JP2010535944A - Method for making an active cathode anti-corrosion coating on steel parts - Google Patents

Abstract

The present invention relates to a method for producing an active corrosion resistant coating on a steel part. Develop active corrosion resistant coatings that can be applied on an industrial scale using conventional means (eg dipping, spraying, flooding) and intended for hot-formed steel parts, especially press-hardened steel parts, with anti-scaling means Therefore, the present invention provides a. Using a steel element provided with an anti-scaling layer; b. Annealing the steel element at a temperature in excess of 600 ° C. in an annealing furnace for the purpose of hardening, semi-hot forming or hot forming, or press hardening, in which case a reaction layer is produced, annealing C. Applying a corrosion resistant coating to the annealed reaction layer.
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Description

  The present invention relates to a method for producing an active corrosion resistant coating on a steel part.

  Hot forming processes are increasingly being used to produce the required class of high strength steel parts, for example, high strength steel parts such as structural body parts for automotive manufacturing. One particular type of hot forming is press hardening, in which special steel (usually manganese-boron steel) is heated in a forming tool to the austenitizing temperature, hot formed and quench hardened. It is a process called. A high mechanical strength martensite microstructure is obtained, which makes it possible to produce parts that are thin and therefore light in weight but high in strength. Austenitization occurs at temperatures above 850 ° C. At this temperature, significant scale formation occurs on the steel surface. The scale forms so rapidly that it undergoes scale formation when it comes into contact with atmospheric oxygen as it is transferred from the furnace to the mold, even in the atmosphere of a protective gas, for example even the part heated in a continuous furnace. In the case of a production line that is configured for the formation of a number of pieces in the manufacture of automobiles, it is an economic or manufacturing aspect to work on all sections of the line (from heating to molding) under protective gas. It is not valid from any of the above.

  Once formed, the scale tends to flake off, has a rough surface and is brittle. Therefore, in order to damage the part and the mold, it must be removed from the part at high cost after press curing, for example by blasting. The standard mold cleaning required substantially increases the cycle time and the material removed by blasting needs to be compensated by using thicker metal sheets. Therefore, it is common to use a steel sheet with a coating that protects against scaling for press hardening.

  Patent Document 1 describes the use of a hot dip aluminized steel type. These are coated with an Al—Si alloy layer of about 20 μm to 30 μm thickness applied by hot dip coating. This Al-Si coating actually exhibits some degree of corrosion protection against hot dip aluminized sheet steel while it is being stored. This means that the sheet and coil need not be oiled for storage and transport purposes. However, after the annealing process used during hot forming, the corrosion resistance effect of the coating is significantly reduced. This becomes evident, for example, when a hot dip aluminized steel sheet annealed at 950 ° C. is tested using the salt spray test according to German standard DIN 50021. Only a few days later, red rust formation is seen across the surface. After the entire automobile body has been assembled and phosphorylated, an electrophoretic dip coating can be applied to the affected parts. This provides the part with the appropriate anticorrosion used for certain applications. However, if the electrophoretic dip coating is damaged, proper active corrosion protection is no longer guaranteed. Under standard conditions of direct press curing, the electrical resistance of the hot dip aluminized sheet is in the range of less than 1 milliohm after the curing process.

  Another form of protection against scaling, as described in US Pat. No. 5,637,077, is based on wet-chemical coating of steel sheets or coils with a coating composition consisting of an organosilicon binder, aluminum particles and a solid lubricant. This can be hot formed or cold formed, protecting against scaling during hot forming. After the hot forming (press curing) process, the inorganic reaction layer is removed by blasting. The time and energy required to do this is significantly lower than that required to remove scale. Removal of this layer by blasting is necessary because the layer does not have the conductivity required for subsequent resistance spot welding. Bare metal sheets are welded, then phosphated and subjected to electrophoretic dip coating.

  The described improved wet-chemical anti-scaling coating, which is the subject of U.S. Patent No. 5,637,086, has the electrical conductivity required for resistance spot welding and electrophoretic dip coating, and therefore remains on the part after press curing. Get the rest. Under standard conditions of press curing, the electrical resistance of these sheets is in the range of less than 5 mOhm after the curing process. If the part is subsequently subjected to a welding process, in particular a resistance spot welding process, or to an electrophoretic hot dip coating, the observation of process parameters that result in the formation of a conductive reactive layer when a steel sheet with an anti-scaling coating is annealed. Especially important. It has been found beneficial to use a protective gas atmosphere (eg, nitrogen or argon) or a low oxygen content (-10%) furnace atmosphere. Short heating also results in high electrical conductivity, thus providing weldability by providing low electrical resistance in the range of less than 3 milliohms. After welding, phosphating and electrophoretic dip coating, such parts exhibit the appropriate corrosion protection used in certain fields. However, even in this case, there is no active anticorrosion that protects the steel in the event of damage to the electrophoretic dip coating.

