WO2023066087A1 - 一种用于预涂覆钢板的热冲压成形方法 - Google Patents

一种用于预涂覆钢板的热冲压成形方法 Download PDF

Info

Publication number
WO2023066087A1
WO2023066087A1 PCT/CN2022/124636 CN2022124636W WO2023066087A1 WO 2023066087 A1 WO2023066087 A1 WO 2023066087A1 CN 2022124636 W CN2022124636 W CN 2022124636W WO 2023066087 A1 WO2023066087 A1 WO 2023066087A1
Authority
WO
WIPO (PCT)
Prior art keywords
hot stamping
coated steel
steel plate
steel sheet
heat treatment
Prior art date
Application number
PCT/CN2022/124636
Other languages
English (en)
French (fr)
Inventor
黄明欣
王舟
Original Assignee
香港大学
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 香港大学 filed Critical 香港大学
Priority to KR1020247014162A priority Critical patent/KR20240096490A/ko
Publication of WO2023066087A1 publication Critical patent/WO2023066087A1/zh

Links

Images

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
    • B21D22/02—Stamping using rigid devices or tools
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D37/00—Tools as parts of machines covered by this subclass
    • B21D37/16—Heating or cooling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D53/00—Making other particular articles
    • B21D53/88—Making other particular articles other parts for vehicles, e.g. cowlings, mudguards
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D11/00—Process control or regulation for heat treatments
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C21/00—Alloys based on aluminium
    • C22C21/02—Alloys based on aluminium with silicon as the next major constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/12—Aluminium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/28—Thermal after-treatment, e.g. treatment in oil bath
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips

