EP3827103A1

EP3827103A1 - Method for producing a hardened steel product

Info

Publication number: EP3827103A1
Application number: EP19749593.0A
Authority: EP
Inventors: Stefan Pohl; Elisabeth Danger; Thorsten LABUDDE; Jürgen Butzkamm
Original assignee: Muhr und Bender KG
Current assignee: Muhr und Bender KG
Priority date: 2018-07-25
Filing date: 2019-07-10
Publication date: 2021-06-02
Also published as: CN112567054A; WO2020020644A1; US20210301364A1; DE102018118015A1

Abstract

The invention relates to a method for producing a hardened steel product, comprising the steps: providing a steel substrate (2) made of a hardenable steel; coating the steel substrate (2) with an aluminum pre-coating (4), the pre-coating (4) being applied to the steel substrate (2) with a thickness (d1) of at least 34 μm; flexibly rolling the pre-coated steel substrate (2) in order to produce a variable thickness over the length of the pre-coated steel substrate (2), the pre-coating being rolled out to a reduced first thickness (d2a) of less than 33 μm in thinner first portions and to a reduced second thickness (d2b), which is thicker than the reduced first thickness (d2a), in thicker second portions; creating a blank (22) from the flexibly rolled steel substrate (2); heating the blank (22) to the austenitization temperature, diffusion processes between the base material and the pre-coating (4) occurring; and hot-forming (S4) the heated blank (22), the heated blank (22) being formed and being quickly cooled in such a way that a hardened steel product (42) having a coating is produced.

Description

Process for producing a hardened steel product

description

The invention relates to a method for producing coated hardened steel products, in particular for use as a structural component of a motor vehicle.

It is known to coat metallic components for corrosion protection and to form them into molded parts by means of hot forming. In practice, aluminum-silicon-coated high-strength and ultra-high-strength tempering steels are used in practice for safety-relevant body components of motor vehicles, in particular manganese-boron-containing tempering steels such as 22MnB5 or 34MnB5.

For example, WO 2009/090555 A1 discloses a method for producing a hot-stamped coated steel section, comprising the steps of: pre-coating a steel strip with aluminum or aluminum alloy by hot dipping, the thickness of the precoating having 20 to 33 micrometers on each side, cutting the precoated steel strip into a steel section, heating the steel section in an oven, transferring the heated steel section into a press tool, hot stamping the steel section in the press tool, and cooling the steel section.

DE 10 2007 019 196 A1 discloses a method for producing flexibly rolled strip material with a cathodic corrosion protection layer. The strip material is coated at a higher strip temperature in a zinc pot (hot dipped galvanized steel). The zinc coating is in the same ratio rolled, like the actual strip thickness, whereby a final coating thickness after flexible rolling of greater than or equal to 7.5 micrometers is aimed for.

A method for producing a sheet metal component is known from WO 2008/1 13426 A2, a hot or cold strip being hot-dip coated or electrolytically coated and then subjected to a flexible rolling process. With the flexible rolling process, different sheet pressures produce different sheet thicknesses of the flexibly rolled steel strip. Coated to the sheet thickness after flexible rolling, the coating is formed to be of different thicknesses during coating, the coating thickness being increased depending on the rolling pressure with increasing rolling pressure to be expected.

WO 2006 097 237 A1 discloses a method and a system for hot-dip coating hot-rolled steel strip. The steel strip passes through a pickling station, a rinsing station, a drying station, a heating furnace and then a melting bath. The finished thickness and the thickness tolerance of the hot-dip coated steel strip are achieved by controlled thickness reduction in a roll stand in the process line by checking the finished thickness in the outlet of the roll stand using a thickness measuring device and tracing deviations from the target thickness as a control signal to the position of the roll stand becomes.

WO 2016/198186 A1 discloses a method for hot forming a steel structure. The steel component is provided with a corrosion-resistant scale protection layer and before hot forming there is a surface oxidation in which a corrosion-resistant oxidation layer is formed on the scale protection layer.

The present invention is based on the object of proposing a method for producing a coated and hardened component, in particular as a structural component for a motor vehicle, which has good corrosion protection resistance in areas with different thicknesses.

