Smelting method of stainless steel and preparation method of flat steel

Abstract

The invention relates to the field of metallurgy, in particular to a smelting method of stainless steel and a preparation method of flat steel. The smelting method provided by the invention mainly faces the material requirements of nuclear fusion, low-temperature wind tunnels and other ultralow-temperature environment service, and aims at the smelting requirements of high alloy ratio, ultralow carbon, low Al, low oxygen and high nitrogen of the material, the alloy material is composed of pure iron, high-carbon ferrochrome, a nickel plate, a copper plate, ferrovanadium, ferrocolumbium, electrolytic manganese and the like, and a low-cost EBT + AOD + LF smelting method is adopted, so that accurate control of main components is realized; and in cooperation with subsequent electroslag remelting, forging and other processes, application of the material in nuclear fusion, low-temperature wind tunnels and other ultralow-temperature environments is achieved. According to the ultralow-carbon high-nitrogen stainless steel electrode bar produced through the method, the carbon and oxygen control is low, C is smaller than or equal to 0.006%, O is smaller than or equal to 30 ppm, N is larger than or equal to 0.28%, the mechanical property meets the design requirement, and compared with a brand new alloy material smelting process adopted by an intermediate frequency furnace, the cost per ton of steel is reduced by about 30,000 yuan / ton.

Description

Technical Field

[0001] This invention relates to the field of metallurgy, and in particular to a method for smelting stainless steel and a method for preparing flat steel. Background Technology

[0002] The new generation nuclear fusion experimental reactor "BEST TF" in China has put forward new requirements for the performance of its supporting structural materials, including magnetic, thermal, mechanical and fatigue properties. Panzhihua Iron & Steel Group Co., Ltd. and the Iron & Steel Research Institute jointly developed a new generation of ultra-low temperature materials. Based on Nitronic50 steel, the control of elements such as C, Cr, Ni, Mo and N was optimized, and small amounts of elements such as Cu, V and Nb were added. It is used in the 4.2K ultra-low temperature environment and is called GY50G steel. Its main elements are: C: ≤0.008%, N: 0.20~0.40%, O: ≤0.0030%, P: ≤0.015%, S: ≤0.005%, Cr: 20.5~21.5%, Ni: 14.8~15.5%, Mo: 1.8~2.5%, Mn: 5.0~6.2%, Si: ≤0.20%, Nb: ≤0.10%, V: 0.15~0.25%, Cu: 0.10~0.15%, Al≤0.02%, Ti≤0.02%, Co≤0.05%, with the balance being Fe and unavoidable impurities, and the alloy content ratio is ≥45%. However, in actual smelting processes, the limit level for carbon control using the EBT+AOD+LF combined smelting method is 0.015%, and oxygen control is 30-50 ppm. Moreover, in order to facilitate precise control of the composition, pure metal smelting is used, resulting in higher smelting costs. Summary of the Invention

[0003] In view of this, the present invention provides a method for smelting stainless steel and a method for preparing flat steel. The smelting method provided by the present invention can achieve the requirements of low carbon, low oxygen, and high nitrogen, while reducing smelting costs, ensuring material performance, and meeting the application requirements in ultra-low temperature environments such as nuclear fusion and low-temperature wind tunnels.

[0004] This invention provides a method for smelting stainless steel, comprising the following steps:

[0005] S1. Ingredients:

[0006] Prepare the raw materials according to the initial batching target;

[0007] The chemical composition of the preliminary ingredient target includes:

[0008] P: ≤0.012%;

[0009] Cr: 21%~23%;

[0010] Ni: 3.0%~5.0%;

[0011] Mo: 0.4%~0.6%;

[0012] Mn: 0.5%~1.5%;

[0013] Si: ≤0.05%;

[0014] Nb: ≤0.05%;

[0015] V: 0.05%~0.10%;

[0016] Cu: 0.05%~0.10%;

[0017] Co: ≤0.05%;

[0018] The balance consists of Fe and unavoidable impurities;

[0019] The raw materials include pure iron and alloy materials; wherein, the alloy materials include: high-carbon ferrochrome, nickel plate, ferroniobium, copper plate, ferrovanadium, aluminum ingot, molybdenum bar, metallic manganese, Benxi steel, and ferrosilicon;

[0020] S2, Electric furnace smelting:

[0021] The pure iron, high-carbon ferrochrome, and nickel plates are loaded into the furnace. After the furnace charge is fully melted, oxygen is blown to remove carbon at a temperature ≥1600℃. Then, ferrosilicon alloy and carbon powder are added for pre-reduction, and then the steel is tapped.

[0022] The tapping temperature is 1640℃, and the carbon content of the tapped steel is ≤2.0%.

[0023] S3, AOD smelting:

[0024] Oxidation:

[0025] The molten steel obtained in step S2 is fed into an AOD furnace. Oxygen and N2 are blown in to decarburize until [C] is 0.30%. Then, N2 is replaced with Ar, and oxygen is blown in to decarburize until [C] is ≤0.003%.

[0026] reduction:

[0027] (1) Switch the smelting mode to the reduction mode, set the basicity of the reduction furnace to 1.8~2.2 for the first reduction; during the first reduction, add ferrosilicon alloy and Al ingot for deoxidation, and add metallic manganese to adjust the Mn composition;

[0028] (2) Slag removal; then, a second reduction is carried out, during which reducing agents such as quicklime and fluorite are added, and copper plates, ferrovanadium, ferroniobium and molybdenum bars are added to adjust the composition; nitrogen is blown to the target composition, so that the composition enters the internal control, and steel is tapped when the slag reaches 1.5~2.5t;

[0029] The Cr content in the AOD-treated steel was adjusted to the lower limit of 20.8%, Mn and Ni were both under internal control, the N content was close to the upper limit of the internal control, [C] was controlled at ≤0.003%, and the steel tapping temperature was 1510℃.

[0030] S4, LF Refining:

[0031] The molten steel obtained in step S3 is fed into the LF furnace, and fluorite is added for reduction. The temperature is controlled at ≥1500℃, and the element content is adjusted to the target controlled composition. When the temperature is >1530℃, argon is blown softly and the ladle is lifted.

