A low-cost high-strength steel with a yield strength of 460 mpa and a method for producing the same

Abstract

This invention discloses a low-cost high-strength steel with a yield strength of 460 MPa and its production method, belonging to the field of metallurgical technology. The chemical composition and mass percentage of the high-strength steel are: C: 0.14-0.16%, Si: 0.20-0.30%, Mn: 1.30-1.40%, P≤0.016%, S≤0.012%, Als: 0.015-0.040%, with the balance being Fe and unavoidable residual elements and impurities from the production process. The production method includes billet heating, controlled rolling, controlled cooling, and slow stacking cooling processes. This invention, through conventional carbon and manganese composition design, eliminates the addition of microalloying agents such as Nb and V, and combines specific rolling, centralized cooling, and slow stacking cooling processes to obtain Q460MC steel that meets the mechanical property requirements of GB / T 1591-2018 standard, achieving low-cost manufacturing of Q460MC.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a low-cost high-strength steel with a yield strength of 460MPa and its production method. Background Technology

[0002] Q460MC, a high-strength steel with a yield strength of 460MPa, is a low-alloy high-strength structural steel. It possesses excellent comprehensive mechanical and processing properties, and its requirements for rolling and cooling equipment on medium plate production lines are relatively low. Most domestic medium plate production lines are capable of producing this steel grade. Products with a thickness of 16-40mm are widely used in structural components of engineering machinery and coal mining machinery, for manufacturing various supporting structural parts, and are used in large quantities. With increasingly fierce competition among steel mills and downstream customers, the demand for low-cost Q460MC is quite urgent.

[0003] Domestic medium plate production lines use thermomechanical rolling to produce this steel grade. The composition design often involves adding one or more microalloying elements such as Nb, V, and Ti to enhance its strength and ensure that the final performance meets GB / T1591-2018 standards. This composition design fully utilizes the grain refinement and precipitation strengthening effects of microalloying elements during rolling and cooling, resulting in good product performance stability. However, the addition of microalloying elements limits further reductions in production costs.

[0004] Patent application CN113416902B discloses "A low-cost hot-formed bridge housing steel plate with a yield strength of 460MPa and its preparation method," which uses appropriate amounts of inexpensive metals such as Mn and B for alloying and strengthens the steel plate through phase transformation to ensure that the strength of the hot-rolled steel plate and the hot-formed bridge housing semi-finished product meets the requirements. However, this patent involves steel grades with a large amount of Nb and V elements, resulting in high alloy costs.

[0005] Patent application CN104313468A discloses a "460MPa grade low-alloy high-strength structural steel plate and its production method," which uses a low-C, low-Nb, and micro-B design to ultimately obtain a mixed microstructure of ferrite, pearlite, and bainite. While meeting the requirements, this method avoids using expensive alloying elements such as Mo, Cr, Cu, Ni, and V, thus saving on alloying costs. However, the carbon content of the steel grade involved in this patent is 0.03-0.09wt%. While significantly reducing the carbon equivalent of the steel plate, this increases the difficulty of deoxidation during the smelting process, thereby increasing smelting costs. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a low-cost high-strength steel with a yield strength of 460MPa, whose comprehensive performance meets GB / T 1591-2018; the present invention also provides a production method for a low-cost high-strength steel with a yield strength of 460MPa, which has low alloy production cost and simple process flow, and solves the defects of the prior art.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a low-cost high-strength steel with a yield strength of 460MPa, wherein the chemical composition and mass percentage of the high-strength steel are: C: 0.14-0.16%, Si: 0.20-0.30%, Mn: 1.30-1.40%, P≤0.016%, S≤0.012%, Als: 0.015-0.040%, and the balance is Fe and unavoidable residual elements and impurities in the production process.

[0008] The chemical composition and mass percentage of the high-strength steel described in this invention are as follows: C: 0.14-0.16%, Si: 0.20-0.30%, Mn: 1.32-1.37%, P≤0.015%, S≤0.010%, Als: 0.015-0.030%, with the remainder being Fe and unavoidable residual elements and impurities from the production process.