The object is achieved by means of a method for producing a hardened steel product with the steps: providing a steel substrate with a Base material made of hardenable steel; Coating the steel substrate with a pre-coating containing aluminum to produce a pre-coated steel substrate, the coating of the pre-coated steel substrate having a thickness (d1) of at least 34 micrometers (gm); Flexible rolling of the pre-coated steel substrate in such a way that successive sections of the pre-coated steel substrate are rolled out to different degrees to produce a variable thickness over the length of the pre-coated steel substrate, the pre-coating after the flexible rolling in thinner first sections being a reduced first Thickness (d2a) of less than 33 micrometers and in thicker second sections a reduced second thickness (d2b) which is thicker than the reduced first thickness (d2a); Working out a board from the flexibly rolled strip material; Heating the circuit board in such a way that the base material of the circuit board is at least partially austenitized, with the diffusion processes taking place between the base material and the precoating due to the heating; Hot forming of the heated blank, the heated blank being deformed and cooled so quickly that a hardened steel product with a coating is produced.

One advantage is that the substrate has a sufficiently thick coating even after flexible rolling. It has been shown that the coating increases during heating for the subsequent hot forming due to the diffusion processes, so that the final thickness of the coating after the hot forming is greater than the respective coating thickness after the flexible rolling and before the heating for the hot forming. Due to the fact that the precoating has a thickness of at least 34 micrometers, the coating is sufficiently thick to provide good protection against corrosion, even in the thinner first sections, due to the subsequent heating for hot forming, despite the reduction in thickness that results from flexible rolling to reach. In the thicker sections of the finished component, which generally have to withstand higher loads, the coating is also correspondingly thicker, so that these sections are particularly well protected. All in all, this results in a load-optimized or weight-reduced component with excellent coating protection in all thickness areas. The steel substrate can be, for example, a hardenable or temperable, in particular manganese-containing, steel material. In addition to manganese, this can contain further microalloying elements. The steel material can contain, for example, the following proportions of alloy elements in percent by weight:

Carbon (C) with at least 0.15% and at most 0.5%, in particular at most 0.4%;

Manganese (Mn) with at least 0.5% and at most 5.0%, in particular at least 0.8% and at most 2.5%;

Aluminum (AI) with a maximum of 0.1%;

Silicon (Si) with at least 0.1% and at most 0.9%, in particular at most 0.5%;

Chromium (Cr) with at least 0.01% and at most 1.0%;

Tital (Ti) with at most 0.02%, in particular at most 0.01%;

Boron (B) with at least 0.0005 and at most 0.080%, in particular at least 0.002% and at most 0.006%;

Phosphorus (P) with at most 0.1%, in particular at most 0.01%;

Sulfur (S) with at most 0.05%, in particular at most 0.01;

optionally further alloying elements with a share of up to 1.55% (1550 ppm); the rest iron (Fe) and unavoidable impurities.

As an optional additional alloying element, the substrate can in each case in percent by weight in particular at least one of:

Copper (Cu) with at most 0.1%;

Nickel (Ni) with at most 0.1%;

Niobium (Nb) with a maximum of 0.1%;

Molybdenum (Mo) with at most 1.0%;

Vanadium (V) with a maximum of 0.25%;

include without being limited to this. The mass fraction of the optional alloying elements can also be lower, for example molybdenum can also be present at a maximum of 0.8%, 0.5% or 0.25%. The mass fraction of the optional alloy elements is a maximum of 1.55%, in particular a maximum of 1.0%, in particular a maximum of 0.8%. The alloy element niobium advantageously brings about a fine-grained structure of a component that is hot-formed from the alloy. In particular, in cooperation with molybdenum, which can inhibit grain growth, a particularly fine-grained structure results, which in turn has a favorable effect on the strength of the component produced therefrom.

Examples of usable steel materials containing boron manganese are 17MnB5, 20MnB5, 20MnB8, 22MnB5, 26MnB5 or 34MnB5. The starting material (strip material) can have a tensile strength of, for example, at least 450 MPa. A molded part produced from the coated steel substrate can have a final tensile strength of, for example, at least 1 100 MPa, in particular at least 1500 MPa. It is also possible for certain sub-areas of the molded part, where necessary, to be set to a lower tensile strength of less than 1,100 MPa and therefore higher ductility. The steel substrate can have an initial thickness of, for example, between 1.0 and 4.0 mm.

