A straight rolling production method of carbon structural steel plate Q235B

Abstract

This invention discloses a direct rolling production method for Q235B carbon structural steel plate. The chemical composition and mass percentage of the Q235B carbon structural steel plate are as follows: C: 0.16-0.19%, Si: 0.10-0.30%, Mn: 0.25-0.40%, P≤0.030%, S≤0.025%, with the balance being Fe and unavoidable residual elements and impurities from the production process. The production method includes continuous casting, billet reheating, rolling, and cooling. The superheat during continuous casting is controlled at 25-40℃, and the specific water content in the secondary cooling zone is controlled at 0.46-0.49 L / kg. The casting speed is controlled at 1.1–1.15 m / min, and the average temperature of the billet exiting the fan-shaped section is controlled between 1170–1220℃. After being cut, the continuously cast billet is conveyed to the steel tapping roller conveyor of the heating furnace without being heated in the heating furnace. The temperature drop during the conveying process is controlled below 2℃ / min. After the billet is sent to the steel tapping roller conveyor of the heating furnace, it enters a heat-replenishing and heat-insulating cover with edge heating function for heat replenishment. The billet temperature at the end of the heat replenishment process is controlled at 1150–1200℃. The carbon structural steel plate of this invention meets the national standards in terms of comprehensive performance, significantly reduces energy consumption costs, and has a simple and efficient process.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical rolling technology, specifically relating to a direct rolling production method for Q235B carbon structural steel plates. Background Technology

[0002] Carbon structural steel with a yield strength of 235MPa, namely Q235B, is characterized by low cost and wide application, and has relatively low requirements for process control and production line equipment. Domestic medium plate production lines are capable of producing this steel grade. Products with a thickness of 16-30mm are widely used in the manufacture of various common structural components, and the usage is substantial. Domestic medium plate production lines use a hot-rolling process to produce this steel grade. To ensure the machinability of the cast billet, the billet is reheated in a heating furnace before being rolled by a rolling mill to obtain the target steel plate dimensions. Heating the cast billet in a heating furnace consumes a large amount of energy, accounting for a major portion of the rolling process energy consumption, which does not meet the steel industry's requirements for low-cost and green development. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a direct rolling production method for Q235B carbon structural steel plate, which produces carbon structural steel plate that meets national standards in terms of comprehensive performance, while significantly reducing energy consumption costs and simplifying and improving the process.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A direct rolling production method for Q235B carbon structural steel plate includes continuous casting, billet reheating, rolling, and cooling; wherein the casting superheat is controlled at 25-40℃, the water content in the secondary cooling zone is controlled at 0.46-0.49L / kg, the casting speed is controlled at 1.1-1.15m / min, and the average temperature of the billet exiting the fan-shaped section is controlled between 1170-1220℃; The continuously cast billet is cut and then conveyed to the steel tapping roller conveyor of the heating furnace without being heated in the heating furnace. The temperature drop during the conveying process is controlled to be below 2℃ / min. After the billet is sent to the steel tapping roller conveyor of the heating furnace, it enters a heat-replenishing and heat-insulating cover with edge heating function for heat replenishment. In the billet reheating process, the billet temperature is controlled at 1150-1200℃ at the end of the reheating process. The chemical composition and mass percentage of the carbon structural steel plate Q235B are as follows: C: 0.16~0.19%, Si: 0.10~0.30%, Mn: 0.25~0.40%, P≤0.030%, S≤0.025%, with the balance being Fe and unavoidable residual elements and impurities from the production process.

[0005] In the above-mentioned direct rolling production method of carbon structural steel plate Q235B, the cut continuous casting billet is kept warm with an insulation cover throughout the process of being conveyed to the steel tapping roller of the heating furnace, so as to ensure that the temperature drop of the cut billet during the conveying process is controlled below 2℃ / min, and the time of conveying to the steel tapping roller of the heating furnace is ≤10min.

[0006] The above-mentioned direct rolling production method for Q235B carbon structural steel plate adopts ACC controlled cooling in the controlled cooling process. The ACC section adopts an intermittent weak cooling mode, with the cooling rate controlled at 3-6℃ / s and the final cooling temperature controlled at 780-820℃.

