system+B coarse system+C coarse system+D coarse system+A fine system+B fine system+C fine system+D fine system+Ds class≤2.5 level). The present invention has simple process, convenient control, low cost, strong practicality and good application prospect. DETAILED DESCRIPTION

[0021] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the technical scheme of the present invention is now described in detail below in conjunction with specific embodiments. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0022] The present invention provides a method for smelting clean high-chromium martensitic stainless steel, comprising the following steps:

[0023] S1. According to the main components of high chromium martensitic stainless steel, the raw materials are placed in an electric furnace for rough refining, and the silicon content in the output steel is controlled to be ≤0.20%;

[0024] S2, the steel produced by the electric furnace is put into the AOD furnace for oxidation treatment and reduction treatment; in the oxidation treatment, lime is added into the furnace, the chromium content is added according to the lower limit of the stainless steel composition, and the content of other elements is added according to the upper limit of the stainless steel composition, and the amount of lime added is controlled according to the ternary basicity of the slag being 2.0-3.0; the reduction treatment includes the first reduction and the second reduction in sequence, and aluminum ingots are used as deoxidizers for all of them, and the silicon content is controlled to be ≤0.05%;

[0025] S3, placing the steel produced by the second reduction in an LF furnace, heating and refining, removing 1 / 2 of the slag to see the molten steel surface; mixing the obtained refined slag, auxiliary materials including lime and alloy, and steel slag to make slag, wherein the amount of lime is controlled according to the ternary basicity of the slag being 3.0-4.0, and the content of the obtained slag components is controlled to be CaO 55%-65%, Al2O3 25%-35%, SiO2≤8%, and the aluminum content in the outgoing molten steel is 0.02-0.03%;

[0026] S4, the molten steel produced by the LF furnace is put into a VD furnace for refining, and maintained under the condition of ultimate vacuum degree ≤ 67Pa for a time ≥ 25 minutes;

[0027] S5, pouring the molten steel produced by the VD furnace, remelting the obtained electrode rod in an electroslag ingot in a protective atmosphere electroslag furnace to obtain clean high-chromium martensitic stainless steel with Si≤0.05% and Al≤0.01%.

[0028] The smelting method of the present invention can smelt clean high-chromium martensitic stainless steel with [Si]≤0.05% and [Al]≤0.005%. The finished product can achieve component control of [Si]≤0.05% and [Al]≤0.005% and high purity control of molten steel, and the process is simple and the cost is low.

[0029] According to the main components of high chromium martensitic stainless steel, the raw materials are placed in an ordinary steelmaking electric furnace (such as a 40-ton electric furnace) for rough refining, and the steel tapping temperature can be 1665-1685° C. The silicon [Si] of the steel tapping is controlled to be ≤0.20%, and the chromium [Cr] element content can be 2.0-10.0%, such as 2.90-9.20%.

[0030] Afterwards, the embodiment of the present invention can use a 40-ton AOD furnace (argon oxygen decarburization refining furnace) to perform AOD smelting (which uses oxygen to react with carbon to generate heat, oxygen and argon to stir the molten steel, and achieve the corresponding refining purpose through oxidation period, reduction period, etc.). After entering the tank, the embodiment of the present invention flows (slags) cleanly, and the amount of molten steel can be 30 to 50 tons, and further 34 to 40 tons. The oxidation period treatment and reduction period treatment in the AOD furnace include:

[0031] (1) Oxidation period (mainly blowing oxygen, adding lime, etc. into the furnace): the Cr content is added according to the lower limit of the chromium component of the stainless steel material design, and the content of other elements is added according to the upper limit of the material design component (such as adding high carbon ferrochrome, etc.). The amount of lime added is controlled according to the ternary basicity R of the slag being 2.0 to 3.0. The temperature of the oxidation period can be 1630 to 1650°C;

[0032] Wherein, the ternary basicity R=CaO wt% / (SiO2 wt%+(Al2O3 wt%÷3)), the same below;

[0033] (2) Reduction period (mainly blowing argon gas, adding lime, deoxidizer, etc.): secondary reduction is preferred, i.e., including the first reduction and the second reduction; aluminum ingots (Al ingots) are used as deoxidizers for deoxidation reduction, and the process controls Si, [Si] ≤ 0.05%; the embodiment of the present invention also adds an appropriate amount of fluorite to increase the fluidity of molten steel, etc.

