Classifications

• • 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
  • C23C2/06—Zinc or cadmium 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
• • 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
  • C23C2/29—Cooling or quenching
• • 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
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/60—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using alkaline aqueous solutions with pH greater than 8
  • C23C22/62—Treatment of iron 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
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/78—Pretreatment of the material to be coated
• • 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
  • B21D22/20—Deep-drawing
  • B21D22/201—Work-pieces; preparation of the work-pieces, e.g. lubricating, coating
• • 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
  • B21D22/20—Deep-drawing
  • B21D22/208—Deep-drawing by heating the blank or deep-drawing associated with heat treatment
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/62—Quenching devices
  • C21D1/673—Quenching devices for die quenching
• • 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
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates

Definitions

• the invention relates to a method for producing hardened steel components with a conditioned zinc alloy corrosion protection layer.
• corrosion protection layers on metal strips can be organic coatings, for example paints, although these paints may also contain corrosion-inhibiting agents.
• metal strips with metal coatings.
• Such metal coatings can consist of an electrochemically more noble metal or a less electrochemically noble metal.
• a coating made of an electrochemically nobler metal or a self-passivating metal, such as aluminum, is referred to as a barrier protective layer.
• a barrier protective layer For example, when aluminum is applied to steel, the steel material will suffer corrosion if this barrier protective layer is no longer present in some areas, for example, due to mechanical damage.
• a common barrier protective layer for steel is the aforementioned aluminum layer, which is usually applied by hot-dip coating.
• an electrochemically less noble metal is applied as a protective layer, this is referred to as a cathodic corrosion coating because, if the corrosion protection coating is mechanically damaged down to the steel material, the electrochemically less noble metal is corroded first before the steel material itself is exposed to corrosion.
• cathodic protective coating on steel is a zinc coating or a zinc-based alloy.
• a common galvanizing process is hot-dip galvanizing (also known as hot-dip galvanizing). This involves immersing steel continuously (e.g., strip and wire) or piece by piece (e.g., components) into a melt of liquid zinc at temperatures of approximately 450°C to 600°C (the melting point of zinc is 419.5°C).
• the molten zinc for example, has a zinc content of at least 98.0 wt.% according to DIN EN ISO 1461.
• a resistant alloy layer of iron and zinc forms on the steel surface, covered by a firmly adhering pure zinc layer whose composition corresponds to the molten zinc.
• the zinc layer In a continuously galvanized strip, the zinc layer has a thickness of 5 ⁇ m to 40 ⁇ m.
• the zinc layer can have thicknesses of 50 ⁇ m to 150 ⁇ m.
• electrolytic galvanizing galvanic galvanizing
• steel strips or steel plates are immersed in a zinc electrolyte rather than in a molten zinc bath.
• the steel to be galvanized is placed in the solution as the cathode, and an electrode made of the purest possible zinc is used as the anode.
• a current is passed through the electrolyte solution.
• the zinc which is present in ionic form (oxidation state +II), is reduced to metallic zinc and deposited on the steel surface.
• thinner zinc layers can be applied with electrolytic galvanizing.
• the zinc layer thickness is proportional to the strength and duration of the current flow, resulting in a layer thickness distribution across the entire workpiece, depending on the workpiece and anode geometry.
• one or more post-treatments can be performed, such as phosphating, oiling, or the application of organic coatings (e.g., cataphoretic dip painting, or KTL for short).
• Quench hardening means selecting a cooling rate above the respective critical cooling rate to adjust the microstructure. This critical cooling rate is approximately 15 to 20 Kelvin per second, but can also be lower depending on the alloy composition.
• a common steel grade that can be hardened through quench hardening is the so-called boron-manganese steels, such as the most commonly used 22MnB5, but also derivatives of this steel, such as 20MnB8 and 30MnB5.
• Non-hardenable steels, such as microalloyed steels can also be hot-formed using the direct or indirect process.
• Such steel grades can be easily formed and cut in the unhardened state.
• the first and somewhat older process is press hardening.
• press hardening a flat blank is cut from a steel sheet strip made of a quench-hardenable steel alloy, such as 22MnB5 or a similar manganese-boron steel. This flat blank is then heated to such a high temperature that the steel microstructure takes on the appearance of gamma iron, or austenite. To achieve this microstructure, the so-called austenitizing temperature Ac 3 must be exceeded, at least if complete austenitization is desired.
• this temperature can be between 820°C and 900°C, with such steel blanks, for example, being heated to approximately 900°C to 930°C and kept at this temperature until the structure has completely changed.
• Such a steel blank is then transferred in its hot state to a press, where, using an upper tool and a lower tool, each of which is shaped accordingly, the hot steel blank is formed into the desired shape with a single press stroke.
