CN104498805B - Production method of high-carbon low-nitrogen steel for strand wires - Google Patents

Abstract

The invention discloses a production method of steel for high-carbon and low-nitrogen strands, which belongs to the technical field of steelmaking application. The converter adopts 80 tons of small converter double slag operation, the end point carbon is controlled by 0.15%, the tapping temperature is 1610°C, the slag is blocked and the steel is tapped, and the thickness of the slag during the tapping process of the converter is controlled between 0 and 40mm; micro-nitrogen carburizer : N: 0.005～0.025%, carbon 6kg/ton steel, Si-Ca-Ba deoxidation, adding amount 2.0kg/ton steel, 4.5kg/ton steel synthetic slag; LF80 tons refining furnace slag-making material uses synthetic slag; Continuous casting of 150mm×150mm billet is adopted, the crystallizer adopts 380A, 4Hz electromagnetic stirring, high alkalinity ladle covering agent, ladle argon sealing, tundish full argon blowing, submerged nozzle full protection casting. The steel for steel strands produced by the present invention is controlled within 40ppm of nitrogen in the steel, reaching the quality level of steel for steel strands produced by the vacuum degassing process and the bloom continuous casting two-fire process, and greatly reducing the steelmaking process Reduce production costs, increase the competitiveness of enterprise products, and have greater economic and social benefits.

Description

A production method of steel for high-carbon and low-nitrogen stranded wire

technical field

The invention belongs to the technical field of steelmaking, and in particular relates to a production method of steel for high-carbon and low-nitrogen strands. Casting non-vacuum process to produce high-carbon and low-nitrogen steel, suitable for converter, LF furnace, and billet continuous casting non-vacuum process to produce high-carbon and low-nitrogen strand steel (carbon content: 0.75-0.83%; nitrogen content: 20- 40ppm) method, applied to the field of high-grade building prestressed concrete.

Background technique

The higher the nitrogen content in the hypereutectoid steel (C>0.77%), the greater the stress between dislocations, the worse the plasticity index of the steel, and the longer the time. Nitrogen in steel under certain conditions reduces the properties of the material, its presence reduces the toughness and plasticity of the steel. Make steel produce strain aging, aging precipitation and aging brittleness. Practice has proved that nitrogen in steel is controlled at different levels, which has a great influence on the plasticity and aging time of steel. Different control processes of nitrogen in the production of high carbon steel SWRH82B by a certain factory (attachment 1): the nitrogen in the steel is controlled between 55-90ppm, and the average content is 65ppm. The area reduction rate on the day of production was maintained at 0-12.5%, and the fracture of the wire rod was basically a brittle fracture or a fracture shape with only slight plastic deformation in the center; the area reduction rate was 21.6% in 10 days; The rate is 28.9%; the 30-day shrinkage rate is 36.5%.

Nitrogen in steel is controlled between 45-70ppm, with an average content of 55ppm. The area reduction rate on the day of production was maintained at 10-14.5%, and the fracture surface of the wire rod basically only had a small plastic deformation in the center; the area reduction rate was 29.2% on the 10th day; the area reduction rate was 32.3% on the 15th day ; The shrinkage rate in 30 days was 37.4%. Nitrogen in steel is controlled between 32-42ppm, with an average content of 38ppm. The surface shrinkage rate of the production line on the same day was 17.5%, and the normal fracture was a plastic deformation fracture shape; the area shrinkage rate of 5 days was 32.7%; the area shrinkage rate of 10 days was 35.5%; the area shrinkage rate fluctuated between 11 and 30 days Between 37.3 and 37.9%, the area shrinkage fluctuates very little. Nitrogen in steel is controlled between 20 and 32ppm, with an average content of 27ppm. The area reduction rate of the first day of production is 26%, the area reduction rate of 2 days is 30%, the area reduction rate of 5 days is 35%, and the area reduction rate of 6-30 days fluctuates between 36-38%.

In general, the lower the nitrogen content in the steel, the higher the area reduction of the wire rod. This is why the steelmaking process always pursues the lower the better the nitrogen content in the steel. This involves a production process Questions of cost and economics.