[0007] The above-mentioned direct rolling production method for Q235B carbon structural steel plate, wherein the rolling process has an initial rolling temperature of 1050-1120℃ and a final rolling temperature controlled at 980-1030℃.

[0008] The above-mentioned direct rolling production method for carbon structural steel plate Q235B, wherein the chemical composition and mass percentage of the carbon structural steel plate Q235B are as follows: C: 0.16~0.18%, Si: 0.15~0.25%, Mn: 0.30~0.40%, P≤0.025%, S≤0.020%, and the rest are Fe and unavoidable residual elements and impurities during the production process.

[0009] The above-mentioned direct rolling production method of carbon structural steel plate Q235B, wherein the carbon structural steel plate Q235B has a thickness of 16-30mm, a yield strength of 253-322MPa, a tensile strength of 395-447MPa, an elongation of 25.7-32.5%, and a room temperature impact energy of 55-127J.

[0010] In the above-mentioned direct rolling production method of carbon structural steel plate Q235B, the controlled cooling process, the intermittent weak cooling mode means that one ACC manifold is turned on every two sets of ACC manifolds, the ACC water volume is set to a small water volume, that is, the water volume is controlled at 180~200L / (min×m2), and the water volume ratio of the upper and lower manifolds of the ACC section is 2.0~2.1.

[0011] This invention ensures that the strength of Q235B steel plate meets GB / T 700-2006 while achieving low-energy manufacturing of the steel plate. The design of the production process parameters is mainly based on the following principles: a. The superheat of the casting is controlled at 25-40℃, the water content in the secondary cooling zone of the continuous casting machine is controlled at 0.46-0.49L / kg, the billet cross-section is 260mm (thickness) × 1900mm (width), the casting speed is controlled at 1.1-1.15m / min, and the liquid core position is controlled at 4m-4.2m before the end of the continuous casting machine. The latent heat of solidification of the liquid core is used to effectively increase the billet temperature. On the one hand, this ensures that the average temperature of the billet exiting the fan-shaped section is controlled between 1170-1220℃, and on the other hand, it reduces the temperature drop during the billet transfer process, providing better temperature conditions for billet reheating and improving reheating efficiency.

[0012] b. After the continuously cast billet is cut to the target size by the cutting machine, it is conveyed to the tapping roller conveyor of the heating furnace via a conveyor roller conveyor, a swing car, and a translation car, without passing through the walking beam type double regenerative heating furnace. During the conveying process, the roller conveyor is covered with an insulation cover throughout. The insulation cover adopts a composite structure of heavy castable and insulation layer to control the temperature drop of the directly conveyed billet during the conveying process to be less than 2℃ / min. The time for the cut billet to be conveyed to the tapping roller conveyor of the heating furnace is ≤10min.

[0013] c. After the billet reaches the tapping roller conveyor in the heating furnace, it enters a heat-replenishing and insulation hood with edge heating function. Because the area near the corners of the billet is subject to two-dimensional heat dissipation and heat loss is relatively fast, it is necessary to replenish the low-temperature area at the edge of the billet. Reheating is performed until the billet temperature reaches 1150–1200℃.

[0014] d. The initial rolling temperature is controlled at 1050–1120℃, and the final rolling temperature is controlled at 980–1030℃. Q235B has low requirements for controlled rolling effect and a relatively wide range of rolling process settings, which can improve the production efficiency of this steel grade. This process design has been mentioned in several documents and is a non-critical but essential process part of this invention.

[0015] e.ACC adopts an intermittent weak cooling model with centralized cooling. The cooling rate of the steel plate in the ACC cooling section is controlled at 3-6℃ / s, and the final cooling temperature is controlled at 780-820℃. At this cooling rate and final cooling temperature, on the one hand, appropriately reducing the final cooling temperature can protect the straightening equipment, and on the other hand, controlling the final cooling temperature at 780-820℃ is conducive to reducing uneven cooling of the steel plate and improving the flatness of the steel plate.