  The comprehensive advantage of wet-chemical anti-scaling coatings described as exceeding hot dip aluminized is that cycle times are reduced because no diffusion layers need to be formed when heating to the austenitizing temperature. It is. In addition, there is no danger of any melting during heating, meaning that induction heating or conduction heating may be used during press curing.

  The applications of Patent Literature 4, Patent Literature 5 and Patent Literature 6 describe methods for producing various hardened steel parts. In either case, the steel is provided with a protective coating consisting of zinc in combination with another element (especially aluminum) that has an affinity for oxygen. This protective coating is applied by a hot dip process in Patent Document 5 and applied by a hot dip process or an electroplating process in Patent Document 4 and Patent Document 6. However, these coatings containing zinc as the main element are very susceptible to oxidation and evaporation at the austenitizing temperature required in the press curing process. A minute amount of dirt (for example, dust) present on the surface burns, and a defect occurs in that portion. The three listed applications are based on US Pat. No. 6,057,031 (“High Strength Corrosion Resistant Sheet Steel Parts”) where the cathode corrosion resistance of the coating is clearly described. In practice, however, when suitable parts that are not damaged on the surface are obtained within a narrow process window, the cathodic corrosion resistance of zinc is no longer similar to that of the first after annealing, and the matrix into the coating Due to the diffusion of iron from the steel, the parts corrode and form red rust relatively easily. The same is true for the zinc coating described in US Pat. No. 6,057,028, which is protected from evaporation under press-hardening conditions by an additional layer of zinc oxide.

European Patent Application Publication No. 1013785 International Publication No. 2006/040030 Pamphlet International Publication No. 2007/076766 Pamphlet International Publication No. 2005/021820 Pamphlet International Publication No. 2005/021821 Pamphlet International Publication No. 2005/021822 Pamphlet Australian Patent No. 41878 European Patent Application Publication No. 1439240

  The object of the present invention can be applied on an industrial scale using conventional means (e.g. dipping, spraying, flooding or rolling) and also for hot-formed steel parts, in particular press-hardened steel parts, provided with anti-scaling means. To develop the intended active corrosion resistant coating.

This purpose is described in the preamble and the following process steps:
a. Using a steel element provided with an anti-scaling layer;
b. Annealing the steel element at a temperature in excess of 600 ° C. in an annealing furnace for the purpose of hardening, semi-hot forming or hot forming, or press hardening, thus producing a reaction layer;
c. Applying a corrosion resistant coating to the annealed reaction layer;
This is achieved by the present invention by a method comprising:

In an alternative embodiment, this purpose is described in the preamble and the following process steps:
a. Using a steel element provided with an anti-scaling layer;
b. Applying a corrosion resistant coating to the anti-scaling layer;
c. Annealing the steel element at a temperature in excess of 600 ° C. in an annealing furnace for the purpose of hardening, semi-hot forming or hot forming, or press hardening, thus producing a reaction layer;
This is achieved by the present invention by a method comprising:

  For this reason, the present invention is based on the use of a special anti-scaling coating on the steel during hot forming at temperatures above 600 ° C., in particular to prevent scale formation during press hardening.

  Surprisingly, special coating compositions consisting of metal oxides and metal pigments, in particular zinc pigments, or zinc pigments and aluminum pigments, have these coating compositions even when the layer thickness is in the small μm range. It has been found that the steel is effectively protected from corrosion whether applied directly on the surface of the metal steel during annealing or on a reactive layer formed from an anti-scale coating. High resistance edge protection is imparted to the part, and it can be overcoated, phosphated or dip coated without any problems, especially by the electrophoretic dip coating process.

  An embodiment of the present invention is that the annealing is performed at a temperature exceeding 850 ° C.

  In accordance with the present invention, hardenable steel is annealed by conduction or induction in a gas-based annealing furnace or an electricity-based annealing furnace.

  A beneficial embodiment of the present invention is that the oxygen content in the annealing furnace atmosphere is 0% to 10%.

  It is also possible that the anti-scaling layer comprises an aluminum alloy, an aluminum pigment, a coating containing an aluminum pigment, a magnesium alloy, a magnesium pigment, a coating containing a magnesium pigment, a zinc alloy, a zinc pigment, or a coating containing a zinc pigment. It is within the scope of the present invention.

