DE102013010025A1 - Method for producing a product from flexibly rolled strip material - Google Patents

Abstract

The invention relates to a method for producing a product from flexibly rolled strip material, comprising the steps: flexible rolling of a strip material from sheet steel, a variable thickness being produced over the length of the strip material; Working out a board from the flexibly rolled strip material; Forming the board into a molded part; Cleaning the molded part in such a way that a maximum of 0.1 ppm of diffusible hydrogen is introduced into the molded part by the cleaning; and coating the molded part with a metallic coating material to produce an anti-corrosion coating.

Description

The invention relates to a method for producing a product made of flexibly rolled strip material and a product made of flexibly rolled strip material, in particular as a structural component for a motor vehicle.

From the DE 10 2004 037 206 A1 a body for a motor vehicle is known, which is joined by individual elements. For this purpose, individual elements made of flexible rolled sheet metal are used along a direction of variable sheet thickness, in which the distribution width of the specific load on the single element is reduced by the choice of sheet thickness distribution. Such sheet metal elements with variable sheet thickness are also referred to as Tailor Rolled Blanks (TRB).

The trend in the automotive industry toward lightweight construction and occupant protection is leading to increased use of high-strength and ultra-high strength bodywork steels. In the course of this development in particular multiphase steels and martensite phase steels are used. The latter steels are generally processed into structural components via an indirect or direct hot forming process.

Usually, structural components for motor vehicles are provided with a coating which is intended to protect the steel sheet from corrosion. The realization of a reliable corrosion protection is difficult, especially with hot-formed steel materials. Various coatings and coating methods are known which differ, among others, in whether the coating is applied before or after hot working.

From the EP 2 327 805 A1 For example, there is known a method and a production line for producing a sheet metal part with a corrosion protection coating. The method comprises the steps of: forming a starting material into a sheet metal part, electrolytically coating the sheet metal part to form the anticorrosion coating and then heat treating the coated sheet metal part.

From the EP 2 412 848 A1 a similar method is known in which a zinc-nickel coating is applied as a corrosion protection coating on the sheet metal part. In this case, a thin nickel layer is first deposited at the beginning of the coating process, which should further prevent hydrogen embrittlement of the steel sheet material.

A method for coating steel components is, for example, galvanic (electrolytic) galvanizing. In galvanic galvanizing, the workpieces are immersed in a zinc electrolyte. Zinc electrodes act as "sacrificial anodes" due to their less noble metal than the workpiece. The workpiece to be galvanized acts as a cathode, which is why the coating is also referred to as cathodic corrosion protection.

Other known coating methods include hot dip galvanizing, thermal spraying, flame spraying, high velocity flame spraying, arc spraying or plasma spraying, sherardizing, galvanizing, electrostatic deposition of metal powder on the surface of the component, or other vapor phase deposition (CVD) processes.

A problem with the large-scale technology implemented coating method for ultra-high strength, especially flexibly rolled structural components is that the corrosion protection of coatings applied before thermoforming adversely affect the properties of the component and the coating by the temperature acting on the coating system before and during thermoforming. It can lead to Lotrissigkeit and micro cracks in the component, which has a negative impact on the material properties of the workpiece result. Coating systems and processes, such as flame spraying and sheradizing, which are applied after thermoforming, have the great disadvantage that the layer thickness has great fluctuations and the processes are very complicated as a whole.

In the case of full-surface galvanizing of components from the liquid phase (hot-dip galvanizing), the galvanizing temperature of over 420 ° C reduces the strength of the component. With electrolytic galvanizing, there is the danger that hydrogen will be introduced into the component through the preceding cleaning process and the galvanic coating process. The induced hydrogen can lead to material failure due to the high strength of the components.

On this basis, the present invention seeks to propose a method for producing a product made of flexibly rolled strip material, which offers a particularly good corrosion protection.

