A non-alloy structural steel s235jr thin slab continuous casting and rolling production process based on carbon equivalent requirement

Abstract

The application discloses a non-alloy structural steel S235JR thin slab continuous casting and rolling production process based on carbon equivalent requirement and belongs to the technical field of sports equipment. The process comprises the following steps: (1) chemical component design, with CE<=0.35% as a target, and setting an internal control component range wt%: C: 0.17-0.19%; Si: <=0.10%; Mn: 0.35-0.55%; P: <=0.020%; S: <=0.010%; Alt: 0.025-0.035%; Als: 0.022-0.032%; Ca: 0.0010-0.0035%; N: <=0.008%; the rest is Fe and impurities; (2) converter smelting; (3) LF refining; (4) CSP continuous casting. The application aims to realize stable control of a narrow window and low CE from converter smelting to continuous casting.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, and in particular relates to a continuous casting and rolling production process for non-alloy structural steel S235JR thin slabs based on carbon equivalent requirements. Background Technology

[0002] Currently, S235JR is a widely used non-alloy structural steel, mainly used in construction, bridges, and machinery manufacturing. With downstream users demanding higher weldability and mechanical stability from steel, production organization based on carbon equivalent (CE) control is gradually becoming an industry trend. Carbon equivalent is an important indicator for evaluating the weldability of steel; the lower the CE value, the better the weldability. The EN 10025-2 standard has specific requirements for the CE value of S235JR (CE ≤ 0.35% when the thickness is ≤ 40mm), but traditional production processes often only focus on whether the finished product composition meets the standard range, lacking proactive control of the CE value and full-process traceability. In existing technologies, the production of S235JR typically adopts a converter smelting → LF refining → continuous casting → hot rolling process. However, in actual operation, the following shortcomings exist: 1. Coarse composition control: Only meeting the finished product composition range is achieved, without narrow-range control of key elements (C, Mn, etc.), leading to large fluctuations in the CE value and affecting the stability of weldability. 2. Low precision in smelting endpoint control: Poor matching of carbon and temperature at the converter endpoint, high replenishment blowing rate, increasing the oxidizability and inclusion content of molten steel. 3. Unsystematic refining treatment: Lack of quantitative standards for calcium treatment and Als control, resulting in unstable inclusion modification effects, affecting continuous casting performance and finished product quality. 4. Lack of a CE-oriented closed-loop process: From converter tapping to continuous casting, there is a lack of dynamic adjustment mechanisms targeting CE, failing to meet the stringent welding performance requirements of high-end users. Therefore, there is an urgent need to develop a systematic production process for S235JR steel with CE value as the core control target. Summary of the Invention

[0003] In order to overcome the shortcomings of low carbon equivalent (CE) control accuracy, large composition fluctuation and unstable welding performance in the existing S235JR steel production process, the purpose of this invention is to provide a continuous casting and rolling production process for non-alloy structural steel S235JR thin slabs based on CE requirements, so as to achieve narrow window and low CE stable control throughout the entire process from converter smelting to continuous casting.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a continuous casting and rolling process for thin slabs of non-alloy structural steel S235JR based on carbon equivalent requirements, comprising the following steps:

[0006] (1) Chemical composition design

[0007] With a target CE ≤ 0.35%, the internal control component range (wt%) is set as follows: C: 0.17–0.19%; Si: ≤ 0.10%; Mn: 0.35–0.55%; P: ≤ 0.020%; S: ≤ 0.010%; Alt: 0.025–0.035%; Als: 0.022–0.032%; Ca: 0.0010–0.0035%; N: ≤ 0.008%; the remainder being Fe and impurities. The CE calculation formula is: CE = C + Mn / 6, with a target CE value controlled within 0.25–0.30%.