• press tools i.e., forming tools
• the contact of the hot steel material with the comparatively cool, particularly cooled, press tools extracts energy from the steel very quickly.
• the heat must be extracted so quickly that the so-called critical hardening rate is exceeded, which is typically between 15° and 25° Kelvin per second.
• austenite structure does not revert to its original ferritic structure, but rather a martensitic structure is achieved. Due to the fact that austenite can dissolve considerably more carbon in its lattice than martensite, carbon precipitation leads to lattice distortion, which leads to the high hardness of the final product. The rapid cooling stabilizes the martensitic state, so to speak. This makes hardnesses and tensile strengths R m of more than 1500 MPa achievable. Hardness profiles can also be adjusted using suitable measures, which will not be discussed in detail here, such as complete or partial reheating.
• hot stamping Another, somewhat newer method for producing hardened steel components, particularly for car body construction, is hot stamping, developed by the applicant.
• hot stamping a flat steel blank is cut from a steel strip, and this flat steel blank is then cold-formed.
• This forming process is not performed with a single press stroke, but rather, as is usual in conventional press lines, for example, in a five-stage process.
• This process allows for significantly more complex shapes, so that the final product can be a complexly shaped component, such as the B-pillar or a longitudinal member of a motor vehicle.
• this component is also austenitized in a furnace and transferred in the austenitized state into a mold, whereby the mold has the contour of the final component.
• the preformed component is shaped before heating in such a way that after heating and thus also after thermal expansion, this component already largely corresponds to the final dimensions of the hardened component.
• This austenitized blank is The component is placed in the austenitized state into the mold, and the mold is closed. Preferably, the component is contacted and clamped by the mold on all sides, and heat is also removed through contact with the mold, creating a martensitic structure.
• motor vehicle bodies usually have a corrosion protection coating, with the corrosion protection layer closest to the metal material forming the body, in particular steel, being a metallic coating, corrosion protection coatings for hardened components have also been sought and developed in the past.
• corrosion protection coatings for components to be hardened are subject to different requirements than corrosion protection coatings for components that are not hardened.
• the corrosion protection coatings must be able to withstand the high temperatures generated during hardening. Since it has long been known that hot-dip aluminized coatings can withstand high temperatures, press-hardened steels with a protective layer of aluminum were initially developed. Such coatings are capable of withstanding not only the high temperatures but also hot-dip galvanizing.
• a disadvantage is that hot-dip galvanizing is not typically used on conventional steel grades in motor vehicles, and it is fundamentally problematic to use different corrosion protection systems, especially when there is a risk of contact corrosion.
• zinc coatings are considerably easier to form than aluminum coatings, as aluminum coatings tend to chip or crack at conventional forming temperatures. This does not happen with zinc.
• the steel sheet is coated with a metallic coating and is hardened by heating and quenching. After hardening, the oxides present on the corrosion protection coating as a result of heating are removed.
• the component is subjected to vibratory grinding to condition the surface of the metallic coating, i.e., the corrosion protection layer.
• the corrosion protection coating is a zinc-based coating, and the surface conditioning is carried out in such a way that oxides lying on or adhering to the corrosion protection layer are ground away and, in particular, microporosity is exposed.
• a method for producing and removing a temporary protective layer for a cathodic coating whereby a steel sheet made of a hardenable steel alloy is provided with a zinc coating using a hot-dip process, whereby the aluminum content in the zinc bath is adjusted so that a superficial oxide skin of aluminum oxide forms during the melt hardening, whereby this thin skin is blasted off or leveled after hardening by irradiating the sheet metal component with dry ice particles.
• An example of this is the EP 1 630 244 B1 or EP 2 233 508 B1 .
• Sol-gel preconditioning of the coating to reduce oxide layer formation and increase weldability is known.
• This is intended to create an oxidation protection coating for press-hardening steel materials, based on silane- and titanium-containing binders and oxide pigments, which are apparently applied in a sol-gel process.
• solvents such as methanol are used here, which are not suitable for use in steel production plants.
• the coating is intended to After press hardening, the coatings fall off on their own, although tests with titanium and silicon-based coatings conducted in 2015/16 were unsuccessful with either thick or thin wet films. The coating neither falls off on its own, nor is it suitable for industrial welding.
• the object of the invention is to create a method for producing hardened steel components in which an existing zinc corrosion protection layer is conditioned in such a way that cleaning of the surface, and in particular cleaning with fluid and/or particle jets after hardening, can be eliminated.
• the method should be able to dispense with the use of tin or tin-containing solutions.
• a further task is to create a galvanized steel strip which is designed in such a way that the removal of an oxide layer is unnecessary.
• a steel sheet plate or a steel strip which has a zinc-based coating.
• This layer can advantageously have a thickness of 5 ⁇ m to 20 ⁇ m per side. This can ensure good corrosion protection.