[0034] The secondary reduction described in the preferred embodiment of the present invention comprises:

[0035] (a) Primary reduction: Add Al ingots, with the amount of Al controlled according to the ternary basicity R of the slag being 2.0-3.0. Smelt for 5-8 minutes, take samples for analysis, and when the composition meets the requirements of [Al]≤0.005%, [Si]≤0.04%, remove 1 / 3 of the slag to see the molten steel surface;

[0036] (b) Secondary reduction: add lime and Al ingots. The amount of lime and Al is adjusted according to the ternary basicity R of the slag of 3.0 to 5.0. The smelting time is 3 to 5 minutes. The molten steel [Al] is controlled to be ≤0.015% when tapping.

[0037] After steel is tapped, the embodiment of the present invention can use a 40-ton LF furnace (ladle furnace) for LF furnace refining. Specifically, it includes: heating, slag removal, process control Al, 1 / 2 of the ladle sees the steel liquid level, and controls the [Al] in the steel liquid to 0.02-0.05%; making new slag, adding slag auxiliary materials, and controlling the amount of lime and Al according to the ternary basicity R of the slag of 3.0-4.0. The target slag composition control range is calcium oxide (CaO): 55%-65%; aluminum oxide (Al2O3): 25%-35%; silicon dioxide (SiO2) ≤8%, the element composition in the steel liquid meets the material setting target, and argon is stirred for 5-8 minutes; [Al] in the steel liquid out of the station: 0.020-0.030%.

[0038] In the LF furnace smelting process of the embodiment of the present invention, it is preferred to add fluorite and then heat up to 1580°C, remove slag, 1 / 2 of the ladle shows the molten steel level, and adjust [Al] in the molten steel to 0.02%. The purpose of LF slag making is desulfurization, deoxidation, improving alloy yield, removing inclusions, etc.; transfer to the LF furnace heating station, add lime and refined slag, heat up and slag, slag slag is completed, add alloy (including nickel plate, ferroniobium, ferrovanadium, ferromolybdenum and metallic manganese, etc.), fine-tune the chemical composition, add steel slag (composite deoxidizer) in batches, and then heat up.

[0039] In a specific embodiment of the present invention, among the raw materials and auxiliary materials, the lime is 95% pure CaO; the aluminum ingot is 98% pure Al ingot; the steel slag contains 15% Al2O3 and 55% Al. In addition, the high carbon ferrochrome involved in the embodiment contains 55% Cr, and the ferrotungsten contains 80% W; it also involves: cobalt plate (98% Co), nickel plate (99% Ni), ferromolybdenum (60% Mo), ferrovanadium (80% V), ferroniobium (65% Nb), and ferroboron (20% B).

[0040] The embodiment of the present invention is converted to a VD station, and a 40-ton VD furnace (vacuum refining furnace) can be used for refining: under the condition of ultimate vacuum degree ≤ 67 Pa, the holding time is ≥ 25 minutes. Break the vacuum, pour calm, soft blowing argon time is preferably 30 minutes, and pour the electrode rod.

[0041] In some preferred embodiments, a 3.0-ton protective atmosphere electroslag furnace is used to remelt the electroslag ingot in the protective atmosphere electroslag furnace, and the oxygen concentration in the electroslag furnace is lower than 1000ppm, so as to obtain clean high-chromium martensitic stainless steel with Si≤0.05% and Al≤0.01%; the remelted slag system uses CaF2 55-65%, Al2O3 20-30%, and CaO 8-18%. In addition, the embodiments of the present invention are not limited by the pipe making equipment and the rod specifications.

[0042] The embodiment of the present invention provides a smelting method for clean high-chromium martensitic stainless steel with Si≤0.05% and Al≤0.01%, adopting the "electric furnace + AOD + LF + VD + protective atmosphere electric slag furnace" process, through the silicon controlled aluminum controlled oxygen controlled slag control technology, to achieve [Si]≤0.05%, [Al]≤0.01% composition control and high purity control of molten steel. The metallurgical quality levels of some finished forgings include: [O] ≤ 0.0025%; non-metallic inclusions: Class A coarse series ≤ 0.5 level, Class B coarse series ≤ 0.5 level, Class C coarse series ≤ 0.5 level, Class D coarse series ≤ 0.5 level, Class A fine series ≤ 0.5 level, Class B fine series ≤ 1.0 level, Class C fine series ≤ 0.5 level, Class D fine series ≤ 1.0 level, Class Ds ≤ 1.0 level, Class A coarse series + Class B coarse series + Class C coarse series + Class D coarse series + Class A fine series + Class B fine series + Class C fine series + Class D fine series + Class Ds ≤ 2.5 level.