Definitions

  • the invention relates to a hot stamping method for precoated steel sheets.
  • ultra-high-strength steel is an ideal material for realizing the lightweight of automobiles while ensuring vehicle safety due to its advantages such as high strength, low cost, and mature technology.
  • Hot stamping refers to the forming process of stamping and deforming fully austenitized steel plates at high temperature, cooling rapidly at the same time, and finally obtaining ultra-high-strength steel components.
  • Hot stamping has the advantages of high forming precision and good weight reduction effect, and is especially suitable for the processing and forming of complex integrated thin-walled parts, such as A-pillars, B-pillars, and roof beams of automobile bodies in white.
  • pre-coating treatment is usually carried out on the steel plate surface.
  • the most widely used one is the high-temperature resistant Al-Si coating patent invented by ArcelorMittal in 1999.
  • the above-mentioned hot-formed steel plate coated with Al-Si coating was commercialized in 2007.
  • the contradiction between the alloying degree of the pre-coating layer and the fracture performance of the steel plate substrate has not been resolved.
  • one of the problems is to increase the degree of alloying of the precoat layer.
  • the pre-coated steel plate will cause problems such as fouling and wear on the furnace roll, forming die, etc., which is very unfavorable to actual production.
  • the insufficient degree of alloying will also lead to a low proportion of ductile phase and a high proportion of brittle phase in the intermetallic compound of the pre-coating layer, which is easy to form coating cracks and affect the coating and corrosion resistance of the pre-coated steel plate. .
  • Patent Document 1 discloses the hot stamping forming process of pre-coated steel, which is the main production process of pre-coated steel at present.
  • Tempering heating and heat preservation process when the thickness of the steel plate is 0.7-1.5mm, the temperature and time are limited to (3 minutes, 930°C), (6 minutes, 930°C), (13 minutes, 880°C), (4.5 minutes, 880°C) inside the quadrilateral; when the thickness of the steel plate is 1.5-3mm, the temperature and time are limited to (4 minutes, 940°C), (8 minutes, 940°C), (13 minutes, 900°C), (6.5 minutes, 900°C) inside the quadrilateral.
  • the above invention patent also stipulates the ratio of Fe 2 Al 5 phase to FeAl phase in the microstructure of the pre-coating layer after hot stamping to ensure the coating, welding and corrosion resistance of the pre-coated steel components after hot stamping. and other performance.
  • the second problem is how to improve the fracture performance of the precoated steel sheet substrate.
  • the aforementioned fracture properties include low-temperature fracture, bending fracture, hydrogen-induced delayed fracture, and the like. Unsatisfactory low-temperature fracture, bending fracture, or hydrogen-induced delayed fracture performance may cause partial crack failure of body components during service or collision, endangering the safety of passengers.
  • the Al-Si coating will be alloyed at high temperature to form brittle intermetallic compounds, brittle high-aluminum high-silicon ferrite, and brittle high-carbon martensite, and these brittle structures will further reduce the fracture performance of hot stamped steel components . In actual industrial production, after hot forming, the fracture performance of precoated steel sheets is significantly lower than that of steel sheets without precoating.
  • the holding temperature and time process window of the existing thermoforming process is relatively narrow, and the requirements for actual industrial production are relatively high.
  • CN106466697B discloses another hot stamping forming process of Al-Si coating pre-coated steel sheet, and clarifies the heating and holding process at 900-950°C for 2.5-10 minutes, preferably the heating furnace temperature It is 935-950°C or 945-950°C, preferably the residence time is 2.5-5 minutes.
  • the heating and heat preservation process in Patent Document 2 is only slightly higher than that in Patent Document 1, in actual production, the heating and heat preservation process in Patent Document 2 will lead to excessively large austenite grains in the steel plate base material, resulting in unsatisfactory fracture performance, which is relatively low. Difficult to be practically applied to body parts.
  • the existing hot forming process cannot simultaneously improve the alloying degree of the pre-coating layer and the fracture performance of the steel sheet substrate, especially, the fracture performance of the pre-coated steel sheet still needs to be improved to meet the fracture performance standards of the automotive industry .
  • expanding the thermoforming process window will also be beneficial to actual industrial production.
  • the object of the present invention is to solve the above-mentioned technical bottleneck problem, to provide a hot stamping forming method for improving the alloying degree of the pre-coating layer of the hot stamping formed steel sheet, a hot stamping forming method for improving the fracture performance of the hot stamping formed steel sheet or a A hot stamping forming method for simultaneously improving the alloying degree and fracture performance of a precoat layer of a hot stamping formed steel sheet.
  • Another object of the present invention is to expand the temperature and time process range of the hot stamping forming process and improve the stability of the hot stamping forming process.
  • the inventors have found that pre-heating the pre-coated steel sheet prior to hot stamping can effectively achieve the above object.
  • the preparatory heat treatment mainly includes a heating and heat preservation step and a cooling step.
  • the present invention provides a method for hot stamping forming of pre-coated steel sheets, said method comprising using a mold to perform hot stamping forming of pre-coated steel sheets at a hot stamping temperature to obtain hot stamping formed components, wherein, the method also includes performing preliminary heat treatment on the pre-coated steel sheet before hot stamping, and the preliminary heat treatment includes:
  • Heating and heat preservation heat the pre-coated steel plate to 850-920°C for 7 to 15 minutes, or heat it to 920-960°C for 5 to 10 minutes, so that the pre-coated steel plate substrate is austenitized , Alloying of the pre-coating layer;
  • Cooling after the heating and holding step is completed, cooling the pre-coated steel sheet to below 300°C at a cooling rate of not less than 5°C/s;
  • the pre-coated steel sheet substrate in addition to iron, also contains the following components expressed in weight percent: carbon 0.2-0.4%; manganese 0.5-1.5%; boron 0-0.005% ; Not more than 1% of one or more alloying elements selected from aluminum, silicon, chromium, molybdenum, niobium, vanadium; and other unavoidable impurity elements.
  • the pre-coated steel sheet substrate in addition to iron, also contains the following components expressed in weight percent: carbon 0.3-0.5%; manganese 0.5-2.5%; boron 0-0.005% %; not more than 3% of one or more alloying elements selected from aluminum, silicon, chromium, molybdenum, niobium, vanadium; and other unavoidable impurity elements.
  • Increasing the content of carbon, manganese, and silicon can improve the hardenability of the steel plate substrate, and at the same time, it is easier to obtain martensite after the preliminary heat treatment, so as to achieve the effect of grain refinement.
  • the content of carbon, manganese, and silicon is too high, it will have an adverse effect on the fracture performance of the steel plate substrate.
  • Adding a very small amount of boron can improve the hardenability of the steel plate substrate without affecting the fracture performance.
  • Aluminum can be deoxidized during smelting while preserving the availability of boron.
  • Other elements such as chromium and molybdenum can also improve hardenability, but disadvantageously, they can significantly increase the cost of the steel plate.
  • vanadium and niobium can refine austenite grains, on the other hand, they can produce precipitation strengthening and improve the strength of hot stamping formed components.
  • the pre-coated steel plate substrate can be selected from commercially available 22MnB5 or 34MnB5 steel.
  • the thickness of the pre-coated steel plate substrate is 0.8-2.5 mm, and the thickness of the pre-coat layer is 6-36 ⁇ m. In some embodiments, the thickness of the precoat layer is 15-27 ⁇ m. In some specific embodiments, the thickness of the pre-coated steel plate base material is 1.0-1.3 mm, which belongs to the typical thickness of the steel plate for vehicle body safety components.
  • the pre-coating layer is aluminum or an aluminum alloy
  • the pre-coating layer is arranged on at least one surface of the pre-coated steel sheet, and the pre-coating layer on each surface
  • the initial thickness of the layer is less than 36 ⁇ m.
  • the pre-coating layer is an Al-Si alloy coating, usually containing 8-11% Si, 2-4% Fe, 85-90% Al and unavoidable of impurities.
  • Al mainly provides the high-temperature stability and oxidation resistance of the coating, but disadvantageously, Al will alloy with the steel plate substrate at high temperatures to form brittle intermetallic compounds, and Si can inhibit the growth of intermetallic compounds and reduce the impact of brittle intermetallic compounds on the coating. Hazards to steel plate fracture properties.
  • the C content of the 22MnB5 steel plate base material represented by weight % is 0.20-0.23%
  • the Mn content is 0.9-1.4%
  • the Si content is 0.20-0.28%.
  • the thickness of the pre-coated Al-Si coating is about 25 ⁇ m.
  • the heating and heat preservation step when the thickness of the pre-coating layer is less than 20 ⁇ m, the heating and heat preservation step is: 850-920° C. for 7 to 15 minutes; when the thickness of the pre-coating layer is greater than or equal to 20 ⁇ m, The heating and heat preservation step is: 920-960° C. for 5 to 10 minutes.
  • the pre-coating layer is an Al-Si coating
  • the holding temperature range is 870-915 ° C, and the total time is 2-7 minutes
  • the thickness of the Al-Si coating is When the thickness is greater than or equal to 20 ⁇ m, the holding temperature range is 890-935°C, and the total time is 4-9 minutes.
  • the choice of heating and heat preservation process in the preparatory heat treatment is mainly to ensure the alloying of the coating and obtain a suitable intermetallic compound structure.
  • the intermetallic compound includes a FeAl phase with a volume fraction not less than 60%. Compared with other intermetallic compounds, the FeAl phase has the advantages of higher melting point and better fracture toughness, which can reduce mold loss, reduce coating cracks, and improve steel plate fracture performance and corrosion resistance.
  • the adverse effects brought about by the austenite growth of the steel plate substrate can be eliminated or alleviated by the martensite or bainite structure obtained after cooling.
  • the above-mentioned martensite or bainite structure can provide more austenite nucleation points and refine the austenite structure during subsequent hot stamping forming, so as to improve the fracture performance of the steel plate base material. Therefore, the process range of the preliminary heat treatment in the present invention is larger than that of the existing hot stamping forming process, which is beneficial to improve process stability.
  • the cooling rate in the preliminary heat treatment mainly depends on the hardenability of the steel plate base material. It should be pointed out that the cooling rate of about 5 °C/s cannot completely avoid the formation of carbides, nor can it obtain the microstructure of all martensite or bainite. However, the inventors have found that a small amount of martensite or bainite microstructure (not less than 30%, or the sum of the two volume fractions is not less than 30%) can also play a role in refining austenite in the subsequent hot stamping process. The role of body grains. At the same time, the uniformly distributed carbides can also provide a large number of austenite nucleation sites during the heating process, which can refine the austenite grains.
  • the cooling rate is not less than 10°C/s.
  • the volume fraction of martensite can reach more than 50% after cooling, pearlite will not be formed, and the carbide particle size is not greater than 0.1 ⁇ m.
  • the cooling rate is not less than 25° C./s.
  • the volume fraction of martensite after cooling is close to 100%.
  • the cooling rate is 25°C/s to 50°C/s.
  • the steel plate In the actual production process, it takes a long time to cool the steel plate after the preliminary heat treatment to room temperature, especially when the temperature is below 200°C, the cooling rate will be significantly slowed down.
  • the steel plate After the preliminary heat treatment step, the steel plate is cooled to below 300°C, and when it is above 200°C, the steel plate is transferred to a heating furnace and reheated. In this case, all or most of the martensite transformation in the cooling process has been completed, which is enough to refine the austenite grains and improve the final fracture performance of the steel plate.
  • the steel plate can be deformed by a stamping die during the cooling process of the preliminary heat treatment.
  • it can reduce the amount of deformation in the subsequent hot stamping forming process, reduce the temperature requirements of the subsequent hot stamping forming process, and make the heating and heat preservation process window of the subsequent hot stamping forming process larger; on the other hand, in the subsequent hot stamping forming process
  • the heating and heat preservation can fill the coating cracks caused by pre-deformation.
  • the amount of deformation required for the subsequent thermoforming process is reduced, and the number and depth of coating cracks are reduced, which in turn can improve the corrosion resistance of the pre-coating layer and reduce the coating. Detrimental effect of cracks on fracture properties.
  • the steel plate is subjected to several preparatory heat treatments, and the same or different process parameters may be used between several preparatory heat treatments.
  • the degree of grain refinement can be improved by the back-and-forth transformation between high-temperature austenite and room-temperature martensite.
  • using different process parameters between several pre-heat treatments can provide more possibilities for the design of the Fe-Al diffusion layer and the intermetallic compound layer in the pre-coating layer (such as Al-Si coating). Therefore, after multiple preliminary heat treatments, the chemical composition and microstructure of the steel plate substrate are more uniform, the grains can be better refined, and at the same time, the degree of alloying of the pre-coating layer is also higher.
