Method for producing 30MnSi through R8 billet continuous casting machine

Abstract

The invention discloses a method for producing 30MnSi by an R8 billet continuous casting machine, which adopts the following process route: molten iron pretreatment, converter smelting, LF (ladle furnace) refining, continuous casting and cold delivery, specifically, in the converter smelting procedure, the molten steel components and temperature at the end point of a converter are accurately controlled by optimizing a scrap steel-molten iron loading system, C-T coordinated tapping and whole-course argon protection; in the LF refining process, purified molten steel is obtained through gradient slagging, precise calcium feeding and soft blowing time-temperature coupling control; and in the continuous casting process, through cooperation of crystallizer electric stirring and tail end electric stirring, casting process parameter optimization and pulling speed-temperature dynamic matching, a high-quality 30MnSi casting blank is obtained. According to the technology, through full-process parameter optimization, refined production of the high-carbon manganese silicon steel square billet is achieved, the technology is particularly suitable for preparing the billet for the wire rod with strict requirements for strength, toughness and machining performance, and the yield and the product quality stability in industrial production can be remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to a method for producing 30MnSi by R8 billet continuous casting machine. BACKGROUND

[0002] 30MnSi is mainly used for high-strength wire rod, disc garden, etc. It is generally applied to prestressed pipe pile reinforcement and can be made into PC steel bar, which is mainly used in the construction industry and is the main steel material in prestressed concrete pipe pile (mainly used in engineering foundation), has the advantages of high strength, material saving, convenient use and easy quality guarantee, and is quite widely used in the construction industry. 30MnSi prestressed concrete steel bar has the advantages of high strength, material saving, convenient use, etc., and is mainly used for pipe pile foundation of coastal, river construction engineering and high-rise building, and is widely used. Low carbon, energy saving, environmental protection and low cost are the goals pursued by the steel metallurgy industry

[0003] The existing production efficiency of 30MnSi prestressed concrete steel bar is low, the purity of molten steel is low, the cost is high, and the comprehensive qualified rate is low. The main performances are as follows:

[0004] 1. Component control limitation: In the traditional converter smelting process, the C element content fluctuation range is usually ±0.03%, and the Si and Mn elements fluctuate in the range of ±0.05% due to unstable alloy adding sequence and recovery rate, which leads to inconsistent strength in the process of wire rod cold drawing. According to the statistical data of a certain enterprise, the standard deviation of tensile strength of 30MnSi wire rod produced by traditional process reaches 15MPa, which cannot meet the demand of high-end wire rod users.

[0005] 2. Insufficient purity of molten steel: The white slag retention time of conventional LF furnace refining is only 10-15min, the T[O] (total oxygen content) in the steel is generally higher than 25×10 -6 , and the proportion of inclusions with a size of more than 10μm reaches 15%, which easily causes fracture defects in wire rod deep processing. In a batch of steel strand production, the waste rate caused by excessive inclusions reaches 8%.

[0006] 3. Frequent continuous casting defects: Under the traditional speed control mode, the speed fluctuation range reaches ±0.2m / min, and the cooling parameters of the crystallizer are unreasonable, the proportion of the surface transverse vibration marks depth of the casting billet exceeding 3mm reaches 20%, and the center porosity level is usually 2.0, which seriously affects the uniformity of the mechanical properties of the wire rod.

[0007] It is urgent to develop a new type of smelting and continuous casting process which can realize: ①C, Si, Mn element fluctuation range ≤±0.01%; ②T[O]≤18×10 -6 and inclusion size ≤5μm; ③casting billet surface vibration mark depth ≤1.5mm, center porosity ≤1.0 level, to meet the production demand of high-end hot-rolled wire rod. SUMMARY

[0008] The present application aims to overcome the above-mentioned deficiencies of the prior art, and provides a method for producing 30MnSi by an R8 square billet continuous casting machine.

[0009] The present application solves its technical problems by using the following technical solutions.

[0010] The present application provides a method for producing 30MnSi by an R8 square billet continuous casting machine, which adopts the following process route: hot metal pretreatment, converter smelting, LF refining, continuous casting and cold feeding, wherein: in the converter smelting process, the steel liquid composition and temperature at the end point of the converter are precisely controlled by optimizing the charging system of scrap steel-hot metal, C-T coordinated tapping and full-process argon protection; in the LF refining process, the purified steel liquid is obtained by gradient slagging, precise calcium feeding and soft blowing time-temperature coupling control; in the continuous casting process, the high-quality 30MnSi billet is obtained by the coordination of crystallizer electric stirring and end electric stirring, optimization of pouring process parameters and dynamic matching of casting speed-temperature.