[0016] The beneficial effects of adopting the above technical solution are as follows: This invention optimizes the continuous casting process, increases the temperature of the billet exiting the fan-shaped section, maintains heat throughout the conveying process, and combines specific reheating and rolling cooling processes to obtain Q235B carbon structural steel that meets the mechanical properties of GB / T 700-2008 standard, while avoiding the reheating process in traditional heating furnaces. The process is simple and easy to implement, significantly reducing the energy consumption for billet heating while ensuring mechanical properties, thus achieving efficient direct rolling of Q235B. Attached Figure Description

[0017] Figure 1 This is a flowchart of the process from continuous casting of the billet to the tapping roller conveyor of the medium plate in this invention; The markings in the diagram are: 1. Billet cutting machine; 2. Insulation cover; 3. Ingot drawing device; 4. Conveying roller conveyor; 5. Transverse pit; 6. Swinging car; 7. Horizontal car; 8. Steel tapping roller conveyor; 9. Heat replenishment and insulation cover. Implementation

[0018] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0019] Examples 1-6 This invention provides a direct rolling production method for Q235B carbon structural steel with a yield strength of 235MPa. The production method includes continuous casting, billet reheating, rolling, and cooling; the specific control methods are as follows: Continuous casting process: The superheat of continuous casting is controlled at 25-40℃, and the specific water volume in the secondary cooling zone is controlled at... The flux density is 0.46–0.49 L / kg, the casting speed is controlled at 1.10–1.15 m / min, and the average temperature of the billet exiting the fan-shaped section is controlled between 1170–1220℃. The liquid core position is controlled 4–4.2 m before the end of the continuous casting machine. The latent heat of solidification of the liquid core effectively increases the billet temperature. On the one hand, this ensures that the average temperature of the billet exiting the fan-shaped section is controlled between 1170–1220℃. On the other hand, it reduces the temperature drop during the billet transfer process, providing better temperature conditions for billet reheating and improving reheating efficiency.

[0020] like Figure 1 As shown, after the continuous casting billet is cut to the target size by the billet cutting machine 1, the first batch of billets is pulled out of the continuous casting machine by the ingot traction device 3. The cut billets are conveyed to the transverse transfer pit 5 via the conveyor roller conveyor 4. During the conveying process, the conveyor roller conveyor 4 is covered with a heat preservation cover 2 for heat preservation. Then, the continuous casting billet is moved by the swing car 6 on the conveyor roller conveyor 4 to the running track of the translation car 7, and then transferred to the translation car 7. The translation car 7 then conveys it to the tapping roller conveyor 8, where it enters the heat preservation cover 9 for heat preservation. After heat preservation, it is conveyed to the rolling mill via the tapping roller conveyor 8 for rolling. This process does not pass through the walking beam type double regenerative heating furnace. During the conveying process, the conveyor roller conveyor 4 is covered with a heat preservation cover 2 throughout. The heat preservation cover 2 adopts a composite structure of heavy castable and heat preservation layer to control the temperature drop of the directly delivered billet during the conveying process to below 2℃ / min. The time for the cut billet to be conveyed to the tapping roller conveyor 8 of the heating furnace is ≤10min.

[0021] After the billet reaches the tapping roller conveyor 8 of the heating furnace, it enters the heat-replenishing and insulation hood 9, which has an edge heating function. Because the corners of the billet experience two-dimensional heat dissipation and rapid cooling, the low-temperature area at the edges needs to be reheated. The reheating process raises the billet temperature to 1150–1200℃, with an energy consumption of 60–65 × 10⁻⁶ tonnes of steel. 6 J, while heating carbon steel in a traditional gas-fired furnace consumes 400-450 × 10 tonnes of energy. 6 J.

[0022] Rolling process: initial rolling temperature 1050~1120℃, final rolling temperature controlled at 980~1030℃; Cooling process: ACC control cooling is adopted. The ACC section adopts intermittent weak cooling mode, the cooling rate is controlled at 3-6℃ / s, and the final cooling temperature is controlled at 780-820℃.

[0023] The chemical composition of the carbon structural steel with a yield strength of 235 MPa obtained in Examples 1-6 is shown in Table 1, the process parameter control is shown in Table 2, the thickness specifications and mechanical properties are shown in Table 3, and the energy consumption per ton of steel is shown in Table 4.