  • the adverse effects caused by the growth of austenite on the steel substrate can be eliminated or alleviated by the martensite or bainite structure obtained after cooling.
  • the above-mentioned martensite or bainite structure can provide more austenite nucleation points and refine the austenite structure during subsequent hot stamping forming, so as to improve the fracture performance of the steel plate base material. Therefore, the process range of the preliminary heat treatment in the present invention is larger than that of the existing hot stamping forming process, which is beneficial to improve process stability.
  • the microstructure of the pre-coated steel plate substrate after preliminary heat treatment has the following characteristics:
  • the microstructure of the pre-coating layer after the preliminary heat treatment is composed of one or more intermetallic compounds and ferrite, wherein the volume fraction of FeAl phase in all intermetallic compounds is not less than 60%.
  • the hot stamping method further includes: after the preliminary heat treatment, reheating the pre-coated steel sheet to 780-940° C. for 1 to 7 minutes, so that the pre-coated The steel plate substrate is completely austenitized; then, the pre-coated steel plate is transferred to a mold while keeping the temperature above 500° C. for hot stamping.
  • the hot stamping forming method further includes: after the preliminary heat treatment, reheating the pre-coated steel sheet to 830-900° C. for 1 to 4 minutes, so that the pre-coated steel sheet substrate is completely austenitic. solidification; then, keeping the temperature above 600° C., transferring the pre-coated steel sheet to a mold for hot stamping.
  • the heat preservation range is 830-900° C., and the total heating and heat preservation time is 1-4 minutes.
  • the martensite lath bundles, lath blocks, and laths will all be refined, which will eventually improve the fracture performance of the hot stamping formed components.
  • the microstructure of the precoated steel sheet substrate after hot stamping is a full martensitic structure.
  • the microstructure of the precoated steel sheet substrate after hot stamping is two phases or multiple phases in ferrite structure, bainite structure, martensite structure and austenite structure composed of mixed tissues.
  • the strength of the hot stamped member decreases and the fracture performance improves.
  • the prior-austenite grain size of the microstructure of the precoated steel sheet substrate after hot stamping is not more than 18 ⁇ m.
  • the prior-austenite grain size in the microstructure of the above-mentioned hot stamping formed component is not more than 10 ⁇ m. At this time, due to the higher degree of grain refinement, the fracture performance of hot stamping steel is better.
  • the microstructure of the above-mentioned hot stamped steel sheet base material is generally all martensitic structure, and in this case, the strength of the hot stamped steel can reach 1.5 GPa.
  • the steel plate is transferred to a heating furnace for reheating and hot stamping.
  • a heating furnace for reheating and hot stamping.
  • the steel plate is transferred to a heating furnace and reheated. In this case, all or most of the martensite transformation in the cooling process has been completed, which is enough to refine the austenite grains and improve the final fracture performance of the steel plate.
  • the production efficiency can be improved and energy can be saved at the same time.
  • the steel plate is transferred to a heating furnace and reheated.
  • this scheme is more suitable for the situation that the alloy content of the base material of the precoated steel plate is higher and the martensitic transformation temperature is lower.
  • the reason why the hot stamping forming method of the present invention can refine the prior austenite grains is mainly related to the following factors: (A) in the heating and heat preservation process of the preliminary heat treatment, the pre-coating layer has been alloyed and formed For the intermetallic compound layer and diffusion layer, in the process of hot stamping, it is no longer necessary to take the alloying of the pre-coating layer as the main consideration, so a lower heating and holding temperature and a shorter heating and holding time can be used to inhibit the austenite Grain growth; (B) During the cooling process of the preliminary heat treatment, the steel plate substrate forms a complete or partial martensite or bainite structure, which has the characteristics of fine grains and high defect density, and the steel plate substrate The distribution of carbides in the material is finer and more uniform. During the reheating process of the hot stamping forming process, more austenite nucleation sites are provided, and the original austenite grains are finally refined.
  • the hot stamping forming technology of the present invention can refine the prior austenite grains, martensite lath bundles, martensite lath blocks and Marsh lath.
  • the above-mentioned grain refinement can reduce the enrichment of impurity elements such as phosphorus and sulfur and hydrogen elements at grain boundaries, and alleviate the adverse effects of impurity elements and hydrogen elements on grain boundary fracture, thereby inhibiting brittle intergranular fracture.
  • cracks need to pass through more large-angle grain boundaries during the propagation process, including prior austenite grain boundaries, martensite lath bundle interfaces, martensite lath block interfaces, etc. Therefore, crack propagation requires more energy and is more difficult, and ultimately improves the fracture performance of hot stamped components.
  • the preliminary heat treatment can improve the alloying degree of the precoat layer, reduce the carbide structure in the steel plate substrate, and obtain the substrate structure of martensite and/or bainite , so that during high-temperature stamping deformation, the loss of the pre-coating layer to the stamping die is reduced, the grains are refined, and the fracture performance of the final hot stamping formed component is improved.
  • the hot stamping forming method of the present invention can be used for automotive safety structural parts, reinforced structural parts, wheel components, high-strength automotive structural parts, etc., including but not limited to A-pillars, B-pillars, and roof beams of automobile body-in-white.
  • Fig. 1 is the schematic diagram of existing hot stamping forming method
  • Fig. 2 is the schematic diagram of hot stamping forming method of the present invention
  • Fig. 3 is the original microstructure diagram of the precoat layer of the 22MnB5 steel plate used in the embodiment and the steel plate substrate;
  • Fig. 4 is the schematic diagram of the microstructure of the Al-Si coating after the preliminary heat treatment of Example 1-3 of the present invention
  • Fig. 5 is the change situation of FeAl phase and intermetallic compound total volume fraction ratio with holding time in the precoating layer after preliminary heat treatment of embodiment 1-3 of the present invention
  • Fig. 6 is the microstructure diagram of the steel plate base material after preliminary heat treatment in Example 2 of the present invention.
  • Fig. 7 is the microstructural diagram of the steel plate base material after the hot stamping forming of Example 4 of the present invention.
  • Example 8 is an inverse pole figure of the microstructure of the steel plate substrate after hot stamping according to Example 4 of the present invention.
  • Fig. 9 is an inverse pole diagram of the microstructure of the steel plate base material after hot stamping in the prior art
  • Fig. 10 is a comparison of the three-point bending test results of the pre-coated hot-stamped steel sheet obtained in Example 4 of the present invention and the prior art.
  • Fig. 1 and Fig. 2 respectively summarize an embodiment of the hot stamping forming process of the present invention and the existing hot stamping forming method. It should be noted that the present invention is not limited to the examples shown in the figure, and the slope in the figure is only used as a schematic representation of the average rate of heating or cooling, and does not represent a real heating or cooling curve.
  • the original microstructure of the pre-coated Al-Si layer of the 22MnB5 steel plate used in the examples and the steel plate substrate is shown in FIG. 3 .
  • the precoating layer is sequentially from the steel plate base material side: a Si-rich intermetallic compound layer, and an Al layer.
  • the pre-coated Al-Si coating structure is a typical commercially available 22MnB5 steel pre-coated coating structure.
  • the steel plate substrate is mainly composed of ferrite, pearlite and carbide. Among them, the size of lamellar pearlite domain can reach more than 2 ⁇ m, and the particle size of spherical carbide can reach more than 0.5 ⁇ m.
  • the pre-coated 22MnB5 steel plate is subjected to the following preliminary heat treatment:
  • the steel plate is cooled to room temperature at a cooling rate of 300° C./s.
  • the Al-Si coating in the above-mentioned steel plate is alloyed, and its microstructure is shown in Figure 4.
  • a Fe—Al diffusion layer mainly containing a ferrite structure
  • an intermetallic compound layer mainly containing FeAl and Fe 2 Al 5 .
  • the thickness of the Fe-Al diffusion layer is 4 to 30 ⁇ m
  • the thickness of the intermetallic compound layer is 15 to 40 ⁇ m.
  • Figure 5 shows the change of the ratio of FeAl phase to the total volume of intermetallic compounds with the holding time.
  • FeAl has a higher melting point and fracture toughness, which can reduce the adverse effects of problems such as furnace roll fouling and mold wear.
  • the volume fraction of the FeAl phase in all Fe—Al intermetallic compounds is not less than 60%.
  • the microstructure of the steel plate substrate after the preliminary heat treatment in Example 2 is shown in Figure 6, wherein there are no spherical cementite particles with a particle size greater than 0.5 ⁇ m, and no lamellar pearlite domains with a particle size greater than 1 ⁇ m;
  • the volume fraction of body or bainite or the sum of the two is not less than 30%.
  • Fig. 7 is the microstructure of the steel plate substrate after the hot stamping forming process.
  • the steel plate substrate After hot stamping, the steel plate substrate obtains all the martensitic structure, and the prior austenite grains in the microstructure are significantly refined, and the prior austenite grain size is reduced from 15-25 ⁇ m after preliminary heat treatment to 3-8 ⁇ m after hot stamping.
  • the alloying degree and microstructure of the Al-Si coating no longer change significantly.
  • Fig. 8 is the inverse polar diagram of the microstructure of the steel plate base material after the hot stamping forming process, in which the prior austenite grain size in the microstructure of the steel plate base material can be observed more clearly, which is the same as that observed in Fig. 7
  • the original austenite grain size is 3-8 ⁇ m.
  • FIG. 9 is an inverse pole diagram of the microstructure of a steel plate substrate obtained by using the existing hot stamping forming technology shown in FIG. 2 (that is, without preliminary heat treatment).
  • the grain size of prior austenite is about 20 ⁇ m.
  • the existing hot stamping forming process has not undergone preparatory heat treatment, so it needs to adopt higher heating and holding temperature and longer heating and holding time, for example, 900-940°C, 5-10 minutes, and the initial microstructure of the existing hot stamping forming process It is ferrite + lamellar pearlite + spherical carbide structure, which cannot play the role of martensite or bainite structure in refining austenite grains. Therefore, the prior austenite grains in the steel plate substrate obtained by the existing hot stamping forming process are much larger than the hot stamping forming process of the present invention.
  • Figure 10 compares the three-point bending test results of the hot stamped steel plate obtained by the existing hot stamping forming method and the method of the present invention.
  • the results of the three-point bending test of the steel plate after hot stamping can reflect the fracture performance of the hot stamping component.
  • the results of the three-point bending test show that compared with the existing hot stamping forming technology, the steel plate obtained by the technology of the present invention after hot stamping can achieve a larger bending load and a larger bending angle, among which, the technology of the present invention can obtain the maximum bending load About 1100N, the bending angle is about 58.4°, the existing technology can only obtain the maximum bending load of about 1000kN, the bending angle is about 52.2°, that is, the maximum bending load is increased by 10%, and the bending angle is increased by 11.9%. Therefore, the three-point bending performance of the hot stamped steel plate obtained by the method of the present invention is better, and correspondingly, the fracture performance of the hot stamped formed component is also better.
  • the method of the present invention can simultaneously improve the alloying degree of the precoat layer and the fracture performance of the steel plate substrate.
  • the reason for improving the fracture performance of the steel plate base material is as follows: the hot stamping forming technology of the present invention can make the distribution of carbon element in the base material more uniform and refine the prior austenite grains and martensite in the microstructure of the hot stamping formed component. Lath Bundles, Martensitic Lath Blocks, and Martensitic Laths.
  • the above-mentioned grain refinement can reduce the enrichment of impurity elements such as phosphorus and sulfur and hydrogen elements at grain boundaries, and alleviate the adverse effects of impurity elements and hydrogen elements on grain boundary fracture, thereby inhibiting brittle intergranular fracture.
  • impurity elements such as phosphorus and sulfur and hydrogen elements
  • grain refinement through grain refinement, cracks need to pass through more large-angle grain boundaries during the propagation process, including prior austenite grain boundaries, martensite lath bundle interfaces, martensite lath block interfaces, etc. Therefore, crack propagation requires more energy and is more difficult, and ultimately improves the fracture performance of hot stamped components.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Heat Treatment Of Articles (AREA)

