Green low-carbon rolling variable-thickness variable-strength B column and production method thereof

Abstract

The invention discloses a green low-carbon rolling variable-thickness variable-strength B column and a production method thereof.The B column is formed by hot forming steel through variable-thickness rolling and hot stamping forming, the B column comprises three thickness areas in the height direction of the B column, the three thickness areas are an upper connecting area with the thickness ranging from 1.0 mm to 1.4 mm and the strength larger than or equal to 800 MPa, and a lower connecting area with the thickness ranging from 1.0 mm to 1.4 mm and the strength larger than or equal to 800 MPa; the thickness of the middle anti-collision area is 1.8-2.2 mm, and the strength is larger than or equal to 1500 MPa; the thickness of the lower connecting area is 1.1-1.5 mm, and the strength is larger than or equal to 800 MPa; thickness continuous transition is formed among the three areas through a rolling technology. Through the combination of variable thickness rolling and the hot stamping process, light-weight, high-strength and low-energy-consumption production of the B column is achieved, and the problems of welding defects, high energy consumption, low material utilization rate and the like in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of automotive body structural component manufacturing technology, specifically to a green and low-carbon rolled variable thickness and variable strength B-pillar and its production method. Background Technology

[0002] As a key load-bearing structural component of the car body, the B-pillar needs to provide sufficient resistance to deformation under conditions such as side collisions, while also meeting the requirements for lightweighting to reduce energy consumption. Current B-pillar manufacturing methods mainly employ the following two approaches: (1) Stamping of steel plates of equal thickness: In order to ensure the strength of key areas, thicker high-strength steel plates are required, which results in the overall weight of the B-pillar being too large, serious material waste, and increased vehicle energy consumption, which is not in line with the trend of environmental protection. (2) Laser welding of variable thickness plate forming: By welding steel plates of different thicknesses to form a variable thickness substrate, local weight reduction can be achieved, but the welding process consumes a lot of electrical energy and there is a risk of welding defects (such as false welding and cracks). Additional inspection process is required afterward, resulting in a long production cycle, high cost, poor performance consistency of parts, and the abrupt weld structure after welding brings different degrees of stamping crack risk to mold design and manufacturing, which is not conducive to the metal flow of materials during stamping.

[0003] Existing technologies suffer from problems such as "difficulty in balancing weight and strength", "high production energy consumption and high cost", and "risk of stamping cracking". There is an urgent need to develop a B-pillar and production method that takes into account economy, environmental protection and performance, to make up for the shortcomings of the welding process and meet the service function requirements of variable thickness parts, thereby improving performance, reducing the weight of parts and achieving automotive lightweighting. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a green and low-carbon rolled variable thickness and variable strength B-pillar and its production method to address the shortcomings of the prior art. By combining variable thickness rolling with hot stamping process, the B-pillar can be produced in a lightweight, high-strength and low-energy-consumption manner, overcoming the problems of welding defects, high energy consumption and low material utilization in the prior art.

[0005] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows: A green, low-carbon rolled variable-thickness, variable-strength B-pillar, wherein the B-pillar is made of hot-formed steel through variable-thickness rolling and hot stamping, and includes three thickness regions along the height direction of the B-pillar: The upper connection area, located at the top of the B-pillar (connected to the side beam of the roof), has a thickness of 1.0 to 1.4 mm and a strength of ≥800 MPa, which is sufficient to meet the connection strength requirements and reduce the amount of material used. The central anti-collision zone, located in the middle of the B-pillar (corresponding to the area from the shoulder to the waist of the car seat, the core load-bearing area of ​​the side collision), has a thickness of 1.8 to 2.2 mm and a strength of ≥1500 MPa, improving its resistance to deformation. The lower connection area, located at the bottom of the B-pillar (connected to the door sill beam), has a thickness of 1.1 to 1.5 mm and a strength of ≥800 MPa, balancing connection strength and lightweight requirements; The three regions are formed by a rolling process to create a continuous thickness transition without welding seams, thus avoiding stress concentration. At the same time, the raw materials adopt a green and low-carbon design to reduce environmental pressure, and the strength change is achieved in the hot stamping die to further improve the performance of the parts.

