EP4029973A2 - Method of manufacturing an electrolytically coated steel sheet - Google Patents

Method of manufacturing an electrolytically coated steel sheet Download PDF

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Publication number
EP4029973A2
EP4029973A2 EP22150305.5A EP22150305A EP4029973A2 EP 4029973 A2 EP4029973 A2 EP 4029973A2 EP 22150305 A EP22150305 A EP 22150305A EP 4029973 A2 EP4029973 A2 EP 4029973A2
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EP
European Patent Office
Prior art keywords
steel sheet
coated steel
target temperature
heat treatment
holding time
Prior art date
Legal status (The legal status 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 status listed.)
Pending
Application number
EP22150305.5A
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German (de)
French (fr)
Other versions
EP4029973A3 (en
Inventor
Oliver Moll
Franz Hinte
Frank Panter
André Samusch
Marc Blumenau
Jörg STEINEBRUNNER
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ThyssenKrupp Steel Europe AG
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ThyssenKrupp Steel Europe AG
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Publication date
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Publication of EP4029973A2 publication Critical patent/EP4029973A2/en
Publication of EP4029973A3 publication Critical patent/EP4029973A3/en
Pending legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/48—After-treatment of electroplated surfaces
    • C25D5/50—After-treatment of electroplated surfaces by heat-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
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • 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
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
    • 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
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
    • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
    • C23C28/322—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only
    • C23C28/3225—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only with at least one zinc-based layer
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
    • C25D5/60—Electroplating characterised by the structure or texture of the layers
    • C25D5/615—Microstructure of the layers, e.g. mixed structure
    • C25D5/617—Crystalline layers
    • 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
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D13/00—Electrophoretic coating characterised by the process
    • C25D13/22—Servicing or operating apparatus or multistep processes