Abstract

本发明提供一种用于预涂覆钢板的热冲压成形方法，包括在热冲压成形之前对预涂覆钢板进行预备热处理，该预备热处理包括：(1)加热保温：将预涂覆钢板加热至850-920℃保温7至15分钟，或者加热至920-960℃保温5至10分钟；(2)冷却：在所述加热保温步骤后，以不小于5℃/s的冷却速率，将所述预涂覆钢板冷却至300℃以下；和(3)任选地重复上述加热保温和冷却步骤一次或多次。所述预备热处理可以提高预涂覆层合金化程度、减少钢板基材中的碳化物组织、获得马氏体和/或贝氏体的基材组织，从而在高温冲压变形时，降低预涂覆层对冲压模具的损耗、并且细化晶粒、提高最终热冲压成形构件的断裂性能。

Description

一种用于预涂覆钢板的热冲压成形方法
本申请要求于2021年10月21日递交的第202111226071.X号中国专利申请的优先权，在此全文引用上述中国专利申请公开的内容以作为本申请的一部分。
技术领域
本发明涉及一种用于预涂覆钢板的热冲压成形方法。
背景技术
随着“碳达峰”与“碳中和”目标的提出，汽车节能减排已经成为当务之急，汽车轻量化则是贯彻节能减排的有效途径。在众多轻量化材料中，超高强度钢因其强度高、成本低、工艺成熟等优势，是实现汽车轻量化同时保障车辆安全性的理想材料。
热冲压成形是指在高温下对全奥氏体化钢板进行冲压变形、同时快速冷却，最终获得超高强度钢构件的成形工艺。热冲压成形具有成形精度高、减重效果好等优点，尤其适用于复杂一体化薄壁零件的加工成形，例如汽车白车身A柱、B柱、背顶横梁等。
在实际热冲压成形过程中，为避免高温在钢表面造成氧化和脱碳，通常会在钢板表面进行预涂覆处理。其中，应用最广泛的是由ArcelorMittal公司于1999年发明的耐高温Al-Si镀层专利，上述预涂覆Al-Si镀层的热成形钢板于2007年实现商业化。但是，在Al-Si镀层发明至今的20多年里，始终未能解决预涂覆层合金化程度与钢板基材断裂性能之间的矛盾。
首先，问题之一是提升预涂覆层的合金化程度。
如果合金化程度不足，预涂覆钢板会在炉辊、成形模具等位置造成结垢与磨损等问题，对实际生产非常不利。同时，合金化程度不足还会导致预涂覆层金属间化合物中的韧性相的比例较低、脆性相的比例较高，易形成镀层裂纹，影响预涂覆钢板的涂装、抗腐蚀等性能。
在预涂覆钢板热冲压成形过程中，为保证合金化程度，通常需要采用较高的加热温度、较长的保温时间。例如，CN101583486B(以下称作专利文献1)公开了预涂覆钢的热冲压成形工艺，是目前预涂覆钢的主要生 产工艺，其中明确了当Al-Si镀层厚度为20-33μm时的奥氏体化加热保温工艺：当钢板厚度为0.7-1.5mm时，温度和时间限定在(3分钟，930℃)、(6分钟，930℃)、(13分钟，880℃)、(4.5分钟，880℃)组成的四边形内部；当钢板厚度为1.5-3mm时，温度和时间限定在(4分钟，940℃)、(8分钟，940℃)、(13分钟，900℃)、(6.5分钟，900℃)组成的四边形内部。上述发明专利还规定了在热冲压成形后的预涂覆层微观组织中Fe 2Al 5相与FeAl相的比例，以保证热冲压成形后的预涂覆钢构件的涂装、焊接、抗腐蚀等性能。
问题之二是如何提高预涂覆钢板基材的断裂性能。
为提高断裂性能，通常需要采用较低的加热温度与较短的保温时间，以避免奥氏体晶粒在高温下过度长大。但是，上述要求与提高预涂覆层合金化程度的要求相互矛盾。现有技术只能在两者之间平衡，无法同时提升预涂覆层合金化程度与钢板基材断裂性能。
值得注意的是，目前的预涂覆钢热冲压成形构件仍无法满足所有汽车厂的断裂性能标准。上述断裂性能包括低温断裂、弯曲断裂、氢致延迟断裂等。不理想的低温断裂、弯曲断裂、或氢致延迟断裂性能都有可能造成车身构件在汽车服役或碰撞过程中发生局部开裂失效，危及乘客安全。尤其是，Al-Si镀层会在高温下发生合金化形成脆性金属间化合物、脆性高铝高硅铁素体、脆性高碳马氏体，这些脆性组织会进一步降低热冲压成形钢构件的断裂性能。在实际工业生产中，在热成形后，预涂覆钢板的断裂性能明显低于没有预涂覆层的钢板。
另外，现有热成形工艺的保温温度与时间工艺窗口较窄，对实际工业生产的要求相对较高。
例如，CN106466697B(以下称作专利文献2)公开了另一种Al-Si镀层预涂覆钢板的热冲压成形工艺，明确了900-950℃、2.5-10分钟的加热保温工艺，优选加热炉温度是935-950℃或945-950℃，优选停留时间是2.5-5分钟。尽管专利文献2中的加热保温工艺仅略高于专利文献1，但在实际生产中，专利文献2中的加热保温工艺会导致钢板基材奥氏体晶粒过大，断裂性能不理想，较难实际应用于车身部件。
综上所述，现有热成形工艺无法同时提升预涂覆层合金化程度与钢板基材断裂性能，尤其是，预涂覆钢板的断裂性能仍亟需提升，以满足汽车工业的断裂性能标准。此外，在现有热成形工艺基础上，扩大热成形工艺 窗口也将有利于实际工业生产。
发明内容
因此，本发明的目的是解决上述技术瓶颈问题，提供一种改善热冲压成形钢板预涂覆层合金化程度的热冲压成形方法、一种改善热冲压成形钢板断裂性能的热冲压成形方法或者一种同时改善热冲压成形钢板预涂覆层合金化程度与断裂性能的热冲压成形方法。本发明的再一个目的是扩大热冲压成形工艺的温度与时间工艺区间，提高热冲压成形工艺的稳定性。
发明人发现，在热冲压成形之前，对预涂覆钢板进行预备热处理，可以有效实现上述目的。该预备热处理主要包括加热保温步骤与冷却步骤。
在此基础上，本发明提供了一种用于预涂覆钢板的热冲压成形方法，所述方法包括采用模具在热冲压温度下对预涂覆钢板进行热冲压成形，获得热冲压成形构件，其中，所述方法还包括在热冲压成形之前对预涂覆钢板进行预备热处理，所述预备热处理包括：
(1)加热保温：将所述预涂覆钢板加热至850-920℃保温7至15分钟，或者加热至920-960℃保温5至10分钟，以使得预涂覆钢板基材奥氏体化、预涂覆层合金化；
(2)冷却：在所述加热保温步骤完成后，以不小于5℃/s的冷却速率，将所述预涂覆钢板冷却至300℃以下；和
(3)任选地重复上述加热保温和冷却步骤一次或多次。
在本发明的一种实施方案中，除铁元素以外，所述预涂覆钢板基材还包含以重量％表示的以下成分：碳0.2-0.4％；锰0.5-1.5％；硼0-0.005％；不超过1％的选自铝、硅、铬、钼、铌、钒中的一种或多种合金元素；以及其他不可避免的杂质元素。
在本发明的另一种实施方案中，除铁元素以外，所述预涂覆钢板基材还包含以重量％表示的以下成分：碳0.3-0.5％；锰0.5-2.5％；硼0-0.005％；不超过3％的选自铝、硅、铬、钼、铌、钒中的一种或多种合金元素；以及其他不可避免的杂质元素。
提高碳、锰、硅的含量可以提升钢板基材的淬硬性，同时在所述预备热处理之后更加容易获得马氏体，实现晶粒细化效果。但是，碳、锰、硅的含量过高之后会对钢板基材的断裂性能产生不利影响。添加极少量的硼可以在不影响断裂性能的情况下，提高钢板基材的淬硬性。铝可以在冶炼 过程中脱氧，同时保护硼的有效性。铬和钼等其他元素也可以提高淬硬性，但是不利地，会显著提升钢板的成本。钒和铌一方面可以细化奥氏体晶粒，另一方面可以产生析出强化作用，提升热冲压成形构件的强度。作为优选的实例，所述预涂覆钢板基材可以选择商购22MnB5或34MnB5钢。
在本发明的实施方案中，所述预涂覆钢板基材厚度为0.8-2.5mm，所述预涂覆层的厚度为6-36μm。在一些实施方案中，所述预涂覆层的厚度为15-27μm。在一些具体的实施方案中，所述预涂覆钢板基材厚度为1.0-1.3mm，这属于车身安全构件用钢板的典型厚度。
在本发明的一些实施方案中，所述预涂覆层为铝或铝合金，所述预涂覆层设置在所述预涂覆钢板的至少一个表面上，并且每个表面上的预涂覆层的起始厚度小于36μm。