At present, the main methods of producing high-carbon and low-nitrogen steels (60Si2Mn, GCr15, SWRH77B and SWRH82B) internationally are: molten iron pretreatment → converter smelting + LF (+RH) refining → die casting (large-section continuous casting billet) →Secondary billet opening→High-speed wire rod controlled rolling→Stelmo most powerful cooling. This is currently the most widely used method in Japan and Europe. For example, the cross-section of the billet in the Sandvik plant in Sweden is 265mm×365mm, the cross-section of the ARBED casting machine in Belgium is 260mm×260mm, and the cross-section of the casting machine in the ROECHLJNG factory in Germany is 240mm×240mm. The casting machine section of Thyssen Ruhrort Plant is 260mm×330mm, and the casting machine section of Nippon Steel is 220mm×220mm. Baosteel adopts die-casting technology, and the billets of 130mm×130mm～160mm×160mm are initially rolled out from the die-cast billets (large-section continuous casting billets). Xinggang adopts 280mm×325mm rectangular billet to be opened and rolled into 150mm×150mm. Its technological advantages are: it meets the production technical requirements of steel strand SWRH82B wire rod to the greatest extent; (such as products of Nippon Steel and Baosteel: T[O]<20ppm; [N]<60ppm), secondary heating billet opening avoids the harm of central segregation and shrinkage cavity of continuous casting billet, with good surface quality and large compression ratio. The disadvantages are complicated process, low finished product rate, high production cost, high energy consumption and heavy pollution.

In order to reduce production costs, domestic iron and steel enterprises have generally canceled the vacuum degassing device when smelting the steel SWRH82B for steel strands, and the nitrogen and hydrogen gas content in the steel is relatively high. At present, the normal level of nitrogen in domestic SWRH82B steel is 50-70ppm. At the same time, during the rolling process, due to forced deformation, forced cooling and phase transformation, there is a large amount of residual stress (rolling stress, temperature stress, phase transformation stress).

Since the release of gas and residual stress takes time, this leads to aging treatment of SWRH82B wire rod before use by users. The main hazard of nitrogen in SWRH82B is that it forms angular and brittle inclusions with titanium, aluminum and other elements in the steel. After a certain amount of plastic deformation, tiny cavities first appear inside. With the increase of deformation, the number of cavities increases. increase and aggregate with each other, eventually causing the material to fracture. Compared with plastic inclusions, brittle inclusions formed by nitrides are more likely to be the origin of ductile failure during cold drawing of high carbon steel.

Most enterprises producing high-carbon steel are limited by the existing smelting equipment, resulting in unstable chemical composition of SWRH77B and SWRH82B steel, and low purity of steel. In particular, the fluctuation range of nitrogen content in the steel fluctuates from the lower limit of the standard to the upper limit, or even exceeds the standard, resulting in a high rate of broken wires during the drawing and twisting process of the wire drawing. The typical fracture morphology caused by the high nitrogen content in the steel is shown in Figure 2 , 3. In this way, the index fluctuation range of product strength and toughness after drawing by the product enterprise is large, and the qualified rate of finished products is low; on the other hand, it is easy to cause brittle fracture during drawing, and it cannot be processed in severe cases.

Contents of the invention

The purpose of the present invention is to provide a production method of steel for high-carbon and low-nitrogen stranded wire, which is produced by using a small converter (80 tons)+LF (80 tons) refining furnace+billet (150mm×150mm) continuous casting non-vacuum flow process The method for high-carbon and low-nitrogen steel is suitable for the production of high-carbon and low-nitrogen steel strands (carbon content 0.75-0.83%; nitrogen content 20-40ppm) in converters, LF furnaces, and billet continuous casting non-vacuum processes; including Molten iron→converter smelting→slag blocking and tapping→ladle carbonization, deoxidation and alloying→ladle slag modification→LF ladle refining→feeding Si-Ca line→ladle bottom blowing with argon and soft blowing→150mm×150mm billet full protection casting →Mold electromagnetic stirring→heating→controlled rolling→controlled cooling. It is used in the field of high-grade building prestressed concrete.