[0032] S5, Pouring:

[0033] The molten steel obtained in step S5 is poured to obtain a stainless steel electrode rod.

[0034] The chemical composition of the stainless steel electrode rod includes:

[0035] C: ≤0.006%;

[0036] N: 0.20%~0.40%;

[0037] O: ≤0.0020%;

[0038] P: ≤0.015%;

[0039] S: ≤0.005%;

[0040] Cr: 20.5%~21.5%;

[0041] Ni: 14.8%~15.5%;

[0042] Mo: 1.8%~2.5%;

[0043] Mn: 5.0%~6.2%;

[0044] Si: ≤0.20%;

[0045] Nb: ≤0.06%;

[0046] V: 0.15%~0.25%;

[0047] Cu: 0.10%~0.15%;

[0048] Al: ≤0.02%;

[0049] Ti: ≤0.02%;

[0050] Co: ≤0.05%;

[0051] The balance consists of Fe and unavoidable impurities.

[0052] Preferably, in step S2:

[0053] The oxygen supply intensity for oxygen blowing for carbon removal is 1250~1350 m³ / h. 3 / h, time 5~10min;

[0054] The amount of ferrosilicon alloy added is 200~500 kg / furnace;

[0055] The amount of carbon powder added is 80~200kg / furnace.

[0056] Preferably, in step S2:

[0057] The pre-reduction time is ≥10 min;

[0058] The tapping temperature is 1640℃; the carbon content of the tapped steel is ≤2.0%.

[0059] Preferably, in step S3:

[0060] The amount of ferrosilicon alloy added is 300~1000 kg / furnace;

[0061] The amount of Al ingots added is 500~1000 kg / furnace;

[0062] The first restoration takes 10-20 minutes.

[0063] Preferably, in step S3:

[0064] The amount of active lime added is 600~1000 kg / furnace;

[0065] The amount of fluorite added is 200~600 kg / furnace;

[0066] The second restoration takes 20-40 minutes.

[0067] Preferably, in step S3: the tapping temperature is 1510℃, and [C] is controlled at ≤0.003%.

[0068] Preferably, in step S4:

[0069] The amount of fluorite added is 200~500 kg / furnace;

[0070] The temperature of the sling is 1490±10℃.

[0071] Preferably, in step S5: within 35 minutes before casting, ensure that the injection pipe is purged with argon for 15-30 minutes, use a slit-type gate with Ar gas protection during casting, control the Ar gas pressure during casting at 0.10-0.30 MPa, accurately align the ladle gate and the middle injection pipe gate, and control the height between the gate and the gate within ≤50 mm; the casting of the ingot body and the riser requires the liquid level to rise steadily, the mold casting protective slag is 1.0-2.0 kg / t, the casting speed is 420-600 s for the ingot body and 240-300 s for the riser.

[0072] The present invention also provides a method for preparing flat steel, comprising: electroslag remelting an electrode rod to obtain a steel ingot; and subjecting the steel ingot to billeting, rolling, and heat treatment to obtain flat steel; wherein the electrode rod is prepared by the preparation method described in the above technical solution.

[0073] Preferably, the heat treatment temperature is 1050~1070℃, and the holding time is 2~4h.

[0074] The smelting method provided by this invention is mainly aimed at the material requirements for use in ultra-low temperature environments such as nuclear fusion and cryogenic wind tunnels. It addresses the smelting requirements of high alloy ratio, ultra-low carbon, low Al and low oxygen, and high nitrogen in materials. The alloy material is composed of pure iron, high-carbon ferrochrome, nickel plate, copper plate, ferrovanadium, ferroniobium, and electrolytic manganese. A low-cost EBT+AOD+LF smelting method is employed to achieve precise control of the main components. Combined with subsequent electroslag remelting and forging processes, this enables the material to be used in ultra-low temperature environments such as nuclear fusion and cryogenic wind tunnels. Ultra-low carbon, high-nitrogen stainless steel electrode rods produced according to this invention have low carbon and oxygen control (C≤0.006%, O≤30ppm, meeting the requirements of C≤0.006%, O≤30ppm, Al≤0.02%, N≥0.28%). The mechanical properties meet design requirements, and compared to medium-frequency furnaces, the use of a new alloy material smelting process reduces the cost per ton of steel by approximately 30,000 yuan.

[0075] Experimental results show that, after forging and heat treatment, the electrode rod prepared by this invention has a non-metallic inclusion rating of A, B, C, and D ≤ 1.0; magnetic permeability μ ≤ 1.03 H / m; mechanical properties: at a test temperature of 300K (i.e., room temperature 26.85℃), the yield strength Rp0.2 is above 440 MPa, the tensile strength Rm is above 790 MPa, the elongation A is above 40%, and the reduction of area Z is above 69%; at a test temperature of 4.2K (i.e., -268.8℃), the yield strength Rp0.2 is above 1330 MPa, the tensile strength Rm is above 1850 MPa, the elongation A is above 32%, the reduction of area Z is above 34%, and the fracture toughness is 150 K(J). IC / MPa·m 1 / 2As can be seen from the above, it has fewer non-metallic inclusions, lower magnetic permeability, and excellent mechanical properties at both room temperature and ultra-low temperatures, enabling its application in ultra-low temperature environments such as nuclear fusion and low-temperature wind tunnels. Detailed Implementation

[0076] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0077] In this article, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions that include the listed features.

[0078] The term “and / or” as used herein includes any and all combinations of one or more of the related listed items.

[0079] In this document, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0080] In this article, when referring to units for data ranges, if the unit is only followed by the right endpoint, it means that the units for the left and right endpoints are the same. For example, 1630~1650℃ means that the units for the left endpoint "1630" and the right endpoint "1650" are both in degrees Celsius.