The solution is a method of manufacturing a flexible rolled strip material product comprising the steps of: flexibly rolling a steel sheet strip material to produce a variable thickness over the length of the strip material; Working out a board from the flexibly rolled strip material; Forming the board into a molded part; Cleaning the molding such that a maximum of 0.1 ppm of diffusible hydrogen is introduced into the molding by the cleaning; and coating the molded article with a metallic coating material to form an anti-corrosion coating.

One advantage is that during the cleaning process, no diffuse hydrogen is introduced into the material, or at most only in extremely small quantities. In this way, unwanted hydrogen embrittlement of the steel material can be avoided or at least reduced. One advantage of the piece coating, that is to say the coating of the already cut-out blanks or the molded parts produced therefrom, is that the layer thickness is uniform over the coated surface, or partial surface, of the workpiece. This in turn has a favorable effect on the quality of the coating and thus on the corrosion resistance of the molded part produced.

The cleaning is preferably carried out so that the proportion of diffusible hydrogen, measured immediately before and after the cleaning, is less than 0.1 ppm (parts per million), in particular less than 0.05 ppm. With immediately before and after cleaning, a time window of up to 10 minutes before or after may be included, within which the content of diffusible hydrogen in the material is measured.

For the production of the product is preferably a hartbarer, especially manganese-containing steel material used. This may include other micro-alloying elements, such as niobium and / or titanium, wherein the mass fraction of these micro-alloying elements in the total mass is preferably at most 1000 ppm. Additional micro-alloying elements may be added in small proportions, such as boron and / or vanadium. Examples of a usable steel material are 17MnB5, 22MnB5, 26MnB5 or 34MnB5. The starting material (strip material) preferably has a tensile strength of at least 450 MPa and / or of at most 850 MPa. The finished molded part may have a ultimate tensile strength of at least 1100 MPa, preferably at least 1300 MPa, more preferably even 1500 MPa, at least in some areas.

Flexible rolling is understood to mean a rolling process in which steel strip of uniform thickness is rolled over its length into variable thickness strip material over its length. The initial thickness before flexible rolling can be up to 8 mm. As strip material for the flexible rolling hot strip or cold strip can be used, these terms are to be understood in the jargon. By hot strip is meant a rolled steel finished product (steel strip) produced by rolling after preheating. By cold strip is meant a cold-rolled steel strip (flat steel) in which the last thickness decrease takes place by rolling without prior heating. For example, after flexible rolling, the strip material may have a maximum thickness of 6.0 mm at the thickest point.

Preferably, the flexible rolling is performed such that at least two sections are produced with different thickness, wherein the ratio of a first thickness of a thinner first portion to a second thickness of a second portion less than 0.8, in particular less than 0.7, preferably less than 0, 6 is. It is understood, however, that in principle any number of sections of different thickness can be produced depending on the requirements of the finished product. In this case, the thickness over the length is adjusted in particular such that the loads of the component are at least substantially uniform, or stress peaks are avoided or at least reduced.

By working out is meant any shape for the production of blanks or shaped cuts from the strip material. This can be done by mechanical cutting, such as punching or cutting, or by laser cutting. Under sinkers are understood in particular rectangular metal sheets that have been cut out of the strip material. Form cuts are understood to be sheet metal elements that have been worked out from the strip material and whose outer contour has already been adapted to the shape of the end product. When producing shaped cuts or sinkers, an edge may remain on the strip material which is not used further, it also being possible to carry out a simple cutting of the strip material into sections in which no edge would remain. In the present case, the term board is used uniformly for both form cuts and for rectangular blanks.

It is understood that in addition to the above-mentioned method steps, further steps can be preceded, intermediate or downstream. For example, a heat treatment of the strip material can take place before the flexible rolling. After the flexible rolling a band straightening can be provided. Furthermore, pre-treatment, such as rinsing and / or pickling (surface activation), of the workpieces may be provided prior to coating. After coating, another heat treatment can be performed.