The steel for steel strands produced by the present invention is controlled within 40ppm of nitrogen in the steel, reaching the quality level of steel for steel strands produced by the vacuum degassing process and the bloom continuous casting two-fire process, and greatly reducing the steelmaking process Reduce production costs, increase the competitiveness of enterprise products, and have greater economic and social benefits.

The technical parameters controlled in the process are as follows:

The converter adopts 80 tons of small converter double slag operation, the carbon at the end point is controlled at 0.15%, the tapping temperature is 1610-1620°C, the slag is blocked and the steel is tapped, and the thickness of the slag during the tapping process of the converter is controlled between 0 and 40mm; Carbon agent: N: 0.005～0.025%, with carbon 6kg/ton steel, deoxidized with Si-Ca-Ba, adding amount 2.0kg/ton steel, 4.5kg/ton steel synthetic slag;

LF (80 tons) refining furnace slagging material uses synthetic slag, active lime: (CaO+MgO): 96.5-98%, SiO ₂ : 1-1.5%, CO ₂ : 1-2.0%, activity (4mol/ml -HCl, temperature 40±1℃, 10min)>350ml; bauxite: Al ₂ O ₃ : 75-97%, SiO ₂ : 0-10%; CaO: 1-5%, MgO: 2-9.5%, H ₂ O: 0-0.5%; Fluorite: CaF ₂ : 85.44-99%, SiO ₂ : 1-14%, S: 0-0.5%, P: 0-0.06%, the total slag content is 1.0-1.2 tons Control, bauxite is controlled within 80-100Kg, Fe-Si powder and calcium carbide are added to the slag surface for deoxidation, white slag and final slag TFe<1.0% will be formed within 15 minutes of power supply, and the content of a[o] and S in the steel will be reduced; At the end of the LF furnace treatment, feed the Ca-Si wire 1m/ton of steel. After feeding the wire, blow argon softly, the flow rate is 40-60L/min, and the time is ≥10min. Floating fully, after refining, target a[o]: 0~10ppm.

150mm×150mm billet continuous casting is adopted, the crystallizer adopts 380A, 4Hz electromagnetic stirring, high alkalinity ladle covering agent, ladle argon sealing, tundish full argon blowing, submerged nozzle full protection casting, pouring according to 1.8 ～2.0m/min constant casting speed control, tundish molten steel superheat controlled at 25～35℃, continuous casting secondary cooling with 0.75L/Kg specific water volume for pouring; use Mg-Ca dry material belt retaining wall tundish , full protection pouring, argon gas flow rate of 30-50L/min in the large bag argon-sealed protective casing, it is strictly forbidden to add covering agent to the impact area of the tundish when no casing is added, the tundish is filled with argon before pouring, and the tundish is selected with high alkalinity Covering agent; mold flux for low viscosity and high alkalinity (viscosity: 1300°C, 4-6 poise; alkalinity (CaO/SiO ₂ ): 0.80-1.1) high-carbon steel flux, mold water flow rate 120 tons/ hour, the secondary cooling water distribution curve selects 0.75L/kg steel specific water; after the dummy head comes out of the crystallizer, the electromagnetic stirring of the crystallizer is turned on, and the electromagnetic stirring is stopped after the stopper of the last furnace is stopped; The liquid level is 700mm, and the liquid level is kept stable; the minimum tundish liquid level is not lower than 400mm for pouring system, and the head and tail of the first billet and the last billet are cut according to the length of 2.0 meters. When continuous pouring is stopped, the casing shall be removed after the pouring is stopped first.

Converter adopts double slag operation, the first batch of dephosphorization slag: oxygen consumption: 820~900m ³ /N; semi-steel temperature 1380~1400℃, binary basicity R of slag: 2.0~2.5; decarburization slag: terminal carbon according to 0.10 ～0.20% control, tapping temperature 1610～1630℃, slag final slag binary basicity R: 3.0～3.5; slag blocking and tapping, control slag thickness between 0～40mm.