在一些具体的实施方案中，所述预涂覆层为Al-Si合金镀层，通常以重量百分比计包含8-11％的Si、2-4％的Fe、85-90％的Al以及不可避免的杂质。Al主要提供镀层的高温稳定性和抗氧化性能，但是不利地，Al在高温下会与钢板基体发生合金化，形成脆性金属间化合物，Si可以抑制金属间化合物的生长，减少脆性金属间化合物对钢板断裂性能的危害。
作为一个实例，可以采用商购的预涂覆Al-Si镀层的22MnB5钢。其中，所述22MnB5钢板基材以重量％表示的C含量为0.20-0.23％，Mn含量为0.9-1.4％，Si含量为0.20-0.28％，此外，预涂覆Al-Si镀层的厚度约为25μm。
作为一种优选实施方案，当所述预涂覆层厚度小于20μm时，所述加热保温步骤为：850-920℃，7至15分钟；当所述预涂覆层厚度大于或等于20μm时，所述加热保温步骤为：920-960℃，5至10分钟。在一些实施方案中，所述预涂覆层为Al-Si镀层，当Al-Si镀层厚度小于20μm时，保温温度范围870-915℃，总时间为2-7分钟；当Al-Si镀层厚度大于或等于20μm时，保温温度范围890-935℃，总时间为4-9分钟。
预备热处理中加热保温工艺的选择主要在于保证镀层的合金化、并获得合适的金属间化合物组织。当所述预涂覆层为铝或铝合金时，所述金属间化合物包括体积分数不小于60％的FeAl相。相比于其他金属间化合物，FeAl相具有熔点较高、断裂韧性较好等优点，可以降低模具损耗，同时可以减少镀层裂纹，提升钢板断裂性能、抗腐蚀性能等。
此外，在预备热处理过程中，钢板基材奥氏体长大带来的不良影响， 可以通过冷却后得到的马氏体或贝氏体组织来消除或缓解。上述马氏体或贝氏体组织可以在后续热冲压成形时，提供更多的奥氏体形核点，细化奥氏体组织，以提高钢板基材的断裂性能。因此，本发明所述预备热处理的工艺范围大于现有热冲压成形工艺，有利于提高工艺稳定性。
预备热处理中的冷却速率主要取决于钢板基材的淬硬性。需要特别指出的是，约5℃/s的冷却速率并不能完全避免碳化物的形成，也不能得到全部马氏体或贝氏体的微观组织。然而，发明人发现，少量马氏体或贝氏体微观组织(不小于30％，或两者的体积分数之和不小于30％)也能够在后续热冲压成形过程中起到细化奥氏体晶粒的作用。同时，均匀分布的碳化物也可以在加热过程中提供大量奥氏体形核位置，起到细化奥氏体晶粒的作用。
优选地，所述冷却速率不小于10℃/s，在这种情况下，冷却后马氏体体积分数可达到50％以上，不会形成珠光体，并且碳化物颗粒尺寸不大于0.1μm。更优选地，所述冷却速率不小于25℃/s，在这种情况下，冷却后马氏体体积分数接近100％。然而，当冷却速率提高至50℃/s时，进一步细化奥氏体晶粒的作用并不明显，经后续热冲压成形后的断裂性能几乎没有进一步改善。因此，最优选地，所述冷却速率为25℃/s至50℃/s。
在实际生产过程中，将上述预备热处理后的钢板冷却至室温需要很长的时间，尤其是在200℃以下时，冷却速率会明显减慢。为了提高生产效率，作为一种优选方案，在预备热处理步骤之后，将所述钢板冷却至300℃以下，200℃以上时，将所述钢板转移至加热炉，开始重新加热。在这种情况下，冷却过程中的马氏体转变已经全部完成或已经完成大部分，足以起到细化奥氏体晶粒、提升钢板最终断裂性能的作用。
优选地，可以在所述预备热处理的冷却过程中通过冲压模具对钢板进行变形。一方面，可以减少后续热冲压成形过程中的变形量，降低后续热冲压成形过程对温度的要求，使后续热冲压成形过程的加热保温工艺窗口更大；另一方面，后续热冲压成形过程中的加热保温能够填充预变形造成的镀层裂纹，同时，后续热成形工艺所需变形量减小，所造成镀层裂纹的数量与深度都会降低，进而可以提升预涂覆层的抗腐蚀性能、减少镀层裂纹对断裂性能的不利影响。
优选地，对所述钢板进行数次预备热处理，数次预备热处理之间可以采用相同或不同工艺参数。通过高温奥氏体与室温马氏体之间的来回转 变，可以提高晶粒细化程度。同时，数次预备热处理之间采用不同工艺参数，可以为预涂覆层(如Al-Si镀层)中Fe-Al扩散层、金属间化合物层的设计提供更多可能性。因此，在多次预备热处理之后，钢板基材的化学成分与微观组织更加均匀，晶粒可以得到更好的细化，同时，预涂覆层的合金化程度也更高。
此外，在预备热处理过程中，钢材基板奥氏体长大带来的不良影响，可以通过冷却后得到的马氏体或贝氏体组织来消除或缓解。上述马氏体或贝氏体组织可以在后续热冲压成形时，提供更多的奥氏体形核点，细化奥氏体组织，以提高钢板基材的断裂性能。因此，本发明所述预备热处理的工艺范围大于现有热冲压成形工艺，有利于提高工艺稳定性。
按照本发明提供的用于预涂覆钢板的热冲压成形方法，预备热处理后的预涂覆钢板基材的微观组织具有如下特征：
(a)马氏体或贝氏体或两者之和的体积分数不小于30％；
(b)不存在粒径大于0.5μm的球状碳化物颗粒，不存在粒径大于1μm的片层状烛光体领域。
其中，所述预备热处理后的预涂覆层的微观组织由一种或多种金属间化合物、以及铁素体组成，其中，FeAl相在所有金属间化合物中所占体积分数不小于60％。
在本发明的一些实施方案中，所述热冲压成形方法还包括：在所述预备热处理之后，将所述预涂覆钢板重新加热至780-940℃保温1至7分钟，以使预涂覆钢板基材完全奥氏体化；然后，保持温度在500℃以上将所述预涂覆钢板转移至模具中进行热冲压成形。
优选地，所述热冲压成形方法还包括：在所述预备热处理之后，将所述预涂覆钢板重新加热至830-900℃保温1至4分钟，以使预涂覆钢板基材完全奥氏体化；然后，保持温度在600℃以上将所述预涂覆钢板转移至模具中进行热冲压成形。
优选地，在所述重新加热步骤中，保温范围为830-900℃，加热保温总时间为1-4分钟。
更为重要的是，随着热冲压成形钢中原奥氏体晶粒细化，马氏体板条束、板条块、板条都会发生细化，最终提高热冲压成形构件的断裂性能。
在本发明的一些实施方案中，热冲压成形后的预涂覆钢板基材微观组织为全马氏体组织。
在本发明的另一些实施方案中，热冲压成形后的预涂覆钢板基材微观组织为铁素体组织、贝氏体组织、马氏体组织、奥氏体组织中的两相或者多相构成的混合组织。在这种情况下，热冲压成形构件的强度下降、断裂性能提高。
进一步地，热冲压成形后的预涂覆钢板基材微观组织的原奥氏体晶粒尺寸不超过18μm。作为一种优选方案，上述热冲压成形构件微观组织中原奥氏体晶粒尺寸不超过10μm。此时，由于晶粒细化程度更高，热冲压成形钢的断裂性能更好。
上述热冲压成形钢板基材的微观组织通常是全部的马氏体组织，在这种情况下，热冲压成形钢的强度可以达到1.5GPa。
在本发明的一些实施方案中，在所述预备热处理之后，将钢板转移至加热炉重新加热，并进行热冲压成形。作为一种优选方案，在预备热处理步骤之后，将所述钢板冷却至300℃以下、200℃以上时，将所述钢板转移至加热炉，开始重新加热。在这种情况下，冷却过程中的马氏体转变已经全部完成或已经完成大部分，足以起到细化奥氏体晶粒、提升钢板最终断裂性能的作用。在200℃以上时将钢板转移至加热炉，可以提升生产效率，同时节约能源。
作为另一种优选方案，在预备热处理步骤之后，将所述钢板冷却至200℃以下、100℃以上时，将所述钢板转移至加热炉，开始重新加热。相比于前述方案，本方案更加适合预涂覆钢板基材合金含量较高、马氏体转变温度较低的情况。