[0081] This invention provides a method for smelting stainless steel, comprising the following steps:

[0082] S1. Ingredients:

[0083] Prepare the raw materials according to the initial batching target;

[0084] The chemical composition of the preliminary ingredient target includes:

[0085] P: ≤0.012%;

[0086] Cr: 21%~23%;

[0087] Ni: 3.0%~5.0%;

[0088] Mo: 0.4%~0.6%;

[0089] Mn: 0.5%~1.5%;

[0090] Si: ≤0.05%;

[0091] Nb: ≤0.05%;

[0092] V: 0.05%~0.10%;

[0093] Cu: 0.05%~0.10%;

[0094] Co: ≤0.05%;

[0095] The balance consists of Fe and unavoidable impurities;

[0096] The raw materials include pure iron and alloy materials; wherein, the alloy materials include: high-carbon ferrochrome, nickel plate, ferroniobium, copper plate, ferrovanadium, aluminum ingot, molybdenum bar, metallic manganese, Benxi steel, and ferrosilicon;

[0097] S2, Electric furnace smelting:

[0098] The pure iron, high-carbon ferrochrome, and nickel plates are loaded into the furnace. After the furnace charge is fully melted, oxygen is blown to remove carbon at a temperature ≥1600℃. Then, ferrosilicon alloy and carbon powder are added for pre-reduction, and then the steel is tapped.

[0099] The tapping temperature is 1640℃, and the carbon content of the tapped steel is ≤2.0%.

[0100] S3, AOD smelting:

[0101] Oxidation:

[0102] The molten steel obtained in step S2 is fed into an AOD furnace. Oxygen and N2 are blown in to decarburize until [C] is 0.30%. Then, N2 is replaced with Ar, and oxygen is blown in to decarburize until [C] is ≤0.003%.

[0103] reduction:

[0104] (1) Switch the smelting mode to the reduction mode, set the basicity of the reduction furnace to 1.8~2.2 for the first reduction; during the first reduction, add ferrosilicon alloy and Al ingot for deoxidation, and add metallic manganese to adjust the Mn composition;

[0105] (2) Slag removal; then, a second reduction is carried out, during which reducing agents such as quicklime and fluorite are added, and copper plates, ferrovanadium, ferroniobium and molybdenum bars are added to adjust the composition; nitrogen is blown to the target composition, so that the composition enters the internal control, and steel is tapped when the slag reaches 1.5~2.5t;

[0106] The Cr content in the AOD-treated steel was adjusted to the lower limit of 20.8%, Mn and Ni were both under internal control, the N content was close to the upper limit of the internal control, [C] was controlled at ≤0.003%, and the steel tapping temperature was 1510℃.

[0107] S4, LF Refining:

[0108] The molten steel obtained in step S3 is fed into the LF furnace, and fluorite is added for reduction. The temperature is controlled at ≥1500℃, and the element content is adjusted to the target controlled composition. When the temperature is >1530℃, argon is blown softly and the ladle is lifted.

[0109] S5, Pouring:

[0110] The molten steel obtained in step S5 is poured to obtain a stainless steel electrode rod.

[0111] The chemical composition of the stainless steel electrode rod includes:

[0112] C: ≤0.006%;

[0113] N: 0.20%~0.40%;

[0114] O: ≤0.0020%;

[0115] P: ≤0.015%;

[0116] S: ≤0.005%;

[0117] Cr: 20.5%~21.5%;

[0118] Ni: 14.8%~15.5%;

[0119] Mo: 1.8%~2.5%;

[0120] Mn: 5.0%~6.2%;

[0121] Si: ≤0.20%;

[0122] Nb: ≤0.06%;

[0123] V: 0.15%~0.25%;

[0124] Cu: 0.10%~0.15%;

[0125] Al: ≤0.02%;

[0126] Ti: ≤0.02%;

[0127] Co: ≤0.05%;

[0128] The balance consists of Fe and unavoidable impurities.

[0129] The stainless steel smelting method provided by this invention is a low-cost smelting method for high-alloy ratio, ultra-low carbon, high-nitrogen, ultra-pure stainless steel electrode rods. Before this invention, the company's EBT+AOD+LF combined smelting method had a carbon control limit of 0.015% and an oxygen control limit of 30-50 ppm, using pure metal smelting, resulting in high smelting costs. However, the carbon control level of this invention, using the same route, can be stably controlled at C≤0.006% and O≤30 ppm, achieving a qualitative leap in carbon and oxygen control. Using low-cost alloy materials such as high-carbon ferrochrome, the cost per ton of steel smelted is reduced by nearly 30,000 yuan / ton compared to medium-frequency furnace smelting.

[0130] Regarding step S1 :

[0131] S1. Ingredients: Ingredients are prepared according to the initial ingredient preparation target.

[0132] In this invention, the ingredients are first proportioned according to a preliminary batching target, and then the composition is adjusted and controlled during the smelting process to ultimately control the product to achieve the final target alloy composition. In this invention, the chemical composition of the preliminary batching target includes:

[0133] P: ≤0.012%;

[0134] Cr: 21%~23%;

[0135] Ni: 3.0%~5.0%;

[0136] Mo: 0.4%~0.6%;

[0137] Mn: 0.5%~1.5%;

[0138] Si: ≤0.05%;

[0139] Nb: ≤0.05%;

[0140] V: 0.05%~0.10%;

[0141] Cu: 0.05%~0.10%;

[0142] Co: ≤0.05%;

[0143] The balance consists of Fe and unavoidable impurities.

[0144] In this invention, the raw materials include: pure iron and alloy materials. The pure iron is preferably ACT pure iron (Anshan Iron and Steel pure iron). The alloy materials do not refer to the raw materials themselves being alloys, but rather to the raw materials used to provide alloying elements, i.e., the raw materials used to alloy with Fe to form alloy products. The alloy materials include: high-carbon ferrochrome, nickel plates, ferroniobium, copper plates, ferrovanadium, aluminum ingots, molybdenum bars, metallic manganese, Benxi steel, and ferrosilicon. The Benxi steel refers to Benxi steel recycled.

[0145] In existing technologies, pure metal smelting is mainly used when smelting GY50G steel to facilitate accurate control of alloy composition (e.g., to achieve ultra-low carbon, low Al, low oxygen, and high nitrogen requirements), resulting in high smelting costs. However, the high-carbon ferrochrome and recycled steel materials used in this invention are low-cost alloy materials, which can greatly reduce smelting costs. However, the aforementioned low-cost alloy materials make it very difficult to control carbon and oxygen in the smelting process. This invention uses the aforementioned low-cost raw materials to reduce costs while controlling the process to simultaneously meet the requirements of precise control of composition, especially to achieve ultra-low carbon, low Al, low oxygen, and high nitrogen requirements. This enables the electrode rod to meet the subsequent electroslag remelting requirements and, in conjunction with subsequent electroslag remelting, forging, and other processes, realize the application of the material in ultra-low temperature environments such as nuclear fusion and cryogenic wind tunnels.

