A high tensile strength > 650mpa grade automotive beam steel and a method of manufacturing the same

Abstract

The application discloses a kind of automobile beam steels of tensile strength ≥650MPa and manufacturing method thereof, belong to hot-rolled steel strip technical field.The chemical composition of the steel is as follows in percentage by mass: C:0.05%~0.10%, Si:0.05%~0.25%, Mn:1.30%~1.80%, P:≤0.020%, S:≤0.0030%, Nb:0.04%~0.07%, Ti:0.03%~0.06%, the balance is Fe and inevitable impurities.Manufacturing method includes successively: hot metal desulphurization, converter blowing, argon blowing, LF furnace refining, continuous casting, rotary descaling, soaking, high-pressure water descaling, seven-stand finish rolling, laminar cooling and coiling.Continuous casting adopts liquid core reduction, soaking temperature is 1180~1250 DEG C, finish rolling temperature is 860~900 DEG C, coiling temperature is 600~650 DEG C, after 5m slight cooling of strip head by laminar cooling, it is cooled at 20~50 DEG C / s.The alloy cost of the application is low, process is simple, and the obtained steel plate has yield strength ≥550MPa, tensile strength ≥650MPa, elongation ≥17%, thinnest specification 1.5mm, with good shape, can realize "thin instead of thick" and "hot instead of cold".

Description

Technical Field

[0001] This invention relates to the field of hot-rolled steel strip technology, specifically to a type of automotive beam steel with a tensile strength ≥650MPa and its manufacturing method. Background Technology

[0002] With the increasing demands for lightweighting and energy conservation in automobiles, the demand for high-strength automotive beam steel is growing in sectors such as heavy-duty trucks and dump trucks. Users not only require steel with high strength and good plasticity, but also desire thinner specifications (as thin as 1.5mm) to replace thicker plain carbon steel, or to replace some cold-rolled sheets to achieve "hot-rolled steel replacing cold-rolled steel," thereby reducing production costs and vehicle weight, and achieving energy conservation and emission reduction.

[0003] Existing manufacturing methods for high-strength automotive beam steel typically suffer from one or more of the following problems: (1) Mechanical properties are improved by adding a large number of alloying elements such as Cu, Cr, V, Mo, etc., which results in high alloy costs; (2) To obtain ultra-thin products, cold rolling and annealing processes are required, which are lengthy, costly, and often result in low elongation. (3) When producing thin-gauge high-strength steel using traditional hot rolling processes, it is difficult to control the plate shape, which can easily lead to production accidents such as steel piling up and low yield. Summary of the Invention

[0004] (a) Technical problems to be solved The technical problem to be solved by the present invention is to provide a steel beam for automobiles with a tensile strength ≥650MPa and a method for manufacturing the same, so as to overcome the defects of high alloy cost, long process flow or difficulty in producing thin-gauge products in the prior art.

[0005] (II) Technical Solution To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: a steel for automobile beams with a tensile strength ≥650MPa, characterized in that its chemical composition by mass percentage is: C: 0.05%~0.10%, Si: 0.05%~0.25%, Mn: 1.30%~1.80%, P: ≤0.020%, S: ≤0.0030%, Nb: 0.04%~0.07%, Ti: 0.03%~0.06%, with the balance being Fe and unavoidable impurities.

[0006] A method for manufacturing automotive beam steel with a tensile strength ≥650MPa, the method comprising the following steps in sequence: hot metal desulfurization, converter blowing, argon blowing, LF furnace refining, continuous casting, rotary descaling, homogenization, high-pressure water descaling, seven-stand precision rolling, laminar flow cooling and coiling.

[0007] As an improvement, the continuous casting process employs liquid core reduction technology to reduce the billet thickness from 70-90 mm to 50-55 mm.

[0008] As an improvement, in the homogenization process, the outlet temperature of the homogenization furnace is 1180-1250℃.

[0009] As an improvement, in the high-pressure water descaling process, the pressure of the descaling manifold is 15-30 MPa.

[0010] As an improvement, the final rolling temperature of the seven-stand finishing rolling process is 860–900℃. As an improvement, the temperature of the winding process is 600–650°C.