[0006] In the above scheme, the hardness of the middle anti-collision area is ≥38HRC, and the hardness of the upper connecting area and the lower connecting area is ≥25HRC.

[0007] The above-mentioned green and low-carbon rolled variable thickness and variable strength B-pillar production method includes the following steps: Variable thickness rolling: After uncoiling and preheating, the high-strength hot-formed steel coil is fed into a single-stand rolling mill with real-time adjustable roll gap for variable thickness rolling, controlling the steel plate to form a preset continuous thickness distribution in the rolling direction. In this step, the steel plate rolling process is controlled and the roll gap is adjusted in real time by a computer, so that the thickness along the rolling direction changes continuously according to a pre-defined plan: The hot-formed steel coil is flattened by an uncoiler and preheated in a heating furnace to 600-700℃ (lower than the traditional hot-forming heating temperature, reducing energy consumption). The preheated steel plate is then fed into a single-stand rolling mill with real-time control and adjustment of roll gap. Based on the functional design required for the service of lightweight variable thickness plate parts, the steel plate is rolled... Variable thickness rolling is performed; the reduction is adjusted in real time. For the intermediate anti-collision area, the reduction is controlled at 10% to 20%, retaining a thickness of 1.8 to 2.2 mm. For the upper and lower connecting areas, the reduction is controlled at 40% to 60%, rolling to a thickness of 1.0 to 1.5 mm. The required variable thickness plate obtained after variable thickness rolling is rolled at a speed controlled at 1.2 to 1.8 m / s. Water mist cooling (replacing traditional oil cooling) is used during the rolling process to reduce pollutant emissions and ensure the stability of the steel plate structure. The principle of variable thickness plate rolling is as follows: during the steel plate rolling process, the gap between the rolls is controlled and adjusted in real time by computer, so that the thickness along the rolling direction changes continuously according to the pre-defined parameters.

[0008] Blanking: The rolled steel plate is straightened, sheared, and laser-bladed to obtain the B-pillar blank; this step straightens, shears, and blanks the thickened hot-formed steel coil or directly blanks the strip into irregular plates; the thickness of the irregular plates is distributed between 1.0 and 2.5 mm, and the maximum thickness shall not exceed twice the minimum thickness.

[0009] Hot stamping: The B-pillar blank is heated to 850-950°C and then placed in a hot forming mold for stamping. After stamping, segmented cooling is used to control the cooling rate of different areas. Specifically, different water channel diameters are designed in the mold to achieve low cooling rate and high cooling rate zone control. By differentially controlling the cooling rate of different areas of the mold, the gradient distribution of the microstructure and mechanical properties of the part is achieved. Post-processing: Deburring (using high-pressure water jet deburring, with no mechanical wear and reduced waste) and hole diameter machining (using CNC drilling for mounting holes with an accuracy of ±0.05mm) are performed to obtain the aforementioned green, low-carbon rolled variable thickness and variable strength B-pillar.

[0010] In the above scheme, during the variable thickness rolling process, the initial thickness of the hot-formed steel coil is 2.2 to 3.5 mm.

[0011] In the above scheme, water mist cooling is used in the variable thickness rolling step, and the cooling pressure is 0.6 to 1.2 MPa.

[0012] In the above scheme, CNC laser cutting is used in the blanking step, and the cutting accuracy is ±0.1mm; the maximum thickness of the B-pillar blank is no more than twice the minimum thickness.

[0013] In the above scheme, the stamping pressure in the hot stamping forming step is 6000-10000kN; the cooling rate of the intermediate anti-collision area in the segmented cooling is 27-35℃ / s, and the cooling rate of the upper connecting area and the lower connecting area is 20-27℃ / s; the temperature of the mold is 200-250℃.