[0011] The present application has the following beneficial effects:

[0012] The present application provides a method for producing 30MnSi by an R8 square billet continuous casting machine. By optimizing the parameters of the whole process of smelting and continuous casting, the fine production of high-carbon manganese silicon steel square billet is realized, which is particularly suitable for the preparation of billets for wire rods with strict requirements on strength, toughness and processing performance, and can significantly improve the yield and product quality stability in industrial production. DETAILED DESCRIPTION

[0013] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0014] A method for producing 30MnSi by an R8 square billet continuous casting machine provided by the embodiments of the present application will be described in detail below.

[0015] The embodiment of the application provides a method for producing 30MnSi by an R8 bloom continuous casting machine, adopts the following process route including: hot metal pretreatment, converter smelting, LF refining, continuous casting and cold feeding, wherein: in the converter smelting process, through optimization of the charging system of scrap steel-hot metal, C-T coordinated tapping and full-process argon protection, the composition and temperature of the molten steel at the converter endpoint are precisely controlled; in the LF refining process, through gradient slagging, precise calcium feeding and soft blowing time-temperature coupling control, purified molten steel is obtained; in the continuous casting process, through the coordination of crystallizer electric stirring and end electric stirring, pouring process parameter optimization and dynamic matching of casting speed-temperature, high-quality 30MnSi billets are obtained. Compared with the traditional process, the above scheme provided by the application can improve the C element hit rate to 98%, reduce T[O] to 15x10 -6 In the following, the casting billet surface defect rate is reduced by 70%, and specifically:

[0016] The converter smelting dynamic control technology includes:

[0017] Charging system optimization: a charging amount dynamic model based on furnace capacity ratio is established, when the Si content of hot metal is greater than or equal to 0.5%, the scrap steel ratio is automatically increased to 22-25t, through scrap steel-hot metal heat balance calculation, the endpoint temperature fluctuation is ensured to be less than or equal to ±10℃. When the Si content of hot metal of a certain furnace is 0.6%, 25t of scrap steel is added according to the model, and the endpoint temperature deviates from the target value by only 5℃. This precise regulation avoids “excessive adjustment” or “insufficient adjustment”, ensures that the endpoint temperature fluctuation is less than or equal to ±10℃, and provides stable molten steel conditions for the subsequent continuous casting process (the continuous casting has very high requirements for the stability of molten steel temperature, and excessive temperature fluctuation will lead to poor melting of the crystallizer protection slag, increasing the risk of leakage).

[0018] Endpoint double-parameter control method: taking C-T (carbon-temperature) coordinated control as the core, the continuous temperature measurement and carbon determination technology of the sub-lance are adopted, when the endpoint C is 0.085% and the temperature is 1680℃, it is determined as the best tapping state, and the hit rate of the control mode with C≥0.08% at the endpoint is 97%, which is 20% higher than that of the traditional experience control.

[0019] Full-process argon protection for tapping: innovative design of "three-stage argon control": strong blowing (flow rate≥900NL / min) to drive oxygen for 3min before tapping→blowing (flow rate 550-650NL / min) to promote alloy melting during tapping→weak blowing (flow rate 250-350NL / min) to prevent nitrogen absorption after tapping, which makes the nitrogen increase of molten steel less than or equal to 5x10 -6 .

[0020] The LF furnace refining clean steel technology includes:

[0021] Gradient slagging process: the first batch of 40-60 kg fluorite was added to break the steel slag shell, and 3 minutes later, two batches of lime (40-60 kg each) were added, and the CaO-SiO-Al O slag system was optimized to quickly increase the slag basicity (CaO / SiO) to 3.2-3.7, and the white slag formation time was shortened to 12 minutes, which was 8 minutes shorter than the traditional process.

[0022] Precise control of calcium treatment: develop a calcium wire feeding amount calculation model: W=0.05×[Al]×V (W is the weight of calcium wire, unit: kg, [Al] is the aluminum content in steel, unit: %, V is the amount of molten steel, unit: t), when the molten steel Al=0.03%, V=120t, feed calcium wire 60m, the calcium aluminate rate of inclusions is more than 90%, and the size is controlled in 3-5μm.

[0023] Soft blowing time-temperature coupling control: establish a soft blowing time-temperature relationship model: t=20+0.1×(T LF出站 -1567)(t is the soft blowing time, unit: min, T LF出站 is the LF furnace exit temperature, unit: ℃), when the exit temperature is 1572℃, the soft blowing time is automatically set to 25min, which ensures that the inclusions float up sufficiently, and the qualified rate of T[O]≤15×10 -6 is 95%.

[0024] Low defect control technology of continuous casting includes:

[0025] Crystallizer electric stirring and end electric stirring synergy: crystallizer electric stirring uses 265-275A current + 5-8Hz frequency to break dendrites in the initial stage of billet shell formation and reduce center segregation; end electric stirring uses 380-405A current + 5-8Hz frequency to promote equiaxed crystal growth, so that the equiaxed crystal rate is increased from 30% to 55%, and the center porosity is ≤1.0 level.