[0008] (2) Converter smelting

[0009] Loading procedure: Total loading volume 230±15 tons, scrap steel addition 20~50 tons, molten iron temperature ≥1280℃, molten iron S≤0.070%. The amount of scrap steel added is dynamically adjusted according to the molten iron temperature and silicon content, with an adjustment coefficient of ±1.2 tons of scrap steel for every ±10℃ of molten iron temperature.

[0010] Oxygen supply system: Use a 5-hole Laval oxygen lance, with the lance position at 1.5-2.5m, and adopt the "high position 2.5m - middle position 2m - high position 2.5m - low position 1.5m" lance position mode. The oxygen main pipe pressure is ≥1.15MPa.

[0011] Slag formation process: Single slag process smelting, final basicity 2.5–3.5;

[0012] Endpoint control: First-time furnace turnover rate ≥ 90%, number of re-blowing cycles ≤ 1. Endpoint C: 0.03~0.10%, P≤0.015%, T: 1600~1660℃;

[0013] Tapping operation: Tapping time is 4-8 minutes, using a sliding plate to block slag, with a slag thickness ≤50mm. During the tapping process, aluminum-manganese-titanium and ferromanganese are added for deoxidation and alloying, with a manganese recovery rate calculated at 95%. After tapping 1 / 5 of the steel, aluminum-manganese-titanium, ferromanganese, synthetic slag, and 300-500 kg / furnace of lime and 300-500 kg / furnace of ladle modifier are added sequentially.

[0014] Bottom-blown argon: Argon is blown from the bottom throughout the process, and high-flow-rate stirring is used during the tapping process to ensure uniform composition and temperature.

[0015] The composition of the refined steel by mass fraction is as follows: C: 0.10~0.16%, Mn: 0.20~0.40%, P≤0.020%, S≤0.040%, Als: 0.020~0.080%;

[0016] (3) LF Refining

[0017] Incoming process: After the ladle is in place, argon gas is turned on, temperature and oxygen are measured, and aluminum wire is added according to the ALS target;

[0018] Slag formation and desulfurization: Add refined slag, control slag basicity ≥ 4.0, white slag retention time ≥ 15 min, target S ≤ 0.010%;

[0019] Component fine-tuning: C and Mn are precisely adjusted according to internal control targets, with C controlled at 0.17-0.19% and Mn controlled at 0.35-0.55%;

[0020] Calcium treatment: Calcium wire is fed in, with a target Ca content of 0.0010-0.0035%, which modifies Al2O3 inclusions into low-melting-point calcium aluminate, improving the castability of molten steel;

[0021] Temperature control: The temperature at the refining station outlet is controlled according to the continuous casting requirements, with a fluctuation range of ±5℃;

[0022] (4) CSP continuous casting

[0023] Protective casting: Argon gas is used to seal the entire process to prevent secondary oxidation;

[0024] Tundish metallurgy: The thickness of the tundish covering agent is ≥50mm, and the superheat of the molten steel in the tundish is 15~25℃;

[0025] Crystallizer control: High-frequency, low-amplitude vibration mode is adopted, and the liquid level fluctuation in the crystallizer is ≤±3mm;

[0026] Secondary cooling: A dynamic secondary cooling model is adopted, and the water volume in each zone is adjusted according to the casting speed and steel grade, so that the surface temperature of the billet drops uniformly and cracks are avoided.

[0027] Pulling speed control: The pulling speed is kept stable at 4.5 to 5.5 m / min.

[0028] Furthermore, the handling of abnormalities and the rules for mixed casting: when abnormal conditions cannot meet the CE requirements, the actual composition shall be changed to Q235B or SS400, and rolled according to the corresponding steel grade process.

[0029] Furthermore, S235JR can be mixed with Q235B and SS400. The mixed billets are rolled according to the Q235B and SS400 processes to ensure the performance of the finished product.

[0030] Furthermore, the chemical composition of the non-alloy structural steel S235JR thin slab by weight percentage is as follows: C: 0.18%; Si: 0.09%; Mn: 0.4%; P: 0.01%; S: 0.008%; Alt: 0.03%; Als: 0.03%; Ca: 0.002%; N: 0.007%; the remainder being Fe and impurities.