Definitions

  • the invention relates to a method for producing an electrolytically coated steel sheet, the method comprising the following steps: - providing a steel sheet; - Electrolytic coating of the steel sheet.
  • Coated steel sheets are formed into components in vehicle construction, which are usually fed to a painting process after shaping, often cathodic dip painting (KTL), which after dip painting requires heat treatment between 160 and 180°C for approx. 20 minutes to bake the paint is downstream.
  • KTL cathodic dip painting
  • Painted components formed from electrolytically coated sheet steel have been found to have scratches on the paintwork, which are presumably caused by outgassing as a result of the temperature effect in the painting process and, as a result, the surface defects and the qualitatively unacceptable appearance mean that the affected components have to be scrapped or costly to rework would lead. There is therefore a need for optimization with regard to the electrolytically coated steel sheets.
  • the invention is therefore based on the object of providing a method for producing an electrolytically coated steel sheet, with which the aforementioned disadvantages can be essentially avoided or at least significantly reduced.
  • the method for producing an electrolytically coated steel sheet comprises: providing a steel sheet; Electrolytic plating of the steel sheet, additionally the step that after the electrolytic plating, the plated steel sheet undergoes a heat treatment, wherein the plated steel sheet is heated to a target temperature between 60°C and 400°C and for a holding time between 0.10s and 300s target temperature is maintained.
  • the electrolytically coated steel sheet is subjected to a heat treatment, so that the heat treatment, if present, recombines gaseous hydrogen in the steel sheet and can thus generate a high pressure, which allows the gas to pass through and thus escape through the closed electrolytically applied coating allows.
  • other gaseous and/or liquid components that are present and embedded in the steel sheet can also escape or be expelled as a result of the heat treatment.
  • These gaseous and/or liquid components were incorporated into the steel/base material or its near-surface structure during the preliminary stages of sheet steel production, e.g. during a pickling or annealing process. This effectively causes outgassing, which can no longer lead to paint irritation or surface defects in the painted state in the later painting process.
  • the heat treatment according to the invention therefore does not correspond to the heat treatment in the painting process.
  • electrolytic coating primarily means the deposition of a coating of zinc (ZE) or a zinc alloy, for example zinc-nickel, which can optionally be optimized with an organic top layer in the form of phosphating and/or chromating.
  • ZE zinc
  • zinc alloy for example zinc-nickel
  • Steel sheet is to be understood as a hot- or cold-rolled steel sheet which, in the planar undeformed state, can be provided in sheet form as a steel sheet blank or in strip form as a steel strip.
  • a cold-rolled and, in particular, recrystallization-annealed steel strip is preferably provided as the steel sheet.
  • the thickness of the steel sheet can be between 0.3 and 4 mm.
  • the thickness is in particular at least 0.4 mm, preferably at least 0.5 mm and is in particular limited to a maximum of 3.5 mm, preferably to a maximum of 3 mm.
  • the thickness of the electrolytic coating can be between 1.5 ⁇ m and 15 ⁇ m (per side).
  • the electrolytic coating of steel sheets, in particular steel strips, is state of the art.
  • the steel sheets can be electrolytically coated on one or both sides, depending on the requirements.
  • Zinc-based coatings are preferably used, which ensure a certain degree of cathodic corrosion protection for the steel sheet.
  • Such coatings are also known in the art under the designation "ZE” (zinc electrolytic) or "EG” (electrogalvanized) in English-speaking countries.
  • the steel sheets coated with ZE are also called “steel sheet” in professional circles. This includes all conceivable compositions of carbon steels which can be coated electrolytically and are preferably used in vehicle construction. This can include soft steels for cold forming according to DIN EN 10152, e.g. B.
  • high and higher strength steels for cold forming according to DIN EN 10268 e.g. B. high-strength IF steels such as HC180Y and higher, e.g. B. isotropic steels such as HC2201 and higher, e.g. B. Bake-hardening steels such as HC180B and higher, e.g. B. micro-alloyed steels such as HC260LA and higher; or multi-phase steels for cold forming according to DIN 10338, on the one hand cold-rolled, e.g. B. Dual phase steels such as HCT450X and higher, e.g. B. retained austenite steels such as HCT690T and higher, e.g. B.
  • complex-phase steels such as HCT600C and higher, or on the other hot-rolled, z.
  • Complex phase steels such as HDT760C and/or CP-W1000, e.g. g. martensite phase steels such as HDT1180G1, see also https://ucpcdn.thyssenkrupp.com/ legacy/UCPthyssenkruppBAMXProcessingEurope/assets.fi les/downloads/tkmpe electrolytically galvanized thin sheet de 20190807.pdf. This enumeration of the possible sheet steel grades and the associated composition of the carbon steels is not intended to be conclusive.
  • the selection of the target temperature and the selection of the holding time must be adapted to the composition (carbon steel) of the steel sheet in particular, so that aging processes in particular are essentially avoided during heat treatment .
  • the target temperature/holding time to be set optimally for the steel sheet used and in particular taking into account the available system technology can be verified either by "trial and error" tests or alternatively or additionally can also be set using specialist knowledge.
  • the target temperature and holding time are to be selected according to the invention in such a way that outgassing/diffusion takes place effectively, the mechanical properties of the steel/base material but not be changed. Furthermore, the target temperature and the holding time are to be selected in particular in such a way that preferably no alloying of the coating with the steel/base material can take place.
  • the target temperature is at least 80° C., in particular at least 100° C., preferably at least 130° C., preferably at least 150° C. and at most 350° C., in particular at most 300° C., preferably at most 280° C., preferably maximum 250 °C.
  • the holding time is at least 0.50 s, in particular at least 1.0 s, preferably at least 1.50 s, preferably at least 2.0 s and at most 200 s, in particular at most 100 s, preferably at most 50 s, preferably at most 30 s, more preferably at most 20 s.
  • the heating to the target temperature can be carried out inductively, in a continuous furnace or by means of radiation sources, depending on the existing system concept and/or installation space.
  • the heating is preferably carried out inductively, for example by means of inductors, which can set a heat pulse in a targeted manner or can be controlled accordingly in order to heat the coated steel sheet relatively quickly.
  • inductive heating heating rates of at least 20 K/s, in particular at least 50 K/s, preferably at least 80 K/s, can be achieved, as a result of which the installation space can be selected to be relatively small, preferably when the heat treatment is considered inline in the process direction, is carried out after the electrolytic plating.
  • the heat treatment is preferably carried out inline as a post-treatment of a continuous electrolytic coating of steel strips.
  • the target temperature can be maintained, for example, within an enclosure through which the heated, coated steel sheet is passed. Holding can thus preferably take place in a continuous furnace.
  • the coated steel sheet is moved in the process direction during the heating, with the coated steel sheet being homogeneously heated transversely to the process direction.
  • Homogeneous heating viewed transversely to the process direction means that over the (entire) width of the coated steel sheet, if possible, no and only small temperature differences/differences are permitted during the heat treatment in order to ensure essentially "full-surface” outgassing over the entire surface of the coated steel sheet .
  • the coated steel sheet is actively cooled after the holding time.
  • Active cooling means that the still warm coated steel sheet is cooled in a targeted manner with suitable means, for example with known and common means that can bring about cooling, for example with a cooling rate of at least 5 K/s, in particular of at least 10 K/s, preferably at least 20 K/s.
  • suitable means for example with known and common means that can bring about cooling, for example with a cooling rate of at least 5 K/s, in particular of at least 10 K/s, preferably at least 20 K/s.
  • the steel sheet is heat-treated inline after the electrolytic coating, it may be that the steel sheet should be cooled to a maximum temperature of 120 °C, in particular a maximum of 100 °C, in order to avoid other components in the process chain that are in contact with the still warm sheet steel, not to be thermally stressed.
  • a steel sheet (1) has been provided in the form of a steel strip, which has been conventionally electrolytically coated or electrolytically galvanized in the opposite direction of the process, not shown, and in the process direction (P) a heat treatment (10th ) is supplied.
  • the electrolytic coated steel sheet (1) may be further phosphated and/or chromated before or after the heat treatment of the present invention.
  • a phosphating and/or chromating to increase the paint adhesion and/or the corrosion resistance is not relevant for the implementation of the heat treatment according to the invention and is therefore not discussed further here.
  • the coated steel sheet (1) undergoes a heat treatment (10) after the electrolytic coating Example inline in process direction (P) after electrolytic coating.
  • the coated steel sheet (1) is heated to a target temperature (T z ) of between 60° C. and 400° C. and held at the target temperature (Tz) for a holding time (tH) of between 0.10 s and 300 s.
  • the heating (11) to the target temperature (Tz) is preferably carried out inductively, since the coated steel sheet (1) moved and coated in the process direction (P) is targeted and rapid, in particular by arranging an inductor (not shown) above and/or below the coated steel sheet (1).
  • a homogeneous heating (11) transverse to the process direction (P) and thus over the (entire) width of the steel sheet (1) can also be ensured.
  • a continuous furnace or a radiation source, not shown, can also be considered for the heating (11).
  • active cooling (13) can take place so that the still warm coated steel sheet (1) cannot have any negative thermal influences on the downstream components inline in the process chain. Active cooling (13) allows the temperature of the coated steel sheet (1) undergoing the heat treatment (10) to be reduced to a maximum of 120° C., for example. After the heat treatment (10) according to the invention, the coated steel sheet (1) can be subjected to further processing steps.
  • FIG 1 a sketched temperature profile of an electrolytically coated steel sheet (1) heat-treated according to the invention in a time (t)-temperature (T) diagram.
  • the temperature profile can be specified or defined individually and depending on the composition of the steel sheet as well as the existing system concept.
  • the heat treatment can also take place offline.
  • the deposited coating may have a more columnar or plate-like crystal structure.
  • the method according to the invention is shown in tests to be independent of the morphology of the coating. Even in the case of a plate-shaped crystal structure with the associated lower porosity, which in particular does not favor outgassing, the task of the invention can still be achieved when the heat treatment is carried out according to the invention.
  • Tests were carried out on electrolytically galvanized steel sheets (1).
  • two steel strips were provided as steel sheet (1), each an identical cold-rolled bake-hardening steel with a thickness of 0.8 mm, which were electrolytically galvanized on both sides with the same parameters with a thickness of 5 ⁇ m per side.
  • the first steel sheet was further processed conventionally as a reference.
  • the second steel sheet (1) was inline, analogous to the outlined figure 1 , fed after the electrolytic coating of a heat treatment (10).
  • the heating (11) took place on both sides via an inductor arranged across the width above and below the steel sheet (1), which in each case applied the second steel sheet (1) at a heating rate of 200 K/s and to a target temperature (Tz) of 220 °C warmed up.
  • the holding time (tH) was 4.50 s at 220°C and the holding was done in a continuous furnace (12) to maintain the target temperature (T z ) of 220°C.
  • the hot coated steel sheet (1) Downstream of the holding zone (12) in the process direction (P), the hot coated steel sheet (1) was actively cooled using a water spray (13) and the hot coated steel sheet (1) was cooled to 70 °C at a cooling rate of 120 K/ s cooled down so that it could be further processed without thermally negatively influencing the other components in the process chain.
  • the number of faults caused by outgassing in the KTL process in the reference samples based on 600 cm 2 was determined as follows for all samples: over 5000 holes and over 100 pustules.
  • the defect pattern in the samples from the second steel sheet (1) based on 600 cm 2 was determined as follows for all samples: under 50 holes and under 15 pustules.
  • the features described can all be combined with one another as far as technically possible.
  • the invention does not have to be carried out inline on a steel strip, but rather it can also be carried out on sheet-like steel sheet blanks before these are further processed. It has also been shown within the scope of the invention that the heat treatment does not necessarily have to include outgassing/effusion of the entire steel/base material. On the other hand, it is sufficient to expel the gaseous and/or liquid components in a near-surface area, for example up to 20 ⁇ m, of the steel/base material, which typically also contains the inclusions from the preliminary stages of sheet steel production, in order to meet the requirements.