[0026] Non-sine vibration parameter optimization: innovative setting of amplitude A=±3.5mm, skew rate 0.15, and frequency f=80 times / minute combination parameters to control the vibration mark depth within 1.2mm, which is 60% lower than the traditional sine vibration (amplitude ±4mm, frequency 100 times / minute), and the statistics of a pouring show that the proportion of vibration mark exceeding 2mm is reduced from 18% to 3%.

[0027] Speed-temperature dynamic matching system: establish a special model for 160×160mm section: V=2.2-0.02×(T 中包 -1510)(V is the pulling speed, unit: m / min, T 中包 is the tundish temperature, unit: ℃), when the temperature is 1515-1530℃, the pulling speed is automatically controlled at 2.2±0.1m / min, and the system reduces the rate of pulling speed fluctuation exceeding the standard from 15% to 4%.

[0028] The application will be further described in connection with the following examples.

[0029] The 30MnSi bloom production in the following examples 1-4 includes the improvement of both equipment and process, wherein the equipment improvement is as follows:

[0030] Converter slag stopping system: on the basis of the original slide plate slag stopping, an automatic slag stopping plug throwing device is added, the slag stopping plug is made of high alumina material (Al2O3≥85%), the diameter is 120 mm, the throwing precision is ≤±10 mm, and the slag stopping efficiency is increased from 75% to 92%.

[0031] LF furnace electrode control system: upgraded to a three-electrode automatic lifting system, using fuzzy PID control algorithm, electrode lifting speed 0.5-1.5 m / min, electrode insertion depth into slag layer during submerged arc heating is controlled at 50-80 mm, ensuring the heating rate ≥5℃ / min.

[0032] Continuous casting crystallizer vibration device: replaced with a servo motor drive system, vibration waveform distortion ≤5%, skew rate adjustment precision 0.01, can adjust vibration parameters online in real time, meet the process requirements of different steel grades.

[0033] The following is the improvement of the process in examples 1-4:

[0034] Example 1

[0035] Taking the production of 160x160mm section 30MnSi bloom as an example, the process route and process parameter control are as follows:

[0036] 1. Converter smelting stage (120t furnace)

[0037] Raw material loading: 100t of molten iron (Si=0.6%, P=0.12%, S=0.03%) + 20t of scrap steel (outer size and single weight meet GB / T4223 standard), using top and bottom combined blowing converter smelting, blowing oxygen time 14min, oxygen purity 99.6%, pressure 0.85MPa.

[0038] End point control: sub-lance detects end point C=0.088%, temperature=1675℃, P=0.011%, S=0.020%, using slide plate + slag stopping plug double slag stopping, slag layer thickness 55mm, phosphorus content 0.002%.

[0039] Tapping alloying: 3 min before tapping, argon was opened (flow rate 900 NL / min), and 1 / 4 of the tapping time, silicon manganese 17.5 kg / t (Mn 65 Si 17), low silicon iron 10 kg / t (Si 41), silicon iron 7.5 kg / t (Si 75), and carbon additive 4 kg / t (C 98.5%) were added in sequence. During the tapping process, the bottom argon flow rate was controlled at 600 NL / min to promote alloy melting. The tapping time was 3.2 min. After tapping, the composition of the molten steel was C = 0.298%, Si = 0.82%, and Mn = 0.97%. After tapping, the bottom argon flow rate was adjusted to 300 NL / min to prevent nitrogen absorption at the liquid surface. The final nitrogen content of the molten steel was ≤5 × 10 -6 .

[0040] 2. LF furnace refining stage

[0041] Slagging process: first, fluorite 50 kg was added, then 3 min later, the first batch of lime 50 kg was added, and the arc was powered to raise the temperature. 5 min later, the second batch of lime 50 kg was added. When the slag turned white at 12 min and the basicity reached 3.5, the white slag was maintained for 22.5 min.

[0042] Component fine tuning: according to the spectral analysis results, silicon manganese 200 kg was added to make Mn reach 0.99%, and calcium wire 60 m (calcium wire diameter 13 mm) was fed. The soft blowing time was 20 + 0.1 × (T LF出站 -1567) = 20.3 min (flow rate 150 NL / min), and the exit temperature was 1570℃ (TL + 76℃).

[0043] 3. Continuous casting stage

[0044] Equipment parameters: crystallizer electric stirring current 270 A, frequency 6 Hz; end electric stirring current 400 A, frequency 6 Hz; vibration parameters: non-sinusoidal vibration, amplitude ± 3.5 mm, skew rate 0.15, frequency 80 times / min, crystallizer cooling water volume 135 m 3 / h.