  It is also within the scope of the present invention that after the formation process, the anti-scaling layer has a maximum electrical resistance of 10 mΩ, preferably a maximum electrical resistance of 5 mΩ.

  Furthermore, it is advantageous for the finished part to have a maximum electrical resistance of 10 mΩ, preferably a maximum electrical resistance of 5 mΩ.

  Two previous measures ensure that resistance spot welding is possible.

  In wet-chemical processes, in particular spraying, flooding, rolling or dipping processes, it is further advantageous to apply a corrosion-resistant layer to the reaction layer annealed from the liquid phase.

  According to the invention, the layer thickness of the corrosion-resistant layer is less than 50 μm, preferably less than 20 μm, in particular less than 10 μm.

  It is within the scope of the present invention to dilute the corrosion resistant layer with a solvent before application.

  In one embodiment of the present invention, the corrosion-resistant layer is applied and then dried at a temperature of room temperature to 400 ° C, preferably room temperature to 250 ° C.

  Furthermore, it is within the scope of the present invention that the corrosion resistant layer contains a binder and a metal pigment.

  In this regard, the corrosion resistant layer is 10 wt. % To 100 wt. %, Preferably 50 wt. % To 100 wt. %, Especially 70 wt. % To 95 wt. It has been found advantageous to contain 1% metallic zinc pigment and / or magnesium pigment.

  In this regard, the corrosion resistant layer has a maximum of 50 wt. It is also advantageous to contain 1% metallic aluminum pigment.

  In a preferred embodiment of the present invention, the binder used in the corrosion resistant layer is 5 wt. % To 100 wt. % Metal oxide, in particular titanium oxide, aluminum oxide or zirconium oxide.

  The binder used for the corrosion resistant layer is up to 50 wt. It is also within the scope of the present invention to contain a binder, silicone, siloxane or wax made by the% sol-gel method.

  Furthermore, it is within the scope of the invention for the corrosion resistant layer to contain a solid state lubricant, in particular graphite or boron nitride.

  The invention resides in that the steel element is in the form of a sheet, coil, part or other solid.

  A particular embodiment of the invention is that the coated substrate is a steel element that has undergone a hardening process.

  It is also within the scope of the present invention for the steel element to be formed in a hydroforming process.

  Another particular embodiment is that the coated substrate is a steel element that is of the kind common in the curing process and is provided with an anti-scale layer that remains on the part.

  Furthermore, the steel element consists of an assembly of parts made of a wide variety of alloy steels with or without a metal coating such as an aluminum coating or zinc coating, or a coating containing metal pigments, welding, bonding, bolts It is within the scope of the present invention to join together by standard joining methods such as tightening or riveting.

  A preferred embodiment of the present invention is to provide a complete or partial coating on the steel element that affects the heating behavior of the steel part (s) prior to annealing.

  In this situation, in order to reduce the heating time, the furnace time and / or the diffusion time, a homogeneous heat ray absorbing coating, for example a black coating, or a non-homogeneous comprising heat ray absorbing areas and heat ray reflecting areas distributed over the surface of the steel element. Coatings such as partially black coatings and partially silver coatings can be provided on the steel element, so that this variation in the absorption of infrared radiation at the surface can, for example, form various hardening zones. It is possible to selectively control the input of energy from region to region. This means may of course be combined with the assembly described so far, where the steel elements comprise a wide variety of parts that are joined together.

  An embodiment of the present invention is that a part or assembly of parts provided with a corrosion-resistant layer can be welded together with a generally weldable alloy steel or with a steel grade provided with a metal coating. .

  A particular embodiment of the invention is that the electrical resistance of the steel elements used is not significantly affected by the corrosion resistant layer.

  Finally, the scope of the present invention relates to machine manufacturing, in particular automobile manufacturing, construction, in particular steel products, process engineering, aerospace engineering, power plant and power plant engineering, electrical engineering, medical engineering, sports equipment, horticulture. Landscaping design, tool making, agricultural machinery, furniture, kitchen, home appliances, toys, sports products, camping equipment, caravans, window and door frames, heating equipment, heat exchangers, air conditioners, escalators, conveyors, oil platforms, jewelry , Locomotives, rails, transport systems, cranes, furnaces, engines and engine accessories, pistons, seal rings, exhaust systems, ABS and brake systems, brake discs, chassis parts, wheels, rims, sanitary products, lamps and design products For the production of corrosion-resistant parts or assemblies according to the invention It extends to the use of the law.

  The present invention will be described below with reference to embodiments.