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Abstract

Die vorliegende Erfindung betrifft ein Verfahren zur Herstellung eines elektrolytisch beschichteten Stahlblechs (1), wobei das Verfahren folgende Schritte umfasst: Bereitstellen eines Stahlblechs; Elektrolytisches Beschichten des Stahlblechs (1). Erfindungsgemäß erfährt das beschichtete Stahlblech (1) nach dem elektrolytischen Beschichten eine Wärmebehandlung (10), wobei das beschichtete Stahlblech (1) auf eine Zieltemperatur (T<sub>Z</sub>) zwischen 60 °C und 400 °C erwärmt und für eine Haltezeit (tH) zwischen 0,10 s und 300 s auf Zieltemperatur (T<sub>Z</sub>) gehalten wird.The present invention relates to a method for producing an electrolytically coated steel sheet (1), the method comprising the following steps: providing a steel sheet; Electrolytic coating of the steel sheet (1). According to the invention, the coated steel sheet (1) undergoes a heat treatment (10) after the electrolytic coating, the coated steel sheet (1) being heated to a target temperature (T<sub>Z</sub>) between 60° C. and 400° C. and for a holding time (tH) between 0.10 s and 300 s is maintained at the target temperature (T<sub>Z</sub>).

Description

Technisches Gebiet (Technical Field)Technical Field

Die Erfindung betrifft ein Verfahren zur Herstellung eines elektrolytisch beschichteten Stahlblechs, wobei das Verfahren folgende Schritte umfasst: - Bereitstellen eines Stahlblechs; - Elektrolytisches Beschichten des Stahlblechs.The invention relates to a method for producing an electrolytically coated steel sheet, the method comprising the following steps: - providing a steel sheet; - Electrolytic coating of the steel sheet.

Technischer Hintergrund (Background Art)Technical Background (Background Art)

Der Einsatz von (metallisch) beschichteten Stahlblechen im Fahrzeugbau ist Stand der Technik. Dabei kommen zwei Beschichtungssysteme, insbesondere zinkbasierte Beschichtungen in Frage. Schmelztauchbeschichtete sowie elektrolytisch beschichtete Stahlbleche. Beide Beschichtungsvarianten sind im Fahrzeugbau seit Jahrzehnten etabliert und haben ihre Vorzüge.The use of (metallically) coated sheet steel in vehicle construction is state of the art. Two coating systems, in particular zinc-based coatings, come into consideration here. Hot-dip coated and electrolytically coated steel sheets. Both coating variants have been established in vehicle construction for decades and have their advantages.

Beschichtete Stahlbleche werden im Fahrzeugbau zu Bauteilen umgeformt, welche in der Regel nach der Formgebung einem Lackierungsprozess zugeführt werden, häufig einer kathodischen Tauchlackierung (KTL), welcher nach der Tauchlackierung eine Wärmebehandlung zwischen 160 und 180°C für ca. 20 min zum Einbrennen des Lacks nachgeschaltet ist. Bei lackierten Bauteilen, welche aus elektrolytisch beschichteten Stahlblechen geformt worden sind, sind Lackirritationen festgestellt worden, welche vermutlich durch Ausgasung als Folge der Temperatureinwirkung im Lackierungsprozess entstanden sind und dadurch aufgrund der Oberflächenfehler und dem qualitativ nicht akzeptablen Erscheinungsbild zum Ausschuss oder zu kostenintensiven Nachbearbeitungen der betroffenen Bauteile führen würden. Daher besteht Optimierungsbedarf hinsichtlich der elektrolytisch beschichteten Stahlbleche.Coated steel sheets are formed into components in vehicle construction, which are usually fed to a painting process after shaping, often cathodic dip painting (KTL), which after dip painting requires heat treatment between 160 and 180°C for approx. 20 minutes to bake the paint is downstream. Painted components formed from electrolytically coated sheet steel have been found to have scratches on the paintwork, which are presumably caused by outgassing as a result of the temperature effect in the painting process and, as a result, the surface defects and the qualitatively unacceptable appearance mean that the affected components have to be scrapped or costly to rework would lead. There is therefore a need for optimization with regard to the electrolytically coated steel sheets.

Zusammenfassung der Erfindung (Summary of Invention)Summary of Invention

Der Erfindung liegt somit die Aufgabe zu Grunde, ein Verfahren zur Herstellung eines elektrolytisch beschichteten Stahlblechs bereitzustellen, mit welchem die vorgenannten Nachteile im Wesentlichen vermieden oder zumindest wesentlich reduziert werden können.The invention is therefore based on the object of providing a method for producing an electrolytically coated steel sheet, with which the aforementioned disadvantages can be essentially avoided or at least significantly reduced.

Gelöst wird diese Aufgabe mit den Merkmalen des Patentanspruchs 1. Weitere vorteilhafte Ausgestaltungen sind in den Unteransprüchen aufgeführt.This problem is solved with the features of patent claim 1. Further advantageous configurations are listed in the dependent claims.

Das Verfahren zur Herstellung eines elektrolytisch beschichteten Stahlblechs, umfasst neben den Schritten: Bereitstellen eines Stahlblechs; Elektrolytisches Beschichten des Stahlblechs, zusätzlich den Schritt, dass nach dem elektrolytischen Beschichten das beschichtete Stahlblech eine Wärmebehandlung erfährt, wobei das beschichtete Stahlblech auf eine Zieltemperatur zwischen 60 °C und 400 °C erwärmt und für eine Haltezeit zwischen 0,10 s und 300 s auf Zieltemperatur gehalten wird.The method for producing an electrolytically coated steel sheet, in addition to the steps, comprises: providing a steel sheet; Electrolytic plating of the steel sheet, additionally the step that after the electrolytic plating, the plated steel sheet undergoes a heat treatment, wherein the plated steel sheet is heated to a target temperature between 60°C and 400°C and for a holding time between 0.10s and 300s target temperature is maintained.