[0045] Pouring control: tundish temperature 1515℃ (TL + 21℃), according to the speed-temperature dynamic matching formula V = 2.2 - 0.02 × (T 中包 -1510), the speed V = 2.2 - 0.02 × (1515 - 1510) = 2.1 m / min was calculated, the immersion nozzle insertion depth was 130 mm, the protective slag layer thickness was 60 mm, the tundish liquid level was 720 mm, the slag was discharged once every 4 heats, and the slag layer thickness was controlled within 90 mm.

[0046] Casting blank quality: after detection, the offline casting blank had no ≥1 mm cracks and ≥2 mm scratches on the surface, the macroscopic inspection center porosity was 0.5 level, the center segregation was 0.5 level, and T[O] = 14 × 10 -6The size of the inclusions is less than or equal to 5 μm.

[0047] Example 2

[0048] The process route and process parameter control are as follows, taking the production of 30MnSi square billet with a cross section of 160x160 mm as an example.

[0049] 1. Converter smelting stage (125 t ladle)

[0050] The raw materials are charged: 105 t of molten iron (Si=0.55%, P=0.11%, S=0.028%) + 20 t of scrap steel (the outer size and unit weight meet the GB / T4223 standard), the top and bottom combined blowing converter is used for smelting, the oxygen blowing time is 14.5 min, the oxygen purity is 99.6%, and the pressure is 0.86 MPa.

[0051] The end point control is as follows: the end point C=0.086%, the temperature=1678°C, P=0.010%, S=0.019% are detected by the sub-lance, the double slag stopping of slide plate + stopper is used, the slag layer thickness is 58 mm, and the phosphorus reversion amount is 0.002%.

[0052] The steel alloying is as follows: the argon is opened (the flow rate is 900 NL / min) 3 min before tapping, the silicon manganese 17.8 kg / t (Mn65Si17), the low silicon iron 10.2 kg / t (Si41), the silicon iron 7.6 kg / t (Si75), and the carbon additive 4.1 kg / t (C98.5%) are sequentially added when the tapping is 1 / 4, the bottom blowing argon flow rate is controlled to be 600 NL / min to promote the alloy melting during the tapping process, the tapping time is 3.3 min, after the tapping, the bottom blowing argon flow rate is adjusted to be 300 NL / min to prevent the nitrogen absorption of the liquid surface, and finally the nitrogen increase amount of the molten steel is less than or equal to 5x10 -6 The composition of the molten steel is as follows: C=0.297%, Si=0.83%, and Mn=0.98%.

[0053] 2. LF furnace refining stage

[0054] The slag making process is as follows: first, 50 kg of fluorite is added, 50 kg of the first batch of lime is added after 3 min, the electric arc is buried to increase the temperature, 50 kg of the second batch of lime is added after 5 min, the slag is white at 12 min, the basicity reaches 3.5, and the white slag is maintained for 23 min.

[0055] The composition fine adjustment is as follows: according to the spectral analysis result, the silicon manganese 210 kg is added to make the Mn reach 1.00%, the calcium wire is fed for 62 m (the calcium wire diameter is 13 mm), the soft blowing time is 20+0.1x(T LF出站 -1567)=20.5 min (the flow rate is 150 NL / min), and the outlet temperature is 1572°C (TL+78°C).

[0056] 3. Continuous casting stage

[0057] Device parameters: crystallizer electric stirring current 270 A, frequency 6 Hz; end electric stirring current 400 A, frequency 6 Hz; vibration parameters: non-sinusoidal vibration, amplitude ±3.5 mm, skew rate 0.15, frequency 80 times / min, crystallizer cooling water amount 136 m 3 / h.

[0058] Pouring control: tundish temperature 1518°C (TL+24°C), according to the speed-temperature dynamic matching formula V=2.2-0.02x(Ttundish-1510), the speed V=2.2-0.02x(1518-1510)=2.04 m / min is calculated, the actual control speed is 2.04 m / min, the submerged entry nozzle insertion depth is 132 mm, the protective slag layer thickness is 61 mm, the tundish liquid level is 725 mm, the slag is discharged once every 4 heats, and the slag layer thickness is controlled within 90 mm.

[0059] Casting blank quality: after detection, the offline casting blank has no ≥1 mm crack and ≥2 mm scratch on the surface, the low-magnification inspection center porosity is 0.6 level, the center segregation is 0.5 level, T[O]=14.5x10 -6 , and the inclusion size is ≤5 μm.

[0060] Example 3

[0061] Taking 160x160 mm section 30MnSi square billet production as an example, the process route and process parameter control are as follows:

[0062] 1. Converter smelting stage (122 t furnace)

[0063] Raw material loading: 102 t of molten iron (Si=0.58%, P=0.115%, S=0.029%) + 20 t of scrap steel (the outer size and single weight meet the GB / T4223 standard), top and bottom combined blowing converter smelting is adopted, oxygen blowing time is 14.2 min, oxygen purity is 99.6%, and pressure is 0.855 MPa.