[0014] In the above scheme, the chemical composition of the hot-formed steel coil by weight percentage is as follows: C: 0.20-0.25%, Si: 0.20-0.30%, Mn: 1.00-1.30%, P≤0.02%, S≤0.01%, Als: 0.02-0.06%, N≤0.005%, B: 0.002-0.004%, Nb≤0.005%, Ti: 0.03-0.05%, with the balance being Fe and unavoidable trace elements.

[0015] Preferably, the chemical composition of the hot-formed steel coil by weight percentage is: C: 0.22%, Si: 0.25%, Mn: 1.20%, P: 0.01%, S: 0.005%, Als: 0.04%, N: 0.002%, B: 0.004%, Nb: 0.004%, Ti: 0.04%, with the balance being Fe and unavoidable trace elements.

[0016] Compared with existing technologies, the beneficial effects of this invention are: (1) This invention provides a green and low-carbon rolled variable thickness and variable strength B-pillar and its production method. The method organically combines variable thickness rolling with variable strength hot stamping. First, the hot-formed steel plate is rolled to a variable thickness, and then blanked to obtain a special-shaped plate. Then, the special-shaped plate is hot-stamped to obtain a lightweight variable thickness plate part. The transition section of the lightweight variable thickness plate part replaces the weld, which not only greatly improves the connection strength and performance of the part and makes up for the shortcomings of the welding process, but also has a significant weight reduction effect. While improving performance, the weight of the parts is reduced, thus realizing the lightweighting of automobiles.

[0017] (2) The rolling variable thickness process provided by the present invention does not require welding, reducing the investment in welding equipment and inspection procedures, and shortening the production cycle by 20% to 30%; the material utilization rate is ≥92%, which is more than 15% higher than that of laser-welded plates, reducing material waste; the preheating temperature and rolling energy consumption are reduced by 15%-20%, and the energy consumption per unit product is reduced to 350-400kJ / kg, which is lower than the 500-550kJ / kg of the traditional process.

[0018] (3) The present invention provides a green and low-carbon rolled variable thickness and variable strength B-column without weld seam, which avoids stress concentration. The maximum deformation during side collision is ≤35mm, which is 10% to 15% lower than that of laser welded B-column. Furthermore, the strength change is achieved through hot stamping die, which further improves the collision energy absorption performance and impact resistance of the part. Attached Figure Description

[0019] Figure 1 This is a schematic cross-sectional view of the rolled steel plate of the present invention.

[0020] Figure 2 This is a schematic diagram of the B-pillar blank of the present invention.

[0021] In the diagram, 1 is the upper connecting area; 2 is the transition area; 3 is the middle anti-collision area; 4 is the transition area; and 5 is the lower connecting area. Detailed Implementation

[0022] The technical solution of the present invention will be described in detail below with reference to specific embodiments. However, the described embodiments are only some embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] A green, low-carbon rolled variable-thickness, variable-strength B-pillar, made of hot-formed steel through variable-thickness rolling and hot stamping, comprising three thickness regions along the height of the B-pillar: The upper connecting area has a thickness of 1.0–1.4 mm and a strength ≥ 800 MPa; The central anti-collision zone has a thickness of 1.8–2.2 mm and a strength of ≥1500 MPa; The lower connecting area has a thickness of 1.1–1.5 mm and a strength ≥ 800 MPa; The three regions are connected by a rolling process to create a continuous thickness transition.

[0024] The hardness of the middle anti-collision area is ≥38HRC, and the hardness of the upper and lower connecting areas is ≥25HRC.

[0025] The above-mentioned green and low-carbon rolled variable thickness and variable strength B-pillar production method includes the following steps: Variable thickness rolling: After uncoiling and preheating, hot-formed steel coils with an initial thickness of 2.2–3.5 mm are fed into a single-stand rolling mill with real-time adjustable roll gap for variable thickness rolling, controlling the steel plate to form a preset continuous thickness distribution in the rolling direction; the preheating temperature is 600–700℃; the rolling speed is 1.2–1.8 m / s; water mist cooling is used, and the cooling pressure is 0.6–1.2 MPa; the reduction in the intermediate anti-collision zone is controlled at 10%–20%, and the reduction in the upper and lower connecting zones is controlled at 40%–60%.

