DE102008027460A9 - Method for producing a sheet steel component with regions of different ductility - Google Patents

Abstract

The invention relates to a method for producing a hardened sheet steel component with areas of different ductility, wherein the behavior of the steel sheet is changed during heating so that the heat absorption capacity of the steel sheet is influenced during the heating for curing depending on the desired degree of hardness, with good heat absorption for high degrees of hardness and for less severe areas a reduced heat absorption behavior can be realized and thereby the structure over the surface of the component or over the surface of the board is made variable, the setting of the structure and the adjustment of the heat absorption behavior is controlled by the surface emissivity.

Description

The The invention relates to a method for producing a sheet steel component with areas of different ductility.

in the Automotive engineering continues to pursue great aspirations Reduce fuel consumption and associated emissions. The desire of the automobile industry in particular is here Foreground, through new materials a weight reduction of Vehicle to make. There are basically two ways be taken. On the one hand, here one goal can be the production of Be steel alloys with a lower specific gravity, which otherwise the previous favorable characteristics maintained. On the other hand, weight reduction by reduction of the component cross-section through the use of high and higher strength Steel materials can be achieved.

It is also known, thermoformed components for For example, structural components such as B-pillars, struts and Side member with over the mold component distributed to produce consistent properties. this happens by a complete heating of the output board or of the molded component with a subsequent hot forming step or Hardening. In various applications of the Automotive technology to form components over certain Areas of high strength, in turn, over other areas a relatively higher ductility exhibit. It is already known about heat treatments to treat a component so that it locally higher areas Having strength or higher ductility.

That's how it shows DE 197 43 802 C2 a method to produce a molded component with areas of different ductility by an output board is only partially heated before or after pressing or deliberately reheated in a previous homogeneous heating in the areas with desired higher ductility. Preferably, the partial heating is done inductively.

The DE 200 14 361 U1 describes a B-pillar which also has areas of different strength. The preparation of the B-pillar is carried out in the thermoforming process, starting from a molding board or a preformed longitudinal profile of this is austenitized in the oven and then converted / cured in a cooled tool. In the oven, large areas of the workpiece can be isolated against the effect of temperature, in these areas the austenitizing temperature is not reached and thus does not adjust in the tool during curing no martensitic structure.

The DE 102 56 621 B3 describes a method in which an output board or a preformed component during transport through a continuous furnace simultaneously passes through at least two adjacent to each other in the direction of passage zones of the continuous furnace with different temperature levels. A zone 1 of the continuous furnace is set to a temperature A and another zone 2 to a temperature B which is higher than temperature A. As a result, the semi-finished product is heated in the areas where it passes through the continuous furnace in zone 1 to temperature A. and in the areas in which it passes through zone 2 to temperature B. Subsequently, the thus differently heated semi-finished product is subjected to a thermoforming process and / or hardening process, whereby in the previously heated to temperature A region 1 of the component in relation to the adjusted to temperature B heated area 2 of the component ductile structure.

The DE 102 08 216 C1 describes a method in which an output board or a preformed component is brought to Austenitisierungstemperatur in a continuous furnace and areas of the first type of the board or the preformed component, which are ductile in the later end component, active from a certain cooling start temperature z. B. quenched with compressed air, wherein the active quenching is stopped when a predetermined stop temperature is reached. Subsequently, these areas are held approximately isothermally for the transformation of the austenite into a structure with a high ferrite and / or pearlite content. Meanwhile, in areas of the second kind, which have relatively lower ductility in the final component, a hardening temperature is reached which is at least high enough for sufficient martensite formation to take place in these areas during a hardening process. While in the areas of the first kind an isothermal transformation takes place, the areas of the second kind are predominantly or entirely kept in the austenite area. An excessive temperature drop can be counteracted here, for example, with a heating device or with a reflecting mirror.

These Some methods have some problems in their implementation or need for successful implementation technical aids such as insulating materials, inductive heating devices or active cooling to the desired different structural areas in the finished component. Isolating by encapsulating in the oven is technically complicated, because in each cycle every single one Part needs its own insulation. Furthermore, it is possible an oven with different temperature zones in the direction of flow technically difficult to realize especially for preformed components.

task The invention is a method for producing a sheet steel component to create, with which easy and inexpensive areas different ductility can be generated.