[0031] Furthermore, S235JR with a thickness of 9.75mm was produced on the 210t converter-LF refining-CSP production line; molten iron conditions: temperature 1320℃, Si 0.45%, S 0.035%; scrap steel addition: 35 tons; converter endpoint: C 0.06%, P 0.012%, T 1635℃; during tapping, 300kg of aluminum-manganese-titanium, 2.2t of high-carbon ferromanganese, 400kg of synthetic slag, 400kg of lime, and 350kg of ladle modifier were added; at the LF refining station, Als 0.035% was added, 50m of aluminum wire was added, white slag was produced for 20 minutes, and 200m of calcium wire was fed; the outlet composition was C 0.18%, Mn 0.46%, Als 0.028%, Ca 0.0022%, S 0.006%, CE=0.18+0.46 / 6=0.257%; continuous casting speed 5.0m / min, superheat 20℃, billet quality is good, hot-rolled plate properties: ReH 285MPa, Rm 420MPa, A% 32%, cold bending qualified.

[0032] Furthermore, the molten iron temperature was 1285℃, Si 0.30%, S 0.045%; the amount of scrap steel added was reduced to 25 tons; the converter endpoint C 0.08%, P 0.014%, T 1610℃; the tapping alloying was calculated based on a target Mn of 0.40%, with the addition of 1.9t of high-carbon ferromanganese; LF refining added 30kg of carbon particles, 30m of aluminum wire, and 200m of calcium treatment, resulting in the following output composition: C 0.18%, Mn 0.41%, Als 0.025%, Ca 0.0018%, S 0.008%, CE=0.18+0.41 / 6=0.248%; the continuous casting speed was 4.8m / min, the superheat was 22℃, the billet quality was qualified, and the plate performance met the standards.

[0033] Furthermore, the molten iron temperature was 1350℃, Si 0.55%, S 0.030%; 42 tons of scrap steel were added; the converter final temperature was C 0.04%, P 0.010%, T 1655℃; the tapping alloying was calculated based on a Mn target of 0.50%, with 2.4t of high-carbon ferromanganese added; 60m of aluminum supplementation wire and 250m of calcium treatment wire were added in the LF refining process; the tapping composition was C 0.19%, Mn 0.51%, Als 0.030%, Ca 0.0028%, S 0.005%, CE=0.19+0.51 / 6=0.275%; the continuous casting speed was 5.2m / min, the superheat was 18℃, the billet was defect-free, and the plate had excellent performance.

[0034] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0035] 1. High CE control precision: Through narrow composition design and dynamic adjustment throughout the entire process, the CE value is stably controlled within 0.25-0.30%, meeting the EN 10025-2 requirement of CE≤0.35% for S235JR, significantly improving weldability. 2. Small composition fluctuations: The internal control range is significantly narrower than the national standard, with fluctuations in key elements such as C and Mn controlled within ±0.01% and ±0.05%, respectively, improving the consistency of mechanical properties. 3. Improved smelting efficiency: The final first-time furnace turnover rate is ≥90%, the reblowing rate is reduced, steel over-oxidation is reduced, and inclusion content is decreased. 4. Improved castability: Through precise calcium treatment, Al2O3 is transformed into liquid inclusions, reducing the nozzle nodule formation rate during continuous casting by more than 80%, and increasing the number of consecutive casting heats. 5. Stable product quality: Improved surface quality and internal density of the billet, uniform properties of hot-rolled plates, suitable for high-requirement welded structural components. Detailed Implementation

[0036] Example 1:

[0037] S235JR steel with a thickness of 9.75mm was produced on a 210t converter-LF refining-CSP production line. Hot metal conditions: temperature 1320℃, Si 0.45%, S 0.035%. 35 tons of scrap steel were added. The converter final concentrations were: C 0.06%, P 0.012%, T 1635℃. During tapping, 300kg of aluminum-manganese-titanium alloy, 2.2t of high-carbon ferromanganese (calculated based on a Mn target of 0.45%), 400kg of synthetic slag, 400kg of lime, and 350kg of ladle modifier were added. LF refining process: Als 0.035% at the inlet, 50m aluminum feed wire, 20min white slag production, 200m calcium feed wire. Outlet composition: C 0.18%, Mn 0.46%, Als 0.028%, Ca 0.0022%, S 0.006%, CE = 0.18 + 0.46 / 6 = 0.257%. Continuous casting speed: 5.0 m / min, superheat: 20℃. Billet quality: good. Hot-rolled plate properties: ReH 285MPa, Rm 420MPa, A% 32%, cold bending qualified.

[0038] Its chemical composition by mass percentage (same as in Example 1) is as follows: C: 0.18%; Si: 0.09%; Mn: 0.4%; P: 0.01%; S: 0.008%; Alt: 0.03%; Als: 0.03%; Ca: 0.002%; N: 0.007%; the remainder being Fe and impurities.

[0039] Example 2:

[0040] The molten iron temperature was low (1285℃), with Si 0.30% and S 0.045%. The amount of scrap steel added was reduced to 25 tons. The converter final temperature was C 0.08%, P 0.014%, and T 1610℃. Alloying at tapping was calculated based on a Mn target of 0.40%, with the addition of 1.9 tons of high-carbon ferromanganese. During LF refining, 30 kg of carbon particles, 30 m of aluminum wire, and 200 m of calcium treatment were added. The final composition at the tapping station was C 0.18%, Mn 0.41%, Als 0.025%, Ca 0.0018%, S 0.008%, and CE = 0.18 + 0.41 / 6 = 0.248%. The continuous casting speed was 4.8 m / min, the superheat was 22℃, the billet quality was qualified, and the plate performance met the standards.

[0041] Its chemical composition by mass percentage is the same as that in Example 1: C: 0.18%; Si: 0.09%; Mn: 0.4%; P: 0.01%; S: 0.008%; Alt: 0.03%; Als: 0.03%; Ca: 0.002%; N: 0.007%; the remainder being Fe and impurities.

[0042] Example 3:

[0043] The molten iron temperature was 1350℃, with Si 0.55% and S 0.030%. 42 tons of scrap steel were added. The converter final temperature was 0.04% C, 0.010% P, and T 1655℃. Alloying at tapping was calculated based on a Mn target of 0.50%, with 2.4 tons of high-carbon ferromanganese added. 60m of aluminum-refining wire and 250m of calcium-treated wire were used in the LF refining process. The final product composition was: C 0.19%, Mn 0.51%, Als 0.030%, Ca 0.0028%, S 0.005%, CE = 0.19 + 0.51 / 6 = 0.275%. The continuous casting speed was 5.2 m / min, the superheat was 18℃, the billet was defect-free, and the plate exhibited excellent performance.

[0044] Its chemical composition by mass percentage is the same as that in Example 1: C: 0.18%; Si: 0.09%; Mn: 0.4%; P: 0.01%; S: 0.008%; Alt: 0.03%; Als: 0.03%; Ca: 0.002%; N: 0.007%; the remainder being Fe and impurities.

[0045] Example 4:

[0046] In the production plan, S235JR and Q235B are mixed and cast. The transition billet is rolled according to the Q235B process. The performance of the sample is tested: ReH275MPa, Rm410MPa, A%30%, which meets the Q235B standard. No performance fluctuations were found, indicating that the mixed casting scheme is feasible.

[0047] Its chemical composition by mass percentage is the same as that in Example 1: C: 0.18%; Si: 0.09%; Mn: 0.4%; P: 0.01%; S: 0.008%; Alt: 0.03%; Als: 0.03%; Ca: 0.002%; N: 0.007%; the remainder being Fe and impurities.

