A method for producing a low-cost structural steel plate ASTM A36

Abstract

The application discloses a production method of low-cost thick-gauge welding structural steel plate ASTM A36, the steel plate contains the following chemical components in percentage by mass: C: 0.13-0.15%, Si: 0.18-0.25%, Mn: 0.85-0.95%, P: <=0.025%, S: <=0.010%, Als: 0.20-0.35%, CEV: <=0.32%; the rest is iron and inevitable impurities; and the production process of the steel plate is desulfurization, converter smelting, LF refining, continuous casting, heating, rolling, cooling, hot straightening, shearing and sampling inspection. The hot rolling process is adopted, the performance and welding performance meet the standard and user use requirements. The narrow component control is adopted, the rolling and cooling process are accurately controlled, and it is ensured that the steel plate has excellent performance, in particular, the thickness performance and weldability meet the high standard requirements of users.

Description

Technical Field

[0001] This invention relates to the field of hot rolling, and more particularly to a low-cost method for producing ASTM A36 welded structural steel plates. Background Technology

[0002] ASTM A36 is a carbon structural steel standard from the American Society for Testing and Materials. It is mainly used for welded structural steel in bridges and buildings. Users have higher requirements for strength, toughness and weldability, so the composition is optimized, the process is redesigned, the process flow is optimized, the cost is reduced and the toughness of the steel plate is improved, while meeting the strength and weldability requirements to meet the user's requirements.

[0003] The patent "A Chromium-Containing ASTM A36 Steel Plate and Its Production Method" provides a method for producing thin ASTM A36 steel plates with a thickness of 6-12mm by adding alloying elements such as Cr and Ti. This method also provides a method for producing low-alloy structural steel with a thickness of 40-100mm. This patent uses a C-Mn composition design, which results in lower alloy costs compared to the literature. The process design is different, and the slab size is different. The literature uses 180mm, while this patent uses 250mm. The 250mm slab has a higher compression ratio and better mechanical properties.

[0004] The literature "Production Practice of Hot-Rolled Steel Plate for A36 Structural Use" provides a method for producing thin-gauge ASTM A36 steel plates with a small impact energy margin. This method employs a C-Mn composition design, uses aluminum deoxidation, and does not add other alloying elements. It allows for precise control of the composition, resulting in a large margin in compositional properties and excellent weldability and impact resistance. Furthermore, the use of a hot-charging method saves energy, shortens working hours, and improves production efficiency compared to the aforementioned patents. Summary of the Invention

[0005] The purpose of this invention is to provide a low-cost production method for ASTM A36 weldable structural steel plates using a hot-rolling process. The steel plate's performance and weldability meet the standards and user requirements. This invention employs narrow composition control and precise control of the rolling and cooling processes to ensure excellent steel plate performance, particularly in thickness and weldability, meeting the high standards required by users.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention discloses a low-cost method for producing ASTM A36 welded structural steel plates, comprising:

[0008] 1) The converter tapping temperature is 1550-1620℃. The single-slag process is used for smelting. Low-carbon ferromanganese and silicon-aluminum-iron alloys are used for deoxidation and alloying. The converter slag layer thickness is less than 50mm. Slag is blocked during tapping. The tapping time is ≥4min. The ladle is guaranteed to be a red-hot turnover ladle during tapping. Argon gas is blown into the bottom before tapping.

[0009] 2) The molten steel undergoes LF refining with precise control over the composition. The amount of quicklime added is ≥5kg / ton of steel. During the refining process, slag samples must be dipped to ensure rapid formation of white slag and to maintain the white slag for a certain period of time.

[0010] 3) The thickness of the continuously cast billet is 250mm. The superheat of the molten steel is controlled at 15-28℃ during casting. The liquid level in the tundish is not less than 25 tons when changing ladles. The argon blowing pressure of the long nozzle is ≥0.1Mpa. The flow rate of the argon blowing pressure gauge between the tundish submersible nozzle plates reaches 6-10L / min, and the pressure gauge pressure is 0.1-0.4Bar.