[0026] Blanking: The rolled steel plate is straightened, sheared, and laser-bladed to obtain the B-pillar blank; CNC laser cutting is used with a cutting accuracy of ±0.1mm; the maximum thickness of the B-pillar blank is no more than twice the minimum thickness.

[0027] Hot stamping: The B-pillar blank is heated to 850-950℃ and then placed in a hot forming mold for stamping. After stamping, segmented cooling is used to control the cooling rate of different areas. The stamping pressure is 6000-10000kN. The cooling rate of the middle anti-collision area in the segmented cooling is 27-35℃ / s, and the cooling rate of the upper and lower connecting areas is 20-27℃ / s. The temperature of the hot forming mold is 200-250℃.

[0028] Post-processing: Deburring and hole diameter machining are performed to obtain a green, low-carbon rolled variable thickness and variable strength B-pillar.

[0029] The chemical composition of the hot-formed steel coil in this invention, by weight percentage, is as follows: C: 0.22%, Si: 0.25%, Mn: 1.20%, P: 0.01%, S: 0.005%, Als: 0.04%, N: 0.002%, B: 0.004%, Nb: 0.004%, Ti: 0.04%, with the balance being Fe and unavoidable trace elements.

[0030] Example 1 This embodiment provides a green, low-carbon rolled variable thickness and variable strength B-pillar, which is made of hot-formed steel through variable thickness rolling and hot stamping, and includes three thickness regions along the height direction of the B-pillar: The upper connecting area has a thickness of 1.2 mm and a strength of ≥800 MPa; The central anti-collision zone has a thickness of 2.0mm and a strength of ≥1500MPa; The lower connecting area has a thickness of 1.3mm and a strength of ≥800MPa; The three regions are connected by a rolling process to create a continuous thickness transition.

[0031] The above-mentioned green and low-carbon rolled variable thickness and variable strength B-pillar production method includes the following steps: Variable thickness rolling: After uncoiling and preheating, the hot-formed steel coil with an initial thickness of 2.3 mm is fed into a single-stand rolling mill with real-time adjustable roll gap for variable thickness rolling, controlling the steel plate to form a preset continuous thickness distribution in the rolling direction; the preheating temperature is 650℃; the rolling speed is 1.5 m / s; water mist cooling is used, and the cooling pressure is 0.8 MPa; the reduction in the intermediate anti-collision zone (height range 400-800 mm) is controlled at 15%, with a thickness of 2.0 mm; the reduction in the upper connecting zone (0-400 mm) is controlled at 50%, with a thickness of 1.2 mm; and the reduction in the lower connecting zone (800-1200 mm) is controlled at 45%, with a thickness of 1.3 mm. In this embodiment, 22MnB5 hot-formed steel coil (initial thickness 2.3 mm, initial yield strength 550 MPa) is selected.

[0032] Blanking: The rolled steel plate is straightened, sheared, and laser-bladed to obtain the B-pillar blank; CNC laser cutting is used, with a laser cutting size of 1200mm×180mm (B-pillar height 1200mm, width 180mm), a cutting accuracy of ±0.1mm, and a material utilization rate of 93%; the maximum thickness of the B-pillar blank is no more than twice the minimum thickness.

[0033] Hot stamping: The B-pillar blank is heated to 900℃ and then placed in a hot forming mold for stamping. After stamping, segmented cooling is used to control the cooling rate of different areas. The stamping pressure is 8000kN. The cooling rate of the middle anti-collision area is 35℃ / s, and the cooling rate of the upper and lower connecting areas is 25℃ / s. The temperature of the hot forming mold is 230℃.

[0034] Post-processing: Deburring and hole diameter machining are performed to obtain a green, low-carbon rolled variable thickness and variable strength B-pillar.

[0035] Figure 1 and Figure 2 These are schematic diagrams of the cross-section of the rolled steel plate and the blank of column B in this embodiment. In the figures, 1, 3, and 5 are the upper connecting area, the middle anti-collision area, and the lower connecting area, respectively, and 2 and 4 are the transition areas.