The coating preferably contains at least 85% by weight of aluminum, which also includes the possibility of using a pure aluminum coating (100% by weight of Al), as well as the use of an alloy which, as the main alloy component, contains aluminum with at least 85% by weight and optionally further Contains alloy components, for example silicon with, for example, between 5 and 15 percent by weight and / or iron with up to 5 percent by weight and / or one or more other alloying elements in smaller proportions. The proportion of the other alloying elements, for example at least one from the group of Mn, Cr, Ti, B, P, S, Cu, Ni, Nb, Mo, V, can together be, for example, up to 1.5% by weight. In the context of the present disclosure, the term aluminum coating or aluminum-based coating is generally used on the basis of the main constituent aluminum, with which the abovementioned possibilities of other alloy compositions are to be conceptually included. The aluminum coating can, for example, be applied to the steel substrate in a hot-dip process in a melt bath with at least 85 percent by weight of aluminum and, if appropriate, other alloy components or other customary coating processes. An exemplary composition of the molten bath or the applied coating can contain up to 3% by weight of iron, 9 to 12% by weight of silicon, optionally one or more contain further alloy elements with up to 1.5 percent by weight, and the rest of aluminum. It is understood that inevitable impurities may also be included. According to a preferred embodiment, the precoating is applied to the steel substrate with a thickness (d1) of at least 36 micrometers, in particular at least 40 micrometers. The steel substrate pre-coated in this way forms the basis for a hardened component with variable thicknesses to be produced therefrom. The coating of the steel substrate can be applied, for example, by means of hot-dip coating, the steel substrate being immersed in a basin with melted coating material. It is understood that other known coating methods can also be used.

The pre-coated steel substrate is rolled flexibly after the pre-coating, it being understood that further steps, such as heating, for unwinding, unwinding, straightening, cleaning or the like can be interposed. Optionally, it can be provided in particular that the steel substrate is heated in the coating system after the application of the precoating in order to achieve pre-diffusion between the precoating and the steel substrate. The pre-diffusion heating is carried out at temperatures below the melting temperature of the coating material, for example in a temperature window between 0.5 times and 0.9 times the melting temperature of the coating material. As a result of the pre-diffusion, a thicker interdiffusion zone is formed between the base material of the steel substrate and the coating material during the coating process. This makes it possible to carry out the heating more quickly in the course of hot forming, which has an overall favorable effect on the cycle times during hot forming.

In flexible rolling, strip material with a substantially uniform sheet thickness is rolled out by changing the roll gap during the process to form strip material with a variable sheet thickness over the length. The sections of different thicknesses produced by the flexible rolling extend transversely to the longitudinal direction or direction of rolling of the strip material. After the flexible rolling, the strip material can be easily rewound into the coil and fed to further processing at another location, or it can be processed directly, for example by cutting the strip material to individual sheet metal elements.

Flexible rolling can be carried out with rolling degrees of at least 1% and / or a maximum of 60% based on the initial thickness (d1) of the precoated steel substrate, in particular with rolling degrees between 3% and 55%. Due to the flexible rolling, the thickness of the pre-coating is reduced accordingly with the steel substrate. The precoating after the flexible rolling in thinner first sections can in particular have a reduced first thickness (d2a) of less than 20 micrometers. Alternatively or in addition, the flexible rolling is carried out in such a way that the precoating after the flexible rolling in thicker second sections has a reduced second thickness (d2b) of more than 33 micrometers, in particular of more than 36 micrometers. It goes without saying that between the thinnest sections and the thickest sections of the strip material, depending on the desired component geometry, there may be any other thickness ranges or transition regions in between.