The The object is achieved with the features of claim 1.

advantageous Further developments are characterized in subclaims.

at The method according to the invention is a sheet steel component generated with areas of different ductility thereby, that specifically in desired surface areas the Behavior of the steel sheet during heating or cooling will be changed. As is known, steel changed when heating or cooling its crystalline Structure so that when heated and / or cooled depending on the temperature-time curve different phases, eg. B. ferrite or Perlite or austenite present. In just as well known this is Phase formation used for certain properties affecting a product made from these steels. An example of this is the curing, in particular the hardening of boron-manganese steels.

at known methods are made of such steels, for example Sheet metal components produced, heated to a temperature at which austenite forms in the structure, or even a complete one Conversion to austenite is achieved and then rapidly cooled, leaving a hardened texture forms, which allows to achieve strengths up to about 1,500 MPa. In the case of incomplete austenitization, i. H. lower Temperatures and / or reduced holding times can damage the structure homogeneous only to a certain part of the absolutely achievable hardness to be brought. Usually, these methods are either performed on the already formed sheet metal part or a Sheet metal plate is heated to the desired temperature, then hot formed and after hot forming so quickly cooled that the desired texture achieved.

at the process of the invention is the structure over the surface of the component or over the surface the board is variable, d. H. it will heat up in the Continuous furnace and / or cooling of the semifinished product during transfer from the continuous furnace to the press areas with different microstructures and thus different ductility or hardness generated. According to the invention, this is achieved by that the sheet metal plate or the sheet steel component with different Surfaces is formed.

different Surfaces in the sense of the invention means that surfaces are present, which differ in heating heat absorb or reflect heat or when cooling different heat radiate. This property is called emissivity. By adjusting the strength of the emissivity can according to the invention very sensitively Heat absorption and heat dissipation behavior of the corresponding Area controlled and thus the corresponding structure both during heating and during cooling.

One inventive approach for influencing Emissivity is the use of a metallic coating on the steel component or the output board and in particular a metallic coating with zinc or based on zinc. generally known form coatings of zinc or on the basis of zinc on surfaces of steel components during heating in the border region between steel zinc alloy layers, depending on the height and duration of use of the temperature as well a Durchlegierung is achievable. It turned out that Coatings with different compositions based on Zinc and iron and different zinc layer thicknesses to different Surface absorbencies or degrees of absorption to lead. This is due to the different strength of the alloy reaction of zinc with the underlying iron, what a different strong formation of surface oxides, in particular zinc oxide compounds, entails. Zinc oxide compounds typically have an im optically visible area slightly greenish to dark brown Coloring and, accordingly, the surface emissivity increases. So lead higher zinc deposits and / or thick Fe-Al Inhibiting layers in the heat treatment to low surface emissivities, while low zinc plating and / or thin Fe-Al Inhibiting layers to high surface emissions to lead. As the inhibiting layer, a layer is referred to by an aluminum additive in the zinc bath between the steel substrate and the zinc layer during the continuous hot dip coating and optionally subsequent heat treatment occurs.

According to the invention the surface emissivity but also by additional Coatings on inorganic and organic basis on one Zinc layer and / or aluminum-silicon layer - so-called Fire aluminized layers - and / or the bare metal or performed by roughening the surface become.

According to the invention, the surface emissivity is adjusted via the starting zinc layer thickness in the hot-dip coating or an electrolytic galvanizing of the steel strip. The starting zinc layer thickness can be adjusted by means of variable adjustment of the stripping pressure or additional electromagnetic fields in hot dip galvanizing. For electrolytic Coatings, the layer thickness to be applied is controlled by the strength of the electrolytically active current.

These Adjustment of the layer thickness already during the coating of the strip is carried out so that over the before already known sectional images of a band to be produced Boards and thus also the areas defined therewith different Emissivity the appropriate control, for example the stripping pressure or the parameters influencing the electrolysis, is determined. Thus, a corresponding steel strip already at the coating position and exact position with different Coating thicknesses formed, which after cutting the board and optionally the forming at a temperature treatment the Areas of different emissivity.