[0064] End point control: the end point C=0.084%, temperature=1676°C, P=0.0105%, and S=0.0195% are detected by the sub-lance, double slag stopping is adopted by using slide plate + stopper, the slag layer thickness is 56 mm, and the phosphorus content is 0.002%.

[0065] Tapping alloying: 3 minutes before tapping, argon was opened (flow rate 950 NL / min), and 1 / 4 of the tapping time, silicon manganese 17.6 kg / t (Mn 65 Si 17), low silicon iron 10.1 kg / t (Si 41), silicon iron 7.55 kg / t (Si 75), and carbon additive 4.05 kg / t (C 98.5%) were added in sequence. During the tapping process, the bottom argon flow rate was controlled at 550 NL / min to promote alloy melting. The tapping time was 3.25 min. After tapping, the bottom argon flow rate was adjusted to 300 NL / min to prevent nitrogen absorption at the liquid surface. The final nitrogen content of the molten steel was ≤5×10 -6 -4. The composition of the molten steel was: C = 0.296%, Si = 0.825%, Mn = 0.975%.

[0066] 2. LF refining stage

[0067] Slagging process: first, 45 kg of fluorite was added, then 45 kg of lime was added after 3 min, and the temperature was raised by electric arc welding. After 5 min, the second batch of lime 45 kg was added. When the slag turned white at 12 min and the basicity reached 3.4, the white slag was maintained for 22.5 min.

[0068] Component fine tuning: according to the spectral analysis results, 205 kg of silicon manganese was added to make Mn reach 0.995%, and calcium wire 59 m (calcium wire diameter 13 mm) was fed. The soft blowing time was 20 + 0.1 × (T LF出站 -1567) = 20.4 min (flow rate 150 NL / min), and the outlet temperature was 1571 ℃ (TL + 77 ℃).

[0069] 3. Continuous casting stage

[0070] Equipment parameters: crystallizer electric stirring current 270 A, frequency 6 Hz; end electric stirring current 400 A, frequency 6 Hz; vibration parameters: non-sinusoidal vibration, amplitude ± 3.5 mm, skew rate 0.15, frequency 80 times / min, crystallizer cooling water flow rate 135.5 m 3 / h.

[0071] Pouring control: tundish temperature 1516 ℃ (TL + 22 ℃), according to the speed-temperature dynamic matching formula V = 2.2 - 0.02 × (T 中包 -1510), the calculated speed V = 2.2 - 0.02 × (1516 - 1510) = 2.08 m / min, the actual control speed was 2.08 m / min, the immersion nozzle insertion depth was 131 mm, the protective slag layer thickness was 60.5 mm, the tundish liquid level was 722 mm, and the slag was discharged once every 4 heats, and the slag layer thickness was controlled within 90 mm.

[0072] The quality of the cast blank: the off-line cast blank was detected, the surface was free of cracks of ≥1 mm, scratches of ≥2 mm, the center porosity was 0.55 grade, the center segregation was 0.5 grade, T[O]=14.2x10 -6 , the size of the inclusions was ≤5 μm.

[0073] Example 4

[0074] Taking the production of 30MnSi square billets with a cross section of 160x160 mm as an example, the process route and process parameter control are as follows:

[0075] 1. Converter smelting stage (123 t of furnace)

[0076] Raw material loading: 103 t of hot metal (Si=0.56%, P=0.112%, S=0.0285%) + 20 t of scrap steel (the external size and single weight meet the GB / T4223 standard), top and bottom combined blowing converter smelting was adopted, the oxygen blowing time was 14.3 min, the oxygen purity was 99.6%, and the pressure was 0.858 MPa.

[0077] End point control: the end point C=0.087%, the temperature=1679°C, P=0.0102%, S=0.0192% were detected by the sub-lance, double slag stopping was adopted by using slide plate + stopper, the slag layer thickness was 57 mm, and the phosphorus reversion amount was 0.002%.

[0078] Steel tapping alloying: argon was opened (the flow rate was 900 NL / min) 3 min before tapping, and silicon manganese 17.7 kg / t (Mn65Si17), low silicon iron 10.15 kg / t (Si41), silicon iron 7.58 kg / t (Si75), and carbon additive 4.08 kg / t (C98.5%) were sequentially added at 1 / 4 of the tapping time. During the tapping process, the bottom argon flow rate was controlled to be 650 NL / min to promote alloy melting, the tapping time was 3.28 min, after the tapping, the bottom argon flow rate was adjusted to be 300 NL / min to prevent nitrogen absorption of the liquid surface, and finally the nitrogen increase amount of the molten steel was ≤5x10 -6 , the molten steel composition: C=0.299%, Si=0.828%, Mn=0.982%.

