EP1350865A2 - Tinned and phosphatised sheet and method for producing such a sheet - Google Patents

Abstract

The present invention relates to a steel sheet for the production of steel components by forming, in particular deep drawing, coated with a phosphate layer, the phosphorus content of which is at most 0.05 g / m ² . In addition, the invention relates to a method for producing a galvanized steel strip provided with a phosphate coating, in which the following steps are carried out: galvanizing the steel strip in a strip galvanizing plant and applying a phosphate layer to the galvanized steel strip, the phosphorus content of which preferably does not exceed 0.05 g / m ² Is 0.005 to 0.02 g / m ² .

Description

The invention relates to a sheet from one Steel material used for the production of Steel components by forming, especially deep drawing, is determined and covered with a phosphate layer. In addition, the invention relates to a method for Production of such a sheet.

Of sheet steel used in the body shop are next to good ductility a high Corrosion resistance required. To the latter too steel sheets are usually met today provided with a zinc coating that the steel material against direct contact with the environment protects. Due to the galvanizing, even those in themselves rust-prone steel alloys for manufacturing more durable, insensitive to corrosive attacks Automotive bodies are used that stand out are characterized by particularly good ductility. This Steel materials allow it to be complex shaped, tall Form resilient components with thin sheet thicknesses. Body components made from such steel are easy to process and own on End of life of the respective vehicle excellent recyclability.

The good protective effect of the zinc layer and that in the The economy has steadily increased in the past modern galvanizing plants have become a strong one Increase in the use of galvanized steel sheets in the Automobile construction led. The zinc coating is thereby usually applied in strip finishing plants. To hot dip galvanizing is suitable, in which the Steel tape in baths made of zinc or zinc alloys a temperature between 440 ° C and 465 ° C is immersed. Alternatively, the zinc coating can also be electrolytic be deposited on the steel material. About that In addition, the steel sheets can be immersed in a zinc or zinc alloy bath to anneal a to get particularly resilient zinc coating ( "Galvanealing").

In addition to corrosion protection, there is a special in Automobile body construction demand in a good Paintability of the processed steel sheets. This affects the paint application on the one hand and the Adhesion of the paint on the sheet. To meet these requirements thin sheets have long been to be met phosphated after painting. With this pretreatment the surface of the steel sheet to be coated into a Phosphating solution immersed or with phosphate solutions splashing. Combined procedures for applying the Phosphate solution are also known.

The phosphating solutions can contain zinc, manganese and nickel ions in addition to the required phosphate ion (PO ₄ ) contents. Such phosphating solutions containing zinc, manganese and nickel ions are also referred to in technical terms as "trication-phosphating solution" (DE 197 56 735 A1).

The phosphating can be carried out piece by piece after the forming of the processed steel sheet and before painting. However, it is also possible to apply the phosphate coating in high-speed belt treatment plants. An essential parameter of the success control is the weight of the coating recorded per unit area. For sheet metal processed in automobile construction, this is usually 0.8 g / m ² to 4 g / m ² , layer weights of 1 g / m ² to 2 g / m ^{2 being} preferred in the prior art. A layer weight of 1 g / m ² corresponds to a phosphorus content (Sg _p ) of 140 mg / m ² in this layer.

In practice, it is common for piece phosphating difficult to get a completely covering phosphate layer achieve. Because of the sometimes unfavorable geometries the body shells, especially in the cavities and Folding, the loading with a tight closed phosphate layer considerably more difficult. This can have an increased susceptibility to corrosion and a Deterioration of the wettability of the sheet surface cause. Therefore one has gone over to the Steel sheets in the pass before they are formed phosphatize. This pre-phosphating does not replace the actual, just before painting the phosphating of the respective component individual components, but leads to a saving of equipment to improve the Uniformity and tightness with which the Phosphate layer is distributed on the sheet surface.