In a process step downstream of the flexible rolling, blanks are produced from the flexibly rolled strip material. This process step is also called separating. The separation can be carried out by mechanical cutting or by laser cutting. In the context of the present disclosure, the term circuit boards is intended to include both rectangular metal sheets that have been cut out of the strip material and shape cuts. Shape cuts are sheet metal elements made from the strip material, the outer contour of which is already adapted to the shape of the end product. The sheet metal blanks are hot-formed after the separation, it being possible for further process steps to be interposed if necessary. For hot forming, the blank is at least in part at the austenitizing temperature heated; then placed in a thermoforming tool and formed in the thermoforming tool and cooled quickly, so that a hardened molded part is produced. The heating is carried out in a suitable heating device, for example in a continuous furnace. Heating to austenitizing temperature means a temperature range in which at least partial austenitizing takes place or is present, that is, a microstructure in the two-phase region of ferrite and austenite. For this, the board is heated to a temperature above Ac1, that is, the temperature at which austenite begins to form. For example, the board can be heated to a temperature of over 880 ° C and / or up to 960 ° C. According to a possible embodiment, the circuit board is heated at least up to a temperature of 700 ° C. with a heating rate of more than 12 K / sec. The manufacturing time is reduced by rapid heating. After heating to the austenitizing temperature and inserting it into the thermoforming tool, the board is formed and quickly cooled. The rapid cooling of the molded part in the forming tool creates a hardened, at least partially martensitic structure in the component. This process of hot forming and rapid cooling in a forming tool is also known as press hardening.

As a result of the heating and hot forming, the pre-coating and the underlying steel substrate form the coating, which increases due to diffusion processes compared to the thickness of the pre-coating. The first final thickness (d3a) is preferably formed in the thinner first sections of the finished component with more than 15 micrometers, in particular more than 20 micrometers, and less than 50 micrometers, in particular less than 40 micrometers. Alternatively or in addition, the coating after the hot forming in the thicker second sections can have a second final thickness (d3b) of less than 60 micrometers, in particular less than 50 micrometers and / or more than 30 micrometers, in particular more than 35 micrometers exhibit. It has surprisingly been found that the coating grows more strongly in the thinner areas in the course of hot forming than in thicker areas. In particular, the coating with a final thickness ratio (d3a / d3b) of the first Final thickness (d3a) to the second final thickness (d3b) is formed, which is greater than an intermediate thickness ratio (d2a / d2b) of the reduced first thickness (d2a) to the reduced second thickness (d2b). In this way, the different coating thicknesses in general adapt advantageously to one another, so that overall good protection against corrosion is achieved in all sections of the component.

According to a first possibility, the hot forming can be carried out as an indirect process, which comprises the sub-steps cold preforming, subsequent heating of the cold preformed component to austenitizing temperature and subsequent hot forming to produce the final contour of the product. According to a second option, hot forming can also be carried out as a direct process, which is characterized in that the component is heated directly to the austenitizing temperature and then hot formed to the desired final contour in one step. A previous (cold) preforming does not take place here.

According to a possible embodiment, the coating can be produced in the forming tool in such a way that a metal oxide layer is formed on the surface. A metal oxide layer is corrosion-resistant and inert, so tool wear during forming is reduced. If a metal oxide layer is formed on the coating surface, the present disclosure for the state after hot forming at given layer thicknesses relates to the total coating thickness, that is to say including the oxide layer. Preferred exemplary embodiments are explained below with reference to the drawing figures. Here shows

Figure 1 shows schematically an inventive method for producing a coated, hardened molded part;

2A shows a detail of the coated steel substrate after the precoating in an enlarged schematic representation; FIG. 2B shows a detail of the coated steel substrate after the flexible rolling in an enlarged schematic illustration; and

Figure 2C shows a detail of the coated and flexibly rolled steel substrate after hot forming in an enlarged schematic representation.

Figures 1 and 2A to 2C are described below together.

FIG. 1 shows a method according to the invention for securing a hardened product from a coated steel substrate 2. The steel substrate is also referred to in strip form as a steel strip or generally as a strip material. When isolated, the steel substrate is also referred to as a circuit board.

Within the scope of the present disclosure, the steel substrate 2 includes a hardenable flat steel product which, for example, can each contain the following proportions of alloy elements in percent by weight:

Carbon (C) with at least 0.15% and at most 0.5%, in particular at most 0.4%;

Aluminum (AI) with a maximum of 0.1%;

Silicon (Si) with at least 0.1% and at most 0.9%, in particular at most 0.5%;

Chromium (Cr) with at least 0.01% and at most 1.0%;

Tital (Ti) with at most 0.02%, in particular at most 0.01%;

Phosphorus (P) with at most 0.1%, in particular at most 0.01%;