According to a preferred method, it is provided that the cleaning of the molded part done mechanically. This means any treatment in which after the forming existing unwanted impurities are mechanically removed from the surface. The advantage of mechanical cleaning is that no unwanted hydrogen is introduced into the workpiece. Preferably, the molding is blasted or brushed. In particular, shot peening, blasting with corundum or with dry ice (CO2) are possible methods of blasting. For shot peening, steel balls having a preferred ball diameter of 0.7 to 0.9 mm may be used. By the blasting process, a rougher surface than in the non-irradiated state is generated, which has a favorable effect on the adhesive properties of a coating to be applied later. However, it is also conceivable in principle that the cleaning of the molded part takes place in a different manner, so that an amount of not more than 0.1 ppm, in particular of not more than 0.05 ppm hydrogen capable of diffusion (H) is introduced into the molded part by the cleaning process ,

After a first procedure, the forming of the workpiece comprises hot working. Hot forming means forming processes in which the workpieces are heated to a temperature in the region of the hot forming prior to forming and in which at least partial regions are hardened during the forming process. The heating is carried out in a suitable heating device, for example an oven. The hot forming may be performed as an indirect process according to a first possibility, comprising the substeps cold preforming the blank into a preformed component, then heating at least portions of the cold preformed component to austenitizing temperature, followed by hot working to produce the final contour of the product. Austenitizing temperature is to be understood as meaning a temperature range in which at least partial austenitization (microstructure in the two-phase region ferrite and austenite) is present. In addition, it is also possible to austenitize only portions of the board, for example, to allow partial curing. The hot forming can also be carried out as a direct process according to a second possibility, which is characterized in that at least portions of the board are heated directly to Austenitisierungstemperatur and then hot-formed and cured to the desired final contour in one step. A previous (cold) preforming does not take place here. Even in the direct process, partial hardening can be achieved by austenitizing partial areas. For both processes, hardening of subareas of the components is also possible by means of tools of different temperatures, or by using a plurality of tool materials which enable different cooling rates. In the latter case, the entire board or the entire component can be completely austenitized.

After an alternative procedure, the sheet metal blanks can also be cold formed. Cold forming refers to forming processes in which the blanks are not specifically heated before forming. The transformation thus takes place at room temperature; the boards heat up by dissipation of the supplied energy. Cold forming is used in particular as a process for forming soft body steels. After cold forming, the moldings may optionally be hardened.

During or after the forming, a heat treatment can be provided as an integrated or separate process step with which regions of different ductility are produced in the workpiece. Ductility is understood to mean the deformability of the steel material without damage or cracking. The ductility can be assessed, for example, on the basis of the elongation at break or fracture constriction in the tensile test. An increased ductility in sub-areas leads there advantageously to a reduced edge crack susceptibility and improve the weldability of the material.

The ductility may in particular be designed in such a way that one or more first regions of the molded part have a greater yield strength of at least 800 MPa and / or that one or more second regions have a lower elastic limit of at most 800 MPa. The strength may be at most 1100 MPa in the first region and / or at least 1100 MPa in the second region.

For the production of areas of different ductility different process management are conceivable. After a first possibility, a temperature gradient can be generated in the workpiece as part of the heat treatment taking place before the forming. After the heat treatment, which can be done in an oven, for example, then there are areas with higher and lower temperature. The subsequent forming leads then in the areas with higher temperature to a greater ductility or lower strength, while in the areas of lower temperature, a lower ductility or higher strength is generated. Alternatively, a temperature gradient in the workpiece can also take place during the transfer process between the heat treatment and the forming, for example by cooling portions of the previously completely heat-treated workpiece prior to insertion into the forming tool. According to another possibility, the ductility can also during the forming process can be adjusted, for example, by different tempering of portions of the tool. For this purpose, the forming tool may have corresponding means, such as channels through which a cooling medium flows. In the cooler areas of the tool, a higher strength and lower ductility is produced in the molded part; Accordingly, the warmer portions of the forming tool cause the formation of lower strengths and higher ductility. According to a further possibility, the areas of high ductility can be generated during the coating, in particular by hot-dip galvanizing. The high temperature of the liquid coating material in the coated areas leads to a softening, that is, a higher ductility.