[0011] 4) Heating adopts a hot charging process, with a slow cooling time of ≤250 min. The slab entry temperature is 500-650℃, and the total furnace time is ≥140 min. The slab is heated using a three-stage walking beam furnace. The heating temperature of the first heating stage is 1100-1150℃, and the heating time is 40-50 minutes; the heating temperature of the second heating stage is 1200-1280℃, and the heating time is 45-60 minutes; the soaking temperature is 1230-1300℃, and the heating time is ≥30 min. The total heating time is not less than 140 min; the slab exit temperature is 1210-1250℃.

[0012] 5) Rolling and Cooling Process: After the slab is heated, it undergoes two-stage controlled rolling. The first stage rolling is completed on a roughing mill, with the initial rolling thickness being the same as the slab thickness. The initial rolling temperature for the first stage is 1070-1240℃, and the single-pass reduction rate during the high-temperature extension stage is not less than 13%. The final rolling temperature for the first stage is ≥880℃, and the first stage rolling continues until the initial rolling thickness of the second stage is reached. The second stage rolling is completed on a finishing mill, with the initial rolling temperature being 860-90℃. At 0℃, the initial rolling thickness in the second stage is 1.2 to 3.0 times the initial rolling thickness, and the final rolling temperature in the second stage is 805-875℃. The reduction rate in the final pass is 5% to 10%. After the steel plate is rolled, it undergoes laminar flow cooling with an ACC water temperature of 17 to 20℃, a cooling rate of 8 to 12℃ / s, and a final cooling temperature of 695 to 745℃. Generally, the head is shaded by 0-2.0m, the tail by 0-2.5m, and the edges by 0-2.0m, controlling the overall temperature difference after the steel plate turns red to ≤50℃.

[0013] The steel plate contains the following chemical composition by mass percentage: C: 0.13-0.15%, Si: 0.18-0.25%, Mn: 0.85-0.95%, P: ≤0.025%, S: ≤0.010%, Als: 0.20-0.35%, CEV: ≤0.32%; the remainder is iron and unavoidable impurities.

[0014] Furthermore, to ensure a certain compression ratio and slab quality, a 250mm thick continuously cast slab is selected, with a center segregation of no more than B2.0.

[0015] Furthermore, the steel plate contains the following chemical composition by mass percentage: C: 0.14%, Si: 0.20%, Mn: 0.88%, P: 0.014%, S: 0.004%, Als: 0.023%, CEV: 0.29%; the balance being Fe and unavoidable impurities.

[0016] Furthermore, the steel plate contains the following chemical composition by mass percentage: C: 0.13%, Si: 0.20%, Mn: 0.92%, P: 0.012%, S: 0.003%, Als: 0.025%, CEV: 0.28%; the balance being Fe and unavoidable impurities.

[0017] Furthermore, the steel plate contains the following chemical composition by mass percentage: C 0.15%, Si 0.24%, Mn 0.93%, P 0.015%, S 0.005%, Als 0.020%, CEV 0.30%, with the balance being Fe and unavoidable impurities.

[0018] Furthermore, the steel plate contains the following chemical composition by mass percentage: C: 0.14%, Si: 0.18%, Mn: 0.95%, P: 0.012%, S: 0.003%, Als: 0.030%, CEV: 0.30%, with the balance being Fe and unavoidable impurities.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0020] (1) The thickness of the steel plate is 40mm-100mm;

[0021] (2) It adopts C-Mn composition design, uses aluminum deoxidation, and does not add other alloying elements;

[0022] (3) The slab adopts a hot charging process to improve production efficiency and reduce energy consumption;

[0023] (4) The composition is precisely controlled, with a large margin in the composition performance, resulting in excellent welding and impact performance;

[0024] The key advantages of this invention are its C-Mn composition design, aluminum deoxidation, and absence of other alloying elements, resulting in low alloy cost, low carbon equivalent, and excellent impact performance. Furthermore, the use of a hot-charging and hot-delivery process reduces energy consumption, broadens the process design window, improves mass production efficiency, and enables stable mass production of 40mm-100mm welded structural steel plates (ASTM A36). Actual production and testing have demonstrated its excellent mechanical properties; the steel plates in each embodiment meet standard requirements for strength, have an elongation greater than 22%, and achieve an impact energy exceeding 150J at 20°C. Detailed Implementation

[0025] The present invention will be further described below with reference to embodiments.