[0011] As an improvement, the laminar flow cooling process includes: slightly cooling the first 5m of the strip at a rate lower than that of the subsequent strip; and turning on the laminar flow cooling water after the first 5m of the strip so that the average cooling rate of the strip is 20-50℃ / s.

[0012] As an improvement, in the laminar flow cooling process, the cooling method is adjusted according to the thickness specifications of the strip steel: For strip steel with a thickness of <2.0mm, slow cooling at the front end is adopted; For strip steel with a thickness of ≥2.0mm, rapid front-end cooling is adopted.

[0013] (III) Beneficial Effects The advantages of this invention compared to the prior art are: (1) The alloy has low cost, using only conventional Nb and Ti micro-alloying without adding expensive alloys; (2) The process flow is short. Hot-rolled strip is produced directly using thin slab continuous casting and rolling technology without cold rolling annealing. It can produce ultra-thin specifications with a minimum thickness of 1.5mm. (3) The process window is wide. By controlling the homogenization temperature, final rolling temperature, coiling temperature and laminar flow cooling, stable microstructure and properties are obtained, and the mechanical properties of the product are uniform. (4) The product has excellent comprehensive performance, high strength, good plasticity, good forming performance and welding performance, and can realize "thin instead of thick" and "hot instead of cold", significantly reducing the cost of downstream users. Detailed Implementation

[0014] 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.

[0015] Example 1

[0016] A type of automotive beam steel with a tensile strength ≥650MPa, characterized in that its chemical composition by mass percentage is: C: 0.05%, Si: 0.05%, Mn: 1.30%, P: 0.020%, S: 0.0030%, Nb: 0.04%, Ti: 0.03%, with the balance being Fe and unavoidable impurities.

[0017] A method for manufacturing automotive beam steel with a tensile strength ≥650MPa, the method comprising the following steps in sequence: hot metal desulfurization, converter blowing, argon blowing, LF furnace refining, continuous casting, rotary descaling, homogenization, high-pressure water descaling, seven-stand precision rolling, laminar flow cooling and coiling.

[0018] The continuous casting process uses liquid core reduction technology to reduce the billet thickness from 70mm to 50mm. In the soaking process, the outlet temperature of the soaking furnace is 1180℃. In the high-pressure water descaling process, the pressure of the descaling manifold is 15MPa. The final rolling temperature of the seven-stand finishing rolling process is 860℃. The temperature of the coiling process is 600℃.

[0019] The laminar flow cooling process includes: slightly cooling the first 5m of the strip at a rate lower than that of the subsequent strip; and after the first 5m of the strip, turning on the laminar flow cooling water to make the average cooling rate of the strip 20℃ / s. In this laminar flow cooling process, the cooling method is adjusted according to the thickness specifications of the strip. For strip steel with a thickness of <2.0mm, slow cooling at the front end is adopted; For strip steel with a thickness of ≥2.0mm, rapid front-end cooling is adopted.

[0020] Example 2

[0021] A type of automotive beam steel with a tensile strength ≥650MPa, characterized in that its chemical composition by mass percentage is: C: 0.08%, Si: 0.1%, Mn: 1.50%, P: 0.020%, S: 0.0030%, Nb: 0.06%, Ti: 0.04%, with the balance being Fe and unavoidable impurities.

[0022] A method for manufacturing automotive beam steel with a tensile strength ≥650MPa, the method comprising the following steps in sequence: hot metal desulfurization, converter blowing, argon blowing, LF furnace refining, continuous casting, rotary descaling, homogenization, high-pressure water descaling, seven-stand precision rolling, laminar flow cooling and coiling.

[0023] The continuous casting process uses liquid core reduction technology to reduce the billet thickness from 80mm to 52mm. In the soaking process, the outlet temperature of the soaking furnace is 1200℃. In the high-pressure water descaling process, the pressure of the descaling manifold is 20MPa. The final rolling temperature of the seven-stand finishing rolling process is 880℃. The temperature of the coiling process is 630℃.

[0024] The laminar flow cooling process includes: slightly cooling the first 5m of the strip at a rate lower than that of the subsequent strip; and after the first 5m of the strip, turning on the laminar flow cooling water to make the average cooling rate of the strip 30℃ / s. In this laminar flow cooling process, the cooling method is adjusted according to the thickness specifications of the strip. For strip steel with a thickness of <2.0mm, slow cooling at the front end is adopted; For strip steel with a thickness of ≥2.0mm, rapid front-end cooling is adopted.