Before, during or after the transformation, a heat treatment can be carried out as an integrated or separate process step with which edge regions with a lower hardness than in the core region are produced in the workpiece. This can be done by targeted edge decarburization, in which in the starting material over the thickness of a depletion of alloying components takes place, that is, the proportion of alloying constituents such as carbon or manganese is greater in a core region of the strip material than in the edge region. The depleted region preferably has a hardness reduced by at least 50 HV _0.1 relative to the core region. The depletion of the alloying elements can be achieved by a heat treatment, for example as part of a Galvannealing treatment or by heating above the AC1 temperature. The character of the edge decarburization is determined by the process parameters in the furnace. This includes in particular the atmosphere in the oven, that is, the gas mixture in the oven, or the temperature.

The coating is carried out in particular with a coating material which has a proportion of at least 50 percent by weight of zinc, preferably at least 90 percent by weight of zinc, wherein the zinc content may also amount to 100 percent (pure zinc coating).

After a first process, the coating can be applied galvanically (electrolytically). For this purpose, anodes of the coating material, that is, of pure zinc or of zinc and other alloying elements are used, which deliver metal ions to the electrolyte when energized. Alternatively, dimensionally stable anodes can also be used; In this case, the coating material is already dissolved in the electrolyte. The zinc ions and optionally ions of the further alloying elements are deposited on the molded part, which is connected as a cathode, as atoms and form the coating. The coating is carried out by immersing the workpiece in a dipping bath with an electrolyte solution, preferably in a continuous process, wherein a flow is generated between the molding and the electrolyte solution. By using a continuous process, that is with continuous movement of the workpiece, a good reproducibility of the coating process is achieved as well as a uniform coating over the surface of the workpiece. However, this is also to include temporal pauses in which the feed is temporarily stopped, to a certain extent, as they occur, for example, in a chain conveyor system. The flow can be generated by moving the mold parts through a dip tank with the aid of a device, that is, the mold parts move relative to the dip tank and to the electrolyte solution. Alternatively or in addition, a flow of the electrolyte solution can be generated by appropriate design of the coating system. For this purpose, the coating system can be equipped with pumps, which put the electrolyte solution in a flow movement relative to the workpiece. Preferably, the Elektrolylösung is blasted by means of nozzles on the moldings, which can be done at a beam angle of 90 ° to ± 45 ° with respect to the workpiece surface. In principle, an inhomogeneous distribution of the current density can be present in electrolyte solutions.

Therefore, the flow of the electrolyte solution relative to the workpieces is adjusted to produce a homogeneous distribution of the current density.

The coating by means of electrolyte solution may in particular comprise the following substeps: in a first station, the electrolytic solution is subjected to pulsed current for coating the molded part; in a subsequent second station, the electrolytic solution is charged with unpulsed current for coating the molded part. By a pulsed energization of an anode pair in the first partial step, a nanocrystalline layer structure is achieved, which may for example have a layer thickness of one to two micrometers. The coating therefore has a particularly fine grain close to the workpiece so that the formation of rust is avoided.

According to an alternative methodology, the coating may also include hot dip galvanizing, the molding being immersed in molten coating material having a temperature of at least 350 ° C, preferably at least 420 ° C, and / or at most the AC1 temperature of the steel material, preferably at most 600 ° C is immersed. In this way, the coated areas are softened due to the introduced heat, so that the material here receives a higher ductility than in the uncoated areas. The coating material is preferably as stated above, that is it has a proportion of at least 50% by weight of zinc, optionally with additional alloying elements. Further conceivable coating methods are flame spraying or chemical vapor deposition (CVD).