本发明所述热冲压成形方法之所以可以细化原奥氏体晶粒，主要与如下因素相关：(A)在所述预备热处理的加热保温过程中，预涂覆层已经获得合金化，形成金属间化合物层及扩散层，在热冲压成形过程中，不必再将预涂覆层合金化作为主要考虑因素，所以可以采用较低的加热保温温度和较短的加热保温时间，抑制奥氏体晶粒长大；(B)在所述预备热处理的冷却过程中，钢板基材形成完全或部分马氏体或贝氏体组织，这些组织具有晶粒细小、缺陷密度较高等特点，并且钢板基材中碳化物分布更加细小、均匀，在热冲压成形工艺重新加热过程中，提供了更多的奥氏体形核位置，最终细化原奥氏体晶粒。
本发明技术改善断裂性能的理由如下：本发明所述热冲压成形技术可以细化热冲压成形构件微观组织中的原奥氏体晶粒、马氏体板条束、马氏 体板条块和马氏板条。一方面，上述晶粒细化可以降低磷、硫等杂质元素和氢元素在晶界处的富集，缓解杂质元素和氢元素对晶界断裂的不利影响，从而抑制脆性沿晶断裂。另一方面，通过晶粒细化，裂纹在扩展过程中需要穿过更多大角晶界，其中包括原奥氏体晶界、马氏体板条束界面、马氏体板条块界面等，因此裂纹扩展需要更多的能量、更加困难，最终提升热冲压成形构件的断裂性能。
因此，根据本发明提供的热冲压成形方法，所述预备热处理可以提高预涂覆层合金化程度、减少钢板基材中的碳化物组织、获得马氏体和/或贝氏体的基材组织，从而在高温冲压变形时，降低预涂覆层对冲压模具的损耗、并且细化晶粒、提高最终热冲压成形构件的断裂性能。
本发明的热冲压成形方法可以用于汽车的安全结构件、增强结构件、车轮构件、高强韧汽车结构件等，其中包括但不限于汽车白车身A柱、B柱、背顶横梁等。
附图说明
以下，结合附图来详细说明本发明的实施方案，其中：
图1是现有的热冲压成形方法的示意图；
图2是本发明的热冲压成形方法的示意图；
图3是实施例中使用的22MnB5钢板的预涂覆层和钢板基材的原始微观组织结构图；
图4是本发明实施例1-3预备热处理后的Al-Si镀层微观组织示意图；
图5是本发明实施例1-3预备热处理后的预涂覆层中FeAl相与金属间化合物总体积分数比值随保温时间的变化情况；
图6是在本发明实施例2预备热处理后的钢板基材微观组织图；
图7是本发明实施例4的热冲压成形后的钢板基材微观组织图；
图8是本发明实施例4的热冲压成形后的钢板基材微观组织反极图；
图9是采用现有技术热冲压成形后的钢板基材微观组织反极图；
图10是本发明实施例4与现有技术获得的预涂覆热冲压成形钢板的三点弯曲试验结果对比。
具体实施方式
下面结合具体实施方式对本发明进行进一步的详细描述，给出的实施 例仅为了阐明本发明，而不是为了限制本发明的范围。
为了具体地说明本发明的热冲压成形方法，图1和图2分别概括总结了本发明的热冲压成形工艺方法和现有的热冲压成形方法的一种实施方案。需要注意的是，本发明不限于图中给出的实施例，图中的斜率仅用作加热或降温平均速率的示意，不代表真实情况下的加热或冷却曲线。
实施例中使用的22MnB5钢板的预涂覆Al-Si层和钢板基材的原始微观组织结构如图3所示。其中，预涂覆层从钢板基材侧开始依次为：富Si金属间化合物层、Al层。该预涂覆Al-Si镀层结构是典型的市购22MnB5钢的预涂覆镀层结构。钢板基材主要由铁素体、珠光体、碳化物构成。其中，片层状珠光体领域的尺寸可达2μm以上，球状碳化物粒径可达0.5μm以上。
实施例1-3
对预涂覆22MnB5钢板进行如下预备热处理：
(1)将三块所述预涂覆钢板加热至930℃，分别保温1分钟(实施例1)、5分钟(实施例2)和10分钟(实施例3)，使预涂覆钢板基材奥氏体化、预涂覆层合金化；
(2)在所述加热保温步骤完成之后，以300℃/s的冷却速率，将所述钢板冷却至室温。
在预备热处理之后，上述钢板中的Al-Si镀层发生合金化，其微观组织如图4所示。从钢板基材侧开始依次为：主要包含铁素体组织的Fe-Al扩散层、主要包含了FeAl、Fe 2Al 5的金属间化合物层。其中，Fe-Al扩散层的厚度为4至30μm，金属间化合物层的厚度为15至40μm。
图5给出了FeAl相与金属间化合物总体积分数比值随保温时间的变化。相比于Fe 2Al 5相，FeAl具有更高的熔点和断裂韧性，可以减小炉辊结垢、模具磨损等问题的不利影响。在本实施例中，FeAl相在所有Fe-Al金属间化合物中所占体积分数不小于60％。
实施例2的预备热处理之后钢板基材的微观组织如图6所示，其中不存在粒径大于0.5μm的球状渗碳体颗粒，不存在粒径大于1μm的片层状珠光体领域；马氏体或贝氏体的体积分数或两者之和的体积分数不小于30％。
大量的平行试验表明：虽然本实施例的冷却速率和温度不在本发明的最优条件范围内，但并不会影响该实施例中的微观组织和结论。也就是说，本发明最优冷却速率范围和温度范围得到的微观组织和结论与上述实施例几乎一样。然而，那些最优条件范围更利于工业化生产。
实施例4
对实施例2得到的钢板进行重新加热和热冲压成形：
(3)将所述钢板重新加热至850℃保温，总时间为1.5分钟，以使得所述钢板完全奥氏体化；
(4)将所述加热钢板转移至模具中，保证移送至模具时，所述加热钢板的温度在500℃以上；
(5)在所述模具中对所述加热钢板进行热冲压成形，获得最终热冲压成形钢构件。
图7是所述热冲压成形工艺之后钢板基材的微观组织结构。在热冲压成形之后，钢板基材获得全部马氏体组织，并且微观组织中的原奥氏体晶粒得到了明显细化，原奥氏体晶粒尺寸从预备热处理后的15-25μm降低至热冲压成形后的3-8μm。同时，因为在热冲压成形工艺中，采用了相对较低的温度与较短的保温时间，Al-Si镀层的合金化程度与微观组织结构不再发生明显变化。
图8是所述热冲压成形工艺之后钢板基材的微观组织反极图，图中可以更清晰地观察到钢板基材微观组织中的原奥氏体晶粒尺寸，与图7中观察到的原奥氏体晶粒尺寸3-8μm相符合。
作为对照，图9是采用图2所示的现有热冲压成形技术(即不进行预备热处理)获得的钢板基材的微观组织反极图。其中，原奥氏体晶粒尺寸约为20μm。现有热冲压成形工艺未经过预备热处理，需要采用较高加热保温温度和较长加热保温时间，例如，900-940℃、5-10分钟，并且，现有热冲压成形工艺的起始微观组织为铁素体+片层状珠光体+球状碳化物组织，无法起到马氏体或贝氏体组织细化奥氏体晶粒的作用。因此，现有热冲压成形工艺获得的钢板基材中的原奥氏体晶粒远大于本发明所述热冲压成形工艺。
图10对比了现有热冲压成形方法与本发明方法获得的热冲压成形后钢板的三点弯曲试验结果。所述热冲压成形后钢板的三点弯曲试验结果， 可以体现热冲压成形构件的断裂性能。三点弯曲试验结果显示，相对于现有热冲压成形技术，本发明技术获得的热冲压成形后钢板可以达到更大的弯曲载荷和更大的弯曲角，其中，本发明技术可获得最大弯曲载荷约1100N，弯曲角约58.4°，现有技术仅可获得最大弯曲载荷约1000kN，弯曲角约52.2°，即最大弯曲载荷提高了10％，弯曲角同时提高了11.9％。因此，本发明方法获得的热冲压成形后钢板的三点弯曲性能更好，所对应地，热冲压成形构件的断裂性能也更好。
由上述实施例可以看出，本发明的方法可以同时提升预涂覆层合金化程度与钢板基材的断裂性能。改善钢板基材断裂性能的理由如下：本发明所述热冲压成形技术可以使碳元素在基材中分布更加均匀与细化热冲压成形构件微观组织中的原奥氏体晶粒、马氏体板条束、马氏体板条块和马氏板条。一方面，上述晶粒细化可以降低磷、硫等杂质元素和氢元素在晶界处的富集，缓解杂质元素和氢元素对晶界断裂的不利影响，从而抑制脆性沿晶断裂。另一方面，通过晶粒细化，裂纹在扩展过程中需要穿过更多大角晶界，其中包括原奥氏体晶界、马氏体板条束界面、马氏体板条块界面等，因此裂纹扩展需要更多的能量、更加困难，最终提升热冲压成形构件的断裂性能。
出于说明和描述的目的，提供了上述的实施例的说明。本领域的技术人员应该清楚的是本发明不限于这些实施例或实验数据。实施例中记载的数据和各种参数仅是示例性的，并不构成对本发明的限制。