[0048] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A continuous casting and rolling production process for thin slabs of non-alloy structural steel S235JR based on carbon equivalent requirements, characterized in that, Includes the following steps: (1) Chemical composition design With a target CE ≤ 0.35%, the internal control component ranges (wt%) are set as follows: C: 0.17–0.19%; Si: ≤ 0.10%; Mn: 0.35–0.55%. P：≤0.020%； S：≤0.010%； Alt: 0.025~0.035%; Als: 0.022–0.032%; Ca: 0.0010–0.0035%; N: ≤0.008%; the remainder is Fe and impurities; the CE calculation formula is: CE = C + Mn / 6, and the target CE value is controlled within 0.25–0.30%. (2) Converter smelting Loading procedure: Total loading amount 230±15 tons, scrap steel addition amount 20~50 tons, molten iron temperature ≥1280℃, molten iron S≤0.070%. The amount of scrap steel added is dynamically adjusted according to the temperature of the molten iron and the silicon content. The adjustment coefficient is: ±10℃ for molten iron temperature corresponds to ±1.2 tons of scrap steel. Oxygen supply system: A 5-hole Laval oxygen lance is used, with the lance position at 1.5 to 2.5 meters. The lance position pattern is "high position 2.5 meters - middle position 2.0 meters - high position 2.5 meters - low position 1.5 meters". The total oxygen pipe pressure is ≥1.15 MPa. Slag formation process: Single slag process smelting, final basicity 2.5–3.5; Endpoint control: First-time furnace turnover rate ≥ 90%, number of re-blowing cycles ≤ 1. Endpoint C: 0.03~0.10%, P≤0.015%, T: 1600~1660℃; Tapping operation: Tapping time is 4-8 minutes, using a sliding plate to block slag, with a slag thickness ≤50mm. During the tapping process, aluminum-manganese-titanium and ferromanganese are added for deoxidation and alloying, with a manganese recovery rate calculated at 95%. After tapping 1 / 5 of the steel, aluminum-manganese-titanium, ferromanganese, synthetic slag, and 300-500 kg / furnace of lime and 300-500 kg / furnace of ladle modifier are added sequentially. Bottom-blown argon: Argon is blown from the bottom throughout the process, and high-flow-rate stirring is used during the tapping process to ensure uniform composition and temperature. The composition of the refined steel by mass fraction is as follows: C: 0.10~0.16%, Mn: 0.20~0.40%, P≤0.020%, S≤0.040%, Als: 0.020~0.080%; (3) LF Refining Incoming process: After the ladle is in place, argon gas is turned on, temperature and oxygen are measured, and aluminum wire is added according to the ALS target; Slag formation and desulfurization: Add refined slag, control slag basicity ≥ 4.0, white slag retention time ≥ 15 min, target S ≤ 0.010%; Component fine-tuning: C and Mn are precisely adjusted according to internal control targets, with C controlled at 0.17-0.19% and Mn controlled at 0.35-0.55%; Calcium treatment: Calcium wire is fed in, with a target Ca content of 0.0010-0.0035%, which modifies Al2O3 inclusions into low-melting-point calcium aluminate, improving the castability of molten steel; Temperature control: The temperature at the refining station outlet is controlled according to the continuous casting requirements, with a fluctuation range of ±5℃; (4) CSP continuous casting Protective casting: Argon gas is used to seal the entire process to prevent secondary oxidation; Tundish metallurgy: The thickness of the tundish covering agent is ≥50mm, and the superheat of the molten steel in the tundish is 15~25℃; Crystallizer control: High-frequency, low-amplitude vibration mode is adopted, and the liquid level fluctuation in the crystallizer is ≤±3mm; Secondary cooling: A dynamic secondary cooling model is adopted, and the water volume in each zone is adjusted according to the casting speed and steel grade, so that the surface temperature of the billet drops uniformly and cracks are avoided. Pulling speed control: The pulling speed is kept stable at 4.5 to 5.5 m / min.