In addition, as a further method step before or after the coating, a heat treatment of the coated molding at a temperature of more than 220 ° C, preferably of more than 230 ° C can be performed. The maximum temperature for the heat treatment is preferably at most the AC1 temperature of the steel material, in particular at most 400 ° C. With the heat treatment, which can also be referred to as effusion annealing, residual stresses in the workpiece or stress peaks in the hardened component are reduced or the elongation at break is increased. At the same time the hydrogen diffusion is accelerated by the selected temperature, so that overall a lower hydrogen embrittlement is achieved on the finished product. The heat treatment can be carried out in a time frame of a few seconds to 3 hours. Further, the heat treatment may take place either after the coating process or between individual coating stages. A heat treatment following the coating advantageously accelerates the drying of the moldings and, when using high-strength steels, the material properties with respect to ductility and elongation at break are improved by tempering.

The solution of the above-mentioned object is further to a product made of flexibly rolled steel sheet according to the above-mentioned method. This results in the stated advantages of a constant layer thickness of the corrosion protection coating over the coated surface of the molded part and a low risk of hydrogen embrittlement. The molded part can be produced according to one or more of the above-mentioned method steps, so that reference is made to the above description with regard to the steps and the associated advantages.

Overall, a molded part is created according to the invention, which is adapted by its sheet thicknesses and the applied corrosion protection system ideally to the requirements in terms of lightweight construction, crash properties and service life (corrosion protection). The molded part can be any body component of a motor vehicle, for example a structural component such as an A, B or C pillar.

A preferred embodiment will be explained below with reference to the drawing figures. Hereby shows:

1 a method according to the invention for the production of a product made of flexibly rolled strip material schematically as a flowchart; and

• A) in Seitenansicht,
• B) im Querschnitt gemäß Schnittlinie A-A aus 2A.

2 the process step of coating schematically as a detail

• A) in side view,
• B) in cross section according to section line AA 2A ,

The 1 and 2 will be described together below. In process step V1, the strip material, which is wound on a coil in the initial state, is rolled, by means of flexible rolling. For this purpose, the strip material, which has a largely constant sheet thickness over the length prior to flexible rolling, is rolled by means of rolls in such a way that it receives a variable sheet thickness along the rolling direction. During rolling, the process is monitored and controlled using the data obtained from a sheet thickness measurement as input to control the rolls. After flexible rolling, the strip material has different thicknesses in the rolling direction. The strip material is rewound to the coil after the flexible rolling, so that it can be fed to the next process step.

The material used for the strip material is a hardenable steel material, such as 17MnB5, 22MnB5, 26MnB5 or 34MnB5. The starting material preferably has a tensile strength of at least 450 MPa and at most 850 MPa. It may be provided for certain components that the starting material over the thickness has a depletion of alloy constituents, that is, the proportion of alloying constituents such as carbon or manganese is greater in a core region of the strip material than in the edge region. The depleted region preferably has a hardness reduced by at least 50 HV _0.1 relative to the core region. The depletion of the alloying elements can be achieved by a heat treatment, for example as part of a Galvannealing treatment or by heating above the AC1 temperature.

After the flexible rolling, the strip material can be smoothed in a band straightening device. The smoothing step is optional and may be omitted.

After the flexible rolling (V1) or smoothing, individual sheet metal blanks are worked out of the strip material in the next method step V2. The working out of the sheet metal blanks from the strip material is preferably carried out by means of punching or cutting. Depending on the shape the sheet metal blanks to be produced can be punched out of the strip material as a shaped cut, wherein an edge remains standing on the strip material, which is not reused, or the strip material can be easily cut to length in sections.

After producing blanks from the strip material, the blanks are subsequently converted to the desired end product. After a first possibility, the boards are hot-formed or, after a second possibility, cold-formed.

Hot forming can be done as a direct or indirect process. In the direct process, the boards are heated to austenitizing temperature prior to forming (step V3), which can be done, for example, by induction or in an oven. Austenitizing temperature is to be understood as meaning a temperature range in which at least partial austenitization (microstructure in the two-phase region ferrite and austenite) is present. However, it is also possible to austenitize only portions of the board in order, for example, to allow partial hardening.