[0079] 2. LF furnace refining stage

[0080] Slag making process: first, 60 kg of fluorite was added, 3 min later, the first batch of lime 60 kg was added, the buried arc was powered and heated, 5 min later, the second batch of lime 60 kg was added, the slag turned white at 12 min, and the basicity reached 3.6, the white slag was maintained for 22.8 min.

[0081] Composition fine adjustment: according to the spectral analysis results, 208 kg of silicon manganese was added to make the Mn reach 0.998%, 61 m of calcium wire (the calcium wire diameter was 13 mm) was fed, and the soft blowing time was 20+0.1x(T LF出站- 1567) = 20.6 min (flow rate 150 NL / min), outlet temperature 1573°C (TL+ 79°C).

[0082] 3. Continuous casting stage

[0083] Equipment parameters: mould electrical stirring current 270 A, frequency 6 Hz; end electrical stirring current 400 A, frequency 6 Hz; vibration parameters: non-sinusoidal vibration, amplitude ± 3.5 mm, skew rate 0.15, frequency 80 times / min, mould cooling water flow rate 135.8 m 3 / h.

[0084] Pouring control: tundish temperature 1519°C (TL+ 25°C), according to the dynamic matching formula V = 2.2 - 0.02 x (Ttundish - 1510), the casting speed V = 2.2 - 0.02 x (1519 - 1510) = 2.02 m / min was calculated, the actual control casting speed was 2.02 m / min, the submerged entry nozzle insertion depth was 133 mm, the thickness of the slag layer was 61.5 mm, the tundish liquid level was 728 mm, the slag was discharged once every 4 heats, and the slag layer thickness was controlled within 90 mm.

[0085] Casting blank quality: after detection of the off-line casting blank, there was no crack ≥ 1 mm, scratch ≥ 2 mm on the surface, the center porosity was 0.6 grade, the center segregation was 0.6 grade, T[O] = 14.8 x 10 -6 -6, and the inclusion size was ≤ 5 μm.

[0086] Comparative Example 1

[0087] The traditional process is: hot metal pretreatment → converter smelting (using traditional experience control, without optimized scrap - hot metal charging system, C-T coordinated tapping and full-process argon protection) → LF refining (without gradient slagging, precise calcium feeding and soft blowing time-temperature coupling control) → continuous casting (without mould and end electrical stirring synergy, pouring process parameter optimization and dynamic matching of casting speed-temperature) → cold delivery.

[0088] Using the traditional process to produce 30MnSi, the C element fluctuation range is ± 0.03%, the T.O content is 25 x 10 -6 -6, the inclusion size > 5 μm accounts for 15%, the casting blank surface crack rate is 12%, the center porosity ≥ 1.5 grade accounts for 30%, and the rod yield is 85%.

[0089] Comparative Example 2

[0090] Similar to the steps of Example 1, the only difference is that in the converter smelting process, the amount of scrap- molten iron charged is 110 tons, and the molten iron and scrap are charged according to a mass ratio of 80:15. The results are as follows: the end temperature fluctuation reaches ±20℃, the C element fluctuation range is ±0.025%, the casting blank quality decreases, the surface crack rate reaches 8%, and the rod yield is reduced to 88%.

[0091] Comparative Example 3

[0092] Similar to the steps of Example 1, the only difference is that in the LF refining process, the soft blowing time is not controlled according to the formula t = 20 + 0.1 x (T LF出站 -1567), and when the LF furnace outstation temperature is 1570℃, the soft blowing time is only 10 min. The results are as follows: the T[O] content is increased to 22 x 10 -6 , the inclusion size >5μm accounts for 12%, the rod cold-drawing wire breakage rate is increased to 4%, and the scrap rate is increased.

[0093] Comparative Example 4

[0094] Similar to the steps of Example 1, the only difference is that in the LF refining process, the gradient slagging process is not used, but 50 kg of fluorite and 100 kg of lime are added at one time. The results are as follows: the slag basicity CaO / SiO is increased to 3.5, the time required is extended to 25 min, the white slag formation time reaches 30 min, which is increased by 18 min compared with Example 1; the T[O] content in the steel is increased to 20 x 10 -6 , the inclusion size >5μm accounts for 12%, and after the casting blank is processed into a rod, the cold-drawing wire breakage rate is increased to 3.5%, and the yield is reduced to 89%.

[0095] Comparative Example 5

[0096] Similar to the steps of Example 1, the only difference is that in the continuous casting process, the crystallizer electric stirring and the end electric stirring are not used for coordinated control, and only the crystallizer electric stirring is turned on. The results are as follows: the equiaxed crystal rate of the casting blank is reduced from 55% to 35%, the center porosity level is increased to 1.2, and the center segregation level is increased to 1.0; the standard deviation of the rod tensile strength reaches 12 MPa, and the yield strength fluctuation range is expanded to ±15 MPa, which cannot meet the production requirements of high-end prestressed steel wire.