[0043] In order to further understand the present invention, the smelting method provided by the present invention is described in detail below in conjunction with the examples, and the protection scope of the present invention is not limited by the following examples. In the examples, each raw reagent and material can be obtained commercially, and the experimental method without specifying the specific experimental conditions is a conventional method and condition known in the art. Unless otherwise specified, all are mass ratios.

[0044] Among the raw materials and auxiliary materials, the lime is 95% pure CaO; the aluminum ingot is 98% pure Al ingot; the steel slag contains 15% Al2O3 and 55% Al. In addition, the high carbon ferrochrome involved in the embodiment contains 55% Cr, and the ferrotungsten contains 80% W; it also involves: cobalt plate (98% Co), nickel plate (99% Ni), ferromolybdenum (60% Mo), ferrovanadium (80% V), ferroniobium (65% Nb), and ferroboron (20% B). The electric furnace, AOD furnace, LF furnace, and VD furnace are all 40 tons; and a 3.0-ton protective atmosphere electric slag furnace is used.

[0045] Example 1: High purity 2Cr12Ni4Mo3VNbN steel used for the final large blade steel

[0046] (I) Electric furnace steelmaking:

[0047] The main element composition of the steel is shown in Table 1, and the steel tapping temperature is 1683℃.

[0048] Table 1 Main element steel composition of electric furnace (Wt%)

[0049] element C Mn Si P S Cr Ni Mo V Nb Analytical Value 1.05 0.12 0.16 0.012 0.035 2.90 3.50 0.89 0.01 0.001

[0050] (II) AOD smelting:

[0051] 1. Entering the tank: the slag flow (slagging) is clean, and the amount of molten steel is 34 tons.

[0052] 2. Oxidation period: 2000Kg of lime, blowing, adding 6200Kg of high carbon ferrochrome, 1450Kg of ferromolybdenum, temperature 1630℃.

[0053] 3. Restoration period:

[0054] 3.1 Primary reduction: Add 360 kg aluminum ingot and 300 kg fluorite, smelt for 6 minutes, take samples, and analyze the main element composition as shown in Table 2. The slag composition is shown in Table 3.

[0055] 3.2 Flow slag, remove slag, and the steel liquid level can be seen at 1 / 3 of the furnace.

[0056] Table 2 AOD primary reduction main element composition (Wt%)

[0057] element C Mn Si P S Cr Ni Mo V Nb Al Analytical Value 0.02 0.09 0.03 0.012 0.033 9.95 3.05 2.88 0.03 0.001 0.001

[0058] Table 3 AOD primary reduction slag composition (Wt%)

[0059] Slag components CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[R=CaO / (SiO2+1 / 3×Al2O3)]]> Analytical Value 57％ 19％ 24％ 2.1

[0060] 3.3 Secondary reduction: add 1200 kg of lime, 300 kg of fluorite powder, 400 kg of high carbon ferrochrome, and 40 kg of aluminum ingots, smelt for 3 minutes, and analyze the main element composition as shown in Table 4. The slag composition is shown in Table 5.

[0061] 4. Steel production.

[0062] Table 4 AOD secondary reduction main element composition (Wt%)

[0063] element C Mn Si P S Cr Ni Mo V Nb N Al Analytical Value 0.07 0.12 0.04 0.012 0.020 10.60 3.05 2.80 0.03 0.005 0.021 0.005

[0064] Table 5 AOD secondary reduction slag composition (Wt%)

[0065] Slag components CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[R=CaO / (SiO2+1 / 3×Al2O3)]]> Analytical Value 74％ 13％ 13％ 4.3

[0066] (III) LF furnace smelting

[0067] 1. Add 200kg of fluorite, raise the temperature to 1580℃, remove the slag, and make sure that 1 / 2 of the ladle is above the molten steel surface. Adjust the [Al] content in the molten steel to 0.02%.

[0068] 2. Transfer to the LF furnace heating station, add 800kg of lime and 360kg of refined slag, heat up and slag, and when slag is finished, add alloy (230kg of nickel plate, 110kg of ferroniobium, 145kg of ferrovanadium, 320kg of ferromolybdenum, 100kg of metallic manganese, 480kg of high carbon ferrochrome, and 150kg of metallic chromium), fine-tune the chemical composition, and add steel slag in batches. The total amount of steel slag is 230kg.