[0146] Regarding step S2 :

[0147] S2. Electric furnace smelting: The pure iron, high-carbon ferrochrome, and nickel plates are loaded into the furnace. After the furnace charge is fully melted, oxygen is blown to remove carbon at a temperature ≥1600℃. Then, ferrosilicon alloy and carbon powder are added for pre-reduction, and then the steel is tapped.

[0148] In this invention, it is preferable to first line the furnace bottom with lime before charging.

[0149] In this invention, pure iron, high-carbon ferrochrome, and nickel plates are charged into an electric furnace for smelting, preferably an EBT furnace. The amount of high-carbon ferrochrome and nickel plates added follows the component ratio in the preliminary batching in step S1. After the furnace charge is fully melted, oxygen is blown to remove carbon at a temperature ≥1600℃; the preferred temperature is 1600~1620℃, specifically 1600℃, 1605℃, 1610℃, 1615℃, and 1620℃. Oxygen blowing removes carbon, degasses, removes inclusions, and reasonably controls the carbon content. The preferred oxygen supply intensity for oxygen blowing to remove carbon is 1250~1350 m³ / s. 3 / h, specifically 1250m 3 / h、1260m 3 / h、1270m 3 / h、1280m 3 / h、1290m 3 / h, 1300m 3 / h、1310m 3 / h、1320m 3 / h、1330m 3 / h、1340m 3 / h, 1350m 3 / h; the oxygen blowing decarburization time is preferably 5~10min, specifically 5min, 6min, 7min, 8min, 9min, or 10min. After oxygen blowing decarburization, ferrosilicon alloy and carbon powder are added for pre-reduction. The amount of ferrosilicon alloy added is preferably 200~500kg / furnace, specifically 200kg / furnace, 250kg / furnace, 300kg / furnace, 350kg / furnace, 400kg / furnace, 450kg / furnace, or 500kg / furnace; the amount of carbon powder added is preferably 80~200kg / furnace, specifically 80kg / furnace, 100kg / furnace, 150kg / furnace, or 200kg / furnace. The above reducing agents are added for pre-reduction, preferably accompanied by nitrogen blowing and stirring during pre-reduction. The pre-reduction temperature is the same as the aforementioned temperature, and the pre-reduction time is preferably ≥10min, more preferably 10~20min. After the pre-reduction is completed, the steel is tapped. The tapping temperature is 1640℃. The carbon content of the steel being produced is ≤2.0%.

[0150] Regarding step S3 :

[0151] S3, AOD smelting.

[0152] The AOD smelting is an argon-oxygen decarburization process, which generally involves injecting molten steel into an argon-oxygen decarburization furnace (AOD furnace). During smelting, a mixture of O2 and Ar / N2 gas is blown in to decarburize the molten steel. In addition, reducing agents are added by the feeding system to adjust the composition and temperature of the molten steel for the smelting of stainless steel materials.

[0153] According to the present invention, in the AOD smelting process, an oxidation operation is performed first, followed by a reduction operation.

[0154] According to the present invention, the oxidation process includes: feeding the molten steel obtained in step S2 into an AOD furnace, blowing oxygen and N2 to decarburize until [C] is 0.30%, then replacing N2 with Ar, and blowing oxygen to decarburize until [C] ≤ 0.003%.

[0155] According to the present invention, the reduction process includes: (1)-(2):

[0156] Regarding (1): In this invention, after the oxidation operation is completed, the smelting mode is switched to the reduction mode, and the basicity of the reduction furnace is set to 1.8~2.2, specifically 1.8, 1.9, 2.0, 2.1, or 2.2. The first reduction time is preferably 10~20 min, more preferably 15 min. During the first reduction, ferrosilicon alloy and Al ingots are added for deoxidation; the ferrosilicon alloy and Al ingots act as reducing agents. The amount of ferrosilicon alloy added is preferably 300~1000 kg / furnace, specifically 300 kg / furnace, 400 kg / furnace, 500 kg / furnace, 600 kg / furnace, 700 kg / furnace, 800 kg / furnace, 900 kg / furnace, or 1000 kg / furnace. The preferred amount of Al ingots added is 500-1000 kg / furnace, specifically 500 kg / furnace, 600 kg / furnace, 700 kg / furnace, 800 kg / furnace, 900 kg / furnace, or 1000 kg / furnace. In addition, metallic Mn is added to adjust the Mn content, ensuring that the Mn content is within the internal control range, i.e., within the target content range.

[0157] Regarding (2): In this invention, after the first reduction, the slag is reduced to ≤800kg. Then, a second reduction is performed. During the second reduction, reducing agents, active lime and fluorite, are added. The amount of active lime added is preferably 600~1000kg / furnace, specifically 600kg / furnace, 700kg / furnace, 800kg / furnace, 900kg / furnace, or 1000kg / furnace. The amount of fluorite added is preferably 200~600kg / furnace, specifically 200kg / furnace, 300kg / furnace, 400kg / furnace, 500kg / furnace, or 600kg / furnace. In addition, alloy materials are added to adjust the composition, specifically copper plates, ferrovanadium, ferroniobium, and molybdenum strips. The time for the second reduction is preferably 20~40min, more preferably 30min. After the second reduction, a full analysis is performed on a sample. During the second reduction, nitrogen is blown to the target composition to bring the composition into internal control. The temperature is ≥1500℃, and steel is tapped when the slag reaches 1.5~2.5t, more preferably when the slag reaches 2t. The Cr content in the tapped steel is adjusted to the lower limit, and Mn and Ni are both brought into internal control. The N composition is 0.30-0.38%, close to the upper limit of internal control, and [C] is controlled at ≤0.003%. The tapping temperature is 1510℃.