[0009] The high-strength steel described in this invention has a thickness of 16-40mm, a yield strength of 488-552MPa, a tensile strength of 628-689MPa, an elongation of 17.5-23.5%, and an impact energy of 98-167J at 0℃.

[0010] Another objective of this invention is to provide a method for producing low-cost high-strength steel with a yield strength of 460 MPa. The method includes billet heating, controlled rolling, controlled cooling, and slow stacking cooling processes. The slow stacking cooling process has a cooling rate controlled at 5.4–8.3 °C / h. The controlled cooling process uses ACC controlled cooling, with the initial cooling temperature controlled at 770–820 °C. The ACC section employs concentrated cooling at the front end, with a cooling rate controlled at 11–15 °C / s, and the final cooling temperature controlled at 600–630 °C.

[0011] The controlled cooling process ACC section of this invention adopts front-end centralized cooling, continuously turning on the ACC front-end water group, and controlling the ACC water flow rate at 300-350 L / (min*m). 2 The ratio of water volume in the upper and lower manifolds of the ACC section is 2.0 to 2.2.

[0012] The slow cooling process of stacking described in this invention utilizes other high-temperature steel plates and high-strength steel for cross-stacking, with the stacking time controlled between 48 and 55 hours.

[0013] The controlled rolling process described in this invention is a two-stage rolling process, with an initial rolling temperature of 1050-1100℃, a waiting-to-heat thickness ≥2.5a, where a is the finished thickness of the steel plate, a final waiting-to-heat temperature ≤860℃, and a final rolling temperature controlled at 820-850℃.

[0014] In the billet heating process described in this invention, the surface temperature of the billet is controlled at 1200-1240℃ at the end of the heating process, and the heating time is ≥100min.

[0015] This invention ensures that the strength of Q460MC steel plate meets GB / T 1591-2018 while achieving low-cost manufacturing of the steel plate. The design of the production process parameters is mainly based on the following principles:

[0016] a. The surface temperature of the slab after being heated in the furnace is controlled between 1200 and 1240°C. Combined with the capacity of the furnace, the heating efficiency of the furnace is improved. At the same time, the machinability of the slab in the first rolling stroke is improved, thereby increasing production efficiency.

[0017] b. Setting the initial rolling temperature of the second stage below 860℃ ensures that deformation occurs within the non-recrystallization temperature range, thus avoiding part of the recrystallization temperature range. Controlling the thickness of the steel plate during the second-stage rolling to be at least 2.5 times the finished product thickness allows for a cumulative reduction rate ≥60%, which is necessary to obtain sufficient dislocations. The high-strength steel plate undergoes repeated rolling and deformation in the non-recrystallization region. After rolling, the deformed microstructure accumulates a large number of dislocations, deformation bands, and microalloying element precipitates of various sizes. This process design is mentioned in several documents and is a non-critical but essential part of this invention. The final rolling temperature is controlled within the range of 820–850℃.

[0018] c. By adjusting the roller conveyor speed and employing ACC centralized cooling, the cooling rate of the steel plate in the ACC cooling section is controlled at 11–15℃ / s, and the final cooling temperature is controlled at 600–630℃. At this cooling rate and final cooling temperature, Q460MC enters the intermediate-temperature bainite transformation zone, forming an intermediate-temperature bainite microstructure with small lath bundle orientation differences, resembling a single grain. Furthermore, controlling the final cooling temperature at 600–630℃ helps reduce uneven cooling of the steel plate and improves its flatness.

[0019] d. Intermediate-temperature bainite is characterized by high strength and high brittleness. After cooling, Q460MC steel plates are rapidly removed from the production line and cross-stacked with other high-temperature steel plates. By adjusting the number of high-temperature plates, the slow cooling rate during stacking is controlled at 5.4–8.3℃ / h, and the stacking time is controlled at 48–55h. After slow cooling through stacking, the carbon-rich regions in the bainite diffuse to the carbon-depleted regions. High-density dislocations caused by uneven cooling and phase transformations in the steel plate move forward and cancel each other out during the stacking process, reducing the dislocation density. Additionally, hydrogen atoms inside the steel plate escape to the surface during stacking, ultimately reducing the brittleness of intermediate-temperature transformed bainite and improving the mechanical properties of the steel plate.