[0069] 3. Raise the temperature to 1680°C, take samples and analyze the main element composition. The main element composition is shown in Table 6, and the slag composition is shown in Table 7.

[0070] 4. Raise the temperature to 1700℃, feed 75 meters of Al wire, remove the slag, and when 1 / 3 of the steel liquid is visible in the ladle, transfer to the VD station.

[0071] Table 6 LF main element composition (Wt%)

[0072] element C Mn Si P S Cr Ni Mo V Nb N Al Analytical Value 0.16 0.35 0.04 0.014 0.005 10.90 3.65 3.04 0.34 0.15 0.025 0.025

[0073] Table 7 LF slag composition (Wt%)

[0074] Slag components CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[R=CaO / (SiO2+1 / 3×Al2O3)]]> Analytical Value 63％ 7％ 30％ 3.7

[0075] (IV) VD furnace smelting

[0076] Under the condition of ultimate vacuum degree ≤ 67Pa, the time was maintained for 25 minutes, the vacuum was broken, 480kg of chromium nitride was added, and the main element composition was analyzed by sampling. The main element composition was shown in Table 8. The vacuum was calmed, the soft argon blowing time was 30 minutes, and the electrode rod was cast.

[0077] Table 8 Main element composition of VD (Wt%)

[0078] element C Mn Si P S Cr Ni Mo V Nb N Al Analytical Value 0.18 0.35 0.04 0.014 0.002 11.60 3.64 3.03 0.34 0.14 0.075 0.008

[0079] (V) Protective atmosphere electroslag remelting

[0080] The slag system adopts CaF2: 60%, Al2O3: 30%, and CaO: 10%.

[0081] The metallurgical quality level of finished forgings is tested for non-metallic inclusions according to GB / T10561, as shown in Table 9.

[0082] Table 9 Purity of finished forgings

[0083]

[0084] The traditional smelting process adopts "vacuum induction furnace + electroslag". The ingredients of this process are 100% precious metals (cobalt plate (98% Co), nickel plate (99% Ni), ferromolybdenum (60% Mo), ferrovanadium (80% V), ferroniobium (65% Nb)) and pure iron. It has high requirements for raw materials, and the cost of using all-metal materials and pure iron is relatively high.

[0085] The main feature of the process of this application is that Si and Al are extremely low, and it contains Nb, B and other easily burnt elements; its material requires low Si and Al content, and through a certain smelting process, it ensures that the molten steel is well deoxidized, thereby obtaining a high-purity product and reducing costs.

[0086] Example 2: 10Cr11Co3W3NiMoVNbNB steel for ultra-supercritical steam turbine

[0087] (I) Electric furnace steelmaking:

[0088] The main element composition of the steel is shown in Table 10, and the steel tapping temperature is 1665℃.

[0089] Table 10 Main element steel composition of electric furnace (Wt%)

[0090] element C Mn Si P S Cr Ni Mo V Nb Co W Analytical Value 0.98 0.17 0.19 0.014 0.020 9.20 0.41 0.14 0.06 0.01 1.35 1.00

[0091] (II) AOD smelting:

[0092] 1. Entering the tank: the slag flow (slagging) is clean, and the amount of molten steel is 40 tons.

[0093] 2. Oxidation period: 2000Kg lime, blowing, 1400Kg high carbon ferrochrome, 700Kg cobalt plate, temperature 1648℃.

[0094] 3. Restoration period:

[0095] 3.1 Primary reduction: Add 480 kg of aluminum ingots and 300 kg of fluorite, smelt for 6 minutes, take samples, and analyze the main element composition as shown in Table 11. The slag composition is shown in Table 12.

[0096] Table 11 AOD primary reduction main element composition (Wt%)

[0097] element C Mn Si P S Cr Ni Mo V Nb Co W Analytical Value 0.033 0.16 0.02 0.014 0.009 11.20 0.44 0.14 0.03 0.002 2.85 1.08

[0098] Table 12 AOD primary reduction slag composition (Wt%)

[0099] Slag components CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[R=CaO / (SiO2+1 / 3×Al2O3)]]> Analytical Value 60％ 20％ 27％ 2.1

[0100] 3.2 Flow slag, remove slag, and the steel liquid level can be seen at 1 / 3 of the furnace.

