Method for manufacturing a press-hardened sheet-formed piece from a hot-rolled and coated steel sheet
By performing precision rolling on hot-rolled steel plates, surface roughness and thickness tolerance are reduced, solving the problems of high energy consumption and instability in the stamping hardening process of hot-rolled steel plates, and achieving the effect of efficiently manufacturing high-strength vehicle components.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BAYERISCHE MOTOREN WERKE AG
- Filing Date
- 2025-02-10
- Publication Date
- 2026-06-16
AI Technical Summary
In the existing technology, hot-rolled steel sheets have high roughness and large thickness tolerance during the stamping hardening process, which leads to high energy consumption and is not conducive to manufacturing sheet metal parts with high stability and high load-bearing capacity.
By precision rolling hot-rolled and coated steel sheets, surface roughness is reduced and thickness tolerance is homogenized. Metal coatings such as zinc or zinc alloys are used, combined with hot-dip galvanizing and precision rolling processes, to ensure that the steel sheets are heated quickly and to reduce oxide formation.
It achieves smooth processing of hot-rolled steel sheets, reduces energy consumption, and improves the stability and load-bearing capacity of sheet metal parts, making it suitable for manufacturing high-strength vehicle components such as longitudinal and transverse beams for electric vehicle bodies.
Smart Images
Figure CN122228338A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method, according to claim 1, for manufacturing stamp-hardened sheet metal parts from hot-rolled and coated steel sheets. The invention also relates to an application, according to the co-claims, of using steel sheets with specific properties to manufacture stamp-hardened sheet metal parts. Background Technology
[0002] Stamp hardening is defined as a process in which a sheet of steel made from sheet material suitable for stamp hardening is heated to austenitize and then quenched and cooled while being formed in a stamp hardening die. High strength is obtained in this process by means of martensitic hardening. In so-called direct stamp hardening, a flat sheet of steel is heated and then formed in a stamp hardening die while being quenched and cooled simultaneously. In indirect stamp hardening, the sheet of steel is first pre-formed, then heated and then finally formed in a stamp hardening die while being quenched and cooled simultaneously. The sheet of steel used may have a coating, particularly a metallic coating, which acts as an anti-corrosion coating and / or an anti-scaling coating. For reference to the prior art, see EP3265365B1, and especially the opening description and cited references.
[0003] For press hardening, either cold-rolled steel sheet (also known as cold-rolled strip) or hot-rolled steel sheet (also known as hot-rolled strip) can be used. Hot-rolled steel sheet is advantageous for larger sheet thicknesses combined with coatings, especially for metal coatings applied by hot-dip galvanizing. The closest prior art, DE69933751T3, describes a hot-rolled sheet strip having a metal coating of 0.2 mm to 20 mm thickness applied by hot-dip galvanizing, which is then used for press hardening (hot stamping and quench hardening). Summary of the Invention
[0004] The present invention is based on the objective of providing an improved method for manufacturing stamped and hardened sheet metal parts from hot-rolled and coated steel sheets.
[0005] This task is solved by the method according to claim 1 of the invention. By means of the parallel claims, the invention also extends to the application of steel sheets pretreated according to the meaning of the invention and thereby constructed with specific properties for the manufacture of stamp-hardened sheet metal parts. Advantageous improvements and embodiments are also derived for both inventive subjects from the dependent claims, the following description of the invention (which explicitly includes features described in both exemplary and alternative ways), and the accompanying drawings.
[0006] The method for manufacturing stamp-hardened sheet metal parts according to the present invention comprises the following steps:
[0007] - Provide hot-rolled and coated, especially metal-coated, steel sheets;
[0008] - The coated steel sheet is precision rolled to reduce its roughness, which refers to the surface roughness of the sheet.
[0009] - Perform a stamping hardening process, in which the steel sheet—here referring to a steel sheet after precision rolling—is heated to the austenitizing temperature and formed into a sheet metal part in a stamping hardening die and hardened, i.e., quenching hardening (direct stamping hardening), or, in this stamping hardening process, the steel sheet is pre-formed, heated to the austenitizing temperature, and finally formed into a sheet metal part in a stamping hardening die and hardened, i.e., quenching hardening (indirect stamping hardening).
[0010] The provided steel sheets are suitable for stamping hardening processes (e.g., 22MnB5 or 20MnB8) and are manufactured by hot rolling. Hot-rolled steel sheets are particularly those manufactured in hot rolling mills or similar equipment at high rolling temperatures, preferably several hundred degrees Celsius or even above the recrystallization temperature, preferably by hot rolling only (i.e., without additional cold rolling at low temperatures, especially at room temperature). Hot-rolled steel sheets typically have high or pronounced roughness and larger sheet thickness tolerances. Unlike cold-rolled steel sheets, hot-rolled steel sheets can also be produced in greater sheet thicknesses. Furthermore, hot-rolled steel sheets (hot-rolled strip) are generally less expensive than cold-rolled steel sheets (cold-rolled strip).