Sulfur (S) with at most 0.05%, in particular at most 0.01%;

optionally further alloying elements with a share of up to 1.55% (1550 ppm); the rest iron (Fe) and unavoidable impurities. This alloy composition includes, for example, boron-manganese-containing steel materials such as 17MnB5, 20MnB5, 20MnB8, 22MnB5, 26MnB5 and 34MnB5. In the initial state, the steel material can have a yield strength of, for example, 150 to 1100 MPa and / or a tensile strength of at least 450 MPa. The optional further alloy elements can be selected from the group: copper (Cu) with at most 0.1%;

Nickel (Ni) with at most 0.1%;

Niobium (Nb) with a maximum of 0.1%;

Molybdenum (Mo) with at most 1.0%;

Vanadium (V) with a maximum of 0.25%;

without being limited to this, the percentages given refer in each case to the percentage by mass of the steel substrate. One or more of the optional alloying elements mentioned can be used. The mass fraction of the optional alloy elements is a maximum of 1.55%, in particular a maximum of 1.0%, preferably a maximum of 0.8%.

In process step S1, the steel substrate 2, which can be wound on a coil 3 in the initial state, is provided with a precoating 4. When applied to the steel substrate, the precoat 4 contains aluminum with at least 85 percent by weight and silicon with up to 15 percent by weight. It goes without saying that other alloying elements can be included at the expense of the silicon content, for example iron and / or other alloying elements with a total of up to 5 percent by weight. The precoating 4 can be applied to the steel substrate 2 using generally known methods. One possibility is the hot dip application. The steel substrate 2 passes through in a coating system 6 a molten bath 5 made of liquid coating material 4, which adheres to the surface of the substrate 2, so that a precoated steel substrate is produced. The melt of the coating material can, for example, 8 to 15 weight percent silicon, 2 to 4 weight percent iron, optionally one or more further alloy elements, such as at least one from the group of Mn, Cr, Ti, B, P, S, Cu, Ni, Nb , Mo, V, of up to 1.5 percent by weight, and the remainder contain aluminum and unavoidable impurities. The precoating 4 is applied to the steel substrate 2 with a thickness d1 of at least 36 micrometers, in particular at least 40 micrometers. The coating thickness d1 can have a maximum thickness of 60 micrometers, in particular up to 50 micrometers in particular. FIG. 2A schematically shows a section of the steel substrate 2 with precoating 4, the combination of steel substrate with precoating being provided with reference number 2 '.

After the application of the first coating 4, the coated steel substrate 2 'is rolled flexibly (S2). For this purpose, the coated steel strip 2 ', which has a largely constant sheet thickness D1 over the length before the flexible rolling, is rolled by means of rollers 7, 8 in such a way that it receives a variable sheet thickness D2a, D2b, D2c along the rolling direction. The coated and flexibly rolled steel substrate is provided with the reference number 12. The process is monitored and controlled during rolling, the data determined by a sheet thickness measurement 9 being used as an input signal for controlling the rolls 7, 8. The flexible rolling is carried out in accordance with the desired target thickness profile of a blank to be cut from the strip material 12 or a component to be produced therefrom. The flexible rolling can be carried out with rolling degrees of at least 1% and / or a maximum of 60% based on the initial thickness D1 of the precoated steel substrate 2 ', in particular with rolling degrees between 3% and 55%. FIG. 2B shows a section of the precoated steel substrate 12 after flexible rolling. It can be seen that the flexibly rolled strip material 12 after the rolling has more rolled out first areas a with a first thickness D2a and less rolled out second areas b with a second thickness D2b as well as intermediate areas c with variable thickness D2c. In the context of flexible rolling, there is a reduction in thickness both in the substrate 2 and accordingly in the precoating 4. Thus, with increasing roller pressure, both the thickness of the substrate 2 and the thickness of the precoating 4 applied thereon decrease. After flexible rolling, the precoating 4 has a reduced first thickness d2a of in particular less than 20 micrometers in the thinner first sections a, and a reduced second thickness d2b of in thicker second sections b in particular more than 33 micrometers, preferably more than 36 micrometers.

After the flexible rolling, the strip material 12 can be rewound into the coil 3 so that it can be transported to a subsequent processing station. After the rolling process, the steel strip 12 can be smoothed in a subsequent process step, which takes place in a strip straightening device. The smoothing step is optional and can also be omitted.