[0026] Example 1

[0027] The slab, after smelting and continuous casting, was hot-charged into a heating furnace and heated for 152 minutes, followed by a soaking time of 35 minutes. The chemical composition of the slab, by mass percentage, was: C: 0.14%, Si: 0.20%, Mn: 0.88%, P: 0.014%, S: 0.004%, Als: 0.023%, CEV: 0.29%; the balance being Fe and unavoidable impurities. The slab was rolled into a 40mm thick steel plate. Detailed rolling processes are shown in Table 1, and its mechanical properties are shown in Table 2.

[0028] Example 2

[0029] The slab, after smelting and continuous casting, was hot-charged into a heating furnace and heated for 148 minutes, followed by a soaking time of 40 minutes. The chemical composition of the slab, by mass percentage, was: C: 0.13%, Si: 0.20%, Mn: 0.92%, P: 0.012%, S: 0.003%, Als: 0.025%, CEV: 0.28%; the balance being Fe and unavoidable impurities. The slab was rolled into a 60mm thick steel plate. Detailed rolling processes are shown in Table 1, and its mechanical properties are shown in Table 2.

[0030] Example 3

[0031] The slab, after smelting and continuous casting, was hot-charged into a heating furnace and heated for 146 minutes, followed by a soaking time of 42 minutes. The chemical composition of the slab was as follows (mass percentage): C 0.15%, Si 0.24%, Mn 0.93%, P 0.015%, S 0.005%, Als 0.020%, CEV: 0.30%, with the balance being Fe and unavoidable impurities. The slab was rolled into a 70mm thick steel plate. Detailed rolling processes are shown in Table 1, and its mechanical properties are shown in Table 2.

[0032] Example 4

[0033] The slab, after smelting and continuous casting, was hot-charged into a heating furnace and heated for 168 minutes, followed by a soaking time of 48 minutes. The chemical composition of the slab, by mass percentage, was: C: 0.14%, Si: 0.18%, Mn: 0.95%, P: 0.012%, S: 0.003%, Als: 0.030%, CEV: 0.30%, with the balance being Fe and unavoidable impurities. The detailed rolling process for the 90mm thick steel plate is shown in Table 1, and its mechanical properties are shown in Table 2.

[0034] Using this composition and process, low-cost, thick-gauge welded structural ASTM A36 steel plates are designed and manufactured. The chemical composition and mechanical properties meet the requirements of ASTM A36 / A36M "Standard Technical Conditions for Carbon Structural Steels". The steel plates have appropriate strength, excellent elongation, and outstanding impact performance. User feedback indicates good weldability.

[0035] Table 1. Process parameters for Examples 1-4

[0036]

[0037] Table 2 Mechanical properties of Examples 1-4

[0038]