[0158] Regarding step S4 :

[0159] S4, LF refining: The molten steel obtained in step S3 is put into the LF furnace, and fluorite is added for reduction. The temperature is controlled at ≥1500℃, and the element content is adjusted to the target control composition. When the temperature is >1530℃, argon is blown softly and the ladle is lifted.

[0160] In this invention, the preferred amount of fluorite added is 200-500 kg / furnace, specifically 200 kg / furnace, 300 kg / furnace, 400 kg / furnace, or 500 kg / furnace. Molten steel and fluorite are fed into the furnace, and then subjected to electric refining and reduction at a temperature controlled at ≥1500℃, preferably 1500-1650℃. Deep deoxidation and desulfurization are achieved through LF furnace refining, followed by full analysis of samples. The elemental content is adjusted to the target controlled composition; the adjusted elemental content can be achieved by adding appropriate metal materials. When the temperature reaches >1530℃, soft argon blowing is performed, and the ladle is lifted. The preferred temperature of the ladle is 1490±10℃, specifically 1480℃, 1490℃, 1497℃, or 1500℃.

[0161] Regarding step S5 :

[0162] S5. Casting: The molten steel obtained in step S5 is cast to obtain a stainless steel electrode rod.

[0163] In this invention, argon must be purged through the injection pipe for 15-30 minutes within 35 minutes before pouring, specifically 15 minutes, 20 minutes, 25 minutes, or 30 minutes. A slit-type nozzle with Ar gas protection is used for pouring, and the Ar gas pressure during the pouring process is controlled at 0.10-0.30 MPa, specifically 0.10 MPa, 0.20 MPa, or 0.30 MPa. The ladle nozzle and the inlet gate of the injection pipe must be accurately aligned, and the height between the nozzle and the gate must be controlled within ≤50 mm. The liquid level must rise steadily during the pouring of the ingot body and the cap. The mold casting flux is 1.0~2.0 kg / t (specifically 1.0 kg / t, 1.5 kg / t, or 2.0 kg / t), the casting speed and ingot body time are 420~600 s (specifically 420 s, 450 s, 500 s, 550 s, or 600 s), the riser time is 240~300 s (specifically 240 s, 250 s, 260 s, 270 s, 280 s, 290 s, or 300 s), the casting electrode rod uses stainless steel mold flux, aluminum exothermic agent, and insulation plate, and is air-cooled after demolding.

[0164] In this invention, the chemical composition of the obtained electrode rod includes:

[0165] C: ≤0.006%;

[0166] N: 0.20%~0.40%;

[0167] O: ≤0.0020%;

[0168] P: ≤0.015%;

[0169] S: ≤0.005%;

[0170] Cr: 20.5%~21.5%;

[0171] Ni: 14.8%~15.5%;

[0172] Mo: 1.8%~2.5%;

[0173] Mn: 5.0%~6.2%;

[0174] Si: ≤0.20%;

[0175] Nb: ≤0.06%;

[0176] V: 0.15%~0.25%;

[0177] Cu: 0.10%~0.15%;

[0178] Al: ≤0.02%;

[0179] Ti: ≤0.02%;

[0180] Co: ≤0.05%;

[0181] The balance consists of Fe and unavoidable impurities.

[0182] The specific content of C can be 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, or 0.006%. The specific content of N can be 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, 0.30%, 0.31%, 0.32%, 0.33%, 0.34%, 0.35%, 0.36%, 0.37%, 0.38%, 0.39%, or 0.40%. The specific content of O can be 0.0010% or 0.0020%. The specific content of P can be 0.010%, 0.011%, 0.012%, 0.013%, 0.014%, or 0.015%. The S content can specifically be 0.001%, 0.002%, 0.003%, 0.004%, or 0.005%. The Cr content can specifically be 20.5%, 20.6%, 20.7%, 20.8%, 20.9%, 21.0%, 21.1%, 21.2%, 21.3%, 21.4%, or 21.5%. The Ni content can specifically be 14.8%, 14.9%, 15.0%, 15.1%, 15.2%, 15.3%, 15.4%, or 15.5%. The Mo content can specifically be 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, or 2.5%. The Mn content can specifically be 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, or 6.2%. The Si content can specifically be 0.03%, 0.05%, 0.10%, 0.15%, or 0.20%. The Nb content can specifically be 0.04%, 0.05%, or 0.06%. The V content can specifically be 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, or 0.25%. The Cu content can specifically be 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, or 0.15%. The Al content can specifically be 0.01% or 0.02%. The Ti content can specifically be 0.01% or 0.02%. The Co content can specifically be 0.01%, 0.02%, 0.03%, 0.04%, or 0.05%.

[0183] This invention primarily addresses the material design requirements for cryogenic environments. Specifically, it proposes an EBT+AOD+LF co-smelting method to meet the smelting demands of high alloy ratios, ultra-low carbon, low Al and low oxygen, and high nitrogen content. The method utilizes electrode rods in electroslag remelting to achieve precise control of major elements, with C ≤ 0.006%, O ≤ 30 ppm, and low content control of elements such as Al, S, and P. The EBT+AOD+LF co-smelting method of this invention can stably control the carbon level to C ≤ 0.006%, and can be applied to the smelting of ultra-low carbon nitrogen-containing austenitic stainless steels such as 022Cr19Ni10N using the same process route. The high alloy ratio, ultra-low carbon, high nitrogen, and ultra-pure stainless steel developed by this invention is widely used in cryogenic environments such as 4.2K and 77K nuclear fusion and cryogenic wind tunnels.

[0184] The present invention also provides a method for preparing flat steel, comprising: electroslag remelting an electrode rod to obtain a steel ingot; and subjecting the steel ingot to billeting, rolling, and heat treatment to obtain flat steel; wherein the electrode rod is prepared by the preparation method described above.

[0185] In this invention, the electroslag remelting method is not particularly limited and can be performed according to conventional electroslag remelting operations in the art. The billet preparation and rolling processes are not particularly limited and can be performed according to conventional processes in the art. The preferred heat treatment temperature is 1050~1070℃, specifically 1050℃, 1055℃, 1060℃, 1065℃, or 1070℃; the preferred heat treatment holding time is 2~4 hours, specifically 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours. After heat treatment, the finished flat steel is obtained.