After flexible rolling (S2) or smoothing (if provided), the coated and flexibly rolled steel strip 12 is separated in step S3. Individual sheet metal blanks 22 are machined out of the steel strip 12, for example by means of a punching and / or cutting device 10. Depending on the shape of the sheet metal blanks 22 to be produced, they can be punched out of the strip material 12 as a shape cut, with an edge which is no longer used being eliminated as scrap , or the strip material 12 can simply be cut to pieces.

The blanks 22 are hot formed in a subsequent step S4, which can also be referred to as press hardening. During hot forming or press hardening, the plate 22 is heated to a temperature which is generally above the AC1 or AC3 temperature of the material, for example between 750 ° C. and 1000 ° C. The heating can be carried out by suitable methods, such as for example by means of inductive heating, conductive heating, heating in the roller hearth furnace, contact heating by hot plates, infrared, or other known methods. After heating to the austenitizing temperature, the board 22 is then placed in a thermoforming tool 11 and shaped therein and cooled or quenched so quickly that at least partially a martensitic hardness structure is produced in the molded part produced in this way. According to a first possibility, hot forming (S4) can be carried out as a direct process. The circuit board 22 is heated directly to the austenitizing temperature and then hot-worked in one step to the desired final contour. shaped. A previous (cold) preforming does not take place here. According to a second possibility, hot forming can also be carried out as an indirect process which comprises the sub-steps of cold preforming, subsequent heating of the cold preformed component to austenitizing temperature and subsequent hot forming to produce the final contour of the molded part.

Due to the heating of the plate 22 carried out as part of the hot forming, diffusion processes take place between the base material of the steel substrate 2 and the coating material 4. Iron diffuses from the steel substrate 2 into the coating material 4, so that the thickness d3 of the coating 4 increases overall compared to the thickness d2 present after flexible rolling, that is to say the coating thicknesses d3a, d3b of the hot-formed component 32 are each thicker than the corresponding ones Coating thicknesses d2a, d2b before hot forming. The holding time for austenitizing the coated board 22 depends on the selected temperature and can be between 4 and 10 minutes. The coating 4 of the hot-formed product 32 in the thinner first sections a preferably has a final coating thickness d3a of more than 15 micrometers, in particular more than 20 micrometers. In the thicker second sections b, the coating 4 can have a second final thickness d3b, in particular of more than 30 micrometers, preferably more than 35 micrometers, after the heating or hot forming. For good weldability of the manufactured component, it is favorable if the final thickness d3a of the coating 4 is less than 50 micrometers, in particular less than 40 micrometers, in the thin regions a, and less than 60 micrometers, in particular less than 50, in the thicker regions b Micrometer.

Optionally, a surface oxidation of the coated and flexibly rolled substrate 2 can be carried out before hot forming (S4). An oxidation layer is formed on the coating 4. This leads to a higher heat absorption, so that the heating-up times can be shortened. In a favorable process, the blank can be heated at least up to a temperature of 700 ° C. with a heating rate of more than 12 K / sec in the course of hot forming. LIST OF REFERENCE NUMBERS

2 steel substrate

3 coil

4 coating

5 weld pool

6 coating device

7 reels

8 reels

9 Thickness control

10 cutting device 1 1 thermoforming tool 12 flexibly rolled substrate 22 circuit board

32 hot molded part

a first section

b second section c transition section

D thickness (2 + 4)

d thickness (4)

S1 -S4 process steps

Claims

Muhr und Bender KG July 10, 2019Mubea-Platz 1 Oy / - (2019007009) 57439 Attendorn Q18103W010 Process for producing a hardened steel product claims

1 . A method of making a hardened steel product comprising:

Providing a steel substrate (2) with a base material made of a hardenable steel;

Coating (S1) the steel substrate (2) with an aluminum-containing pre-coating (4), the pre-coating (4) having a thickness (d1) of at least 34 micrometers (pm) being applied to the steel substrate (2);

Flexible rolling (S2) of the precoated steel substrate (2), with successive sections (a, b, c) of the precoated steel substrate (2) being rolled out to different extents, the precoating by the flexible rolling in thinner first sections (a) reduced first thickness (d2a) of less than 33 micrometers and in thicker second sections (b) to a reduced second thickness (d2b) which is thicker than the reduced first thickness (d2a);

Working out (S3) a board (22) from the flexibly rolled steel substrate (2);

Heating the circuit board (22) in such a way that the base material of the circuit board (22) is at least partially austenitized, with diffusion processes taking place between the base material and the precoating (4) by the heating; and

Hot forming (S4) of the heated plate (22), the heated plate (22) being shaped and cooled so quickly that a hardened steel product (32) with a coating is produced.