[0036] The performance of a green, low-carbon rolled variable thickness and variable strength B-pillar sample prepared in this embodiment was tested, and the results are as follows: ① The hardness of the middle area is 47 HRC, which corresponds to a strength greater than 1500 MPa according to ISO 18265 standard; the hardness of the upper and lower areas is 26 HRC, which corresponds to a strength greater than 800 MPa according to ISO 18265 standard. ② Side impact test (according to GB / T 37337-2019 standard): maximum deformation 32mm, energy absorption ≥80kJ; ③ The unit product energy consumption is 380kJ / kg, the production cycle is 45s / piece, and the waste amount is 7%.

[0037] Example 2 This embodiment provides a green, low-carbon rolled variable thickness and variable strength B-pillar, which is made of hot-formed steel through variable thickness rolling and hot stamping, and includes three thickness regions along the height direction of the B-pillar: The upper connecting area has a thickness of 1.0 mm and a strength of ≥800 MPa; The central anti-collision zone has a thickness of 2.0mm and a strength of ≥1500MPa; The lower connecting area has a thickness of 1.1 mm and a strength of ≥800 MPa; The three regions are connected by a rolling process to create a continuous thickness transition.

[0038] The above-mentioned green and low-carbon rolled variable thickness and variable strength B-pillar production method includes the following steps: Variable thickness rolling: After uncoiling and preheating, the hot-formed steel coil with an initial thickness of 2.5 mm is fed into a single-stand rolling mill with real-time adjustable roll gap for variable thickness rolling, controlling the steel plate to form a preset continuous thickness distribution in the rolling direction; the preheating temperature is 700℃; the rolling speed is 1.8 m / s; water mist cooling is used, and the cooling pressure is 1.0 MPa; the reduction in the intermediate anti-collision zone (height range 420-820 mm) is controlled at 20%, with a thickness of 2.0 mm; the reduction in the upper connecting zone (0-420 mm) is controlled at 60%, with a thickness of 1.0 mm; and the reduction in the lower connecting zone (820-1250 mm) is controlled at 55%, with a thickness of 1.1 mm. In this embodiment, 22MnB5 hot-formed steel coil (initial thickness 2.5 mm, initial yield strength 550 MPa) is selected.

[0039] Blanking: The rolled steel plate is straightened, sheared, and laser-bladed to obtain the B-pillar blank; CNC laser cutting is used, with a laser cutting size of 1250mm×190mm (B-pillar height 1250mm, width 190mm), a cutting accuracy of ±0.1mm, and a material utilization rate of 92.5%; the maximum thickness of the B-pillar blank is no more than twice the minimum thickness.

[0040] Hot stamping: The B-pillar blank is heated to 950℃ and then placed in a hot forming mold for stamping. After stamping, segmented cooling is used to control the cooling rate of different areas. The stamping pressure is 9000kN. The cooling rate of the middle anti-collision area is 33℃ / s, and the cooling rate of the upper and lower connecting areas is 23℃ / s. The temperature of the hot forming mold is 225℃.

[0041] Post-processing: Deburring and hole diameter machining are performed to obtain a green, low-carbon rolled variable thickness and variable strength B-pillar.

[0042] The performance of a green, low-carbon rolled variable thickness and variable strength B-pillar sample prepared in this embodiment was tested, and the results are as follows: ① The hardness of the middle area is 46HRC, which corresponds to a strength greater than 1500MPa according to ISO 18265 standard; the hardness of the upper and lower areas is 26HRC, which corresponds to a strength greater than 800MPa according to ISO 18265 standard. ② Side impact test: maximum deformation 30mm, energy absorption ≥85kJ; ③ The unit product energy consumption is 395kJ / kg, the production cycle is 42s / piece, and the waste amount is 7.5%.

[0043] In summary, this invention provides a green and low-carbon rolled variable thickness and variable strength B-pillar and its production method. By combining variable thickness rolling with hot stamping, the invention achieves lightweight, high strength, and low energy consumption production of the B-pillar, overcoming problems such as welding defects, high energy consumption, and low material utilization in existing technologies.