It has been found that phosphated sheets not only have improved painting properties, but can also be shaped particularly well. So is for example in EP 0 489 105 B1 (DE 690 10 207 T) a process for deep drawing metal sheets has been proposed according to the prior to deep drawing a salt of the sheet metal or the deep-drawing tool Alkali metal such as Li, Na or K, and one related to the metal forming the sheet chemically inert anions, selected from the group of phosphates, deposited the deposition of the salt by application an aqueous solution. The salt should on the Tool in deep drawing by reaction with one Deep drawing oil form a soap through which the friction between tool and workpiece is significantly reduced.

The object of the invention was one for Forming into a component, especially for the Deep drawing to create particularly suitable steel sheet, which is easy to paint and also with high degrees of forming in the forming tool the risk of Cracking and similar component defects is minimized. In addition, a procedure should be specified with which such sheets are made in a simple manner can be.

This object is achieved in relation to the product by a sheet metal produced from a steel material, which is intended for the production of steel components by forming, in particular deep drawing, and is covered with a phosphate layer, the phosphorus content of which is at most 0.05 g / m ² P. ,

Particularly advantageous results are obtained with a phosphorus content of 0.005-0.02 g / m ² . The effect becomes very small below 0.005 g / m ² , and further improvements can then be achieved above 0.02 g / m ² .

With regard to the method, the above-mentioned object is achieved in that, in the production of a galvanized steel strip provided with a phosphate coating, the steel strip is first provided with a zinc coating in a strip galvanizing plant and that a phosphate layer is then applied to the galvanized steel strip, the phosphorus content of which is at most Is 0.05 g / m ² .

According to the invention is to be deformed Steel sheet applied a layer of phosphate, the one very small thickness and a correspondingly small Maximum phosphorus content of 50 mg P per square meter having. Surprisingly, sheets can be used a thin layer of phosphate much better than Deform phosphate-free sheets in a forming tool and can be compared with sheets that are known in the Has been covered with larger phosphate layer thicknesses are. This is particularly evident in deep-drawing operations with high degrees of deformation that when in use Sheet metal coated according to the invention is a clear one Reduction of friction between tool and sheet established. This reduction in friction allows such Sheets, the deformability itself because of the conventional procedure in the forming tool occurring voltages is limited beyond these limits to deform out. In this way, the for example in the production of complex shaped Minimize components involved. simultaneously have sheets obtained according to the invention excellent paintability, since the thin, with low Layer thickness applied phosphate layer especially evenly distributed on the sheet surface and so one good basis for the further piece by piece on the component applied phosphate coating forms.

The invention proves to be particularly favorable in such cases Sheets in which the phosphate layer on one on the Steel material trained zinc layer is applied. The success of the invention is independent of the type and how the zinc coating is applied. So the zinc layer can be used in sheets according to the invention Generate electrolytically or by hot-dip galvanizing. As well it is possible to hot dip galvanize with subsequent annealing (galvanealing). The In this case, annealing is carried out in a known manner above the melting point of zinc Temperatures. This from the combination of Dip galvanizing and annealing formed the galvanizing process is also known as "galvanealing" designated. It leads to a zinc coating, which in It consists essentially only of iron-zinc compounds and good adhesion with particularly good Formability distinguishes.

Depending on the requirement profile of the automobile manufacturer the phosphate layer also on sheets according to the invention one-sided on only one of the belt surfaces or on both sides on the top and on the Bottom of the sheet to be applied.

The method according to the invention can be particularly effective perform economically by the individual Work steps carried out in a production line become. With such an "inline" successive Implementation of the various coating steps stands at high when leaving the production line Throughput a product is available which immediately afterwards to form a sheet metal component leaves.

If necessary, the invention phosphate coated tape before it is deformed with a Oil sprayed to reduce friction during the To further reduce the deformation process.

The dilute phosphating solution used to produce the thin phosphate layer, which according to the invention is kept thin and limited to a phosphorus content of 0.05 g / m ² , can be sprayed onto the steel strip to be coated. However, practical tests have shown that particularly good coating results are obtained if the applied volume flow is dimensioned such that the surface of the steel strip to be coated is completely rinsed with phosphate solution.