Example 1
A degreased 22MnB5A steel strip moving at 60 m / min is roll coated with a coating material according to US Pat. The coating material is cured at a PMT (Peak Metal Temperature) of 200 ° C. to 250 ° C. The coated steel strip is cut into a compatible material and pre-drawn into a preform in the cold forming process. This preform was treated with 10 vol. In a nitrogen atmosphere having a maximum oxygen content of 5%, heat to a temperature of 950 ° C. for 4 minutes in an electric continuous furnace, transfer to a mold, hot mold there, and quench hardening by cooling to 200 ° C. for 20 s. I do.

  A suitable corrosion resistant coating for the described press-cured parts is made as follows.

  23.6 g of aluminum pigment paste (eg, Decomet Hochglanz Al 1002/10 from Schlenk) and 138.1 g of zinc pigment paste (Eckart's Tapa TE Zinc AT) are stirred into 74.4 g of 1-butanol solvent. And homogeneously mixed for 20 minutes using a dissolver operating at a speed of 1000 rpm. 163.3 g of tetrabutyl orthotitanate (from Fluka) is stirred into this solution. Add 5 g Byk 348 wetting agent (byk chemie) before further processing.

The coating solution is applied to the entire surface of the press-cured part using a paint spray gun (eg, Sat Jet, 1.2 mm nozzle) that produces a layer thickness of 3 μm to 10 μm after drying and curing. The coating solution cures within 1 hour of application at room temperature or within 20 minutes at 180 ° C.
Example 2:
Parts with an aluminum anti-scaling coating (eg, Usibor) are subjected to a press hardening process as in Example 1.

  A suitable corrosion resistant coating for this part is made as follows.

  138.1 g of zinc pigment paste (Stapa TE Zinc AT from Eckart) is stirred in 400 g of 1-butanol solvent and homogeneously mixed for 20 minutes using a dissolver operating at a speed of 1000 rpm. 163.3 g of tetrabutyl orthotitanate (from Fluka) is stirred into this solution.

  A mixture of 40 g methyltriethoxysilane (from Fluka) and 10 g tetraethoxysilane (from Fluka) is hydrolyzed by stirring with 15 g of 1% orthophosphoric acid. After 5 hours of stirring, the reaction mixture is single phase and the reaction mixture is stirred into the dispersion to make a homogeneous solution.

  A coating solution is prepared in an amount sufficient to fill a suitably controlled immersion bath. The part is lowered into a dipping bath containing the coating solution by a crane, and the whole surface is uniformly wetted and then lifted again. After all of the excess coating solution has been dropped, the parts are transferred to an oven that cures the coating at 180 ° C. for 20 minutes.

After processing, the composite element comprising steel, aluminum and corrosion resistant layer has a resistance of less than 10 mOhm and can be joined without difficulty to other sheets by resistance spot welding.
Example 3:
A body part is produced from a steel material provided with an Al-Si dip coating by press hardening and a steel material coated according to Patent Document 3. These are joined with uncoated steel parts by resistance spot welding to form an assembly.

  A corrosion resistant coating suitable for this assembly is made as follows.

  33.0 g aluminum oxide powder (eg Aeroxide Alu C from Degussa), 41.3 g zinc powder (Standard Zink Flake AT from Eckart), and 4.5 g Aerosil R972 (from Degussa), 250 g of 1 Add to butanol solvent. Prior to further processing, 20 g of a suitable powdered wax (Licowax C from Clariant) is added to the mixture and mixed homogeneously using a dissolver for at least 2 hours.

The coating solution is applied to the entire surface of the press-cured assembly using a spray coating device (eg HVLP pressurized air nozzle having a diameter of 1.2 mm) that produces a layer thickness of 3 μm to 10 μm after drying and curing. To do. Also, the solution is particularly sprayed into the voids, gaps and joints. Curing is performed at a temperature of 180 ° C. for 20 minutes.
Results The parts and assemblies according to Examples 1 to 3 are each coated with a 3 to 10 μm thick silver white corrosion resistant layer that adheres firmly to the substrate. After 1000 hours of salt spray testing, such as DIN EN ISO 9227, the coating showed no red rust formation on the surface or on the cruciform lesion. The coated parts and assemblies have an electrical resistance of less than 10 mΩ and can be welded to other steel parts, for example to assemble an automobile body.