[0097] The following table is the test results of 30MnSi square billets obtained by Comparative Example 1 (traditional process) and Examples 1-4 (process of the present application) (the average values are in the table):

[0098] Technical index Traditional process Process of the present application Lifting range C element fluctuation range ±0.03％ ±0.01％ 66.7％ T.O content 25 x 10 -6 ]] 15 x 10 -6 ]] 40％ Inclusion size > 5 μm ratio 15％ 5％ 66.7％ Casting blank surface crack rate 12％ 3.6％ 70％ Center porosity ≥ 1.5 level proportion 30％ 8％ 73.3％ Rod bar material yield 85％ 93-95％ 8-10％

[0099] From the above table, it can be seen that the method for producing 30MnSi provided by the R8 square billet continuous casting machine has significant improvements in C element control, molten steel purity, inclusion size, casting billet surface quality, center porosity, and material yield compared with the traditional process. Each embodiment can stably produce high-quality 30MnSi casting billets.

[0100] In summary, the embodiment of the present application provides a method for producing 30MnSi by an R8 square billet continuous casting machine. By optimizing the process parameters of converter smelting, LF refining, and continuous casting, precise control of the entire production process of 30MnSi is achieved, effectively solving the problems of large composition fluctuation, low molten steel purity, and many casting billet defects in the traditional process. In the converter smelting stage, the precise control of the composition and temperature of the final converter liquid steel is ensured by optimizing the scrap-molten iron charging system, C-T coordinated tapping, and full-range argon protection. In the LF refining stage, the purity of the molten steel is improved by gradient slag making, precise calcium feeding, and soft blowing time-temperature coupling control. In the continuous casting stage, the high quality of the casting billet is ensured by the coordination of crystallizer electric stirring and end electric stirring, optimization of casting process parameters, and dynamic matching of casting speed and temperature. Each process parameter is indispensable and works together to enable the production method of the present application to stably and efficiently produce 30MnSi products that meet high-end requirements.

[0101] As can be seen above, the scheme provided by the embodiment of the present application has the following advantages and characteristics compared with the prior art:

[0102] The quality improvement benefits are as follows:

[0103] Mechanical property uniformity: The standard deviation of the tensile strength of the 30MnSi wire rod produced by the present process is reduced from 15 MPa to 8 MPa, the yield strength fluctuation range is ≤10 MPa, and the elongation is ≥25%, meeting the production requirements of high-strength prestressed steel wire.

[0104] Processing performance optimization: Due to the refinement and uniform distribution of inclusions, the wire rod cold drawing breakage rate is reduced from 5% to 1.2%, the wire drawing die life is extended by 50%, and the single ton wire rod die consumption cost is reduced by 15 yuan after using the billet of the present process.

[0105] Surface quality improvement: After the surface of the casting billet is ground, the vibration mark depth is ≤1.5 mm, the incidence of defects such as iron oxide skin indentation and inclusions is reduced from 8% to 1.5%, the wire rod surface finish is Ra1.6 μm, meeting the surface quality requirements of high-grade construction steel.

[0106] The economic benefit analysis is as follows:

[0107] The yield rate is improved: the yield rate of the wire rod is improved from 85% to 94%, and the qualified wire rod of 2 million tons of 30MnSi wire rod per year can be produced, and the annual output value of 9 million yuan is increased according to the market average price of 5000 yuan per ton.

[0108] Energy consumption is reduced: the white slag retention time of the LF furnace is shortened by 8 min, the power consumption per ton of steel is reduced from 50 kWh to 38 kWh, and 0.6 million kWh of electricity is saved per year.

[0109] The waste rate is reduced: the surface defect waste rate is reduced from 12% to 3.6%, the annual waste loss is reduced by 20000x(12%-3.6%)x5000=840 million yuan; the inclusion over-standard waste rate is reduced from 8% to 2%, the annual loss is reduced by 20000x(8%-2%)x5000=600 million yuan, and the total annual waste loss is reduced by 144 million yuan.

[0110] The social benefits are as follows:

[0111] Green production: through the whole process of argon protection and less slag smelting, the dust emission per ton of steel is reduced by 30%, the oil content of waste water is reduced by 50%, the latest environmental protection emission standard is met, and a demonstration process for green smelting of the steel industry is provided.

[0112] Technical innovation: the process breaks through the bottleneck of high-carbon manganese silicon steel cleanliness control, and the related technology can be popularized to 40MnSi, 50Mn and other series steel production, promotes the progress of special steel continuous casting technology in China, and improves the international competitiveness of high-end wire rod products.

[0113] Standardization construction: a complete set of 30MnSi process standards for R8 square billet continuous casting machine is formed, which provides replicable technical specifications for the industry and promotes the overall improvement of the quality of wire rod steel.