[0020] The beneficial effects of adopting the above technical solution are as follows: This invention, through conventional carbon and manganese composition design, avoids the addition of microalloying agents such as Nb and V, and combines specific rolling, centralized cooling, and slow stacking cooling processes to achieve the mechanical property requirements of Q460MC as specified in GB / T 1591-2018 standard. The rolling, cooling, and stacking processes of the steel grade of this invention are simple and easy to implement, and while ensuring mechanical properties, they also minimize the addition of microalloying agents, achieving low-cost manufacturing of Q460MC. Attached Figure Description

[0021] Figure 1 This is a 200× microstructure image of Q460MC from Example 1;

[0022] Figure 2 This is a 200× microstructure image of Q460MC in Example 2;

[0023] Figure 3 This is a 200× microstructure image of Q460MC in Example 3;

[0024] Figure 4 This is a 200× microstructure image of Q460MC in Example 4;

[0025] Figure 5 This is a 200× microstructure image of Q460MC in Example 5;

[0026] Figure 6 This is a 200× microstructure image of Q460MC in Example 6. Detailed Implementation

[0027] 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.

[0028] Examples 1-6

[0029] A method for producing low-cost high-strength steel with a yield strength of 460 MPa includes billet heating, controlled rolling, controlled cooling, and slow cooling by stacking. The specific control methods are as follows:

[0030] 1) Billet heating process: The surface temperature of the billet is controlled at 1200~1240℃ at the end of heating, and the heating time is ≥100min;

[0031] 2) Control the rolling process, which is a two-stage rolling process. The initial rolling temperature is 1050~1100℃, the thickness waiting to be heated is ≥2.5a, where a is the thickness of the finished steel plate, the final temperature waiting to be heated is ≤860℃, and the final rolling temperature is controlled at 820~850℃.

[0032] 3) Controlled cooling process: ACC controlled cooling is adopted, with the starting temperature controlled at 770-820℃. The ACC section adopts centralized front-end cooling, continuously operating the front-end water unit of the ACC, and the ACC water flow rate is controlled at 300-350L / (min*m). 2 The ratio of water flow in the upper and lower manifolds of the ACC section is 2.0 to 2.2; the cooling rate is controlled at 11 to 15℃ / s; and the final cooling temperature is controlled at 600 to 630℃.

[0033] 4) Stacking and slow cooling process: Other high-temperature steel plates and high-strength steel are stacked in a cross-stacking manner. The cooling rate of the stacking and slow cooling process is controlled at 5.4 to 8.3℃ / h, and the stacking time is controlled at 48h to 55h.

[0034] The chemical composition of the low-cost high-strength steel with a yield strength of 460 MPa obtained in Examples 1-6 is shown in Table 1, the process parameter control is shown in Table 2, and the thickness specifications and mechanical properties are shown in Table 3.

[0035] Examples 1-6 show that the mechanical properties of the produced Q460MC grade steel plate fully meet the requirements of the national standard GB / T1591-2018; Figure 1-6 It can be seen that the microstructure of the steel plates in each embodiment is a mixed rolled structure of ferrite with a proportion of less than 15% and bainite with the balance being 15%. The sufficient content of bainite can ensure that the strength of Q460MC in the low-cost alloy system of the present invention meets the requirements of GB / T 1591-2018.