Claims (22)

A method for producing an active cathodic corrosion resistant coating on a steel part comprising the following process steps:
a. Using a steel element provided with an anti-scaling layer;
b. Annealing the steel element at a temperature in excess of 600 ° C. in an annealing furnace for the purpose of hardening, semi-hot forming or hot forming, or press hardening, and thus producing a reaction layer;
c. Applying a corrosion resistant coating to the annealed reaction layer;
A method for producing an active cathode corrosion resistant coating on a steel part. A method for producing an active cathodic corrosion resistant coating on a steel part comprising the following process steps:
a. Using a steel element provided with an anti-scaling layer;
b. Applying a corrosion resistant coating to the anti-scaling layer;
c. Annealing the steel element at a temperature in excess of 600 ° C. in an annealing furnace for the purpose of hardening, semi-hot forming or hot forming, or press hardening, and thus producing a reaction layer;
A method for producing an active cathode corrosion resistant coating on a steel part.   The method according to claim 1, wherein the annealing is performed at a temperature exceeding 850 ° C.   2. A method according to claim 1, characterized in that the annealing is carried out by conduction or induction in a gas-operated annealing furnace or an electrically-operated annealing furnace.   The method according to claim 1, wherein the oxygen content in the annealing furnace atmosphere is 0% to 10%.   The anti-scaling layer comprises an aluminum alloy, a coating containing an aluminum pigment, a magnesium alloy, a coating containing a magnesium pigment, a zinc alloy, or a coating containing a zinc pigment. Method.   2. Method according to claim 1, characterized in that after formation, the anti-scaling layer has a maximum electrical resistance of 10 m [Omega], preferably a maximum electrical resistance of 5 m [Omega].   2. A method according to claim 1, characterized in that the finished part has a maximum electrical resistance of 10 mΩ, preferably a maximum electrical resistance of 5 mΩ.   The method according to claim 1, characterized in that the corrosion-resistant layer is applied from the liquid phase to the annealing reaction layer in a wet-chemical process, in particular a spraying, flooding, rolling or dipping process.   9. Method according to claim 8, characterized in that the thickness of the corrosion-resistant layer is less than 50 [mu] m, preferably less than 20 [mu] m, in particular less than 10 [mu] m.   The method according to claim 8, wherein the corrosion-resistant layer is diluted with a solvent before application.   The method according to claim 1, wherein after applying the corrosion-resistant layer, drying is performed at a temperature of room temperature to 400 ° C, preferably room temperature to 250 ° C.   The method according to claim 1, wherein the corrosion-resistant layer contains a binder and a metal pigment.   The corrosion-resistant layer has a thickness of 10 wt. % To 100 wt. %, Preferably 50 wt. % To 100 wt. %, Especially 70 wt. % To 95 wt. The process according to claim 12, characterized in that it contains% metallic zinc pigment and / or magnesium pigment.   The corrosion resistant layer has a maximum of 50 wt. The process according to claim 12, characterized in that it contains% metallic aluminum pigment.   The binder used for the corrosion-resistant layer is 5 wt. % To 100 wt. 13. A method according to claim 12, characterized in that it contains% metal oxide, in particular titanium oxide, aluminum oxide or zirconium oxide.   The binder used for the corrosion resistant layer has a maximum of 50 wt. The process according to claim 12, characterized in that it contains a binder, silicone, siloxane or wax made by the% sol-gel process.   13. A method according to claim 12, characterized in that the corrosion-resistant layer contains a solid state lubricant, in particular graphite or boron nitride.   19. A method according to any one of the preceding claims, characterized in that the steel element is in the form of a sheet, a coil, a part or other solid.   The steel element consists of an assembly of parts made of a wide variety of alloy steels with or without a metal coating, such as an aluminum coating or zinc coating, or a coating containing a metal pigment, and is welded, bonded, bolted The method according to any one of claims 1 to 18, wherein the members are joined to each other by a standard joining method such as riveting.   21. Any one of claims 1 to 20, characterized in that, prior to annealing, the steel element is completely or partially provided with a coating that affects the heating behavior of the steel part (s). The method according to item.   20. Use of the method according to any one of claims 1 to 19, relating to machine manufacturing, in particular automotive manufacturing, construction, in particular steel products, process engineering, aerospace engineering, power plant and Power plant engineering, electrical engineering, medical engineering, sports equipment, horticulture and landscaping design, tool making, agricultural machinery, furniture, kitchen, household equipment, toys, sports products, camping equipment, caravans, window and door frames, heating equipment, heat Exchanger, air conditioner, escalator, conveyor, oil platform, jewelry, locomotive, rail, transport system, crane, furnace, engine and engine accessories, piston, seal ring, exhaust system, ABS and brake system, brake disc, Chassis parts, wheels, wheel rims, sanitary products, lamps and design products For producing consumable parts or assembly, use of a method according to any one of claims 1 to 19.