Erfindungsgemäß ist vorgesehen, dass das elektrolytisch beschichtete Stahlblech einer Wärmebehandlung zugeführt wird, so dass durch die Wärmebehandlung, falls vorhanden, im Stahlblech befindlicher, gasförmiger Wasserstoff rekombiniert und so einen hohen Druck erzeugen kann, welcher einen Durchtritt und dadurch ein Entweichen des Gases durch die geschlossene elektrolytisch aufgebrachte Beschichtung ermöglicht. Alternativ oder zusätzlich können durch die Wärmebehandlung auch andere im Stahlblech vorhandene und eingelagerte gasförmige und/oder flüssige Bestandteile austreten respektive ausgetrieben werden. Diese gasförmigen und/oder flüssigen Bestandteile wurden während der Vorstufen der Stahlblechherstellung in den Stahl-/Grundwerkstoff bzw. dessen oberflächennahe Struktur eingelagert, z.B. während eines Beiz-/ oder Glühprozesses. Dadurch wird quasi eine Ausgasung bewirkt, die im späteren Lackierungsprozess nicht mehr zu Lackirritationen respektive Oberflächenfehler im lackierten Zustand führen kann. Die erfindungsgemäße Wärmebehandlung entspricht somit nicht der Wärmebehandlung im Lackierungsprozess.According to the invention, it is provided that the electrolytically coated steel sheet is subjected to a heat treatment, so that the heat treatment, if present, recombines gaseous hydrogen in the steel sheet and can thus generate a high pressure, which allows the gas to pass through and thus escape through the closed electrolytically applied coating allows. As an alternative or in addition, other gaseous and/or liquid components that are present and embedded in the steel sheet can also escape or be expelled as a result of the heat treatment. These gaseous and/or liquid components were incorporated into the steel/base material or its near-surface structure during the preliminary stages of sheet steel production, e.g. during a pickling or annealing process. This effectively causes outgassing, which can no longer lead to paint irritation or surface defects in the painted state in the later painting process. The heat treatment according to the invention therefore does not correspond to the heat treatment in the painting process.

Mit elektrolytischer Beschichtung ist hier vorrangig die Abscheidung eines Überzugs aus Zink (ZE) oder einer Zinklegierung, beispielsweise Zink-Nickel, gemeint, welcher optional mit einer organischen Deckschicht in Form einer Phosphatierung und/oder Chromatierung optimiert sein kann.Here, electrolytic coating primarily means the deposition of a coating of zinc (ZE) or a zinc alloy, for example zinc-nickel, which can optionally be optimized with an organic top layer in the form of phosphating and/or chromating.

Als Stahlblech ist ein warm- oder kaltgewalztes Stahlblech zu verstehen, welches im ebenen unverformten Zustand blechförmig als Stahlblechzuschnitt oder bandförmig als Stahlband bereitgestellt werden kann. Bevorzugt wird als Stahlblech ein kaltgewalztes und insbesondere rekristallisierend geglühtes Stahlband bereitgestellt. Die Dicke des Stahlblechs kann zwischen 0,3 und 4 mm betragen. Die Dicke beträgt insbesondere mindestens 0,4 mm, vorzugsweise mindestens 0,5 mm und ist insbesondere auf maximal 3,5 mm, vorzugsweise auf maximal 3 mm begrenzt. Die Dicke der elektrolytischen Beschichtung kann (pro Seite) zwischen 1,5 µm und 15 µm betragen.Steel sheet is to be understood as a hot- or cold-rolled steel sheet which, in the planar undeformed state, can be provided in sheet form as a steel sheet blank or in strip form as a steel strip. A cold-rolled and, in particular, recrystallization-annealed steel strip is preferably provided as the steel sheet. The thickness of the steel sheet can be between 0.3 and 4 mm. The thickness is in particular at least 0.4 mm, preferably at least 0.5 mm and is in particular limited to a maximum of 3.5 mm, preferably to a maximum of 3 mm. The thickness of the electrolytic coating can be between 1.5 µm and 15 µm (per side).

Das elektrolytische Beschichten von Stahlblechen, insbesondere von Stahlbändern ist Stand der Technik. Die Stahlbleche können sowohl ein- als auch beidseitig, je nach Anforderung, elektrolytisch beschichtet werden. Bevorzugt kommen zinkbasierte Beschichtungen zur Anwendung, welche einen gewissen kathodischen Korrosionsschutz des Stahlblechs sicherstellen. Derartige Beschichtungen sind in den Fachkreisen auch unter der Bezeichnung "ZE" (Zink elektrolytisch) bzw. "EG" (electrogalvanized) im englischsprachigen Raum bekannt. Die mit ZE beschichteten Stahlbleche werden in Fachkreisen auch "Stahlfeinblech" bezeichnet. Hierunter fallen alle denkbaren Zusammensetzungen von Kohlenstoffstählen, welche elektrolytisch beschichtbar sind und vorzugsweise im Fahrzeugbau eingesetzt werden. Dies können u. a. weiche Stähle zum Kaltumformen nach DIN EN 10152, z. B. DC01 bis DC07; hoch und höherfeste Stähle zum Kaltumformen nach DIN EN 10268, z. B. hochfeste IF-Stähle wie HC180Y und höher, z. B. isotrope Stähle wie HC2201 und höher, z. B. Bake-Hardening-Stähle wie HC180B und höher, z. B. mikrolegierte Stähle wie HC260LA und höher; oder Mehrphasenstähle zum Kaltumformen nach DIN 10338, zum einen kaltgewalzt, z. B. Dualphasen-Stähle wie HCT450X und höher, z. B. Restaustenit-Stähle wie HCT690T und höher, z. B. Komplexphasen-Stähle wie HCT600C und höher, oder zum anderen warmgewalzt, z. B. Ferrit-Bainit-Stähle wie HDT450F und höher, z. B. Dualphasen-Stähle wie HDT580X, z. B. Komplexphasen-Stähle wie HDT760C und/oder CP-W1000, z. B. Martensitphasen-Stähle wie HDT1180G1, betreffen, vgl. auch
https://ucpcdn.thyssenkrupp.com/ legacy/UCPthyssenkruppBAMXProcessingEurope/assets.fi les/downloads/tkmpe elektrolytisch verzinktes feinblech de 20190807.pdf. Diese Aufzählung der mögliche Stahlblech-Güten respektive der damit verbundenen Zusammensetzung der Kohlenstoffstähle soll insbesondere nicht als abschließend gelten.The electrolytic coating of steel sheets, in particular steel strips, is state of the art. The steel sheets can be electrolytically coated on one or both sides, depending on the requirements. Zinc-based coatings are preferably used, which ensure a certain degree of cathodic corrosion protection for the steel sheet. Such coatings are also known in the art under the designation "ZE" (zinc electrolytic) or "EG" (electrogalvanized) in English-speaking countries. The steel sheets coated with ZE are also called "steel sheet" in professional circles. This includes all conceivable compositions of carbon steels which can be coated electrolytically and are preferably used in vehicle construction. This can include soft steels for cold forming according to DIN EN 10152, e.g. B. DC01 to DC07; high and higher strength steels for cold forming according to DIN EN 10268, e.g. B. high-strength IF steels such as HC180Y and higher, e.g. B. isotropic steels such as HC2201 and higher, e.g. B. Bake-hardening steels such as HC180B and higher, e.g. B. micro-alloyed steels such as HC260LA and higher; or multi-phase steels for cold forming according to DIN 10338, on the one hand cold-rolled, e.g. B. Dual phase steels such as HCT450X and higher, e.g. B. retained austenite steels such as HCT690T and higher, e.g. B. complex-phase steels such as HCT600C and higher, or on the other hot-rolled, z. B. Ferrite-bainite steels such as HDT450F and higher, e.g. B. Dual-phase steels such as HDT580X, e.g. B. Complex phase steels such as HDT760C and/or CP-W1000, e.g. g. martensite phase steels such as HDT1180G1, see also
https://ucpcdn.thyssenkrupp.com/ legacy/UCPthyssenkruppBAMXProcessingEurope/assets.fi les/downloads/tkmpe electrolytically galvanized thin sheet de 20190807.pdf. This enumeration of the possible sheet steel grades and the associated composition of the carbon steels is not intended to be conclusive.