After heating to austenitizing temperature, the heated board is formed in a forming tool and simultaneously cooled at high cooling rate, the component is given its final contour and cured at the same time. This process, which is referred to as hot working, is shown as process step V4. A special form of hot forming is press hardening, which is performed at high pressures.

In indirect hot forming, the blank is subjected to preforming prior to austenitizing. The preforming takes place in a cold state of the board, that is without prior heating. When preforming the component receives a profile that does not yet correspond to the final shape, but is approximated to this. After preforming, austenitizing and thermoforming then take place, as in the direct process, whereby the component receives its final contour and is hardened.

As part of the forming, areas with different ductility and / or areas with different strength can be produced in the workpiece.

The steel material, provided that hot working (direct or indirect), should contain at least 0.1% to 0.35% by weight of carbon. Regardless of the type of hot forming, the complete workpiece or only partial areas can be hardened. When carrying out the hot forming in such a way that only partial areas are hardened, the molded part has areas with reduced strength and at the same time increased elongation at break. By applying a coating in a later process step exclusively in these soft zones, the risk of hydrogen embrittlement is reduced here.

As an alternative to hot forming as a shaping process, the blanks can also be cold formed. The cold forming is particularly suitable for soft body steels or components that have substantially strengths of less than 1200 MPa. During cold forming, the blanks are reshaped at room temperature.

After forming (method step V4), the molded parts are subjected to a cleaning process in method step V5. The cleaning of the moldings is carried out such that a maximum of 0.1 ppm, preferably of at most 0.05 ppm of diffusible hydrogen (H) is introduced into the molded part. For this purpose, a mechanical cleaning process is preferably provided in which undesired contaminants are mechanically removed from the surface of the molded part. In particular, shot peening or brushes are suitable for cleaning the molded parts, the shot peening preferably being carried out with steel balls having a particle size of about 0.7 mm to 0.9 mm. By shot peening, the surface of the molding receives a roughened surface, resulting in a good adhesion of a later applied coating.

After cleaning, in the next method step (V6), the mold part can be trimmed to the final contour, for example by means of a laser, or the mold part can be oiled as corrosion protection during a subsequent intermediate storage. However, if the workpiece can be further processed directly, oiling is meaningfully not carried out.

After the intermediate step (V6), the moldings are provided with a corrosion protection. For this purpose, the moldings undergo an electrolytic coating system comprising several stations.

In a process step (V7), the moldings are first rinsed. After rinsing, the moldings are decanted in process step (V8). For this purpose, the moldings are removed by immersion in a dilute acid of unwanted oxides.

After picking the moldings are provided in step V9 with a corrosion protection layer. For coating is preferably a coating material with a proportion of at least 50 percent by weight of zinc, in particular at least 90 percent by weight of zinc used, with a pure zinc coating conceivable. The coating material may include other alloying elements.

The coating can be carried out galvanically by means of an electrolyte solution, in which the moldings are immersed. A corresponding coating device is in the 2A and 2 B shown schematically. They are molded parts 12 recognizable in the feed direction R relative to dimensionally stable anodes 13 and nozzle sticks 14 each with several nozzles 15 to be moved. The moldings 12 For example, structural components of the body of a motor vehicle, such as A, B or C pillars or other body parts. The anodes 13 are designed in the form of lattices, so that they from the nozzle devices 14 can be flowed through leaking electrolyte solution. These are nozzle devices 14 arranged on both sides of the dip tank, between which the moldings 12 . 12 ' be moved along. The electrolyte flow is schematically as 16 located. She is on the moldings 12 . 12 ' directed and ensures a uniform distribution of the current density in the electrolyte solution and thus a uniform layer structure on the surface of the moldings 12 . 12 ' ,