Use micro-nitrogen carburizer (N: 0.005～0.025%) 6kg/ton steel to increase carbon, use silicon-calcium-barium alloy 2.0kg/ton steel to deoxidize, 4.5kg/ton steel synthetic slag; enter LF refining station to control oxygen activity 8 ～18ppm, the final refining slag Fe+MnO≤1.0%; feed Ca-Si wire 1m/ton steel for inclusion denaturation treatment, soft argon blowing time is 10 minutes.

The crystallizer is equipped with electromagnetic stirring to reduce carbon segregation and shrinkage cavity in the center of the slab, the superheat of molten steel in the tundish is controlled to 25-35°C, the casting speed is 1.80-2.0m/min for full protection casting, and the secondary specific water volume is 0.75kg/L , the nitrogen content in steel ranges from 0.0020 to 0.0033%, with an average of 0.0027%, and the nitrogen control level exceeds molten iron pretreatment → converter smelting + LF (+RH) refining → die casting (large-section continuous casting billet) → secondary opening The control level of billet process.

Specific process route:

Molten iron → 80 tons of converter smelting (double slag operation) → slag blocking and tapping → ladle deoxidation alloying → ladle slag modification → LF (80 tons) ladle refining (including temperature raising, alloy fine-tuning, desulfurization) → feeding Si-Ca line → Ladle soft blowing and argon blowing → 150mm×150mm billet continuous casting machine full protection casting, mold electromagnetic stirring → billet inspection → heating → controlled rolling → controlled cooling.

Main technological measures:

—When molten iron Si:0.30～0.60%; S<0.040%, it can be smelted into the furnace. The converter adopts double slag operation, the first batch of dephosphorization slag: the oxygen consumption is controlled according to 880m ³ /N; the semi-steel temperature is controlled within the range of 1360-1400℃, the basicity of dephosphorization slag is controlled according to 2.0, and the blowing time is controlled according to 240 seconds. The end carbon is controlled by 0.15%, P≤0.015%, S≤0.020%, and the final slag basicity (CaO/SiO ₂ )>3.0. The tapping temperature is controlled at 1610-1630°C. The slag blocking ball in the early stage cooperates with the slag blocking cone in the later stage to control the thickness of the ladle slag layer from 0 to 40mm.

- Use 6kg/ton steel micro-nitrogen recarburizer (N: 0.005～0.025%) for carbon distribution in front of the furnace, and use ordinary recarburizers for the rest; use Si-Ca-Ba for deoxidation, and the addition amount is 2.0kg/t steel. Using Mn-Fe with manganese and Si-Fe with silicon, the absorption rate is controlled according to 92%.

- Tapping time ≥ 5min. The slag is used to tap the steel, and the thickness of the slag under the converter in the ladle is ≤40mm; the binary synthetic slag is added at 4kg/ton of steel synthetic slag when tapping; argon is blown at the bottom during the tapping process (the pressure of the argon gas must be guaranteed to be between 1.0-1.1MPa) between).

— Pre-blow argon for 3 minutes after the molten steel arrives at the refining station (flow rate 300-400NL/min), and make appropriate adjustments according to the churning of the liquid level. The slagging material uses synthetic slag, active lime (CaO+MgO: 93-99%, activity (4mol/ml-HCl, temperature 40±1°C, 10min)>350ml), bauxite (Al ₂ O ₃ : 75 ～95%; SiO ₂ : 0～10%)), fluorite (CaF ₂ : 90～98%; SiO ₂ : 0～9%), the amount of slag should be controlled at 1.2 tons (less addition of bauxite should be controlled within 100Kg ), add Fe-Si powder and calcium carbide deoxidation to the slag surface, strive to form white slag and final slag TFe<1.0% within 15 minutes of power supply, and reduce the content of a _o and S in the steel as much as possible. To ensure rapid slag melting, various slag materials should be added as soon as possible. The last batch of alloys is adjusted and stirred with argon blowing for ≥5min (flow rate 300-400NL/min) to ensure uniform alloy composition.

—At the end of the LF furnace treatment, feed the Ca-Si wire 1m/ton steel furnace to carry out inclusion deformation treatment. After feeding the wire, the time of soft argon blowing (flow rate 40-60L/min) must be guaranteed to be ≥ 10min, and the slag surface will slightly surge It is advisable not to expose the steel, so that the inclusions in the steel can fully float up. Target a[o] after refining treatment: 0~10ppm.