[0186] In existing technologies, pure metal smelting is mainly used when smelting GY50G steel to facilitate accurate control of alloy composition (e.g., to achieve ultra-low carbon, low Al, low oxygen, and high nitrogen requirements), resulting in high smelting costs. However, the high-carbon ferrochrome and recycled steel materials used in this invention are low-cost alloy materials, which can greatly reduce smelting costs. However, the aforementioned low-cost alloy materials make it very difficult to control carbon and oxygen in the smelting process. This invention uses the aforementioned low-cost raw materials to reduce costs while controlling the process to simultaneously meet the requirements of precise control of composition, especially to achieve ultra-low carbon, low Al, low oxygen, and high nitrogen requirements. This enables the electrode rod to meet the subsequent electroslag remelting requirements and, in conjunction with subsequent electroslag remelting, forging, and other processes, realize the application of the material in ultra-low temperature environments such as nuclear fusion and cryogenic wind tunnels.

[0187] Experimental results show that, after forging and heat treatment, the electrode rod prepared by this invention has a non-metallic inclusion rating of A, B, C, and D ≤ 1.0; magnetic permeability μ ≤ 1.03 H / m; mechanical properties: at a test temperature of 300K (i.e., room temperature 26.85℃), the yield strength Rp0.2 is above 440 MPa, the tensile strength Rm is above 790 MPa, the elongation A is above 40%, and the reduction of area Z is above 69%; at a test temperature of 4.2K (i.e., -268.8℃), the yield strength Rp0.2 is above 1330 MPa, the tensile strength Rm is above 1850 MPa, the elongation A is above 32%, the reduction of area Z is above 34%, and the fracture toughness is 150 K(J). IC / MPa·m 1 / 2 As can be seen from the above, it has fewer non-metallic inclusions, lower magnetic permeability, and excellent mechanical properties at both room temperature and ultra-low temperatures, enabling its application in ultra-low temperature environments such as nuclear fusion and low-temperature wind tunnels.

[0188] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0189] Example 1

[0190] 1. Preparation of electrode rods

[0191] S1. Ingredients: Ingredients are prepared according to the initial ingredients preparation target;

[0192] The chemical composition of the preliminary ingredients includes: P: ≤0.012%; Cr: 21-23%; Ni: 3.0-5.0%; Mo: 0.40-0.60%; Mn: 0.5-1.5%; Si: ≤0.50%; Nb: ≤0.05%; V: 0.05-0.10%; Cu: 0.05-0.10%; Co: ≤0.05%; the balance being Fe and unavoidable impurities.

[0193] S2, Electric furnace smelting:

[0194] Before charging, lime is placed at the bottom of the furnace. Pure iron, high-carbon ferrochrome, and nickel plates are then charged into the furnace. After the furnace charge is fully melted, deoxidation and carbon blowing (oxygen supply intensity of 1300 m³ / h) are carried out at a temperature of 1600℃. 3 / h, time is 7min), degassing and inclusion removal, and reasonable control of C content. Then, ferrosilicon alloy (300kg / furnace) and carbon powder (100kg / furnace) are added for pre-reduction, the pre-reduction time is 15min, during which nitrogen is blown and stirred, the tapping temperature is 1640℃, and the tapping carbon content is 1.72%.

[0195] S3, AOD smelting:

[0196] Oxidation:

[0197] The molten steel obtained in step S2 is fed into an AOD furnace. When oxygen and N2 are blown to decarburize to [C] of 0.30%, N2 is replaced with Ar, and oxygen is blown to decarburize to [C] of 0.003%.

[0198] reduction:

[0199] (1): Switch the smelting mode to the reduction mode for the first reduction. Set the basicity of the reduction furnace to 1.8 and the reduction time to 15 min. During the process, add ferrosilicon alloy (700 kg / furnace) and Al ingot (700 kg / furnace) for deoxidation. Also add metallic Mn (2000 kg / furnace) to adjust the Mn content so that the Mn component enters the internal control.

[0200] (2): After the first reduction, the slag is pulled to ≤800kg; a second reduction is carried out, during which the reducing agent active lime (800kg / furnace), fluorite (400kg / furnace), and alloy materials copper plate (40kg / furnace), ferrovanadium (60kg / furnace), ferroniobium (30kg / furnace), and molybdenum bar (700kg / furnace) are added. The second reduction lasts for 30 minutes. After that, the whole sample is taken for analysis. Nitrogen is blown to 0.34% during the second reduction. The temperature is 1510℃. When the slag reaches about 2t, the steel is tapped. The AOD of the tapped steel is adjusted to the lower limit of 20.8%. Mn and Ni are both under internal control. The N content is close to the upper limit of the internal control of 0.40%. [C] is controlled at 0.0028%. The tapping temperature is 1510℃.

[0201] S4, LF Refining:

[0202] The molten steel obtained in step S3 is fed into the LF furnace, and fluorite powder (300 kg / furnace) is added to the ladle for refining and reduction, followed by slag formation. The temperature is 1510℃, and deep deoxidation and desulfurization are performed. Samples are taken for full analysis. The content of each element is adjusted to the target control composition. When the temperature reaches 1535℃, soft argon blowing is performed for 15 minutes, and the ladle is lifted at a temperature of 1497℃.

[0203] S5, Pouring:

[0204] Argon blowing must be ensured in the injection pipe for 25 minutes within 35 minutes before pouring. Ar gas protection is used during pouring with a slit-type gate, and the Ar gas pressure is controlled at 0.20 MPa. The ladle gate and the gating in the middle injection pipe must be accurately aligned, and the height between the gate and the gating must be controlled within 45 mm. The liquid level must rise steadily during the pouring of the ingot body and the gating cap. The mold casting flux is 1.5 kg / t. The pouring time for the ingot body is 480 s, and the riser time is 260 s. A Φ570 mm electrode rod is poured using stainless steel mold flux, aluminum exothermic agent, and an insulating plate. Air cooling is performed after demolding.

[0205] The results of the electrode rod composition analysis are shown in Table 1:

[0206] Table 1: Compositional Analysis Results of the Electrode Rod in Example 1

[0207]

[0208] 2. Preparation of flat steel

[0209] The obtained Φ570mm electrode rod was electroslag remelted into a Φ770mm steel ingot, and then forged and rolled to produce 91×520mm flat steel. After heat treatment (temperature 1060℃, time 2.5h), the finished flat steel was obtained.