[0101] 3.3 Secondary reduction: add 600 kg of lime, 200 kg of fluorite powder, and 40 kg of aluminum ingots, smelt for 3 minutes, and analyze the main element composition as shown in Table 13. The slag composition is shown in Table 14.

[0102] 4. Steel production.

[0103] Table 13 AOD secondary reduction main element composition (Wt%)

[0104] element C Mn Si P S Cr Ni Mo V Nb Co W Analytical Value 0.04 0.16 0.02 0.014 0.010 11.12 0.43 0.14 0.03 0.002 2.85 1.08 element Al N B Analytical Value 0.005 0.035 /

[0105] Table 14 AOD secondary reduction slag composition (Wt%)

[0106] Slag components CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[R=CaO / (SiO2+1 / 3×Al2O3)]]> Analytical Value 67％ 15％ 18％ 3.2

[0107] (III) LF furnace smelting

[0108] 1. Add 200kg of fluorite, raise the temperature to 1580℃, remove the slag, and make sure that 1 / 2 of the ladle is above the molten steel surface. Adjust the [Al] content in the molten steel to 0.02%.

[0109] 2. Transfer to the LF furnace heating station, add 800kg of lime and 360kg of refined slag, heat up and slag, and when slag is finished, add alloy (40kg of nickel plate, 73kg of ferroniobium, 100kg of ferrovanadium, 60kg of ferromolybdenum, 165kg of metallic manganese, 230kg of cobalt plate, 850kg of ferrotungsten), fine-tune the chemical composition, and add steel slag in batches. The total amount of steel slag is 180kg.

[0110] 3. Raise the temperature to 1680°C, take samples and analyze the main element composition. The main element composition is shown in Table 15, and the slag composition is shown in Table 16.

[0111] 4. Raise the temperature to 1720℃, feed 75 meters of Al wire, remove the slag, and when 1 / 3 of the steel liquid is visible in the ladle, transfer to the VD station.

[0112] Table 15 LF main element composition (Wt%)

[0113] element C Mn Si P S Cr Ni Mo V Nb Co W Analytical Value 0.082 0.46 0.045 0.015 0.005 10.70 0.55 0.22 0.18 0.082 3.10 2.5 element Al N B Analytical Value 0.02 0.04 /

[0114] Table 16 LF slag composition (Wt%)

[0115] Slag components CaO <![CDATA[SiO2]]> <![CDATA[Al2O3]]> <![CDATA[R=CaO / (SiO2+1 / 3×Al2O3)]]> Analytical Value 62％ 8％ 28％ 3.6

[0116] (IV) VD furnace smelting

[0117] Under the condition of ultimate vacuum degree ≤67Pa, maintain the time for 25 minutes, break the air, add 62kg of ferroboron, take samples for analysis of main element composition, the main element composition is shown in Table 17, calm down, soft argon blowing time for 30min, and cast electrode rods.

[0118] Table 17 VD main element composition (Wt%)

[0119] element C Mn Si P S Cr Ni Mo V Nb Co W Analytical Value 0.09 0.49 0.04 0.015 0.001 10.65 0.58 0.22 0.20 0.083 3.10 2.52 element Al N B Analytical Value 0.01 0.02 0.02

[0120] (V) Protective atmosphere electroslag remelting

[0121] The slag system adopts CaF: 58%, Al2O3: 20%, and CaO: 18%.

[0122] The metallurgical quality level of finished forgings is tested for non-metallic inclusions according to GB / T10561, as shown in Table 18.

[0123] Table 18 Purity of finished forgings

[0124]

[0125] As can be seen from the above embodiments, the embodiments of the present invention mainly adopt a specific smelting process of roughing in an electric furnace, oxidation and reduction treatment in an AOD furnace, refining in an LF furnace and refining in a VD furnace, and remelting in an electric slag furnace in a protective atmosphere. The present invention realizes the clean smelting of high-chromium martensitic stainless steel containing easily oxidizable elements such as B and Nb with Si≤0.05%, Al≤0.01% by using certain oxygen, silicon, aluminum and slag control technologies, and controlling Si and Al in the whole smelting process, thereby achieving the control of Si and Al components and high purity of molten steel. The embodiment of the present invention realizes the control of finished product [Si]≤0.05%, [Al]≤0.01%, and the molten steel is of high purity ([O]≤0.0025%, non-metallic inclusions A coarse system≤0.5 level, B coarse system≤0.5 level, C coarse system≤0.5 level, D coarse system≤0.5 level, A fine system≤0.5 level, B fine system≤1.0 level, C fine system≤0.5 level, D fine system≤1.0 level, Ds class≤1.0 level, A coarse system+B coarse system+C coarse system+D coarse system+A fine system+B fine system+C fine system+D fine system+Ds class≤2.5 level). The present invention has simple process, convenient control, low cost and strong practicality.