The The steel strip produced in this way is subsequently platinum plated in such a way that the Board, from which later the component by direct or indirect hot forming is made, at least two areas of different Starting zinc layer thickness, wherein the finished component more ductile microstructure using surface emissivity for structural adjustment when heating in a continuous furnace in the range of high output zinc coating or when exploiting the Surface emissivity for microstructure adjustment during cooling in the time of transfer of the board or of the preformed component from the furnace to the press in the area of lower initial zinc deposit comes to rest.

The Surface treatment of the steel strip to already before and / or during the furnace runtime different surface emissions can also be done in different ways.

This can according to the invention by a matting treatment, a dressage, d. H. a micro-contour of the surface, or an additional inorganic and / or organic Coating done.

additional inorganic and / or organic coatings can According to the invention, for example, phosphate-containing Substances that are defined on the steel strip but also on the Board or the preformed component, for example, by dipping, Spraying or steaming can be applied.

It is thus possible, the semi-finished areas in the final state have a high surface emissivity, form a particularly strong absorbing, on the one hand when heating in the continuous furnace, a rapid achievement of the austenitizing temperature or on the other hand a rapid cooling after removal of the furnace and thus to allow the formation of a mixed structure, even before the actual hardening or cooling process starts. The semi-finished parts can be a frosted, little received reflective or trained surface or with a temporary dark protective layer or for example provided with a metal oxide and / or metal nitride surface be, which is a particularly good absorption or release of heat radiation allows.

at The invention is advantageous in that it is possible to harden Steels used for curing a heat treatment have to be subjected to different areas To develop ductility, this training different Ductilities inline on the tape takes place, which is a significant Cost savings in addition but also high process reliability guaranteed. It is also advantageous that a harmonious Gradual hardness transition is achieved in contrast to several sheets of different hardness properties taylored welded blanks, have the abrupt transitions.

Furthermore, the semifinished product area, which in the end component is a hardened, martensitic structure should have, by a in the infrared range reflective element and / or an additional heating element, for example, in the form of a steel plate or molding as integral Component of the semi-finished carrier system in passing to Removal from the oven hampered by too rapid a cooling be, since in this case a free cooling in the ambient air is prevented.

It is also possible according to the invention, the different existing or in the continuous furnace differently forming To exploit surface dissimilarities in that for example, in a zonal continuous furnace only in the last separate Zone in a semi-finished parts area with high surface emissivity the austenitizing temperature is exceeded while in other semifinished areas with significantly lower surface emissivity the Austenitisierungstemperatur not reached at kiln removal and thus in the subsequent direct and / or indirect hot forming again areas of different ductility arise.

The The invention will be explained by way of example with reference to a drawing. It show here:

1 : the temperature-time profile of a 1 mm thick board with different initial zinc coating in a 900 ° C radiation furnace;

2 : Areas of different emissivity of a board after furnace removal with low and high initial zinc deposit;

3 : the temperature-time profile of a 1 mm thick board with a homogeneous, high initial zinc coating, wherein a region to produce a different emissivity with a zinc phosphate layer is coated in a radiation oven at 900 ° C;

4 : Areas of different emissivity of a board before and after heating with a zinc phosphate covered area 1b and a low initial zinc bearing area 2b;

5 : the temperature-time profile of a 1 mm thick board with different initial zinc coating after removal from the radiation furnace at 900 ° C;

6 : the temperature-time profile of a 1 mm thick board with a homogeneous, low initial zinc coating, wherein a region for generating a different emissivity with a boron nitride base solution is coated after removal from a radiation furnace at 900 ° C;

7 : Regions of different emissivity of a board after furnace removal with low initial zinc deposit 1c and an area with an additional boron nitride base coating 2c;

1 shows the temperature-time course of a 1 mm thick board ( 2 ) with different zinc coating in a 900 ° C radiation oven. While the area 1a of the board coated with a Z140 g / m ² hot dip coating rapidly heats up to over austenitizing temperature due to the surface oxides being formed, the temperature of the other area 2a of the board increased with a hot dip coating of Z275 g / m2. m ^{2 is} coated, comparatively slowly and is - while the other area is already fully austenitic - still below the Austenitisierungstemperatur. Only after a longer residence time in the oven, it comes to an equalization of the two temperatures. If the board thus heated is hardened between two water-cooled steel plates, even before the area 2a reaches the austenitizing temperature, two different microstructure areas are established. While region 1a becomes fully martensitic, in region 2a a mixed structure of preferably ferrite, pearlite and bainite with typical mechanical properties of R _p0.2 > 300-400 MPa, R _m > 500-700 MPa and A> 16% appears.