—150mm×150mm billet continuous casting, the crystallizer adopts 380A, 4Hz electromagnetic stirring, high alkalinity ladle covering agent, ladle argon seal, tundish full argon blowing, submerged nozzle full protection casting, pouring according to 1.80 The casting speed is controlled by m/min, the superheat of molten steel in the tundish is controlled at 25-35°C, and the secondary cooling of continuous casting is poured with a specific water volume of 0.75L/Kg.

—The ladle adopts long nozzle with Ar seal to protect pouring. Use Mg-Ca dry-type materials with retaining wall tundish, fully protected pouring, argon gas flow rate of 30-50L/min in the large ladle protective casing, and it is strictly forbidden to add covering agent to the impact area of the tundish when no casing is added. The tundish is filled with argon before pouring. The tundish is made of high-alkalinity covering agent; the mold powder is used for high-carbon steel with low viscosity and good thermal insulation performance, so as to avoid mold slag entrainment.

—The crystallizer water flow rate is 120-130m ³ /h, and the secondary cooling water distribution curve adopts 0.75L/kg steel specific water volume. Turn on the electromagnetic stirring of the mold after the dummy head exits the crystallizer, and stop the electromagnetic stirring after the stopper of the last furnace stops pouring. Crystallizer electromagnetic stirring parameters: 380A, 4Hz. Keep pouring at the liquid level of the high and middle ladle, and keep the liquid level stable at 700mm during the process. Strictly implement the minimum tundish liquid level not lower than 400mm. Cut the head and tail of the first billet and the last billet according to the length of 2.0 meters. When continuous pouring is stopped, the casing should be stopped first and then the casing should be removed. Bare pouring is strictly prohibited.

Description of drawings

Figure 1 shows the aging data of SWRH82B in different stages of a factory.

Figure 2 is a photo of the wire drawing and splitting.

Figure 3 is a photograph of wire drawing transverse cracks.

detailed description

The present invention can be implemented in iron and steel complexes, and the following is the steelmaking plant of Shougang Changzhi Iron and Steel Co., Ltd., which adopts the example produced by the invention.

The process route is: high-quality molten iron → LD (80 tons) converter smelting → converter slag blocking and tapping → ladle deoxidation alloying → LF (80 tons) ladle refining furnace → feeding Si-Ca line → ladle bottom blowing argon soft blowing → 150mm× 150mm billet continuous casting machine → billet.

Main process parameters of LD converter smelting:

Volume after bricklaying: 58.5m3; Volume ratio [V/T]: 0.83; Tapping hole diameter [D]: 150mm; Tapping hole angle: 10° Nozzle type: Four-hole Laval; Throat diameter: 31.86 mm; outlet diameter: 41.05mm; angle between the nozzle hole and the center line of the oxygen lance: 12°40′; Mach number: 1.98; oxygen working pressure: 0.75-0.95MPa; Alumina-magnesia-carbon bricks and spinel castables.

Main process parameters of LF ladle refining furnace:

A bottom-blowing air brick is used to carry out bottom-blowing refining (all use argon). Ladle baking: adopt regenerative baking device (using coke oven gas). Refining system: online argon blowing and wire feeding behind the furnace; 80-ton double-station LF ladle refining furnace with a heating capacity of 3-5°C/min and a power of 14MVA.

Main process parameters of continuous casting:

Basic arc radius of 5-machine 5-strand billet continuous casting machine: R10m; pouring section: 150mm×150mm; fixed length: 3.8-12m. Section: 150mm×150mm. Pulling speed: 1.5~3m/min, average 2.5m/min. Crystallizer: copper tube length 1000mm. Crystallizer vibration type: sinusoidal vibration. Frequency: 60~240 times/min. Amplitude ±5mm. Liquid level automatic control method: Ce137 radioactive source. Detection accuracy: ±3mm. Crystallizer water flow: 160m3/h. Electromagnetic stirring specifications: electromagnetic stirrer rated current: 350A; rated voltage: 380V. Apparent power: 230KVA Active power: 40KW(max) Frequency: 2～8Hz(6Hz). Insulation class: H class. Crystallizer water flow: 150m3/h. Infrared sizing control system: detection sizing length 9 ~ 12m; dummy rod form: flexible chain dummy rod.