Da das elektrolytische Beschichten im Vergleich zum Schmelztauchbeschichten keinen nennenswerten thermischen Einfluss auf das Stahlblech hat, ist insbesondere die Wahl der Zieltemperatur und die Wahl der Haltedauer insbesondere auf die Zusammensetzung (Kohlenstoffstahl) des Stahlblechs anzupassen, so dass bei der Wärmebehandlung insbesondere Alterungsprozesse im Wesentlichen vermieden werden. So können entweder über "trial and error"-Versuche das für das eingesetzte Stahlblech und insbesondere unter Berücksichtigung der verfügbaren Anlagentechnik optimale einzustellende Zieltemperatur/Haltezeit verifiziert werden bzw. alternativ oder zusätzlich auch über das Fachwissen eingestellt werden.Since electrolytic coating has no significant thermal influence on the steel sheet compared to hot-dip coating, the selection of the target temperature and the selection of the holding time must be adapted to the composition (carbon steel) of the steel sheet in particular, so that aging processes in particular are essentially avoided during heat treatment . The target temperature/holding time to be set optimally for the steel sheet used and in particular taking into account the available system technology can be verified either by "trial and error" tests or alternatively or additionally can also be set using specialist knowledge.

Zieltemperatur und Haltezeit sind dabei erfindungsgemäß so zu wählen, dass eine Ausgasung/ Diffusion effektiv erfolgt, die mechanischen Eigenschaften des Stahl-/Grundwerkstoffs aber nicht verändert werden. Des Weiteren sind die Zieltemperatur und die Haltezeit insbesondere so zu wählen, dass vorzugsweise keine Legierungsbildung der Beschichtung mit dem Stahl-/Grundwerkstoff stattfinden kann.The target temperature and holding time are to be selected according to the invention in such a way that outgassing/diffusion takes place effectively, the mechanical properties of the steel/base material but not be changed. Furthermore, the target temperature and the holding time are to be selected in particular in such a way that preferably no alloying of the coating with the steel/base material can take place.

Weitere vorteilhafte Ausgestaltungen und Weiterbildungen gehen aus der nachfolgenden Beschreibung hervor. Ein oder mehrere Merkmale aus den Ansprüchen, der Beschreibung wie auch der Zeichnung können mit einem oder mehreren anderen Merkmalen daraus zu weiteren Ausgestaltungen der Erfindung verknüpft werden. Es können auch ein oder mehrere Merkmale aus den unabhängigen Ansprüchen durch ein oder mehrere andere Merkmale verknüpft werden.Further advantageous configurations and developments emerge from the following description. One or more features from the claims, the description and the drawing can be combined with one or more other features from them to further refine the invention. One or more features from the independent claims can also be linked by one or more other features.

Gemäß einer Ausgestaltung des erfindungsgemäßen Verfahrens beträgt die Zieltemperatur mindestens 80 °C, insbesondere mindestens 100 °C, vorzugsweise mindestens 130 °C, bevorzugt mindestens 150 °C und maximal 350 °C, insbesondere maximal 300 °C, vorzugsweise maximal 280 °C, bevorzugt maximal 250 °C.According to one embodiment of the method according to the invention, the target temperature is at least 80° C., in particular at least 100° C., preferably at least 130° C., preferably at least 150° C. and at most 350° C., in particular at most 300° C., preferably at most 280° C., preferably maximum 250 °C.

Gemäß einer Ausgestaltung des erfindungsgemäßen Verfahrens beträgt die Haltezeit mindestens 0,50 s, insbesondere mindestens 1,0 s, vorzugsweise mindestens 1,50 s, bevorzugt mindestens 2,0 s und maximal 200 s, insbesondere maximal 100 s, vorzugsweise maximal 50 s, bevorzugt maximal 30 s, weiter bevorzugt maximal 20 s.According to one embodiment of the method according to the invention, the holding time is at least 0.50 s, in particular at least 1.0 s, preferably at least 1.50 s, preferably at least 2.0 s and at most 200 s, in particular at most 100 s, preferably at most 50 s, preferably at most 30 s, more preferably at most 20 s.

Gemäß einer Ausgestaltung des erfindungsgemäßen Verfahrens kann die Erwärmung auf Zieltemperatur induktiv, in einem Durchlaufofen oder mittels Strahlungsquellen durchgeführt werden, je nach vorhandenem Anlagenkonzept und/oder Bauraum. Vorzugsweise wird die Erwärmung induktiv durchgeführt, beispielsweise mittels Induktoren, welche gezielt einen Wärmeimpuls setzen können bzw. entsprechend angesteuert werden können, um das beschichtete Stahlblech relativ schnell zu erwärmen. Bei einer induktiven Erwärmung können Erwärmungsraten von mindestens 20 K/s, insbesondere von mindestens 50 K/s, vorzugsweise von mindestens 80 K/s erzielt werden, wodurch insbesondere der Bauraum relativ klein gewählt werden kann, vorzugsweise wenn die Wärmebehandlung inline in Prozessrichtung betrachtet, nach dem elektrolytischen Beschichten durchgeführt wird. Aus Prozess- und Kostensicht vorteilhaft erfolgt die Wärmebehandlung bevorzugt inline als Nachbehandlung einer kontinuierlichen elektrolytischen Beschichtung von Stahlbändern.According to one embodiment of the method according to the invention, the heating to the target temperature can be carried out inductively, in a continuous furnace or by means of radiation sources, depending on the existing system concept and/or installation space. The heating is preferably carried out inductively, for example by means of inductors, which can set a heat pulse in a targeted manner or can be controlled accordingly in order to heat the coated steel sheet relatively quickly. In the case of inductive heating, heating rates of at least 20 K/s, in particular at least 50 K/s, preferably at least 80 K/s, can be achieved, as a result of which the installation space can be selected to be relatively small, preferably when the heat treatment is considered inline in the process direction, is carried out after the electrolytic plating. From a process and cost point of view, the heat treatment is preferably carried out inline as a post-treatment of a continuous electrolytic coating of steel strips.