[0025] Example 3

[0026] A type of automotive beam steel with a tensile strength ≥650MPa, characterized in that its chemical composition by mass percentage is: C: 0.10%, Si: 0.25%, Mn: 1.80%, P: 0.020%, S: 0.0030%, Nb: 0.07%, Ti: 0.06%, with the balance being Fe and unavoidable impurities.

[0027] A method for manufacturing automotive beam steel with a tensile strength ≥650MPa, the method comprising the following steps in sequence: hot metal desulfurization, converter blowing, argon blowing, LF furnace refining, continuous casting, rotary descaling, homogenization, high-pressure water descaling, seven-stand precision rolling, laminar flow cooling and coiling.

[0028] The continuous casting process uses liquid core reduction technology to reduce the billet thickness from 90mm to 55mm. In the soaking process, the outlet temperature of the soaking furnace is 1250℃. In the high-pressure water descaling process, the pressure of the descaling manifold is 30MPa. The final rolling temperature of the seven-stand finishing rolling process is 900℃. The temperature of the coiling process is 650℃.

[0029] The laminar flow cooling process includes: slightly cooling the first 5m of the strip at a rate lower than that of the subsequent strip; and after the first 5m of the strip, turning on the laminar flow cooling water to make the average cooling rate of the strip 50℃ / s. In this laminar flow cooling process, the cooling method is adjusted according to the thickness specifications of the strip. For strip steel with a thickness of <2.0mm, slow cooling at the front end is adopted; For strip steel with a thickness of ≥2.0mm, rapid front-end cooling is adopted.

[0030] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents. In short, if those skilled in the art are inspired by these claims and design similar structural methods and embodiments without departing from the inventive spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A type of automotive beam steel with a tensile strength ≥650MPa, characterized in that, Its chemical composition by mass percentage is as follows: C: 0.05%~0.10%, Si: 0.05%~0.25%, Mn: 1.30%~1.80%, P: ≤0.020%, S: ≤0.0030%, Nb: 0.04%~0.07%, Ti: 0.03%~0.06%, with the balance being Fe and unavoidable impurities.

2. The method for manufacturing automotive beam steel with a tensile strength ≥650MPa according to claim 1, characterized in that, The method includes the following steps in sequence: hot metal desulfurization, converter blowing, argon blowing, LF furnace refining, continuous casting, rotary descaling, homogenization, high-pressure water descaling, seven-stand precision rolling, laminar flow cooling and coiling.

3. The method for manufacturing automotive beam steel with a tensile strength ≥650MPa according to claim 2, characterized in that, The continuous casting process employs liquid core reduction technology to reduce the billet thickness from 70-90 mm to 50-55 mm.

4. The method for manufacturing automotive beam steel with a tensile strength ≥650MPa according to claim 2, characterized in that, In the homogenization process, the outlet temperature of the homogenization furnace is 1180–1250°C.

5. The method for manufacturing automotive beam steel with a tensile strength ≥650MPa according to claim 2, characterized in that, In the high-pressure water descaling process, the pressure in the descaling manifold is 15–30 MPa.

6. The method for manufacturing automotive beam steel with a tensile strength ≥650MPa according to claim 2, characterized in that, The final rolling temperature of the seven-stand finishing rolling process is 860–900℃.

7. The method for manufacturing automotive beam steel with a tensile strength ≥650MPa according to claim 2, characterized in that, The temperature of the winding process is 600–650°C.

8. The method for manufacturing automotive beam steel with a tensile strength ≥650MPa according to claim 2, characterized in that, The laminar flow cooling process includes: slightly cooling the first 5m of the strip at a rate lower than that of the subsequent strip; and turning on the laminar flow cooling water after the first 5m of the strip to make the average cooling rate of the strip 20-50℃ / s.

9. A method for manufacturing automotive beam steel with a tensile strength ≥650MPa according to claim 8, characterized in that, In the laminar flow cooling process, the cooling method is adjusted according to the thickness specifications of the strip steel: For strip steel with a thickness of <2.0mm, slow cooling at the front end is adopted; For strip steel with a thickness of ≥2.0mm, rapid front-end cooling is adopted.