It is favorable for a good reproducibility of the process if the coating takes place continuously, wherein between the molded parts 12 . 12 ' and the electrolyte solution is generated a flow. The flow is present by moving the moldings 12 . 12 ' produced by a dip tank, wherein the electrolyte solution can be added alternatively or additionally by pumping in a flow movement relative to the moldings. For electrolytic coating are anodes 13 from the coating material, that is, used from pure zinc or zinc and other alloying elements, which release metal ions to the electrolyte when energized (Lösestation 9 ). The zinc ions and optionally ions of the further alloying elements are deposited on the molded part 12 . 12 ' , which is connected as a cathode, deposited as atoms and form the anti-corrosion coating.

It is particularly favorable if a pulsed current is used for coating in a first partial step (V91). As a result, a particularly fine-grained layer having a thickness of, for example, 1 to 2 micrometers is formed directly on the surface of the workpieces. Subsequently, in a second partial step (V92), the electrolytic solution or the anodes for coating the molded part are subjected to unpulsed current until the anticorrosive layer reaches the complete thickness of, for example, 7 to 8 micrometers. The coating system can be designed in practice so that an elongated dip tank is provided, through which the individual molded parts 12 . 12 ' be moved continuously in the longitudinal direction R. In this case, in a first section of the dip tank, a first arrangement of anodes 13 be provided, which are acted upon by pulsed current while the workpieces are passed to it. In a second section following the first section in the conveying direction R of the workpieces, the anodes provided there are provided 13 charged with unpulsed electricity while the workpieces 12 . 12 ' these happen.

In the present case, the galvanic coating of the molded parts by means of electrolyte solution is described. It is understood, however, that the process step V9 of the coating can also be carried out alternatively by hot-dip galvanizing, flame spraying or chemical vapor deposition (CVD).

Regardless of the type of coating process, the moldings may be completely or even partially coated. If only partial sections of the molded parts are coated, the expense and thus the costs can be reduced, as well as simplify an optionally subsequent welding process for connecting the molded part with other components. Furthermore, hydrogen in the uncoated areas can easily be allowed to run, reducing the risk of hydrogen embrittlement. It is particularly advantageous if the moldings are provided locally only in the corrosion-prone areas with the anti-corrosion coating. These are, for example, areas that are increasingly exposed to wetness in motor vehicles and are therefore also referred to as wet area.

After coating, the moldings are optionally subjected to rinsing in method step V10.

After rinsing (V10), the moldings can be heat-treated in process step V11. The heat treatment can in principle be carried out in any technically suitable manner, for example in a bell annealer or else by inductive heating, to name only two methods by way of example. The heat treatment may be carried out at a temperature of more than 220 ° C, preferably more than 230 ° C. The maximum temperature for the heat treatment is preferably lower than the AC1 temperature of the steel material, in particular at most 400 ° C.

With the heat treatment, which can also be referred to as Effusionsglühe be Reduced residual stress in the workpiece or stress peaks in the cured component or increases the elongation at break. At the same time the hydrogen diffusion is accelerated by the selected temperature, so that overall a lower hydrogen embrittlement is achieved. The heat treatment can be carried out in a time frame of several seconds to 3 hours. Conducting the heat treatment after coating accelerates the drying of the components, and when high-strength steels are used, the material properties with respect to ductility and elongation at break are improved by tempering.

A special feature of the method according to the invention is that the electrolytic coating (V9) takes place after the flexible rolling (V1), after the cutting out of the sinkers (V2) and after the forming (V4). The coating applied to the moldings has a uniform thickness regardless of the thickness of the workpiece. Even the thicker rolled-out areas have a sufficiently thick coating that reliably protects against corrosion. Another special feature is the step of preferably mechanical cleaning (V5), whereby the entry of unwanted hydrogen in the workpiece and thus the hydrogen embrittlement is avoided. Due to the upstream or downstream heat treatment in a temperature range between preferably 230 ° C and 600 ° C internal stresses in the workpiece are reduced and the hydrogen is accelerated, which also leads to a lower hydrogen embrittlement of the material.