[0036] Table 1. Chemical composition and mass percentage (wt%) of high-strength steels in Examples 1-6

[0037]

[0038]

[0039] Table 2 Control parameters for billet heating, controlled rolling, controlled cooling, and stacking processes in Examples 1-6

[0040]

[0041] Table 3 Thickness specifications and mechanical properties of Examples 1-6

[0042] Example Thickness / mm Yield strength / MPa Tensile strength / MPa Elongation / % Impact energy at 0℃ / J 1 16 488 640 18.0 155 / 149 / 152 2 20 507 645 20.5 151 / 160 / 151 3 25 496 628 21.5 156 / 155 / 157 4 30 524 656 23.5 140 / 153 / 167 5 35 462 629 19.5 134 / 147 / 140 6 40 552 689 17.5 99 / 98 / 98

[0043] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A low-cost, high-strength steel with a yield strength of 460 MPa, characterized in that, The chemical composition and mass percentage of the high-strength steel are as follows: C: 0.14-0.16%, Si: 0.20-0.30%, Mn: 1.32-1.40%, P≤0.016%, S≤0.012%, Als: 0.015-0.040%, with the balance being Fe and unavoidable residual elements and impurities from the production process; The high-strength steel has a yield strength of 488–552 MPa, a tensile strength of 628–689 MPa, and an impact energy of 98–167 J at 0℃. The production method includes billet heating, controlled rolling, controlled cooling, and stacking slow cooling processes; the cooling rate of the stacking slow cooling process is controlled at 5.4 to 8.3℃ / h; the controlled cooling process adopts ACC controlled cooling, with the initial cooling temperature controlled at 770 to 820℃, the ACC section adopts front-end centralized cooling, the cooling rate is controlled at 13 to 15℃ / s, and the final cooling temperature is controlled at 605 to 630℃. The controlled cooling process (ACC) section employs centralized front-end cooling, with the ACC front-end water system continuously activated and the ACC water flow rate controlled at 300–350 L / (min*m). 2 The ratio of water flow in the upper and lower manifolds of the ACC section is 2.0 to 2.

2. The stacking and slow cooling process utilizes other high-temperature steel plates and high-strength steels to be stacked crosswise, with the stacking time controlled between 48 and 55 hours. The controlled rolling process consists of two stages: an initial rolling temperature of 1050–1100℃, a waiting-to-heat thickness of ≥2.5a (where a is the finished steel plate thickness), a final waiting-to-heat temperature of ≤860℃, and a final rolling temperature controlled at 820–850℃.

2. The low-cost, high-strength steel with a yield strength of 460 MPa according to claim 1, characterized in that, The chemical composition and mass percentage of the high-strength steel are as follows: C: 0.14-0.16%, Si: 0.20-0.30%, Mn: 1.32-1.37%, P≤0.015%, S≤0.010%, Als: 0.015-0.030%, with the remainder being Fe and unavoidable residual elements and impurities from the production process.

3. A low-cost, high-strength steel with a yield strength of 460 MPa according to claim 1 or 2, characterized in that, The high-strength steel has a thickness of 16-40mm and an elongation of 17.5-23.5%.

4. A method for producing low-cost, high-strength steel with a yield strength of 460 MPa according to any one of claims 1-3, characterized in that, The production method includes billet heating, controlled rolling, controlled cooling, and stacking slow cooling processes; the cooling rate of the stacking slow cooling process is controlled at 5.4 to 8.3℃ / h; the controlled cooling process adopts ACC controlled cooling, with the initial cooling temperature controlled at 770 to 820℃, the ACC section adopts front-end centralized cooling, the cooling rate is controlled at 13 to 15℃ / s, and the final cooling temperature is controlled at 605 to 630℃. The controlled cooling process (ACC) section employs centralized front-end cooling, with the ACC front-end water system continuously activated and the ACC water flow rate controlled at 300–350 L / (min*m). 2 The ratio of water flow in the upper and lower manifolds of the ACC section is 2.0 to 2.

2. The stacking and slow cooling process utilizes other high-temperature steel plates and high-strength steels to be stacked crosswise, with the stacking time controlled between 48 and 55 hours. The controlled rolling process consists of two stages: an initial rolling temperature of 1050–1100℃, a waiting-to-heat thickness of ≥2.5a (where a is the finished steel plate thickness), a final waiting-to-heat temperature of ≤860℃, and a final rolling temperature controlled at 820–850℃.

5. The method for producing low-cost high-strength steel with a yield strength of 460 MPa according to claim 4, characterized in that, In the billet heating process, the surface temperature of the billet is controlled at 1200-1240℃ at the end of the heating process, and the heating time is ≥100min.

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