[0210] 3. Product Testing

[0211] (3.1) Non-metallic inclusions

[0212] The test results of non-metallic inclusions in the obtained finished flat steel are shown in Table 2:

[0213] Table 2: Test results of non-metallic inclusions in finished flat steel in Example 1

[0214]

[0215] Note: A1 / 4T refers to 1 / 4 of the thickness of the head; A1 / 2T refers to 1 / 2 of the thickness of the head; H1 / 4T refers to 1 / 4 of the thickness of the tail; H1 / 2T refers to 1 / 2 of the thickness of the tail.

[0216] (3.2) Magnetic permeability

[0217] The permeability test results show that its permeability μ is 1.003H / m.

[0218] (3.3) Mechanical properties

[0219] The room temperature mechanical properties are shown in Table 3:

[0220] Table 3: Room temperature mechanical properties of finished flat steel from Example 1

[0221]

[0222] Mechanical properties at 4.2K are shown in Table 4:

[0223] Table 4: Mechanical properties of finished flat steel (4.2K) from Example 1

[0224]

[0225] For fracture toughness at 4.2K, please refer to Table 5:

[0226] Table 5: Fracture toughness of finished flat steel (4.2K) in Example 1

[0227]

[0228] Example 2

[0229] 1. Preparation of electrode rods

[0230] S1. Ingredients: Ingredients are prepared according to the initial ingredients preparation target;

[0231] The chemical composition of the preliminary ingredients includes: P: ≤0.012%; Cr: 21-23%; Ni: 3.0-5.0%; Mo: 0.40-0.60%; Mn: 0.5-1.5%; Si: ≤0.50%; Nb: ≤0.05%; V: 0.05-0.10%; Cu: 0.05-0.10%; Co: ≤0.05%; the balance being Fe and unavoidable impurities.

[0232] S2, Electric furnace smelting:

[0233] Before charging, lime is placed at the bottom of the furnace. Pure iron, high-carbon ferrochrome, and nickel plates are then charged into the furnace. After the furnace charge is fully melted, deoxidation and carbon blowing (oxygen supply intensity of 1300 m³ / h) are carried out at a temperature of 1600℃. 3 / h, time is 7min), degassing and inclusion removal, and reasonable control of C content. Then, ferrosilicon alloy (300kg / furnace) and carbon powder (100kg / furnace) are added for pre-reduction, the pre-reduction time is 14min, during which nitrogen is blown and stirred, the steel tapping temperature is 1640℃, and the steel tapping carbon content is 1.53%.

[0234] S3, AOD smelting:

[0235] Oxidation:

[0236] The molten steel obtained in step S2 is fed into an AOD furnace. When oxygen and N2 are blown to decarburize to [C] of 0.30%, N2 is replaced with Ar, and oxygen is blown to decarburize to [C] of 0.0027%.

[0237] reduction:

[0238] (1): Switch the smelting mode to the reduction mode for the first reduction. Set the basicity of the reduction furnace to 1.8 and the reduction time to 15 min. During the process, add ferrosilicon alloy (700 kg / furnace) and Al ingot (750 kg / furnace) for deoxidation. Also add metallic Mn (2100 kg / furnace) to adjust the Mn content so that the Mn component enters the internal control.

[0239] (2): After the first reduction, the slag is pulled to ≤800kg; a second reduction is carried out, during which the reducing agent active lime (700kg / furnace), fluorite (450kg / furnace), and alloy materials copper plate (38kg / furnace), ferrovanadium (65kg / furnace), ferroniobium (35kg / furnace), and molybdenum bar (720kg / furnace) are added. The second reduction lasts for 30 minutes. After that, the whole sample is taken for analysis. Nitrogen is blown to 0.35% during the second reduction. The temperature is 1520℃. When the slag reaches about 2t, the steel is tapped. The AOD of the tapped steel is adjusted to the lower limit of 20.8%. Mn and Ni are both under internal control. The N content is close to the upper limit of the internal control of 0.40%. [C] is controlled at 0.003%. The tapping temperature is 1510℃.

[0240] S4, LF Refining:

[0241] The molten steel obtained in step S3 is fed into the LF furnace, and fluorite powder (300 kg / furnace) is added to the ladle for refining and reduction, followed by slag formation. The temperature is 1520℃, and deep deoxidation and desulfurization are performed. Samples are taken for full analysis. The content of each element is adjusted to the target control composition. When the temperature reaches 1540℃, soft argon blowing is performed for 20 minutes, and the ladle is lifted at a temperature of 1497℃.

[0242] S5, Pouring:

[0243] Argon blowing must be ensured in the injection pipe for 25 minutes within 35 minutes before pouring. Ar gas protection is used during pouring with a slit-type gate, and the Ar gas pressure is controlled at 0.20 MPa. The ladle gate and the gating in the middle injection pipe must be accurately aligned, and the height between the gate and the gating must be controlled within 45 mm. The liquid level must rise steadily during the pouring of the ingot body and the gating cap. The mold casting flux is 1.5 kg / t. The pouring time for the ingot body is 480 s, and the riser time is 260 s. A Φ400 mm electrode rod is poured using stainless steel mold flux, aluminum exothermic agent, and an insulating plate. Air cooling is performed after demolding.

[0244] The results of the electrode rod composition analysis are shown in Table 6:

[0245] Table 6: Compositional Analysis Results of the Electrode Rod in Example 2

[0246]

[0247] 2. Preparation of flat steel

[0248] The obtained Φ400mm electrode rod was electroslag remelted into a Φ770mm steel ingot, and then forged and rolled to produce 78×600mm flat steel. After heat treatment (temperature 1060℃, time 2h), the finished flat steel was obtained.

[0249] 3. Product Testing

[0250] (3.1) Non-metallic inclusions

[0251] The test results of non-metallic inclusions in the obtained finished flat steel are shown in Table 7:

[0252] Table 7: Test results of non-metallic inclusions in finished flat steel in Example 2

[0253]

[0254] (3.2) Magnetic permeability

[0255] The permeability test results show that its permeability μ is 1.003H / m.