It is understood that the process control according to the invention can also be modified. For example, intermediate steps which are not separately shown here can also be provided between the mentioned steps. For example, the moldings may be provided with an intermediate layer prior to electrolytic coating, in particular with a nickel, aluminum or manganese layer. This intermediate layer provides additional surface protection and improves the adhesion of the subsequently applied zinc-containing coating.

LIST OF REFERENCE NUMBERS

V1

Flexible rolling

V2

Working out of circuit boards

V3

heat treatment

V4

reshape

V5

Clean

V6

intermediate step

V7

do the washing up

V8

pickling

V9

coating

V91

first part coating

V92

second part coating

V10

do the washing up

V11

heat treatment

12

molding

13

anode

14

nozzle device

15

jet

16

electrolyte flow

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102004037206 A1 [0002]
• EP 2327805 A1 [0005]
• EP 2412848 A1 [0006]

Claims (15)

A method of making a product from flexibly rolled strip material comprising the steps of: Flexible rolling (V1) a strip material of steel sheet, wherein a variable thickness over the length of the strip material is produced; Working out (V2) a board from the flexibly rolled strip material; Forming (V4) the board into a molded part; Cleaning (V5) of the molded part such that a maximum of 0.1 ppm of diffusible hydrogen is introduced into the molded part by the cleaning; and Coating (V9) at least a portion of the molding with a metallic coating material to produce a corrosion protection coating. A method according to claim 1, characterized in that the cleaning of the molded part takes place mechanically. A method according to claim 1 or 2, characterized in that the cleaning takes place by means of blasting or brushing. Method according to one of the preceding claims, characterized in that the flexible rolling is performed such that at least two sections are produced with different thickness, wherein a first thickness is smaller than a second thickness and the ratio of first thickness to second thickness less than 0, 8, in particular less than 0.7, preferably less than 0.6. Method according to one of the preceding claims, characterized in that the forming is a hot working with simultaneous curing, with the following substeps: heating at least a portion of the board austenitizing temperature; and thermoforming the board with rapid cooling, wherein the at least one heated portion is cured. Method according to one of the preceding claims, characterized in that the forming is a cold forming, wherein the cold-formed molding is cured before coating (V9). Method according to one of the preceding claims, characterized in that the coating (V9) is carried out with a coating material which has a mass fraction of zinc of at least 50%. Method according to one of the preceding claims, characterized in that the coating (V9) is carried out in an immersion bath with an electrolyte solution, wherein between the molding and the electrolyte solution, a flow is generated. Method according to one of the preceding claims, characterized in that the coating is carried out in a continuous process. Method according to one of the preceding claims, characterized in that the coating (V9) by means of electrolytic solution comprises the following substeps: in a first substep (V91), the electrolytic solution is subjected to pulsed current for coating the molded part; in a subsequent second partial step (V92), the electrolytic solution for coating the molded part is subjected to unpulsed current. Method according to one of the preceding claims, characterized in that the coating (V9) comprises a hot-dip galvanizing, wherein the molding is immersed in a dipping bath of molten coating material having a temperature of at least 350 ° C and at most the AC1 temperature of the steel material. Method according to one of the preceding claims, characterized in that as a further method step after coating (V9) is provided: heat treating (V11) of the coated molding at a temperature of at least 200 ° C, in particular at least 220 ° C, and / or at a Temperature of at most the AC1 temperature of the steel material, in particular at most 400 ° C. Method according to one of the preceding claims, characterized in that the steel material comprises manganese and at least one of the micro-alloying elements niobium or titanium, wherein the total proportion of these micro-alloying elements in the total mass is at most 1000 ppm. Method according to one of the preceding claims, characterized in that regions of different ductility are produced in the molded part, in particular either during the hot forming or during the coating. Product of flexibly rolled steel sheet, produced according to a method according to one of claims 1 to 14.

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