Favorable for the usage properties of the It is the phosphate coating produced according to the invention also if the phosphate solution in addition to zinc ions additional Contains cations. So there is the received Phosphate layer when Mn and Ni ions are added to the for the coating not only used phosphate solution Zinc based Hopeit, but it also contains Ni and Mn-modified hop components. The manganese content causes the formation of small, densely packed Crystals leading to increased alkali resistance lead and thus improve the corrosion protection. nickel promotes the formation of a thin one Phosphate layer and increases the infiltration and Stone chip resistance on the phosphate layer applied paint.

Fig. 1

den Nachbehandlungsabschnitt einer Fertigungslinie zum Beschichten eines Stahlbands in schematischer Darstellung;

Diag. 1

die beim Tiefziehen eines erfindungsgemäß beschichteten Stahlblechs und eines konventionellen Blechs auftretenden Ziehspannungen Z_spg aufgetragen über die Normalkraft F_N;

Diag. 2

den sich bei einem erfindungsgemäß beschichteten Stahlblech einstellenden reduzierten Reibwert µ_red aufgetragen über das Schichtgewicht der Phophatschichtdicke Sg_p;

The invention is explained in more detail below on the basis of a drawing illustrating an exemplary embodiment. Show it:

Fig. 1

the post-treatment section of a production line for coating a steel strip in a schematic representation;

Diag. 1

the drawing stresses Z _spg occurring during deep drawing of a steel sheet coated according to the invention and a conventional sheet plotted against the normal force F _N ;

Diag. 2

the reduced coefficient of friction μ _red which occurs in a steel sheet coated according to the invention, plotted against the layer weight of the phosphate layer thickness Sg _p ;

The aftertreatment section 1 one to manufacture one coated according to the invention, for forming into car body components certain steel sheet S used Production line points among others, not here facilities shown a first Cleaning device 2, an activation device 3, a phosphate rinsing device 4, a passivation device 5, a dryer 6, a trimming shear 7, one Signing device 8, an inspection device 9, a Oiling device 10 and a reeling device 11. These devices 2 to 10 are from the steel strip S "inline" successively in the pass until it into a coil 12 in the coiler 11 coiled and then further processed is fed.

The aftertreatment section 1 in the conveying direction F. incoming, previously in a known manner Hot dip galvanizing with subsequent annealing comprehensive galvanizing treatment zinc coated Steel strip S is in the cleaning device 2 first rinsed with an alkaline detergent that Dirt particles removed from the steel strip S and one Pickling of the belt surface causes. When leaving the Cleaning device 2 has the steel strip S degreased, perfectly water-wettable surfaces.

Immediately afterwards, the steel strip S runs into the Activation device 3, in which one Activation solution to be coated Belt surfaces is sprayed. As an activation solution are aqueous dispersions of Titanium orthophosphates based on sodium phosphates used.

The purpose of applying the activation solution is targeted crystallization nuclei on the strip surface multiply. This way the number of crystals per unit area increased and, accordingly, the Crystal size and the layer weight reduced. About that In addition, the crystallization nuclei cause that in the subsequently carried out small phosphating Zinc phosphate crystals are formed. little one Zinc phosphate crystals prove to be cheap because they are when forming the steel strip into components also under high effective forming forces the risk of tearing the Reduce the phosphate layer.

After activation, the steel strip S enters the phosphate rinsing device 4. Rinsing nozzles, not shown here, are installed therein, via which the phosphating solution is rinsed onto the surfaces of the steel strip S to be coated. The phosphating solution used for this purpose is a solution known per se under the trade name "Granodine 5854 E10", but is very dilute for carrying out the process according to the invention. This solution is composed according to the "tri-cation system" and contains not only zinc ions but also Ni and Mg ions in order to ensure optimized usage properties of the phosphate layer applied to the belt surfaces. The dilution of the phosphating solution is chosen so that the phosphate coatings produced on the surfaces of the steel strip S have a maximum phosphorus content of 10 mg / m ² .