Embodiment 1: furnace number 6A201382

Converter smelting:

Hot metal condition C: 4.25%, Si: 0.56%, Mn: 0.51%, P: 0.12%, S: 0.022%, temperature: 1318°C.

Charge structure: 68.4 tons of molten iron, 4.4 tons of steel scrap.

Consumption of the first batch of dephosphorization slag: lime 850kg, light-burned dolomite 1099kg; Austrian mine 1900kg; oxygen consumption 880m ³ /N; blowing time: 238 seconds; semi-steel temperature: 1320℃. Semi-steel slag sample: CaO: 42.09%, SiO ₂ : 21.46%, TFe: 11.71%, R: 1.96. BOF endpoint: C: 0.14%, P: 0.014%, S: 0.018%. Final slag sample: CaO: 46.43%, SiO ₂ : 13.44%, TFe: 17.82%, R: 3.46. The tapping temperature is 1610°C. The tapping time is 5 minutes and 21 seconds, and the slag back is 34mm. Deoxidation alloying: micro-nitrogen carburizer 6kg/ton steel; silicon calcium barium 2kg/ton steel; ferromanganese 450kg, ferrosilicon 150kg, carbon ferrochrome 110kg.

LF ladle refining furnace:

910kg of lime; 112kg of refining slag; 145kg of submerged arc slag; 180kg of fluorite; 100kg of bauxite; 100kg of ferrosilicon powder; Outbound a[o]: 9.8ppm.

Continuous casting process:

Crystallizer electromagnetic stirring parameters: 380A, 4Hz; crystallizer water flow rate 120t/h, 0.75L/kg specific water volume for secondary cooling; tundish molten steel superheat 25°C; casting speed 1.80m/min.

Changes of carbon and nitrogen content at each station of SWRH82B: Converter (C: 0.15%; N: 0.0016%) → into LF furnace (C: 0.65%; N: 0.0017%) → out of LF furnace (C: 0.75%; N: 0.002 %) → tundish (C: 0.76%; N: 0.0021%) → rolled material (C: 0.76%; N: 0.0022%).

Embodiment 2: furnace number 6A201383

Converter smelting:

Hot metal condition C: 4.15%, Si: 0.43%, Mn: 0.36%, P: 0.129%, S: 0.011%, temperature: 1288°C.

Charge structure: 69.1 tons of molten iron, 5.1 tons of steel scrap.

Consumption of the first batch of dephosphorization slag: lime 1800kg, lightly burned dolomite 475kg; Austrian ore 807kg; oxygen consumption 900m ³ /N; blowing time: 242 seconds; semi-steel temperature: 1399℃. Semi-steel slag sample: CaO: 47.50%, SiO ₂ : 20.41%, TFe: 11.05%, R: 2.31. Converter endpoint: C: 0.16%, P: 0.012%, S: 0.015%. Final slag sample: CaO: 52.53%, SiO ₂ : 14.94%, TFe: 13.42%, R: 3.52. The tapping temperature is 1612°C. The tapping time is 5 minutes and 25 seconds, and the slag is 30mm behind. Deoxidation alloying: Micro-nitrogen carburizer 6kg/ton of steel; silicon calcium barium 2kg/ton of steel; ferromanganese 440kg, ferrosilicon 155kg, carbon ferrochrome 115kg.

LF ladle refining furnace:

912kg of lime; 110kg of refining slag; 135kg of submerged arc slag; 150kg of fluorite; 110kg of bauxite; 90kg of ferrosilicon powder; Outbound a[o]: 7.8ppm.

Continuous casting process:

Crystallizer electromagnetic stirring parameters: 380A, 4Hz; crystallizer water flow rate 120t/h, 0.75L/kg specific water volume for secondary cooling; tundish molten steel superheat 29°C; casting speed 1.82m/min.