[0044] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and its improved concept, should be covered within the scope of protection of the present invention.

Claims

1. A green, low-carbon rolled variable thickness and variable strength B-pillar, characterized in that, The B-pillar is made of hot-formed steel through variable-thickness rolling and hot stamping, and the B-pillar includes three thickness regions along its height direction: The upper connecting area has a thickness of 1.0–1.4 mm and a strength ≥ 800 MPa; The central anti-collision zone has a thickness of 1.8–2.2 mm and a strength of ≥1500 MPa; The lower connecting area has a thickness of 1.1–1.5 mm and a strength ≥ 800 MPa; The three regions are connected by a rolling process to create a continuous thickness transition.

2. The green, low-carbon rolled variable thickness and variable strength B-pillar according to claim 1, characterized in that, The hardness of the middle anti-collision area is ≥38HRC, and the hardness of the upper connecting area and the lower connecting area is ≥25HRC.

3. A method for producing a green, low-carbon rolled variable thickness and variable strength B-pillar according to any one of claims 1 to 2, characterized in that, Includes the following steps: Variable thickness rolling: After the hot-formed steel coil is uncoiled and preheated, it is fed into a single-stand rolling mill with real-time adjustable roll gap for variable thickness rolling, controlling the steel plate to form a preset continuous thickness distribution in the rolling direction. Blanking: The rolled steel plate is straightened, sheared, and laser-bladed to obtain the B-pillar blank; Hot stamping: The B-pillar blank is heated to 850-950°C and then placed in a mold for stamping, and segmented cooling is used to control the cooling rate of different areas; The cooling rate of the segmented cooling is 20–35 °C / s; Post-processing: Deburring and hole diameter machining are performed to obtain the green, low-carbon rolled variable thickness and variable strength B-pillar.

4. The production method of a green, low-carbon rolled variable thickness and variable strength B-pillar according to claim 3, characterized in that, During the variable thickness rolling process, the initial thickness of the hot-formed steel coil is 2.2 to 3.5 mm.

5. The production method of a green, low-carbon rolled variable thickness and variable strength B-pillar according to claim 3, characterized in that, In the variable thickness rolling step, the preheating temperature is 600-700℃; the rolling speed is 1.2-1.8m / s.

6. The method for producing a green, low-carbon, rolled variable thickness and variable strength B-pillar according to claim 3, characterized in that, In the variable thickness rolling step, water mist cooling is used, and the cooling pressure is 0.6 to 1.2 MPa.

7. The method for producing a green, low-carbon, rolled variable thickness and variable strength B-pillar according to claim 3, characterized in that, In the variable thickness rolling step, the reduction of the intermediate anti-collision area is controlled at 10% to 20%, and the reduction of the upper connecting area and the lower connecting area is controlled at 40% to 60%.

8. The method for producing a green, low-carbon, rolled variable thickness and variable strength B-pillar according to claim 3, characterized in that, The blanking step uses CNC laser cutting with a cutting accuracy of ±0.1mm; the maximum thickness of the B-pillar blank is no more than twice the minimum thickness.

9. The method for producing a green, low-carbon rolled variable thickness and variable strength B-pillar according to claim 3, characterized in that, In the hot stamping forming step, the stamping pressure is 6000-10000kN; in the segmented cooling, the cooling rate of the intermediate anti-collision area is 27-35℃ / s, and the cooling rate of the upper connecting area and the lower connecting area is 20-27℃ / s; the temperature of the mold is 200-250℃.

10. The method for producing a green, low-carbon, rolled variable thickness and variable strength B-pillar according to claim 3, characterized in that, The chemical composition of the hot-formed steel coil by weight percentage is as follows: C: 0.20-0.25%, Si: 0.20-0.30%, Mn: 1.00-1.30%, P≤0.02%, S≤0.01%, Als: 0.02-0.06%, N≤0.005%, B: 0.002-0.004%, Nb≤0.005%, Ti: 0.03-0.05%, with the balance being Fe and unavoidable trace elements.

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