[0011] The provided hot-rolled steel sheet may have a thickness of 2.4 mm or greater, preferably 2.6 mm or greater, and especially 2.8 mm or greater. This large sheet thickness, which is unusual for stamping hardening, enables the manufacture of stamping hardened sheet metal parts that are highly stable or have strong load-bearing capacity, and is particularly suitable for vehicle components with high structural requirements (e.g., for electric vehicles). Preferably, the provided steel sheet has at least approximately uniform sheet thickness while still maintaining sheet thickness tolerances (see above).
[0012] The coating is applied after hot rolling. The coating is preferably applied to both sides of the sheet, i.e., on both sides of the sheet. The coating is preferably a metallic coating, particularly composed of zinc, zinc alloys (e.g., zinc-iron alloys), or aluminum alloys (e.g., aluminum-silicon alloys). The metallic coating is preferably applied by hot-dip galvanizing. During hot-dip galvanizing, the steel sheet is cleaned, heated, typically in a continuous furnace, guided through the molten pool, and blown away. Here, the high roughness inherent in the aforementioned hot-rolled steel sheet (see above) proves advantageous because it allows for rapid heating of the steel sheet even with significant sheet thickness, thereby saving energy and costs. The metallic coating, especially when made of zinc or zinc alloys, can have a thickness of 7 μm to 13 μm, particularly 9 μm to 11 μm.
[0013] The finishing rolling of coated steel sheets is carried out, particularly in a cold state, preferably at room temperature, and in this respect can also be referred to as cold finishing rolling. Finish rolling is performed to reduce the roughness of the coated steel sheet, that is, to make the surface smooth, especially on both sides of the sheet. The Ra value (average roughness value) preferably achieved in finishing rolling is less than or equal to 2.5 μm, preferably less than or equal to 2.0 μm, and especially less than or equal to 1.5 μm, referring here to the Ra value of the coated sheet surface, especially on both sides of the sheet. Finish rolling can also achieve uniformity of sheet thickness or reduction of sheet thickness tolerance, and / or the generation of a defined surface texture. Preferably, finishing rolling is carried out without producing a significant reduction in sheet thickness (the reduction is at most less than or equal to 2%), and is therefore fundamentally different from variable rolling used to produce so-called custom rolled billets.
[0014] Finishing rolling is preferably carried out using a single roll pair (upper roll and lower roll) or, if necessary, multiple roll pairs. The surface roughness achievable during finishing rolling depends on the texture of the rolls (work rolls), particularly their surface texture. The rolls can be constructed with specific surface structures (e.g., EDT, LBT, SBT, and EBT) to obtain the desired roughness value and / or specific surface texture in finishing rolling. Preferably, the two rolls in a single roll pair (for finishing rolling) are constructed substantially identically, particularly having the same surface structure. The rolls in a single roll pair (for finishing rolling) can also be constructed differently, particularly having different surface structures, thereby producing different roughness values and / or surface textures on opposite sides of the sheet.
[0015] For press hardening, hot-rolled, coated, and finish-rolled steel sheets are heated to the austenitizing temperature (greater than or equal to Ac1 or greater than or equal to Ac3) after preforming, if necessary, especially in a furnace or similar apparatus. Heating can be performed locally or in sections at different temperatures. The heated steel sheet is then formed or finally hardened in a press hardening die, where multiple sequentially arranged press hardening dies can also be used in coordination. Pre-cooling or intercooling can be selectively performed before placement into the press hardening die, which can also be performed locally or in sections at different temperatures. Additional steps, such as trimming and / or punching, can also be included. Trimming and / or punching can be performed, particularly after preforming.
[0016] By employing the precision rolling method according to the present invention, the microscopic surface of the coated steel sheet is leveled and thus smoothed, thereby reducing its roughness. Compared to conventional hot-rolled and coated steel sheets, the steel sheet is therefore significantly smoother. The smoothing process may involve only the coating, or it may involve the coating and the steel sheet itself, or the steel sheet substrate. In either case, the smoothing process, or roughness reduction, achieves the following: significantly less oxide or scale is formed on the surface of the steel sheet when it is heated to the austenitizing temperature, thereby protecting the stamping hardening die and simplifying subsequent cleaning, welding, and / or painting processes that may occur after stamping hardening. The purpose of the precision rolling method according to the present invention is to reduce the formation of oxides or scale during the subsequent austenitizing of the steel sheet, or when the steel sheet is heated to the austenitizing temperature (during stamping hardening).
[0017] Furthermore, the surface roughness of the steel plate measured before or after finishing rolling can determine the "real" or "actual" surface, which includes the unevenness or roughness profile. This surface can be approximated as a characteristic value to characterize the tendency of oxidation formation, and can also be used to set process parameters and / or describe the process.
