A method for producing a low-alloy high-toughness steel

Abstract

This invention discloses a method for preparing low-alloy high-strength and high-toughness steel, belonging to the field of iron and steel metallurgy and rolling technology. The method includes: sequentially subjecting a continuously cast billet to rough rolling, finish rolling, and coiling; the composition of the continuously cast billet, by mass percentage, is C≤0.08wt%, Si 0.05-0.2wt%, Mn 0.8-1.2wt%, P≤0.02wt%, Al 0.018-0.05wt%, Nb 0.01-0.02wt%, Ti 0.045-0.06wt%, with the balance being iron and unavoidable impurities; the process parameters are controlled as follows: continuous casting billet exit temperature 1100-1150℃, rough rolling exit temperature 1000-1050℃, finish rolling inlet temperature 950-1010℃, exit temperature 800-860℃, and coiling temperature 580-620℃. Furthermore, the rough rolling process employs five passes with decreasing reduction, followed by finishing rolling and cooling to the coiling temperature at 10-20°C / s. This invention, through the synergistic optimization of low-carbon microalloying composition design and thermomechanical control processes, effectively refines grains and improves microstructure, thereby reducing production costs while achieving an excellent balance of strength and toughness in the steel.

Description

Technical Field

[0001] This invention relates to the fields of iron and steel metallurgy and steel rolling technology, specifically to a method for preparing low-alloy high-strength and high-toughness steel. Background Technology

[0002] In numerous fields such as automobiles, construction, bridges, ships, and engineering machinery, increasingly higher requirements are being placed on the strength and toughness of structural steel materials. Insufficient strength and toughness of materials is one of the main causes of component failure, safety accidents, and economic losses. Once failure occurs due to insufficient strength and toughness, subsequent treatment and performance optimization are often time-consuming and costly.

[0003] Currently, one common method to improve the strength and toughness of steel materials is to add more alloying elements. However, this not only increases production costs but also fails to fundamentally simplify the process. At present, for low-alloy high-strength and high-toughness steels, there is a lack of a complete composition system and process parameter scheme that balances excellent performance with low cost, has a clear process window, and is easy to industrialize. Summary of the Invention

[0004] (a) Technical problems to be solved The technical problem this invention aims to solve is a method for preparing low-alloy high-strength and high-toughness steel. This method, through optimized alloy composition design and matching with specific thermomechanical control processes, effectively controls production costs while ensuring the material possesses good strength and toughness.

[0005] (II) Technical Solution To solve the above-mentioned technical problems, the technical solution provided by the present invention is: a method for preparing low-alloy high-strength and high-toughness steel, comprising the following steps: The continuous casting billet is subjected to rough rolling, fine rolling and coiling in sequence to obtain low alloy high strength and toughness steel. The composition of the continuously cast billet, by mass percentage, includes: C ≤ 0.08 wt%, Si 0.05-0.2 wt%, Mn 0.8-1.2 wt%, P ≤ 0.02 wt%, Al 0.018-0.05 wt%, Nb 0.01-0.02 wt%, Ti 0.045-0.06 wt%, with the balance being iron and unavoidable impurities; The process parameters are controlled as follows: The tapping temperature of the continuously cast billet is 1100-1150℃; The exit temperature of the roughing mill is 1000-1050℃; The inlet temperature of the finishing mill is 950-1010℃, and the outlet temperature of the finishing mill is 800-860℃. The winding temperature is 580-620℃.

[0006] As an improvement, the roughing process consists of 5 passes, with the reduction amount decreasing sequentially in each pass.

[0007] As an improvement, the thickness of the intermediate billet obtained after rough rolling is 50-58 mm.

[0008] As an improvement, after the finishing rolling and before coiling, the coiling temperature is cooled to the coiling temperature at a cooling rate of 10°C / s to 20°C / s.

[0009] (III) Beneficial Effects The advantages of this invention compared to the prior art are: Using a low-carbon (C≤0.08wt%) C-Si-Mn base composition system reduces the carbon content, which is beneficial for obtaining a strong and ductile ferrite and bainite structure during later phase transformations, reduces the formation of hard martensite, and improves the material's toughness. The addition of trace amounts of Nb (0.01-0.02wt%) and Ti (0.045-0.06wt%) refines the grains and promotes precipitation strengthening, avoiding the need for large amounts of expensive alloying elements and thus reducing costs.

[0010] By controlling the furnace exit temperature to a lower level (1100-1150℃), the original austenite grains were effectively refined. Combined with a rolling process of five roughing passes with decreasing reduction, the strain rate decreased, increasing the degree of recrystallization and further refining the grains.

[0011] By employing a lower finishing rolling temperature (800-860℃) and combining it with a large reduction during finishing rolling, the deformation energy storage of austenite is increased, forming more deformation substructures, which is beneficial for grain refinement after phase transformation. Ultra-rapid cooling (10-20℃ / s) after finishing rolling suppresses high-temperature precipitation, promotes fine-grain strengthening and phase transformation strengthening, ultimately resulting in a material with excellent strength and toughness matching. Detailed Implementation

[0012] The invention will now be described in further detail with reference to specific embodiments, but this should not be construed as limiting the scope of the subject matter of the invention to the following embodiments.