[0114] The above is only a preferred embodiment of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for producing 30MnSi by an R8 bloom caster, characterized in that, The process route comprises: hot metal pretreatment, converter smelting, LF refining, continuous casting and cold delivery, wherein: in the converter smelting process, by optimizing the charging system of scrap steel-hot metal, C-T coordinated tapping and full-process argon protection, the composition and temperature of the molten steel at the end point of the converter are precisely controlled; in the LF refining process, by gradient slagging, precise calcium feeding and soft blowing time-temperature coupling control, purified molten steel is obtained; in the continuous casting process, by the coordination of crystallizer electric stirring and end electric stirring, optimization of casting process parameters and dynamic matching of casting speed-temperature, high-quality 30MnSi cast slab is obtained.

2. The method of claim 1, wherein, In the converter smelting process, the optimization of the charging system of scrap steel-hot metal includes: setting the charging amount to 120-125 t, charging hot metal and scrap steel according to a mass ratio of 95-105:18-25, and ensuring that the terminal temperature fluctuation is ≤±10℃ through scrap steel-hot metal heat balance calculation.

3. The method of claim 1, wherein, In the converter smelting process, C-T coordinated tapping includes: using the continuous temperature measurement carbon determination technology of the sub-lance to determine the optimal tapping state when the end point C≤0.085% and the temperature≥1680℃, and using the above control mode to make the hit rate of end point C≥0.08% reach 97%. Preferably, it further includes: during tapping, using slide plate+slag dam plug to control the slag layer thickness≤60mm, and the phosphorus content≤0.003%.

4. The method of claim 2, wherein, In the converter smelting process, the full-process argon protection includes: using a three-stage argon control mode. Preferably, the three-stage argon control mode comprises: 3 minutes before tapping, the argon flow rate of the ladle bottom blowing is above 900 NL / min to drive out the air in the ladle; during tapping, the argon flow rate of the bottom blowing is controlled to be 550-650 NL / min to promote alloy melting; after tapping, the argon flow rate of the bottom blowing is controlled to be 250-350 NL / min to prevent liquid surface nitrogen absorption, so that the nitrogen increase of the molten steel is ≤5×10 -6 .

5. The method of claim 2, wherein, In the LF refining process, gradient slagging includes: first adding 40-60 kg of fluorite to the molten steel to break the steel slag shell, then adding 40-60 kg of lime in two batches at an interval of 3 min, and optimizing the CaO-SiO2-Al2O3 slag system to rapidly increase the slag basicity CaO / SiO2 to 3.2-3.7, and shorten the white slag formation time to 12 min. Preferably, it further includes: using a three-electrode automatic lifting system to control the electrode lifting speed to be 0.5-1.5 m / min, and control the electrode insertion depth in the slag layer to be 50-80 mm during submerged arc heating, to ensure that the heating rate is≥5℃ / min.

6. The method of claim 1, wherein, In the LF refining process, precise calcium feeding includes: precisely determining the calcium wire feeding amount by using the following formula (1) to make the calcium aluminate rate of inclusions reach more than 90% and the size be controlled within 3-5 μm: W=0.05×[Al]×V (1) Wherein: W is the weight of calcium wire, unit: kg, [Al] is the aluminum content in steel, unit: %, V is the molten steel volume, unit: t.

7. The method of claim 1, wherein, In the LF refining process, the soft blowing time-temperature coupling control includes: using the following formula (2) to accurately control the soft blowing time, to ensure that the inclusions are fully floated, and to make T[O]≤15×10 -6 The qualified rate reaches 95%: t = 20 + 0.1 x (T LF出站 -1567)(2) Where: t is the soft blowing time, in min, T LF出站 is the LF furnace exit temperature, in °C.

8. The method of claim 1, wherein, In the continuous casting process, the coordination of crystallizer electric stirring and end electric stirring includes: controlling the crystallizer electric stirring parameters as follows: current 265-275 A, frequency 5-8 Hz; and controlling the end electric stirring parameters as follows: current 380-405 A, frequency 5-8 Hz. Preferably, it further includes: replacing the continuous casting crystallizer vibration device with a servo motor driving system, controlling the vibration waveform distortion to be≤5%, and the skew rate adjustment accuracy to be 0.01, to realize online real-time adjustment of vibration parameters.

9. The method of claim 1, wherein, In the continuous casting process, the non-sinusoidal vibration parameter optimization includes: setting the casting process parameters as follows: amplitude A=±3.5 mm, skew rate 0.15, frequency f=80 times / minute, to control the vibration mark depth within 1.2 mm.

10. The method of claim 1, wherein, In the continuous casting process, the dynamic matching of the casting speed and the temperature comprises: precisely controlling the casting speed by using the following formula (3), so that the over-standard rate of the casting speed fluctuation is reduced from 15% to 4%: V = 2.2 - 0.02 x (T 中包 -1510)(3) wherein: V is the withdrawal speed in m / min, T 中包 is the tundish temperature in °C.