Insbesondere das Halten auf Zieltemperatur kann beispielsweise innerhalb einer Einhausung erfolgen, durch welches das erwärmte beschichtete Stahlblech hindurchgeführt wird. Das Halten kann somit vorzugsweise in einem Durchlaufofen erfolgen.In particular, the target temperature can be maintained, for example, within an enclosure through which the heated, coated steel sheet is passed. Holding can thus preferably take place in a continuous furnace.

Gemäß einer Ausgestaltung des erfindungsgemäßen Verfahrens wird das beschichtete Stahlblech während der Erwärmung in Prozessrichtung bewegt, wobei das beschichtete Stahlblech quer zur Prozessrichtung homogen erwärmt wird. Eine quer zur Prozessrichtung betrachtete homogene Erwärmung bedeutet, dass über die (gesamte) Breite des beschichteten Stahlblechs möglichst keine und nur geringe Temperaturunterschiede/-differenzen während der Wärmebehandlung zugelassen werden, um eine im Wesentlichen "vollflächige" Ausgasung über die gesamte Fläche des beschichteten Stahlblechs sicherzustellen.According to one embodiment of the method according to the invention, the coated steel sheet is moved in the process direction during the heating, with the coated steel sheet being homogeneously heated transversely to the process direction. Homogeneous heating viewed transversely to the process direction means that over the (entire) width of the coated steel sheet, if possible, no and only small temperature differences/differences are permitted during the heat treatment in order to ensure essentially "full-surface" outgassing over the entire surface of the coated steel sheet .

Gemäß einer Ausgestaltung des erfindungsgemäßen Verfahrens wird das beschichtete Stahlblech nach der Haltezeit aktiv abgekühlt. Unter "aktiver" Abkühlung ist zu verstehen, dass das noch warme beschichtete Stahlblech mit geeigneten Mitteln, beispielsweise mit bekannten und gängigen Mitteln, die eine Abkühlung bewirken können, gezielt abgekühlt wird, beispielsweise mit einer Abkühlrate von mindestens 5 K/s, insbesondere von mindestens 10 K/s, vorzugsweise von mindestens 20 K/s. Wird das Stahlblech beispielsweise inline nach dem elektrolytischen Beschichten wärmebehandelt, kann es sein, dass das Stahlblech auf eine Temperatur von maximal 120 °C, insbesondere von maximal 100 °C abgekühlt werden sollte, um weitere Komponenten in der Prozesskette, welche in Kontakt mit dem noch warmen Stahlblech stehen, thermisch nicht zu belasten.According to one embodiment of the method according to the invention, the coated steel sheet is actively cooled after the holding time. "Active" cooling means that the still warm coated steel sheet is cooled in a targeted manner with suitable means, for example with known and common means that can bring about cooling, for example with a cooling rate of at least 5 K/s, in particular of at least 10 K/s, preferably at least 20 K/s. For example, if the steel sheet is heat-treated inline after the electrolytic coating, it may be that the steel sheet should be cooled to a maximum temperature of 120 °C, in particular a maximum of 100 °C, in order to avoid other components in the process chain that are in contact with the still warm sheet steel, not to be thermally stressed.

Beschreibung der bevorzugten Ausführungsformen (Best Mode for Carrying out the Invention)Description of the preferred embodiments (Best Mode for Carrying out the Invention)

Die einzige Figur 1 stellt eine mögliche Ausführung der Erfindung schematisch dar. Ein Stahlblech (1) ist in Form eines Stahlbands bereitgestellt worden, welches in entgegengesetzter Richtung des Prozesses konventionell elektrolytisch beschichtet respektive elektrolytisch verzinkt worden ist, nicht dargestellt, und in Prozessrichtung (P) einer Wärmebehandlung (10) zugeführt wird. Optional kann das elektrolytische beschichtete Stahlblech (1) vor oder nach der erfindungsgemäßen Wärmebehandlung weiterhin phosphatiert und/oder chromatiert werden. Eine Phosphatierung und/oder Chromatierung zur Steigerung der Lackhaftung und/oder des Korrosionswiderstands ist für die erfindungsgemäße Durchführung der Wärmebehandlung nicht von Relevanz und ist daher hier nicht weiter ausgeführt. Das beschichtete Stahlblech (1) erfährt nach dem elektrolytischen Beschichten eine Wärmebehandlung (10), in diesem Beispiel inline in Prozessrichtung (P) nach dem elektrolytischen Beschichten. Das beschichtete Stahlblech (1) wird auf eine Zieltemperatur (Tz) zwischen 60 °C und 400 °C erwärmt und für eine Haltezeit (tH) zwischen 0,10 s und 300 s auf Zieltemperatur (Tz) gehalten. Vorzugsweise erfolgt die Erwärmung (11) auf Zieltemperatur (Tz) induktiv, da gezielt und schnell das in Prozessrichtung (P) bewegte und beschichtete Stahlblech (1) insbesondere über eine Anordnung eines nicht dargestellten Induktors oberhalb und/oder unterhalb des beschichteten Stahlblechs (1) auch eine quer zur Prozessrichtung (P) und somit über die (gesamte) Breite des Stahlblechs (1) homogene Erwärmung (11) sichergestellt werden kann. Alternativ können auch ein Durchlaufofen oder eine Strahlungsquelle, nicht dargestellt, für die Erwärmung (11) berücksichtigt werden. Nachdem das auf Zieltemperatur (Tz) erwärmte und für eine Haltezeit (tH) auf Zieltemperatur (Tz) gehaltene beschichtete Stahlband (1) eine Haltezone (12) in Prozessrichtung (P) durchlaufen hat, welche beispielsweise als Durchlaufofen (12) ausgebildet sein kann, kann eine aktive Abkühlung (13) erfolgen, so dass das noch warme beschichtete Stahlblech (1) keine negativen thermischen Einflüsse auf die nachfolgenden Komponenten inline in der Prozesskette haben kann. Durch eine aktive Abkühlung (13) kann die Temperatur des die Wärmebehandlung (10) durchlaufenen beschichteten Stahlblechs (1) beispielweise auf maximal 120°C gesenkt werden. Das beschichtete Stahlblech (1) kann nach der erfindungsgemäßen Wärmebehandlung (10) weiteren Bearbeitungsschritten zugeführt werden. Des Weiteren zeigt die Figur 1 einen skizzierten Temperaturverlauf eines erfindungsgemäß wärmebehandelten elektrolytisch beschichteten Stahlblechs (1) in einem Zeit(t)-Temperatur(T)-Diagramm. Der Temperaturverlauf kann individuell und in Abhängigkeit von der Zusammensetzung des Stahlblechs wie auch des vorhandenen Anlagenkonzepts vorgeben respektive definiert sein. Auch kann die Wärmebehandlung offline erfolgen.The only figure 1 shows a possible embodiment of the invention schematically. A steel sheet (1) has been provided in the form of a steel strip, which has been conventionally electrolytically coated or electrolytically galvanized in the opposite direction of the process, not shown, and in the process direction (P) a heat treatment (10th ) is supplied. Optionally, the electrolytic coated steel sheet (1) may be further phosphated and/or chromated before or after the heat treatment of the present invention. A phosphating and/or chromating to increase the paint adhesion and/or the corrosion resistance is not relevant for the implementation of the heat treatment according to the invention and is therefore not discussed further here. The coated steel sheet (1) undergoes a heat treatment (10) after the electrolytic coating Example inline in process direction (P) after electrolytic coating. The coated steel sheet (1) is heated to a target temperature (T z ) of between 60° C. and 400° C. and held at the target temperature (Tz) for a holding time (tH) of between 0.10 s and 300 s. The heating (11) to the target temperature (Tz) is preferably carried out inductively, since the coated steel sheet (1) moved and coated in the process direction (P) is targeted and rapid, in particular by arranging an inductor (not shown) above and/or below the coated steel sheet (1). a homogeneous heating (11) transverse to the process direction (P) and thus over the (entire) width of the steel sheet (1) can also be ensured. Alternatively, a continuous furnace or a radiation source, not shown, can also be considered for the heating (11). After the coated steel strip (1), which has been heated to the target temperature (Tz) and held at the target temperature (Tz) for a holding time (tH), has passed through a holding zone (12) in the process direction (P), which can be designed as a continuous furnace (12), for example, active cooling (13) can take place so that the still warm coated steel sheet (1) cannot have any negative thermal influences on the downstream components inline in the process chain. Active cooling (13) allows the temperature of the coated steel sheet (1) undergoing the heat treatment (10) to be reduced to a maximum of 120° C., for example. After the heat treatment (10) according to the invention, the coated steel sheet (1) can be subjected to further processing steps. Furthermore, the figure 1 a sketched temperature profile of an electrolytically coated steel sheet (1) heat-treated according to the invention in a time (t)-temperature (T) diagram. The temperature profile can be specified or defined individually and depending on the composition of the steel sheet as well as the existing system concept. The heat treatment can also take place offline.