After leaving the phosphating device 4, the coated strip surfaces in the passivation device 5 with an inorganic, containing titanium and zircon Solution wetted to chemically inactivate it. Around any deposits on the belt surfaces to remove and suppress their formation the belt surfaces then with deionized water rinsed.

The steel strip S then runs through the dryer 6. It leaves this with dry surfaces, then the Wishes of the respective customer in the Trimming scissors 7 to be trimmed. In the Signing device 8 is then carried out without contact a marking of the steel strip S

The finished coated and marked steel strip S is then in the inspection device 9 on the Quality of its surface quality and Dimensional accuracy checked before it is in the oiling device 10 is sprayed with an oil. This oil protects the Belt surface during transport and diminishes above in addition, the shape of the steel sheet S occurring friction.

After reeling in the reel-up device 11, the steel strip S is delivered as a coil 12 and deep-drawn by the processor into body components. From Diag. 1 shows that in the case of processing steel sheets S _Erf coated with a phosphate layer (layer weight Sg _p = 5 mg / m ² ) according to the invention, with increasingly higher normal forces F _N compared to conventionally oiled but not phosphate- _coated steel sheets S _{sdT, they are} becoming ever smaller Tensile stresses Zspg occur. Accordingly, Diag. 2 that phosphate coatings with a layer weight Sg _{p of} > 0 g / m ² but not more than 0.02 g / m ² lead to a reduced coefficient of friction µ _red . If the upper limit of 20 mg / m ^{2 to be} observed according to the invention is exceeded, there is no significant improvement in the coefficient of friction μ _red .

reference numeral

1

treatment section

2

cleaning device

3

activation device

4

Phosphatspüleinrichtung

5

Passivation device

6

dryer

7

trimming shears

8th

signing device

9

inspection device

10

Einöleinrichtung

11

Aufhaspeleinrichtung

12

coil

F

conveying direction

S

steel strip

Claims (15)

Steel sheet for the production of steel components by forming, in particular deep drawing, covered with a phosphate layer, the phosphorus content of which is at most 0.05 g / m ² . Sheet according to claim 1, characterized in that the phosphorus content of the phosphate layer is 0.005 to 0.02 g / m ² . Sheet according to claim 1 or 2, characterized in that the phosphate layer is applied to a zinc layer formed on the steel material. Sheet according to claim 3, characterized in that the zinc layer is produced electrolytically. Sheet according to claim 3, characterized in that the zinc layer is produced by hot-dip galvanizing. Sheet according to claim 5, characterized in that the zinc layer is produced with subsequent annealing (galvanealing). Sheet according to one of the preceding claims, characterized in that the phosphate layer is applied to its top and bottom. Method for producing a galvanized steel strip with a phosphate coating, in which the following steps are carried out: Galvanizing the steel strip in a strip galvanizing plant, Application of a phosphate layer on the galvanized steel strip, the phosphorus content at most 0.05 g / m ^2, preferably 0.005 to 0.02 g / m ² . A method according to claim 8, characterized in that the work steps are carried out in a production line. Method according to one of claims 8 or 9, characterized in that the steel strip is electrolytically zinc-coated. Method according to one of claims 8 or 9, characterized in that the steel strip is hot-dip galvanized. A method according to claim 11, characterized in that the steel strip undergoes a subsequent annealing at temperatures above the melting point of the zinc. Method according to one of claims 8 to 12, characterized in that a diluted phosphating solution is rinsed onto the surface of the steel strip to be coated in order to apply the phosphate layer. A method according to claim 13, characterized in that the phosphate solution contains additional cations in addition to zinc ions. A method according to claim 14, characterized in that the phosphate solution contains manganese and nickel ions.

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