[0256] (3.3) Mechanical properties

[0257] The room temperature mechanical properties are shown in Table 8:

[0258] Table 8: Room temperature mechanical properties of finished flat steel from Example 2

[0259]

[0260] Mechanical properties at 4.2K are shown in Table 9:

[0261] Table 9: Mechanical properties of finished flat steel (4.2K) from Example 2

[0262]

[0263] For fracture toughness at 4.2K, please refer to Table 10:

[0264] Table 10: Fracture toughness of finished flat steel (4.2K) in Example 2

[0265]

[0266] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for smelting stainless steel, characterized in that, Includes the following steps: S1. Ingredients: Prepare the raw materials according to the initial batching target; The chemical composition of the preliminary ingredient target includes: P：≤0.012%； Cr：21%~23%； Ni: 3.0%~5.0%; Mo: 0.4%~0.6%; Mn: 0.5%~1.5%; Si: ≤0.05%; Nb: ≤0.05%; V：0.05%~0.10%； Cu: 0.05%~0.10%; Co: ≤0.05%; The balance consists of Fe and unavoidable impurities; The raw materials include pure iron and alloy materials; wherein, the alloy materials include: high-carbon ferrochrome, nickel plate, ferroniobium, copper plate, ferrovanadium, aluminum ingot, molybdenum bar, metallic manganese, Benxi steel, and ferrosilicon; S2, Electric furnace smelting: The pure iron, high-carbon ferrochrome, and nickel plates are loaded into the furnace. After the furnace charge is fully melted, oxygen is blown to remove carbon at a temperature ≥1600℃. Then, ferrosilicon alloy and carbon powder are added for pre-reduction, and then the steel is tapped. The tapping temperature is 1640℃, and the carbon content of the tapped steel is ≤2.0%. S3, AOD smelting: Oxidation: The molten steel obtained in step S2 is fed into an AOD furnace. Oxygen and N2 are blown in to decarburize until [C] is 0.30%. Then, N2 is replaced with Ar, and oxygen is blown in to decarburize until [C] is ≤0.003%. reduction: (1) Switch the smelting mode to the reduction mode, set the basicity of the reduction furnace to 1.8~2.2 for the first reduction; during the first reduction, add ferrosilicon alloy and Al ingot for deoxidation, and add metallic manganese to adjust the Mn composition; (2) Slag removal; then, a second reduction is carried out, during which reducing agents such as quicklime and fluorite are added, and copper plates, ferrovanadium, ferroniobium and molybdenum bars are added to adjust the composition; nitrogen is blown to the target composition, so that the composition enters the internal control, and steel is tapped when the slag reaches 1.5~2.5t; The Cr content in the AOD-treated steel was adjusted to the lower limit of 20.8%, Mn and Ni were both under internal control, the N content was close to the upper limit of the internal control, [C] was controlled at ≤0.003%, and the steel tapping temperature was 1510℃. S4, LF Refining: The molten steel obtained in step S3 is fed into the LF furnace, and fluorite is added for reduction. The temperature is controlled at ≥1500℃, and the element content is adjusted to the target controlled composition. When the temperature is >1530℃, argon is blown softly and the ladle is lifted. S5, Pouring: The molten steel obtained in step S5 is poured to obtain a stainless steel electrode rod. The chemical composition of the stainless steel electrode rod includes: C：≤0.006%； N：0.20%~0.40%； O：≤0.0020%； P：≤0.015%； S：≤0.005%； Cr：20.5%~21.5%； Ni: 14.8%~15.5%; Mo: 1.8%~2.5%; Mn: 5.0%~6.2%; Si: ≤0.20%; Nb: ≤0.06%; V：0.15%~0.25%； Cu: 0.10%~0.15%; Al：≤0.02%； Ti: ≤0.02%; Co: ≤0.05%; The balance consists of Fe and unavoidable impurities.

2. The preparation method according to claim 1, characterized in that, In step S2: The oxygen supply intensity for oxygen blowing for carbon removal is 1250~1350 m³ / h. 3 / h, time 5~10min; The amount of ferrosilicon alloy added is 200~500 kg / furnace; The amount of carbon powder added is 80~200kg / furnace.

3. The preparation method according to claim 1, characterized in that, In step S2: The pre-reduction time is ≥10 min; The tapping temperature is 1640℃; the carbon content of the tapped steel is ≤2.0%.

4. The preparation method according to claim 1, characterized in that, In step S3: The amount of ferrosilicon alloy added is 300~1000 kg / furnace; The amount of Al ingots added is 500~1000 kg / furnace; The first restoration takes 10-20 minutes.

5. The preparation method according to claim 1, characterized in that, In step S3: The amount of active lime added is 600~1000 kg / furnace; The amount of fluorite added is 200~600 kg / furnace; The second restoration takes 20-40 minutes.

6. The preparation method according to claim 1, characterized in that, In step S3: the tapping temperature is 1510℃, and [C] is controlled at ≤0.003%.

7. The preparation method according to claim 1, characterized in that, In step S4: The amount of fluorite added is 200~500 kg / furnace; The temperature of the sling is 1490±10℃.

8. The preparation method according to claim 1, characterized in that, In step S5: ensure argon blowing in the injection pipe for 15-30 minutes within 35 minutes before pouring, use slit-type gate with Ar gas protection during pouring, control the Ar gas pressure during pouring at 0.10-0.30 MPa, accurately align the ladle gate and the gate in the middle injection pipe, and control the height between the gate and the gate within ≤50 mm; for the ingot body and the cap, the liquid level should rise steadily, the mold casting protective slag should be 1.0-2.0 kg / t, the pouring speed for the ingot body should be 420-600 s, and the pouring speed for the riser should be 240-300 s.

9. A method for preparing flat steel, characterized in that, include: The electrode rod is electroslag remelted to obtain a steel ingot; the steel ingot is then billeted, rolled, and heat-treated to obtain a flat steel bar; wherein the electrode rod is prepared by any one of claims 1 to 8.

10. The preparation method according to claim 9, characterized in that, The heat treatment temperature is 1050~1070℃, and the holding time is 2~4h.

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