[0126] The above examples are only used to illustrate the technical features and implementation process of the present invention, rather than to limit the technical solution of the present invention. It should be pointed out that for ordinary technicians in this field, the present invention can still be modified or replaced by equivalents, and modifications or replacements that do not deviate from the principles of the present invention are all covered by the protection of the present invention.

Claims

1. A method for smelting clean high-chromium martensitic stainless steel, characterized in that: The following steps are involved: S1. According to the main components of high chromium martensitic stainless steel, the raw materials are placed in an electric furnace for rough refining, and the silicon content in the output steel is controlled to be ≤0.20%; S2, the steel produced by the electric furnace is put into the AOD furnace for oxidation treatment and reduction treatment; in the oxidation treatment, lime is added into the furnace, the chromium content is added according to the lower limit of the stainless steel composition, and the content of other elements is added according to the upper limit of the stainless steel composition, and the amount of lime added is controlled according to the ternary basicity of the slag being 2.0-3.0; the reduction treatment includes the first reduction and the second reduction in sequence, and aluminum ingots are used as deoxidizers for all of them, and the silicon content is controlled to be ≤0.05%; S3, placing the steel produced by the second reduction in an LF furnace, heating and refining, removing slag, and the steel liquid level is 1 / 2 of the ladle; mixing the obtained refined slag, auxiliary materials including lime and alloy, and steel slag to make slag, wherein the amount of lime is controlled according to the ternary basicity of the slag being 3.0-4.0, and the content of the obtained slag components is controlled to be CaO55%-65%, Al2O3 25%-35%, SiO2≤8%, and the aluminum content in the outgoing steel liquid is 0.02-0.03%; S4, the molten steel produced by the LF furnace is put into a VD furnace for refining, and maintained under the condition of ultimate vacuum degree ≤ 67Pa for a time ≥ 25 minutes; S5, pouring the molten steel produced by the VD furnace, remelting the obtained electrode rod in an electroslag ingot in a protective atmosphere electroslag furnace to obtain clean high-chromium martensitic stainless steel with Si≤0.05% and Al≤0.01%.

2. The smelting method according to claim 1, characterized in that: A 40-ton electric furnace is used in step S1; and / or a 40-ton AOD furnace is used in step S2.

3. The smelting method according to claim 1, characterized in that: In the step S2, the first reduction comprises: adding aluminum ingots according to the ternary basicity of the slag of 2.0-3.0, and when the composition meets the requirements of Al≤0.01% and Si≤0.05%, removing 1 / 3 of the slag to see the steel liquid surface.

4. The smelting method according to claim 3, characterized in that: In the step S2, the second reduction comprises: adding lime and aluminum ingots, wherein the amounts of the lime and aluminum ingots are controlled according to the ternary basicity of the slag being 3.0-5.0, and the aluminum content in the output steel material is controlled to be ≤0.015%.

5. The smelting method according to claim 4, characterized in that: In step S2, fluorite is also added in both the first reduction and the second reduction.

6. The smelting method according to claim 1, characterized in that: In the step S3, a 40-ton LF furnace is used; the alloy includes nickel plate, ferroniobium, ferrovanadium, ferromolybdenum and metallic manganese.

7. The smelting method according to claim 1, characterized in that: A 40-ton VD furnace is used in step S4.

8. The smelting method according to claim 1, characterized in that: In the step S5, the pouring calming time is 30 minutes of soft argon blowing time.

9. The smelting method according to claim 8, characterized in that: In the step S5, a 3.0-ton protective atmosphere electric slag furnace is used; the remelting slag system is CaF2 55-65%, Al2O3 20-30%, and CaO 8-18%.

10. The smelting method according to any one of claims 1 to 9, characterized in that: The lime in the raw materials and auxiliary materials is 95% CaO; the steel slag contains 15% Al2O3 and 55% Al; the purity of the aluminum ingot is 98%.

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