[0024] Examples 1-6 show that the mechanical properties of the produced Q235B fully meet the requirements of the national standard GB / T 700-2006; while the energy consumption is far lower than the heating energy consumption of using a heating furnace.

[0025] Table 1 Chemical composition and mass percentage (wt%) of high-strength steels in Examples 1-6

[0026] Table 2 Control parameters for continuous casting, heating, controlled rolling, and controlled cooling processes in Examples 1-6

[0027] Table 3 Thickness specifications and mechanical properties of Examples 1-6

[0028] Note: Charpy (V-notch) impact absorption energy is tested using a set of 3 individual samples. The impact test temperature for Q235B is 20℃. The three values ​​listed in Table 3 for the impact energy at 20℃ are the individual values ​​of the 3 samples tested in a set of Charpy impact absorption energy tests.

[0029] Table 4 Heating energy consumption of Examples 1-6 .

Claims

1. A direct rolling production method for Q235B carbon structural steel plate, characterized in that: The process includes continuous casting, reheating of the continuously cast billet, rolling, and controlled cooling; the casting superheat is controlled at 25-40℃, the water content in the secondary cooling zone is controlled at 0.46-0.49L / kg, the casting speed is controlled at 1.1-1.15m / min, and the average temperature of the continuously cast billet exiting the fan-shaped section is controlled between 1170-1220℃. After being cut, the continuous casting billet is conveyed to the steel tapping roller conveyor (8) of the heating furnace without being heated by the heating furnace. During the conveying process, the temperature drop is controlled to be below 2℃ / min. After the continuous casting billet is sent to the steel tapping roller conveyor (8) of the heating furnace, it enters the heat-replenishing and heat-insulating cover (9) with the edge heating function for heat replenishment. In the continuous casting billet reheating process, the temperature of the continuous casting billet at the end of the reheating process is controlled at 1150-1200℃. The chemical composition and mass percentage of the carbon structural steel plate Q235B are as follows: C: 0.16~0.19%, Si: 0.10~0.30%, Mn: 0.25~0.40%, P≤0.030%, S≤0.025%, with the balance being Fe and unavoidable residual elements and impurities from the production process.

2. The direct rolling production method of Q235B carbon structural steel plate as described in claim 1, characterized in that: During the process of conveying the cut continuous casting billet to the steel tapping roller conveyor (8) of the heating furnace, the billet is kept warm by the heat insulation cover (2) throughout the process to ensure that the temperature drop during the conveying process of the cut continuous casting billet is controlled below 2℃ / min and the time for conveying to the steel tapping roller conveyor (8) of the heating furnace is ≤10min.

3. The direct rolling production method of Q235B carbon structural steel plate as described in claim 1, characterized in that: The controlled cooling process adopts ACC controlled cooling. The ACC section adopts an intermittent weak cooling mode, with the cooling rate controlled at 3-6℃ / s and the final cooling temperature controlled at 780-820℃.

4. The direct rolling production method of Q235B carbon structural steel plate as described in claim 1, characterized in that: The rolling process has an initial rolling temperature of 1050–1120°C and a final rolling temperature controlled at 980–1030°C.

5. The direct rolling production method of Q235B carbon structural steel plate as described in claim 1, characterized in that: The chemical composition and mass percentage of the carbon structural steel plate Q235B are as follows: C: 0.16-0.18%, Si: 0.15-0.25%, Mn: 0.30-0.40%, P≤0.025%, S≤0.020%, and the rest are Fe and unavoidable residual elements and impurities in the production process.

6. A direct rolling production method for Q235B carbon structural steel plate as described in any one of claims 1-4, characterized in that: The carbon structural steel plate Q235B has a thickness of 16-30mm, a yield strength of 253-322MPa, a tensile strength of 395-447MPa, an elongation of 25.7-32.5%, and an impact energy of 55-127J at room temperature.

7. The direct rolling production method of Q235B carbon structural steel plate as described in claim 3, characterized in that: In the controlled cooling process, the intermittent weak cooling mode means that one ACC manifold is turned on every two sets of ACC manifolds, and the ACC water flow is set to: the water supply is controlled at 180-200L / (min*m). 2 The ratio of water volume in the upper and lower manifolds of the ACC section is 2.0 to 2.1.

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