• the coating can be a Z40, Z60, Z80, Z120, Z140, or Z180 according to DIN EN 10346.
• Zinc-based corrosion protection layers can have a comparatively high zinc content of 85 wt.% to 99.8 wt.%, in particular 95 wt.% to 99.5 wt.%, preferably 98 wt.% to 99.5 wt.%, and in addition to unavoidable impurities also contain aluminum in the range of 0.2 to 2 wt.%.
• the zinc-based metallic corrosion protection layer can be applied using a hot-dip galvanizing process. This can be a simple and robust application method.
• the oxide growth during the hardening process can be designed in such a way that subsequent mechanical surface conditioning, such as centrifugal blasting, vibratory grinding, or Dry-egg blasting is unnecessary, as is treatment with tin or tin-containing solutions.
• lithium and/or potassium apparently modify the surface in such a way that any kind of cleaning is unnecessary.
• the total concentration [c] can be set between 50 and 120 to further increase the effectiveness.
• an aqueous alkaline solution is applied by means of, for example, a roll coater to a galvanized surface after skin rolling and before cold forming or annealing and hardening process.
• Very thin layer thicknesses are used, which are 0.5-3 ⁇ m in aqueous solution, in particular 0.5 - 1.5 ⁇ m, and 50-300 nm thick when dried, in particular 75 - 125 nm, in particular 80 - 100 nm.
• the solution can also be applied by dipping and squeezing or spraying or other application methods.
• the potassium occupancy when using potassium hydroxide KOH is 1-140 mg potassium hydroxide per m 2 , in particular 30-100 mg/m 2 potassium hydroxide.
• the lithium occupancy when using LiOH is 1-40 mg lithium hydroxide per m 2 , in particular 15-35 mg/m 2 , and in particular 20-30 mg/m 2 lithium hydroxide.
• Treatment with potassium and/or lithium hydroxide causes an increase in emissivity in the first 780°C until the gamma phase decays.
• the invention thus relates in particular to a method for producing hardened steel components, wherein a blank is cut out of a strip of a hardenable steel alloy coated with a zinc-based coating, and the blanks are then cold formed into a component blank and subsequently heated to a temperature that causes a structural change towards austenite, wherein the austenitized component blank is then fed to a form-hardening tool in which the component blank is held in a form-fitting manner by means of an upper and lower tool which have a shape substantially corresponding to the component blank, wherein the contact of the material of the component blank against the particularly cooled tools extracts heat from the steel material so quickly that cooling at a cooling rate above the critical cooling rate leads to martensitic hardening, wherein after the galvanizing of the metal strip and before the temperature increase for the purpose of austenitization, an aqueous potassium hydroxide solution and/or lithium hydroxide solution is applied to the surface of the strip or the blank or the component blank. becomes.
• An advantageous further development provides for the application of an aqueous potassium and/or lithium solution which is alkaline.
• the alkaline or basic aqueous solution is applied with a layer thickness of 0.5 - 3 ⁇ m, in particular 0.5 - 1.5 ⁇ m, wherein the dried layer thickness is 50 - 300 nm, in particular 75 - 125 nm, in particular 80 - 100 nm.
• the potassium occupancy is 1 - 140 mg/m2 potassium hydroxide, and in particular 50 - 100 mg/m2 potassium hydroxide.
• the lithium coverage is 1 - 40 mg/m2 lithium hydroxide, in particular 15 - 35 mg/m2 lithium hydroxide, and in particular 20 - 30 mg/m2 lithium hydroxide.
• a further aspect of the invention relates to a galvanized metal strip, in particular steel strip, coated with 30 - 100 mg/m2 potassium.
• galvanized metal strip in particular steel strip, is coated with 5 - 30 mg/m2 lithium.
• the combination of potassium and lithium as a coating on the steel strip can be particularly advantageous.
• the zinc-based coating to have a zinc content of 85 wt.% to 99.8 wt.%, preferably 98 wt.% to 99.5 wt.%, aluminum in the range of 0.2 to 2 wt.%, and unavoidable impurities.
• a high zinc content can ensure cathodic corrosion protection.
• good processability can be ensured if the layer consists predominantly of zinc and the remainder of aluminum.
• Other elements, such as magnesium, may affect the emissivity and thus influence the heating rate.
• the steel strip is formed from a hardenable steel alloy, in particular a boron-manganese steel and particularly preferably a 22MnB5 or 20MnB8 or 34MnB5.
• a further aspect of the invention relates to the use of such a steel strip, which is produced by an aforementioned method, in a process in which a steel sheet is heated for the purpose of austenitization and is then formed and quench-hardened.
• the surface of a galvanized metal sheet, in particular steel sheet, which is first cold formed in a form hardening process in several stages and then heated as a component blank, transferred to a form hardening tool and hardened therein, is conditioned with lithium and/or potassium solution, the conditioning being discussed below.