[0039] 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 low-cost method for producing ASTM A36 welded structural steel plates, characterized in that: include: 1) The converter tapping temperature is 1550-1620℃. The single-slag process is used for smelting. Low-carbon ferromanganese and silicon-aluminum-iron alloys are used for deoxidation and alloying. The converter slag layer thickness is less than 50mm. Slag is blocked during tapping. The tapping time is ≥4min. The ladle is guaranteed to be a red-hot turnover ladle during tapping. Argon gas is blown into the bottom before tapping. 2) The molten steel undergoes LF refining with precise control over the composition. The amount of quicklime added is ≥5kg / ton of steel. During the refining process, slag samples must be dipped to ensure rapid formation of white slag and to maintain the white slag for a certain period of time. 3) The thickness of the continuously cast billet is 250mm. The superheat of the molten steel is controlled at 15-28℃ during casting. The liquid level in the tundish is not less than 25 tons when changing ladles. The argon blowing pressure of the long nozzle is ≥0.1Mpa. The flow rate of the argon blowing between the tundish submersible nozzle plates reaches 6-10L / min, and the pressure of the standby pressure gauge is 0.1-0.4Bar. 4) Heating adopts a hot charging process, with a slow cooling time of ≤250 min. The slab entry temperature is 500-650℃, and the total furnace time is ≥140 min. The slab is heated using a three-stage walking beam furnace. The heating temperature of the first heating stage is 1100-1150℃, and the heating time is 40-50 minutes; the heating temperature of the second heating stage is 1200-1280℃, and the heating time is 45-60 minutes; the soaking temperature is 1230-1300℃, and the heating time is ≥30 minutes. The total heating time is not less than 140 minutes; the slab exit temperature is 1210-1250℃. 5) Rolling and cooling process: After the slab is heated, it is subjected to two-stage controlled rolling. The first stage rolling is completed on the roughing mill. The first stage rolling thickness is the slab thickness. The first stage rolling temperature is 1070-1240℃. The single-pass reduction rate in the high-temperature extension stage is not less than 13%. The first stage finishing rolling temperature is ≥880℃. The first stage rolling continues until the second stage rolling thickness is reached. The second stage of rolling is completed on a finishing mill. The initial rolling temperature of the second stage is 860-900℃, and the final rolling temperature of the second stage is 805-875℃. The reduction rate of the last pass is 5%-10%. After the steel plate is rolled, it is subjected to laminar flow cooling with an ACC water temperature of 17-20℃, a cooling rate of 8-12℃ / s, and a final cooling temperature of 695-745℃. The head is shielded for 0-2.0m, the tail for 0-2.5m, and the edge for 0-2.0m. The overall temperature difference after the steel plate turns red-hot is controlled to be ≤50℃. This yields 40mm-100mm welded structural steel plates of ASTM A36. The steel plate contains the following chemical composition by mass percentage: C: 0.13-0.15%, Si: 0.18-0.25%, Mn: 0.85-0.95%, P: ≤0.025%, S: ≤0.010%, Als: 0.20-0.35%, CEV: ≤0.32%; the remainder is iron and unavoidable impurities.

2. The method for producing low-cost welded structural steel plate ASTM A36 according to claim 1, characterized in that: To ensure a certain compression ratio and slab quality, a 250mm thick continuously cast slab is selected, with a center segregation of no more than B2.

0.

3. The method for producing low-cost welded structural steel plate ASTM A36 according to claim 1, characterized in that: The steel plate contains the following chemical composition by mass percentage: C: 0.14%, Si: 0.20%, Mn: 0.88%, P: 0.014%, S: 0.004%, Als: 0.023%, CEV: 0.29%; the balance being Fe and unavoidable impurities.

4. The method for producing low-cost welded structural steel plate ASTM A36 according to claim 1, characterized in that: The steel plate contains the following chemical composition by mass percentage: C: 0.13%, Si: 0.20%, Mn: 0.92%, P: 0.012%, S: 0.003%, Als: 0.025%, CEV: 0.28%; the balance being Fe and unavoidable impurities.

5. The method for producing low-cost welded structural steel plate of ASTM A36 according to claim 1, characterized in that: The steel plate contains the following chemical composition by mass percentage: C 0.15%, Si 0.24%, Mn 0.93%, P 0.015%, S 0.005%, Als 0.020%, CEV: 0.30%, with the balance being Fe and unavoidable impurities.

6. The method for producing low-cost welded structural steel plate ASTM A36 according to claim 1, characterized in that: The steel plate contains the following chemical composition by mass percentage: C: 0.14%, Si: 0.18%, Mn: 0.95%, P: 0.012%, S: 0.003%, Als: 0.030%, CEV: 0.30%, with the balance being Fe and unavoidable impurities.

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