Changes of nitrogen content at each station of SWRH82B: converter (C: 0.16%; N: 0.0018%) → into LF furnace (C: 0.67%; N: 0.0020%) → out of LF furnace (C: 0.77%; N: 0.0022%) → Tundish (C: 0.77%; N: 0.0016%) → Rolled material (C: 0.77%; N: 0.0025%).

Embodiment 3: furnace number 6A201384

Converter smelting:

Hot metal condition C: 4.23%, Si: 0.56%, Mn: 0.51%, P: 0.12%, S: 0.025%, temperature: 1320°C.

Charge structure: 68.4 tons of molten iron, 4.4 tons of steel scrap.

Consumption of the first batch of dephosphorization slag: lime 850kg, light-burned dolomite 1099kg; Austrian mine 1900kg; oxygen consumption 880m ³ /N; blowing time: 238 seconds; semi-steel temperature: 1320℃. Semi-steel slag sample: CaO: 44.66%, SiO ₂ : 20.16%, TFe: 13.36%, R: 2.22. Converter endpoint: C: 0.15%, P: 0.012%, S: 0.018%. Final slag sample: CaO: 48.78%, SiO ₂ : 15.22%, TFe: 13.01%, R: 3.21. The tapping temperature is 1615°C. The tapping time is 5 minutes and 09 seconds, and the slag back is 39mm. Deoxidation alloying: micro-nitrogen carburizer 6kg/ton steel; silicon calcium barium 2kg/ton steel; ferromanganese 450kg, ferrosilicon 150kg, carbon ferrochrome 110kg.

LF ladle refining furnace:

880kg of lime; 1102kg of refining slag; 150kg of submerged arc slag; 170kg of fluorite; 110kg of bauxite; 120kg of ferrosilicon powder;

Continuous casting process:

Crystallizer electromagnetic stirring parameters: 380A, 4Hz; crystallizer water flow rate 120t/h, 0.75L/kg specific water volume for secondary cooling; tundish molten steel superheat 25°C; casting speed 1.81m/min.

Changes of nitrogen content at each station of SWRH82B: Converter (C: 0.15%; N: 0.0022%) → into LF furnace (C: 0.70%; N: 0.0025%) → out of LF furnace (C: 0.78%; N: 0.0026%) → Tundish (C: 0.80%; N: 0.0028%) → Rolled material (C: 0.81%; N: 0.0030%).

Embodiment 4: furnace number 6A201385

Converter smelting:

Hot metal condition C: 4.2%, Si: 0.56%, Mn: 0.51%, P: 0.12%, S: 0.022%, temperature: 1318°C.

Charge structure: 68.4 tons of molten iron, 4.4 tons of steel scrap.

Consumption of the first batch of dephosphorization slag: lime 850kg, light-burned dolomite 1099kg; Austrian ore 1810kg; oxygen consumption 870m ³ /N; blowing time: 238 seconds; semi-steel temperature: 1320℃. Semi-steel slag sample: CaO: 42.09%, SiO ₂ : 21.46%, TFe: 11.71%, R: 1.96. BOF endpoint: C: 0.14%, P: 0.014%, S: 0.018%. Final slag sample: CaO: 46.43%, SiO ₂ : 13.44%, TFe: 17.82%, R: 3.46. The tapping temperature is 1618°C. The tapping time is 5 minutes and 21 seconds, and the slag back is 34mm. Deoxidation alloying: micro-nitrogen carburizer 6kg/ton steel; silicon calcium barium 2kg/ton steel; ferromanganese 450kg, ferrosilicon 150kg, carbon ferrochrome 110kg.

LF ladle refining furnace:

910kg of lime; 112kg of refining slag; 145kg of submerged arc slag; 180kg of fluorite; 100kg of bauxite; 100kg of ferrosilicon powder;

Continuous casting process:

Crystallizer electromagnetic stirring parameters: 380A, 4Hz; crystallizer water flow rate 120t/h, 0.75L/kg specific water volume for secondary cooling; tundish molten steel superheat 35°C; casting speed 1.85m/min.