3 shows the temperature-time course of a 1 mm thick board ( 4 ) with a homogeneous zinc coating of Z275 g / m ² - wherein the partial area 1 b is covered with a zinc phosphate layer - in a 900 ° C radiation oven. While the area 1b of the board coated with a Z275 g / m ² hot dip coating and a zinc phosphate layer rapidly heats up to austenitizing temperature due to the forming surface oxides and the optically darker phosphate-containing layer, the temperature of the area 2b of the board rises, which is coated with a hot-dip coating of Z275 g / m ² , comparatively slowly and is - while the other area is already fully austenitic - still below the Austenitisierungstemperatur. Only after a longer residence time in the oven, it comes to an equalization of the two temperatures. If the board thus heated is hardened between two water-cooled steel plates, even before the area 2b reaches a temperature of about 820 ° C., two different microstructure areas are established. While area 1b becomes fully martensist, in area 2b a mixed structure of preferably ferrite, pearlite and bainite with typical mechanical properties of R _p0.2 > 300-400 MPa, R _m > 500-700 MPa and A> 16% is shown.

5 shows the temperature-time course of a 1 mm thick board ( 2 ) with different zinc coating after removal from a radiation oven at 900 ° C, the entire board was heated to approximately furnace temperature, that is fully austenitic. While the area 1a of the board coated with a Z140 g / m ² hot dip coating and rapidly cooling due to the surface oxides forming, ie having a high surface emissivity, in the ambient air, the temperature of the other area 2a of the board, the coated with a hot-dip coating of Z275 g / m ² , comparatively slowly from. If the board between water-cooled steel plates hardened so that the area 1a has passed through the temperature range between about 700 ° C and about 600 ° C to form a mixed structure and that the area 2a has not fallen below a temperature of about 700 ° C. , two different structural areas are established. While area 2a becomes fully martensitic, area 1a shows a mixed structure of preferably ferrite, pearlite and bainite with typical mechanical properties of R _p0.2 > 300-400 MPa, R _m > 500-700 MPa and A> 16%.

6 shows the temperature-time profile of a 2 mm thick board ( 7 ) with a homogeneous Zinc deposit of Z140 g / m ² - wherein the portion 2c is covered with a boron nitride layer - after removal from a radiation oven at 900 ° C, the entire board was heated to approximately furnace temperature, that is fully austenitic. While the area 1c of the board, only with a melt dip coating of Z140 g / m ^{2 is} coated, and rapidly cools due to the surface oxides forming, ie with a high surface emissivity, in the ambient air, the temperature of the other area 2c of the board, which is coated with boron nitride and a comparatively low surface emissivity decreases after removal of the furnace, it slowly decreases relative to the area 1c. If the board between water-cooled steel plates hardened so that the area 1c has passed through the temperature range between about 700 ° C and about 600 ° C to form a mixed structure and that the area 2c has not fallen below a temperature of about 700 ° C. , two different structural areas are established. While region 2c becomes fully martensitic, in region 1c a mixed structure of preferably ferrite, pearlite and bainite with typical mechanical properties of R _p0.2 > 300-400 MPa, R _m > 500-700 MPa and A> 16% is found.

The Invention is not applicable to hardenable steels, For example, the type 22MnB5, limited. The described Method is such. B. also on dual-phase steels, but complex phase steels also TRIP steels (transformation induced plasticity) or TWIP steels (Twinning Induced Plasticity) applicable.

As shown, it succeeds with the invention, the structure over the surface of a component or over the surface to make a board variable, where it succeeds during heating and cooling, areas with different microstructures and thus different ductility or hardness to create.

in this connection is the process according to the invention particularly favorable, because it succeeds inline the surface of the sheet steel strip, d. H. in a running tape process. at the steel straps can be fixed from the beginning where the areas of different ductility are positioned should. Accordingly, with variable wiping nozzles or electric fields in these areas the zinc coating like desired to be set. In the further process can then the appropriate cuts and punches are made.

alternative this or in addition, the predetermined Areas of different ductility with coatings, Roughening, etc. also two-dimensional on the output board or be formed over the preformed component. These The procedure is especially for the selective local Coating and thus adjusting the surface emissivity suitable, which locally on the finished component, the ductility can be adjusted depending on the requirement. A possibility consists, for example, of the additional inorganic and / or organic coatings by selective brushing or rolling, d. H. a transmission over a rotating roller to apply to the metal surface. The application can also by selective spraying, spraying or imprinting by means of a suitable spraying, spraying or printing device (for example by screen printing) or a suitable printer system or a known per se Way done.