[0018] This invention takes into account, to some extent, the following: the inherent high roughness of hot-rolled steel sheets is advantageous for coatings, especially hot-dip galvanized coatings, but disadvantageous for press hardening. Furthermore, the inherently large thickness tolerance of hot-rolled steel sheets can also be detrimental to press hardening. The precision rolling method of this invention enables the use of hot-rolled (preferably only hot-rolled) and coated (preferably metallic) steel sheets for press hardening applications (especially with larger sheet thicknesses), thereby generating a significant cost advantage. This invention is also particularly suitable for the mass production of press-hardened sheet metal parts.
[0019] Hot-rolled and coated steel sheets can be supplied as strips or plates. The strips or plates can then be finish-rolled, specifically, finish-rolling is performed over the entire length and width of the strip or the entire length and width of the plate. Finish-rolling of the strips or plates can be performed at the steel sheet manufacturer, at a contract manufacturer, or at an outsourced processing plant, or only at a steel sheet processing plant (which also performs the stamping hardening process). Preferably, after finish-rolling, the strips or plates are cut into slabs, especially so-called shaped slabs (this process is also called slab cutting), and the stamping hardening process is performed therefrom. It can also be specified that slab cutting is performed before finish-rolling, or finish-rolling is performed after slab cutting, wherein the slab is preferably finish-rolled over its entire length and width.
[0020] The surface roughness achievable during finishing rolling depends on the quality of the rolls used (see above). Furthermore, the surface roughness achievable during finishing rolling can also be influenced by the roll clamping force, or rolling pressure, and / or by the tension acting on the steel sheet. This tension specifically refers to the tension applied to the steel sheet on the feed side (opposite to the feed direction) and / or on the discharge side (in the discharge direction) for finishing rolling rolls. Thus, during finishing rolling, tensile stress is generated in the steel sheet, creating a multiaxial stress state that facilitates smoothing. (For sheet / strip fed from a coil or uncoiler, a so-called strip tension or uncoiling tension can be set, thereby applying tension or tensile stress to the sheet / strip on the feed side. Tension rolls can be used to apply tension or tensile stress to the sheet / strip on the discharge side.) Higher roll clamping force and / or higher tension can achieve a more pronounced smoothing effect, or lower surface roughness. Therefore, the surface roughness achieved during finishing rolling can be adapted or adjusted by changing the roll clamping force and / or the tension, especially to achieve a specific Ra value or upper limit Ra value (e.g., Ra ≤ 2.5 μm, ≤ 2.0 μm, or ≤ 1.5 μm). The roll clamping force and / or tension can be changed between two rolling strokes or during a single rolling stroke. This can also be done in a closed-loop control circuit.
[0021] The invention also extends to the use of hot-rolled, coated (especially metallic coating and / or double-sided coating) and (after coating) precision-rolled steel sheets for manufacturing stamp-hardened sheet metal parts, wherein the hot-rolled, coated and precision-rolled steel sheet is heated to an austenitizing temperature and formed into a sheet metal part in a stamp-hardening die and then hardened; or wherein the hot-rolled, coated and precision-rolled steel sheet is pre-formed, heated to an austenitizing temperature and finally formed into a sheet metal part in a stamp-hardening die and then hardened.
[0022] Therefore, the hot-rolled, coated, and finish-rolled steel sheet can be provided as a strip or in sheet form. As previously explained, the finish rolling of the hot-rolled, coated steel sheet can be performed at the steel sheet manufacturer, a specially commissioned contract manufacturer, or an outsourced processing plant, or only at the steel sheet processing plant (which also performs the stamping hardening process). The hot-rolled, coated, and finish-rolled steel sheet can have an Ra value of less than or equal to 2.5 μm, preferably less than or equal to 2.0 μm, and especially less than or equal to 1.5 μm. The hot-rolled, coated, and finish-rolled steel sheet is coated, in particular, by hot-dip galvanizing. The coating of the hot-rolled, coated, and finish-rolled steel sheet can have a layer thickness of 7 μm to 13 μm, preferably 9 μm to 11 μm. The hot-rolled, coated, and finish-rolled steel sheet can have a sheet thickness of greater than or equal to 2.4 mm, preferably greater than or equal to 2.6 mm, and especially greater than or equal to 2.8 mm. The above values refer to the state before austenitization and stamping hardening. Furthermore, all the preceding and following explanations apply in the same way.