Claims (10)

  1. 一种用于预涂覆钢板的热冲压成形方法，所述方法包括采用模具在热冲压温度下对预涂覆钢板进行热冲压成形，获得热冲压成形构件，其特征在于，所述方法还包括在热冲压成形之前对预涂覆钢板进行预备热处理，所述预备热处理包括：
    (1)加热保温：将所述预涂覆钢板加热至850-920℃保温7至15分钟，或者加热至920-960℃保温5至10分钟，以使得预涂覆钢板基材奥氏体化、预涂覆层合金化；
    (2)冷却：在所述加热保温步骤完成后，以不小于5℃/s的冷却速率，将所述预涂覆钢板冷却至300℃以下；和
    (3)任选地重复上述加热保温和冷却步骤一次或多次。
  2. 根据权利要求1所述的热冲压成形方法，其中，除铁元素以外，所述预涂覆钢板基材还包含以重量％表示的以下成分：碳0.2-0.4％；锰0.5-1.5％；硼0-0.005％；不超过1％的选自铝、硅、铬、钼、铌、钒中的一种或多种合金元素；以及其他不可避免的杂质元素；或者
    所述预涂覆钢板基材还包含以重量％表示的以下成分：碳0.3-0.5％；锰0.5-2.5％；硼0-0.005％；不超过3％的选自铝、硅、铬、钼、铌、钒中的一种或多种合金元素；以及其他不可避免的杂质元素；
    优选地，所述预涂覆钢板基材厚度为0.8-2.5mm。
  3. 根据权利要求1所述的热冲压成形方法，其中，所述预涂覆层为铝或铝合金，优选为铝合金，更优选为Al-Si合金；优选地，所述预涂覆层的厚度为6-36μm，更优选为15-27μm。
  4. 根据权利要求1至3中任一项所述的热冲压成形方法，其中，当所述预涂覆层厚度小于20μm时，所述加热保温步骤为：850-920℃，7至15分钟；当所述预涂覆层厚度大于或等于20μm时，所述加热保温步骤为：920-960℃，5至10分钟。
  5. 根据权利要求1至3中任一项所述的热冲压成形方法，其中，所述冷却速率不小于10℃/s；更优选地，所述冷却速率不小于25℃/s，最优选地，所述冷却速率为25℃/s至50℃/s；
    优选地，在步骤(2)的冷却过程中通过冲压模具对预涂覆钢板进行 变形。
  6. 根据权利要求1至3中任一项所述的热冲压成形方法，其中，所述预备热处理后的预涂覆钢板基材的微观组织具有如下特征：
    (a)马氏体或贝氏体或两者之和的体积分数不小于30％；
    (b)不存在粒径大于0.5μm的球状碳化物颗粒，不存在粒径大于1μm的片层状烛光体领域。
  7. 根据权利要求1至3中任一项所述的热冲压成形方法，其中，所述预备热处理后的预涂覆层的微观组织由一种或多种金属间化合物、以及铁素体组成，其中，FeAl相在所有金属间化合物中所占体积分数不小于60％。
  8. 根据权利要求1至3中任一项所述的热冲压成形方法，其中，所述方法还包括：在所述预备热处理之后，将所述预涂覆钢板重新加热至780-940℃保温1至7分钟，以使预涂覆钢板基材完全奥氏体化；然后，保持温度在500℃以上将所述预涂覆钢板转移至模具中进行热冲压成形；
    优选地，所述方法还包括：在所述预备热处理之后，将所述预涂覆钢板重新加热至830-900℃保温1至4分钟，以使预涂覆钢板基材完全奥氏体化；然后，保持温度在600℃以上将所述预涂覆钢板转移至模具中进行热冲压成形。
  9. 根据权利要求1至3中任一项所述的热冲压成形方法，其中，热冲压成形后的预涂覆钢板基材微观组织为全马氏体组织；或者
    热冲压成形后的预涂覆钢板基材微观组织为铁素体组织、贝氏体组织、马氏体组织、奥氏体组织中的两相或者多相构成的混合组织。
  10. 根据权利要求1至3中任一项所述的热冲压成形方法，其中，热冲压成形后的预涂覆钢板基材微观组织的原奥氏体晶粒尺寸不超过18μm，优选不超过10μm。
PCT/CN2022/124636 2021-10-21 2022-10-11 一种用于预涂覆钢板的热冲压成形方法 WO2023066087A1 (zh)