By the described procedure can be desired ductile and less ductile areas of almost any shape with simple coating systems at low cost very simple, apply quickly and precisely. The described methods allow a high degree of flexibility and flexibility are especially for three-dimensional preformed steel components suitable for a wide variety of geometries. So can In a simple manner, three-dimensional stampings are selectively involved Coatings for targeted adjustment of surface emissivity be provided.

There these processes not only on the finished board or the reshaping Component should take place, but already at a very early Stadium, the effort is minimized and thus the costs are reduced.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• DE 19743802 C2 [0004]
• - DE 20014361 U1 [0005]
• - DE 10256621 B3 [0006]
• - DE 10208216 C1 [0007]

Claims (10)

Method for producing a hardened sheet steel component with areas of different ductility, the behavior of the steel sheet when heated changed so will that heat absorption capacity of the steel sheet during curing dependent on curing is influenced by the desired degree of hardness, where for high degrees of hardness a good heat absorption behavior and for less severe areas a reduced heat absorption behavior be realized and thereby the structure over the surface of the component or over the surface of the Board is designed variably, with the adjustment of the microstructure and the setting of the heat absorption behavior over the surface emissivity is controlled. Method for producing a hardened sheet steel component with areas of different ductility, the behavior the steel sheet during cooling changed so will that heat dissipation capacity of the steel sheet during a transfer to subsequent Abhühleinrichtungen and / or on cooling, depending on the desired Hardness is influenced, with high degrees of hardness a reduced heat dissipation behavior and for less hard areas realized a good heat dissipation behavior and thereby the structure over the surface of the component or over the surface of the board variable is designed, the attitude of the structure and the Setting the heat dissipation behavior over the Surface emissivity is controlled. Method according to claim 1 or 2, characterized that the surface emissivity of the steel sheet is realized by metallic supports, wherein the metallic Pads with different thicknesses are applied to the steel sheet, so that during heating depends on the thickness of the metallic Conditions and / or by the reaction of the support with the steel sheet Surfaces with varying degrees of emissivity be created. Method according to one of claims 1 to 3, characterized in that the surface emissivity by coatings on metallic and / or inorganic and / or organic base on the steel sheet and / or a first metallic one Layer are formed on the steel sheet. Method according to one of the preceding claims, characterized in that the surface emissivity brought about by mechanical treatments of the surface wherein the mechanical treatment is a roughening, a temper rolling step, a jet step with particles, a grinding or polishing step is. Method according to one of the preceding claims, characterized in that the areas of the sheet steel component, in the final state a high surface emissivity should be designed to be highly absorbent to the Heating in the oven to reach the necessary for curing Austenitizing temperature or on the other hand, a rapid cooling after removal of the furnace and thus the formation of a mixed structure to enable. Method according to one of the preceding claims, characterized in that the metallic coating comprises a zinc layer, Zinc alloy layer, a zinc-aluminum layer, an aluminum-zinc layer or an aluminum-silicon layer or other aluminum alloy layer is. Method according to one of the preceding claims, characterized in that to achieve different ductility the steel strip at least two areas of different output metal layer thicknesses having, in the finished component ductile structural area exploiting surface emissivity for microstructure adjustment Heating in the oven in the area of the high initial metal coating or by exploiting the surface emissivity for structural adjustment when cooling down in time the transfer of the board or the preformed component from the furnace into the press in the area of lower initial metal pad lie comes. Method according to one of the preceding claims, characterized in that the areas of high surface emissivity are designed to be very absorbent, in addition to metal layers these areas a frosted, little reflective or trained Surface preserved or with a temporary absorbent layer, for example with a metal oxide surface and / or Metallnitidoberfläche are provided. Method according to one of claims 1 to 8, characterized in that the areas of low surface emissivity are designed to be highly reflective, in addition to metal layers these areas with a temporary reflective layer, for example with a metal oxide surface and / or Metal nitride surface are provided.