[0013] Example 1

[0014] A method for preparing a low-alloy high-strength and high-toughness steel, wherein the chemical composition by mass percentage is: C≤0.08wt%, Si 0.05-0.2wt%, Mn 0.8-1.2wt%, P≤0.02wt%, Al 0.018-0.05wt%, Nb 0.01-0.02wt%, Ti 0.045-0.06wt%, with the balance being iron and unavoidable impurities.

[0015] Its process parameters are as follows: Continuous casting billet tapping temperature: 1100℃; Rough rolling: Five passes are used, with the reduction decreasing in each pass. The exit temperature of the rough rolling mill is 1000℃, and the thickness of the intermediate billet is 58mm. Finishing mill: Finishing mill inlet temperature 950℃, finishing mill outlet temperature 800℃; Cooling: After finishing rolling, ultra-fast cooling is performed at a cooling rate of 20℃ / s; Winding: Winding temperature is 580℃.

[0016] The mechanical properties of the low-alloy high-strength and high-toughness steel obtained in this embodiment are shown in Table 1.

[0017] Example 2

[0018] A method for preparing a low-alloy high-strength and high-toughness steel, the chemical composition of which is the same as that in Example 1.

[0019] Its process parameters are as follows: Continuous casting billet tapping temperature: 1150℃; Rough rolling: Five passes are used, with the reduction decreasing in each pass. The exit temperature of the rough rolling mill is 1050℃, and the thickness of the intermediate billet is 50mm. Finishing mill: Finishing mill inlet temperature 1010℃, finishing mill outlet temperature 860℃; Cooling: After finishing rolling, ultra-fast cooling is performed at a cooling rate of 10℃ / s; Winding: The winding temperature is 620℃.

[0020] The mechanical properties of the low-alloy high-strength and high-toughness steel obtained in this embodiment are shown in Table 1.

[0021] Example 3

[0022] A method for preparing a low-alloy high-strength and high-toughness steel, the chemical composition of which is the same as that in Example 1.

[0023] Its process parameters are as follows: Continuous casting billet tapping temperature: 1100℃; Rough rolling: Five passes are used, with the reduction decreasing in each pass. The exit temperature of the rough rolling mill is 1050℃, and the thickness of the intermediate billet is 50mm. Finishing mill: Finishing mill inlet temperature 1010℃, finishing mill outlet temperature 800℃; Cooling: After finishing rolling, ultra-fast cooling is performed at a cooling rate of 20℃ / s; Winding: The winding temperature is 590℃ (Note: It is automatically matched according to the cooling rate and thickness, and falls within the range of 580-620℃).

[0024] The mechanical properties of the low-alloy high-strength and high-toughness steel obtained in this embodiment are shown in Table 1.

[0025] Example 4

[0026] A method for preparing a low-alloy high-strength and high-toughness steel, the chemical composition of which is the same as that in Example 1.

[0027] Its process parameters are as follows: Continuous casting billet tapping temperature: 1150℃; Rough rolling: Five passes are used, with the reduction decreasing in each pass. The exit temperature of the rough rolling mill is 1000℃, and the thickness of the intermediate billet is 50mm. Finishing mill: Finishing mill inlet temperature 950℃, finishing mill outlet temperature 860℃; Cooling: After finishing rolling, ultra-fast cooling is performed at a cooling rate of 10℃ / s; Winding: Winding temperature is 600℃ (Note: Automatically matched according to cooling rate and thickness, within the range of 580-620℃).

[0028] The mechanical properties of the low-alloy high-strength and high-toughness steel obtained in this embodiment are shown in Table 1.

[0029] Example Yield strength (MPa) Tensile strength (MPa) Elongation (%) Impact energy per unit value A (J) Impact energy per unit value B (J) Impact energy per unit C (J) Average impact energy (J) Example 1 534 611 22 331 329 320 327 Example 2 447 531 29 286 282 264 277 Example 3 489 574 26.5 238 223 220 227 Example 4 487 495 586 242 232 285 253 Table 1.

Claims

1. A method for preparing low-alloy high-strength and high-toughness steel, characterized in that, Includes the following steps: The continuous casting billet is subjected to rough rolling, fine rolling and coiling in sequence to obtain low alloy high strength and toughness steel. The composition of the continuously cast billet, by mass percentage, includes: C ≤ 0.08 wt%, Si 0.05-0.2 wt%, Mn 0.8-1.2 wt%, P ≤ 0.02 wt%, Al 0.018-0.05 wt%, Nb 0.01-0.02 wt%, Ti 0.045-0.06 wt%, with the balance being iron and unavoidable impurities; The process parameters are controlled as follows: The tapping temperature of the continuously cast billet is 1100-1150℃; The exit temperature of the roughing mill is 1000-1050℃; The inlet temperature of the finishing mill is 950-1010℃, and the outlet temperature of the finishing mill is 800-860℃. The winding temperature is 580-620℃.

2. The method for preparing a low-alloy high-strength and high-toughness steel according to claim 1, characterized in that, The roughing process consists of 5 passes, with the reduction amount decreasing sequentially in each pass.

3. The method for preparing a low-alloy high-strength and high-toughness steel according to claim 1, characterized in that, The thickness of the intermediate billet obtained after rough rolling is 50-58 mm.

4. The method for preparing a low-alloy high-strength and high-toughness steel according to claim 1, characterized in that, After the finishing rolling and before coiling, the coiling temperature is cooled to the coiling temperature at a cooling rate of 10°C / s to 20°C / s.