2. The continuous casting and rolling production process for non-alloy structural steel S235JR thin slabs based on carbon equivalent requirements according to claim 1, characterized in that, Abnormal handling and mixed casting rules: When abnormal conditions cannot meet CE requirements, the actual composition shall be changed to Q235B or SS400 and rolled according to the corresponding steel grade process.

3. The continuous casting and rolling production process for non-alloy structural steel S235JR thin slabs based on carbon equivalent requirements according to claim 1 or 2, characterized in that, S235JR can be mixed with Q235B and SS400. The mixed billets are rolled according to the Q235B and SS400 processes to ensure the performance of the finished product.

4. The continuous casting and rolling production process for non-alloy structural steel S235JR thin slabs based on carbon equivalent requirements according to claim 1, characterized in that, The chemical composition of the non-alloy structural steel S235JR thin slab by weight percentage is: C: 0.18%; Si: 0.09%; Mn: 0.4%. P：0.01%； S: 0.008%; Alt: 0.03%; Als: 0.03%; Ca: 0.002%; N: 0.007%; the remainder is Fe and impurities.

5. The continuous casting and rolling production process for non-alloy structural steel S235JR thin slabs based on carbon equivalent requirements according to claim 4, characterized in that, S235JR steel with a thickness of 9.75mm was produced on a 210t converter-LF refining-CSP production line. Hot metal conditions: temperature 1320℃, Si 0.45%, S 0.035%; scrap steel input: 35 tons; converter final concentration: C 0.06%, P 0.012%, T 1635℃; tapping process: 300kg aluminum-manganese-titanium, 2.2t high-carbon ferromanganese, 400kg synthetic slag, 400kg lime, and 350kg ladle modifier added; LF refining: Als 0.035%, 50m aluminum feed wire, 20min white slag production, 200m calcium feed wire; final output composition: C 0.18%, Mn 0.46%, Als 0.028%, Ca 0.0022%, S... 0.006%, CE=0.18+0.46 / 6=0.257%; continuous casting speed 5.0m / min, superheat 20℃, billet quality is good, hot-rolled plate properties: ReH 285MPa, Rm 420MPa, A% 32%, cold bending qualified.

6. The continuous casting and rolling production process for non-alloy structural steel S235JR thin slabs based on carbon equivalent requirements according to claim 4, characterized in that, The molten iron temperature was 1285℃, Si 0.30%, S 0.045%; the amount of scrap steel added was reduced to 25 tons; the converter endpoint C 0.08%, P 0.014%, T 1610℃; the tapping alloying was calculated based on a target Mn of 0.40%, with the addition of 1.9t of high-carbon ferromanganese; LF refining added 30kg of carbon particles, 30m of aluminum wire, and 200m of calcium treatment; the outlet composition was C 0.18%, Mn 0.41%, Als 0.025%, Ca 0.0018%, S 0.008%, CE=0.18+0.41 / 6=0.248%; the continuous casting speed was 4.8m / min, the superheat was 22℃, the billet quality was qualified, and the plate performance met the standards.

7. The continuous casting and rolling production process for non-alloy structural steel S235JR thin slabs based on carbon equivalent requirements according to claim 4, characterized in that, The molten iron temperature was 1350℃, Si 0.55%, S 0.030%; 42 tons of scrap steel were added; the converter final temperature was C 0.04%, P 0.010%, T 1655℃; the tapping alloying was calculated based on a Mn target of 0.50%, with 2.4t of high-carbon ferromanganese added; 60m of aluminum was added to the LF refining line, and 250m of calcium was treated; the tapping composition was C 0.19%, Mn 0.51%, Als 0.030%, Ca 0.0028%, S 0.005%, CE=0.19+0.51 / 6=0.275%; the continuous casting speed was 5.2m / min, the superheat was 18℃, the billet was defect-free, and the plate had excellent performance.