Changes of nitrogen content at each station of SWRH82B: Converter (C: 0.14%; N: 0.0023%) → into LF furnace (C: 0.74%; N: 0.0026%) → out of LF furnace (C: 0.81%; N: 0.0028%) → Tundish (C: 0.83%; N: 0.0030%) → Rolled material (C: 0.83%; N: 0.0033%).

Claims (1)

1. A method for producing steel for high-carbon and low-nitrogen strands, the process comprising: molten iron desulfurization and slag removal → converter smelting → slag blocking and tapping → ladle deoxidation and alloying → ladle slag modification → LF ladle refining → feeding Si- Ca line → ladle bottom blowing argon soft blowing → 150mm×150mm billet full protection casting → crystallizer electromagnetic stirring; the characteristic is that the technical parameters controlled in the process are as follows: The converter adopts 80 tons of small converter double slag operation, the carbon at the end point is controlled at 0.15%, the tapping temperature is 1610-1620°C, the slag is blocked and the steel is tapped, and the thickness of the slag during the tapping process of the converter is controlled between 0 and 40mm; Carbon agent: N: 0.005～0.025%, with carbon 6kg/ton steel, deoxidized with Si-Ca-Ba, adding amount 2.0kg/ton steel, 4.5kg/ton steel synthetic slag; 80 tons of LF refining furnace slagging material uses synthetic slag, active lime: CaO+MgO: 96.5-98%, SiO ₂ : 1-1.5%, CO ₂ : 1-2.0%, activity > 350ml, activity test conditions : 4mol/ml-HCl, temperature 40±1℃, 10min; bauxite: Al ₂ O ₃ : 75-97%, SiO ₂ : 0-10%, CaO: 1-5%, MgO: 2-9.5% , H ₂ O: 0~0.5%; Fluorite: CaF ₂ : 85.44~99%, SiO ₂ : 1~14%, S: 0~0.5%, P: 0~0.06%, the amount of slag is 1~1.2 tons Control, bauxite is controlled at 80-100Kg, Fe-Si powder and calcium carbide are added to the slag surface to deoxidize, white slag and final slag TFe<1.0% will be formed within 15 minutes of power supply, and the content of a _[o] and S in the steel will be reduced; LF Feed Ca-Si wire 1m/ton of steel at the end of furnace treatment, blow argon softly after feeding the wire, flow rate 40-60L/min, time ≥ 10min, it is advisable that the slag surface is slightly surging and the steel is not exposed, so that the inclusions in the steel are fully Float up, after refining treatment target a _[o] : 0～10ppm; 150mm×150mm billet continuous casting is adopted, the crystallizer adopts 380A, 4Hz electromagnetic stirring, high alkalinity ladle covering agent, ladle argon sealing, tundish full argon blowing, submerged nozzle full protection casting, pouring according to 1.8 ～2.0m/min casting speed control, tundish molten steel superheat controlled at 25～35℃, continuous casting secondary cooling with 0.75L/kg specific water volume for pouring; use Mg-Ca dry material belt retaining wall tundish, Full protection pouring, argon flow rate of 30-50L/min in the protective casing of large argon seal, it is strictly forbidden to add covering agent to the impact area of the tundish when no casing is added, the tundish is filled with argon before pouring, and the tundish is covered with high alkalinity agent; low-viscosity and high-alkalinity special high-carbon steel mold flux for crystallizer: viscosity: 1300°C, 4-6 poise; CaO/SiO ₂ alkalinity: 0.80-1.1, crystallizer water flow rate 120-130m ³ /h, secondary The cooling water distribution curve adopts 0.75L/kg steel specific water volume; the electromagnetic stirring of the crystallizer is turned on after the dummy head comes out of the crystallizer, and the electromagnetic stirring is stopped after the stopper of the last furnace is stopped; the liquid level of the high tundish is kept pouring, and the liquid level is 700mm during the process , keep the liquid level stable; the minimum tundish liquid level is not lower than 400mm for pouring system, the first billet and the last billet cutting head and tail are cut according to the length of 2.0 meters; when continuous pouring stops, the first Remove the casing after stopping pouring.