In Abhängigkeit der Prozessbedingungen der elektrolytischen Beschichtung kann die abgeschiedene Beschichtung eine eher säulenförmige oder plattenförmige Kristallstruktur aufweisen. Das erfindungsgemäße Verfahren zeigt sich in Versuchen unabhängig von der Morphologie der Beschichtung. Auch bei einer plattenförmigen Kristallstruktur mit der damit verbundenen geringeren Porosität, welche eine Ausgasung insbesondere nicht begünstigt, kann bei der erfindungsgemäßen Ausführung der Wärmebehandlung die Aufgabenstellung an die Erfindung dennoch erfüllt werden.Depending on the process conditions of the electrolytic coating, the deposited coating may have a more columnar or plate-like crystal structure. The method according to the invention is shown in tests to be independent of the morphology of the coating. Even in the case of a plate-shaped crystal structure with the associated lower porosity, which in particular does not favor outgassing, the task of the invention can still be achieved when the heat treatment is carried out according to the invention.

An elektrolytisch verzinkten Stahlfeinblechen (1) wurden Untersuchungen durchgeführt. Um einen Vergleich durchführen zu können, wurden als Stahlfeinblech (1) zwei Stahlbänder bereitgestellt, jeweils ein identischer kaltgewalzter Bake-Hardening-Stahl mit einer Dicke von 0,8 mm, welche jeweils mit gleichen Parametern elektrolytisch beidseitig mit einer Dicke von 5 µm pro Seite verzinkt wurden. Das erste Stahlfeinblech wurde als Referenz konventionell weiterprozessiert. Das zweite Stahlfeinblech (1) wurde inline, analog zur skizzierten Figur 1, nach dem elektrolytischen Beschichten einer Wärmebehandlung (10) zugeführt. Das Erwärmen (11) erfolgte beidseitig über jeweils einen über die Breite oberhalb und unterhalb des Stahlfeinblechs (1) angeordneten Induktor, welcher jeweils das zweite Stahlfeinblech (1) mit einer Erwärmungsrate von 200 K/s beaufschlagte und auf eine Zieltemperatur (Tz) von 220 °C erwärmt hatte. Die Haltezeit (tH) betrug 4,50 s bei 220 °C und das Halten erfolgte in einem Durchlaufofen (12), um die Zieltemperatur (Tz) von 220 °C aufrecht zu halten. In Prozessrichtung (P) der Haltezone (12) nachgelagert wurde das warme beschichtete Stahlfeinblech (1) aktiv abgekühlt, wobei eine Wasserbrause (13) zum Einsatz kam und das warme beschichtete Stahlfeinblech (1) auf 70 °C mit einer Abkühlrate von 120 K/s abkühlte, so dass es weiterprozessiert werden konnte, ohne die weiteren Komponenten in der Prozesskette thermisch negativ zu beeinflussen.Tests were carried out on electrolytically galvanized steel sheets (1). In order to be able to carry out a comparison, two steel strips were provided as steel sheet (1), each an identical cold-rolled bake-hardening steel with a thickness of 0.8 mm, which were electrolytically galvanized on both sides with the same parameters with a thickness of 5 µm per side. The first steel sheet was further processed conventionally as a reference. The second steel sheet (1) was inline, analogous to the outlined figure 1 , fed after the electrolytic coating of a heat treatment (10). The heating (11) took place on both sides via an inductor arranged across the width above and below the steel sheet (1), which in each case applied the second steel sheet (1) at a heating rate of 200 K/s and to a target temperature (Tz) of 220 °C warmed up. The holding time (tH) was 4.50 s at 220°C and the holding was done in a continuous furnace (12) to maintain the target temperature (T z ) of 220°C. Downstream of the holding zone (12) in the process direction (P), the hot coated steel sheet (1) was actively cooled using a water spray (13) and the hot coated steel sheet (1) was cooled to 70 °C at a cooling rate of 120 K/ s cooled down so that it could be further processed without thermally negatively influencing the other components in the process chain.

Aus den beiden prozessierten Stahlfeinblechen (1) wurde mehrere Proben entnommen, welche im Labormaßstab bei gleichen Parametern unverformt einer Standard-Phosphatierung und einem Standard-KTL-Prozess zugeführt wurde, mit einer nach dem Tauchbad nachgelagerten Einbrennbehandlung von 20 min bei 170 °C. An den Oberflächen der Proben wurden jeweils auf einer Testfläche von 600 cm2 digital Fehlstellen qualifiziert und quantifiziert, so dass alle Proben, welche aus dem zweiten Stahlfeinblech (1) entnommen worden sind und die erfindungsgemäße Wärmebehandlung (10) erfahren hatten, überraschend weniger qualitative und quantitative Oberflächenfehler aufzeigten als die Proben, welche der Referenz entnommen worden sind.Several samples were taken from the two processed steel sheets (1), which were supplied undeformed to a standard phosphating and a standard KTL process on a laboratory scale with the same parameters, with a subsequent baking treatment of 20 minutes at 170 °C after the immersion bath. On the surfaces of the samples, flaws were digitally qualified and quantified on a test area of 600 cm 2 so that all samples that were taken from the second steel sheet (1) and had undergone the heat treatment (10) according to the invention were surprisingly less qualitative and quantitative surface defects than the samples taken from the reference.