[0023] The stamped, hardened sheet metal parts to be manufactured are preferably vehicle components, especially for battery electric vehicles (BEVs). These vehicle components can be body longitudinal beams or body transverse beams. They can also be battery load-bearing or battery protection components for traction batteries, for example, constructed as floor longitudinal beams or floor transverse beams. Due to the relatively large weight of vehicles, these vehicle components also have particularly high strength requirements, especially for collision conditions. Attached Figure Description
[0024] The invention will now be described in detail in a non-limiting manner with reference to the accompanying drawings. The features described and / or shown in the drawings, even when departing from specific combinations of features, can constitute the general features of the invention and correspondingly improve the invention.
[0025] Figure 1 A schematic flowchart illustrates a method for manufacturing stamp-hardened sheet metal parts according to the present invention. Detailed Implementation
[0026] exist Figure 1In the method shown, a hot-rolled and coated steel sheet S in the form of a strip B (also referred to as hot-rolled strip steel) is provided. The strip B is fed out from a coil or by means of a traction roll pair 10 (where the so-called strip tension or uncoiling tension can be set), and is finished rolled by a roll pair 20 specifically provided for this purpose to reduce the roughness of the steel sheet S. Regarding the running direction D of the strip B, a tension roll pair 30 is provided downstream of the roll pair 20, which can be optionally provided or selectively contacted with the strip B. By means of the tension roll pair, tension or stress affecting the achievable roughness can be applied to the strip B, as described above. The finished strip B, or steel sheet S, can be rewound onto a coil or directly subjected to subsequent processing.
[0027] Slab P is cut from hot-rolled, coated, and finish-rolled sheet strip B, or steel plate S. To perform the press hardening process, the steel plate S, or slab P, is heated to the austenitizing temperature in furnace 50, and then formed and hardened in press hardening die 60 to obtain a press hardened sheet metal part T (direct press hardening). Alternatively, the steel plate S, or slab P, is first pre-formed (typically cold-formed) into a pre-formed part in one or more pre-forming dies 40, then heated to the austenitizing temperature in furnace 50 and finally formed and hardened in press hardening die 60 to obtain a press hardened sheet metal part T (indirect press hardening).
[0028] Other features and alternative implementations of this method have been described above.
[0029] List of reference numerals
[0030] 10 traction rolls paired
[0031] 20-roll pairing (for finish rolling)
[0032] 30 tension roll pairing
[0033] 40 pre-forming mold
[0034] 50 furnace body
[0035] 60 stamping hardening die
[0036] B-plate strip
[0037] D direction of travel
[0038] P slab
[0039] S steel plate
[0040] T-sheet molded parts
Claims
1. A method for manufacturing a stamped hardened sheet metal part (T), the method comprising the following steps: - Provide hot-rolled and coated steel sheets (S); - The coated steel sheet (S) is precision rolled in order to reduce the roughness of the steel sheet; - Perform a stamping hardening process in which the steel sheet (S) is heated to the austenitizing temperature and formed into a sheet metal part (T) in a stamping hardening die (60) and hardened, or in the stamping hardening process the steel sheet (S) is pre-formed, heated to the austenitizing temperature and finally formed into a sheet metal part (T) in a stamping hardening die (60) and hardened.
2. The method according to claim 1, characterized in that, During finishing rolling, the Ra value should be less than or equal to 2.5 μm, preferably less than or equal to 2.0 μm, and especially less than or equal to 1.5 μm.
3. The method according to any one of the preceding claims, characterized in that, The provided steel plate (S) has a plate thickness of 2.4 mm or more, preferably 2.6 mm or more, and especially 2.8 mm or more.
4. The method according to any one of the preceding claims, characterized in that, Finish rolling is performed using a pair of rolls (20), and the roughness achieved during finish rolling is adjusted by changing the roll clamping force and / or changing the tension acting on the steel plate (S).
5. The application of hot-rolled, coated and precision-rolled steel sheet (S) for manufacturing stamp-hardened sheet metal parts (T) by: heating the steel sheet (S) to the austenitizing temperature and forming it into a sheet metal part (T) in a stamp-hardening die (60) and hardening it; or, preforming the steel sheet (S), heating it to the austenitizing temperature and finally forming it into a sheet metal part (T) in a stamp-hardening die (60) and hardening it.
6. The application according to claim 5, characterized in that, The steel plate (S) has an Ra value of less than or equal to 2.5 μm, preferably less than or equal to 2.0 μm, and especially less than or equal to 1.5 μm.
7. The application according to claim 5 or 6, characterized in that, The steel plate (S) is coated by hot-dip galvanizing.
8. The application according to any one of claims 5 to 7, characterized in that, The coating has a thickness of 7 μm to 13 μm, preferably 9 μm to 11 μm.
9. The application according to any one of claims 5 to 8, characterized in that, The steel plate (S) has a thickness of 2.4 mm or more, preferably 2.6 mm or more, and especially 2.8 mm or more.
10. The application according to any one of claims 5 to 9, characterized in that, The stamped and hardened sheet metal parts (T) to be manufactured are vehicle components, especially battery carriers or battery protection components for traction batteries.