2. The method according to claim 1,

characterized,

that the precoating (4) with a thickness (d1) of at least 36 micrometers, in particular at least 40 micrometers, is applied to the steel substrate (2).

3. The method according to claim 1 or 2,

characterized,

that the precoating (4) is given a reduced first thickness (d2a) of less than 20 micrometers by the flexible rolling (S2) in the thinner first sections (a).

4. The method according to any one of claims 1 to 3,

characterized,

that the precoating (4) has a reduced second thickness (d2b) of more than 33 micrometers, in particular of more than 36 micrometers, due to the flexible rolling (S2) in the thicker second sections (b).

5. The method according to any one of claims 1 to 4,

characterized,

that the coating is formed from the precoating (4) by heating and hot forming (S4),

with a first final thickness (d3a) in the thinner first sections (a), which is greater than the reduced first thickness (d2a) and in particular between 15 to 50 micrometers, and

with a second final thickness (d3b) in the thicker second sections (b), which is greater than the reduced second thickness (d2b) and in particular between 30 to 60 micrometers.

6. The method according to any one of claims 1 to 5,

characterized,

that the coating is formed with a final thickness ratio (d3a / d3b) of the first final thickness (d3a) to the second final thickness (d3b) which is greater than one Intermediate thickness ratio (d2a / d2b) of the reduced first thickness (d2a) to the reduced second thickness (d2b).

7. The method according to any one of claims 1 to 6,

characterized,

that steel substrate (2) with an initial thickness of 1.0 to 4.0 mm is used.

8. The method according to any one of claims 1 to 7,

characterized,

that the flexible rolling (S2) with rolling degrees of at least 1% and / or a maximum of 60% is carried out starting from the initial thickness of the steel substrate (2).

9. The method according to any one of claims 1 to 8,

characterized,

that the coating (4) is applied to the steel substrate (2) by means of hot-dip coating.

10. The method according to claim 9,

characterized,

that the steel substrate (2) is heated after the application of the precoat (4) in the coating system (6) in order to achieve a pre-diffusion between the precoat (4) and the steel substrate (2).

1 1. The method according to any one of claims 1 to 10,

characterized,

that a hardenable steel is used as the steel substrate (2), which contains the following proportions of alloying elements in each case in percent by weight:

Carbon (C) of more than 0.15% and less than 0.5%;

Manganese (Mn) with more than 0.5% and less than 5.0%;

Aluminum (AI) less than 0.1%;

Silicon (Si) with more than 0.1% and less than 0.9%;

Chromium (Cr) with more than 0.01% and less than 1.0%; Tital (Ti) less than 0.2%;

Boron (B) with more than 0.0005 and less than 0.080%;

Phosphorus (P) less than 0.1%;

Sulfur (S) less than 0.05%;

optionally further alloying elements with a share of up to 1.55%; the rest iron (Fe) and unavoidable impurities.

12. The method according to claim 1 1,

characterized,

that as an optional further alloy element at least one of:

Copper (Cu) with at most 0.1%;

Nickel (Ni) with at most 0.1%;

Niobium (Nb) with a maximum of 0.1%;

Molybdenum (Mo) with at most 1.0%;

Vanadium (V) with a maximum of 0.25%;

each in percent by weight is used.

13. The method according to any one of claims 1 to 12,

characterized,

that the precoat (4) contains at least 85% by weight of aluminum and can optionally contain 5 to 15% by weight of silicon.

14. The method according to any one of claims 1 to 13,

characterized,

that a metal oxide layer is formed on the surface of the coated steel substrate (2) before hot forming.

15. The method according to any one of claims 1 to 14,

characterized,

that the board (22) for austenitizing is heated at least up to a temperature of 700 ° C. with a heating rate of more than 12 K / sec.