Die Anzahl der Störungen bedingt durch die Ausgasung im KTL-Prozess in den Referenz-Proben bezogen auf 600 cm2 wurde bei allen Proben wie folgt ermittelt: über 5000 Löcher und über 100 Pusteln. Das Fehlerbild bei den Proben aus dem zweiten Stahlfeinblech (1) bezogen auf 600 cm2 wurde bei allen Proben wie folgt ermittelt: unter 50 Löcher und unter 15 Pusteln.The number of faults caused by outgassing in the KTL process in the reference samples based on 600 cm 2 was determined as follows for all samples: over 5000 holes and over 100 pustules. The defect pattern in the samples from the second steel sheet (1) based on 600 cm 2 was determined as follows for all samples: under 50 holes and under 15 pustules.

Das Ergebnis war somit eindeutig, dass die erfindungsgemäße Wärmebehandlung (10) von elektrolytisch beschichtetem Stahlblech (1) zu weniger Oberflächenfehlern während des Lackierungsprozess führt, so dass den Anforderungen an die Qualität von elektrolytisch beschichten und lackierten Stahlblechen (1) entsprochen und insbesondere verbessert werden kann.The result was thus clear that the inventive heat treatment (10) of electrolytically coated steel sheet (1) leads to fewer surface defects during the painting process, so that the quality requirements of electrolytically coated and painted steel sheets (1) can be met and, in particular, improved .

Die beschriebenen Merkmale sind alle, soweit technisch möglich, miteinander kombinierbar. Die Erfindung muss nicht inline an einem Stahlband durchgeführt werden, sondern es kann auch an blechförmigen Stahlblechzuschnitten durchgeführt werden, bevor diese weiterprozessiert werden. Es hat sich auch im Rahmen der Erfindung gezeigt, dass die Wärmebehandlung nicht zwangsläufig eine Ausgasung/Effusion des gesamten Stahl-/Grundwerkstoffs umfassen muss. Es ist hingegen ausreichend, die gasförmigen und/oder flüssigen Bestandteile in einem oberflächennahen Bereich beispielsweise bis zu 20 µm des Stahl-/Grundwerkstoffs auszutreiben, in welchem sich typischerweise auch die Einlagerungen aus den Vorstufen der Stahlblecherzeugung befinden, um den Anforderungen zu genügen.The features described can all be combined with one another as far as technically possible. The invention does not have to be carried out inline on a steel strip, but rather it can also be carried out on sheet-like steel sheet blanks before these are further processed. It has also been shown within the scope of the invention that the heat treatment does not necessarily have to include outgassing/effusion of the entire steel/base material. On the other hand, it is sufficient to expel the gaseous and/or liquid components in a near-surface area, for example up to 20 μm, of the steel/base material, which typically also contains the inclusions from the preliminary stages of sheet steel production, in order to meet the requirements.

Claims (10)

Verfahren zur Herstellung eines elektrolytisch beschichteten Stahlblechs (1), wobei das Verfahren folgende Schritte umfasst: - Bereitstellen eines Stahlblechs; - Elektrolytisches Beschichten des Stahlblechs (1); dadurch gekennzeichnet, dass nach dem elektrolytischen Beschichten das beschichtete Stahlblech (1) eine Wärmebehandlung (10) erfährt, wobei das beschichtete Stahlblech (1) auf eine Zieltemperatur (Tz) zwischen 60 °C und 400 °C erwärmt und für eine Haltezeit (tH) zwischen 0,10 s und 300 s auf Zieltemperatur (Tz) gehalten wird.A method of manufacturing an electrolytically coated steel sheet (1), the method comprising the steps of: - Providing a steel sheet; - Electrolytic coating of the steel sheet (1); characterized in that after the electrolytic coating, the coated steel sheet (1) undergoes a heat treatment (10), the coated steel sheet (1) being heated to a target temperature (T z ) of between 60 °C and 400 °C and for a holding time (tH ) is kept at the target temperature (Tz) between 0.10 s and 300 s. Verfahren nach Anspruch 1, wobei die Zieltemperatur (Tz) zwischen 80 °C und 350 °C beträgtA method according to claim 1, wherein the target temperature (T z ) is between 80°C and 350°C Verfahren nach Anspruch 2, wobei die Zieltemperatur (Tz) zwischen 100 °C und 300 °C beträgt.A method according to claim 2, wherein the target temperature (T z ) is between 100°C and 300°C. Verfahren nach Anspruch 3, wobei die Zieltemperatur (Tz) zwischen 130 °C und 280 °C beträgt.A method according to claim 3, wherein the target temperature (T z ) is between 130°C and 280°C. Verfahren nach einem der vorgenannten Ansprüche, wobei die Haltezeit (tH) zwischen 0,50 s und 200 s beträgt.Method according to one of the preceding claims, in which the holding time (tH) is between 0.50 s and 200 s. Verfahren nach Anspruch 5, wobei die Haltezeit (tH) zwischen 1,0 s und 100 s beträgt.Method according to claim 5, wherein the holding time (tH) is between 1.0 s and 100 s. Verfahren nach Anspruch 6, wobei die Haltezeit (tH) zwischen 1,50 s und 50 s beträgt.Method according to Claim 6, in which the holding time (tH) is between 1.50 s and 50 s. Verfahren nach einem der vorgenannten Ansprüche, wobei die Erwärmung (11) auf Zieltemperatur (Tz) induktiv, in einem Durchlaufofen oder mittels Strahlungsquellen durchgeführt wird.Method according to one of the preceding claims, in which the heating (11) to the target temperature (Tz) is carried out inductively, in a continuous furnace or by means of radiation sources. Verfahren nach einem der vorgenannten Ansprüche, wobei das beschichteten Stahlblech (1) während der Erwärmung (11) in eine Prozessrichtung (P) bewegt wird, wobei das beschichtete Stahlblech (1) quer zur Prozessrichtung (P) homogen erwärmt wird.Method according to one of the preceding claims, wherein the coated steel sheet (1) is moved in a process direction (P) during the heating (11), the coated steel sheet (1) being heated homogeneously transversely to the process direction (P). Verfahren nach einem der vorgenannten Ansprüche, wobei das beschichtete Stahlblech (1) nach der Haltezeit (tH) aktiv abgekühlt wird.Method according to one of the preceding claims, in which the coated steel sheet (1) is actively cooled after the holding time (tH).
EP22150305.5A 2021-01-13 2022-01-05 Method of manufacturing an electrolytically coated steel sheet Pending EP4029973A3 (en)

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