• the concentration of the lithium solution [LiOH ⁇ H 2 O] is between 0 and 100 g/l and the potassium solution [KOH] is between 0 and 200 g/l.
• Very thin layer thicknesses are used, which are 0.5-3 ⁇ m in aqueous solution, in particular 0.5 - 1.5 ⁇ m, and 50-300 nm thick when dried, in particular 75 - 125 nm, in particular 80 - 100 nm.
• an aqueous layer thickness of 0.5 - 3 ⁇ m is desired, with a dried layer thickness of 50 - 3000 nm and a tin content of 30 - 90 mg/m 2 in the form of K 2 [SnO 3 ].
• the potassium coverage when using potassium hydroxide KOH is 0-140 mg potassium hydroxide per m 2 , in particular 50 - 100 mg/m 2 potassium hydroxide.
• the lithium coverage when using lithium hydroxide is 10 - 40 mg lithium hydroxide per m 2 , in particular 15 - 35 mg/m 2 , and in particular 20 - 30 mg/m 2 lithium hydroxide.
• Figure 3 shows a variant of this, the so-called phs-multiform process, in which, after austenitization and optional pre-cooling to temperatures ranging from 450 °C to 650 °C, a multi-stage process with several forming steps, or cutting and punching operations, subsumed under the term "hot forming steps,” takes place.
• the sheets heat-treated in this way have a surface layer, particularly of aluminum oxide and zinc oxide, which is preferably cleaned off.
• the Figures 4 and 5 show a hot-dip galvanizing plant and an electrolytic galvanizing plant.
• the application of the stannate can preferably be carried out in the area of chemical passivation (in Figure 4 ) or the station "Passivation” (in Figure 5 ) can be made.
• KOH and LiOH The effectiveness limits of KOH and LiOH can be seen in various examples.
• an aqueous solution with the corresponding values in g/l of KOH or LiOH was applied to a 22MnB5 steel strip with a Z140 zinc coating on a 1.5 mm thick steel sheet. This aqueous solution was applied using a roll coater, and a 1 ⁇ m thick aqueous solution was created with the appropriate addition of KOH and/or LiOH.
• the values in mg/ m2 of potassium and/or lithium in the table are calculated. For 1 ⁇ m thick aqueous solution layers, analogous values in g/l are obtained. For other layer thicknesses, this would have to be converted accordingly for the solution in g/l.
• the table shows the average heating rate in K/s when heating the steel sheet, blank, or blank from room temperature to the austenitizing temperature Ac3.
• the examples according to the invention have a significantly increased heating rate, so that heating can be carried out more quickly, which can enable energy savings or CO2 savings.
• phosphatability paint penetration
• weldability weldability
• contact resistance phosphatability (paintability), paint penetration, weldability, and contact resistance.
• "--" indicates a significantly negative effect
• "-" indicates a slightly negative effect
• " ⁇ ” indicates a comparable effect
• "+” indicates a slightly improved effect
• "++” indicates a significantly improved effect compared to the state of the art, i.e., in this case, compared to a 22MnB5 with a 1.5 mm sheet thickness and a Z140 coating without the inventive conditioning.
• FIG. 7 A heating curve is shown using 22MnB5 Z140 at a sheet thickness of 1.5 mm, using conditioning according to the invention, compared to a heating curve according to the prior art.
• the aqueous solution used was 70 mgK/m 2 and 4 mgLi/m 2 .
• the coating can be applied inline on the strip before it is cut into individual blanks. Furthermore, the blanks cut from the strip can also be coated accordingly.
• circuit boards are then formed into a component blank in a particularly multi-stage process. It is also conceivable to first coat the component blank with the potassium and/or lithium-containing solution. However, it has been shown that the potassium and/or lithium coating also tolerates the forming processes well.
• the resulting component blank is then heated to a temperature that causes a structural change toward austenite.
• the austenitized component blank is then fed to a hot stamping tool, where the component blank is hardened in a single stroke by the contact of an upper and lower tool, which essentially have the same shape as the blank or correspond to it.
• the contact of the component blank material against the cooled tools extracts heat from the steel so quickly that martensitic hardening occurs.
• the invention has the advantage that it is possible to condition the surface of a steel sheet intended for hot-dip or press hardening in such a way that a final mechanical cleaning to remove oxide surface layers can be omitted, so that such sheets can be processed in the same way as, for example, hot-dip aluminized sheets, but with the advantage that a high cathodic corrosion protection effect is achieved compared to hot-dip aluminized sheets.

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Citations (8)

• 2024
  • 2024-04-19 EP EP24171230.6A patent/EP4636119A1/fr active Pending
• 2025
  • 2025-04-16 WO PCT/EP2025/060542 patent/WO2025219470A1/fr active Pending

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