Priority Applications (1)

Application Number Priority Date Filing Date Title
KR1020247014162A KR20240096490A (ko) 2021-10-21 2022-10-11 프리코팅 강판용 핫 스탬핑 성형 방법

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CN202111226071.X 2021-10-21
CN202111226071.XA CN116000169A (zh) 2021-10-21 2021-10-21 一种用于预涂覆钢板的热冲压成形方法

Publications (1)

Publication Number Publication Date
WO2023066087A1 true WO2023066087A1 (zh) 2023-04-27

Family

ID=86023487

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/CN2022/124636 WO2023066087A1 (zh) 2021-10-21 2022-10-11 一种用于预涂覆钢板的热冲压成形方法

Country Status (3)

Country Link
KR (1) KR20240096490A (zh)
CN (1) CN116000169A (zh)
WO (1) WO2023066087A1 (zh)

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101583486A (zh) 2006-10-30 2009-11-18 安赛乐米塔尔法国公司 涂覆的钢带材、其制备方法、其使用方法、由其制备的冲压坯料、由其制备的冲压产品和含有这样的冲压产品的制品
CN106466697A (zh) 2016-08-12 2017-03-01 宝山钢铁股份有限公司 一种带铝或者铝合金镀层的钢制热冲压产品及其制造方法
CN109518114A (zh) * 2018-08-08 2019-03-26 宝山钢铁股份有限公司 带铝硅合金镀层的热冲压部件的制造方法及热冲压部件
CN110168116A (zh) * 2017-01-17 2019-08-23 日本制铁株式会社 热冲压成形体及其制造方法
CN110180957A (zh) * 2018-06-28 2019-08-30 镕凝精工新材料科技(上海)有限公司 一种镀锌钢板的热处理方法及热冲压工艺
WO2020189767A1 (ja) * 2019-03-20 2020-09-24 日本製鉄株式会社 ホットスタンプ成形体

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN101583486A (zh) 2006-10-30 2009-11-18 安赛乐米塔尔法国公司 涂覆的钢带材、其制备方法、其使用方法、由其制备的冲压坯料、由其制备的冲压产品和含有这样的冲压产品的制品
CN106466697A (zh) 2016-08-12 2017-03-01 宝山钢铁股份有限公司 一种带铝或者铝合金镀层的钢制热冲压产品及其制造方法
CN110168116A (zh) * 2017-01-17 2019-08-23 日本制铁株式会社 热冲压成形体及其制造方法
CN110180957A (zh) * 2018-06-28 2019-08-30 镕凝精工新材料科技(上海)有限公司 一种镀锌钢板的热处理方法及热冲压工艺
CN109518114A (zh) * 2018-08-08 2019-03-26 宝山钢铁股份有限公司 带铝硅合金镀层的热冲压部件的制造方法及热冲压部件
WO2020189767A1 (ja) * 2019-03-20 2020-09-24 日本製鉄株式会社 ホットスタンプ成形体

Also Published As

Publication number Publication date
KR20240096490A (ko) 2024-06-26
CN116000169A (zh) 2023-04-25

Similar Documents

Publication Publication Date Title
CN109097705B (zh) 一种800MPa级冷轧热镀锌双相钢及其生产方法
JP7269588B2 (ja) ホットスタンピングに使用される鋼、ホットスタンピング方法および成形された構成要素
JP5726419B2 (ja) 延性が改善された装置レス熱間成形または焼入れ用鋼
JP7207660B2 (ja) 熱間スタンプ成形用鋼材、熱間スタンプ成形方法、および熱間スタンプ成形部材
JP6580123B2 (ja) プレス硬化用の鋼板を製作するための方法、および当該方法によって得られた部品
CN109371325A (zh) 一种冷弯性能优良的锌系镀覆热成型钢板或钢带及其制造方法
CN104928569B (zh) 一种800MPa级高延展性的低密度钢及其制造方法
KR101485306B1 (ko) 공구로 열간 성형 이후 석출 및/또는 담금질을 통해 경화된 초고강도 및 연성을 갖는 압연 강 및 이를 제조하는 방법
WO2010085983A1 (en) Fabrication process of coated stamped parts and parts prepared from the same
JP2014507556A (ja) 硬度および／または延性の異なる領域を有する硬化部品の製造方法
CN109365606A (zh) 一种耐腐蚀性优良的锌系镀层钢板或钢带的成形方法
CN104364408A (zh) 合金化热浸镀锌热轧钢板及其制造方法
US20160340755A1 (en) Hot-dip galvanized steel sheet and hot-dip galvannealed steel sheet having improved hole expansion ratio, and manufacturing methods thereof
JP2020522614A (ja) 改善された延性を備えた高強度鋼製部品の製造方法、及び前記方法により得られた部品
CN108374118A (zh) 一种具有易于成型特性的热镀锌双相钢板及其制造方法
CN111172466A (zh) 一种塑性增强的抗拉强度590MPa级冷轧双相钢及其生产方法
CN111411295B (zh) 一种多相钢构件及其制备方法、应用
CN105543666B (zh) 一种屈服强度960MPa汽车大梁钢及其生产方法
CN108977726B (zh) 一种抗延迟开裂的马氏体超高强度冷轧钢带及其制造方法
CN112442632A (zh) 一种高抗弯曲性热轧热成形用钢及其制备方法
JP2022535352A (ja) ホットスタンプされた部品を製造するための鋼ストリップ、シート又はブランク、部品、及びブランクを部品にホットスタンプする方法
FI124825B (fi) Menetelmä metallipinnoitetun ja kuumamuokatun teräskomponentin valmistamiseksi ja metallipinnoitettu teräsnauhatuote
CN110172636A (zh) 一种低碳热成形钢及其制备方法
CN109136759A (zh) 轮辐用厚规格1300MPa级热成形钢及制备方法
WO2023066087A1 (zh) 一种用于预涂覆钢板的热冲压成形方法

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 22882697

Country of ref document: EP

Kind code of ref document: A1

WWE Wipo information: entry into national phase

Ref document number: 2022882697

Country of ref document: EP

NENP Non-entry into the national phase

Ref country code: DE

ENP Entry into the national phase

Ref document number: 2022882697

Country of ref document: EP

Effective date: 20240521