EP0305914A2 - Process for the treatment of rolled steel for increasing corrosion resistance - Google Patents

Process for the treatment of rolled steel for increasing corrosion resistance Download PDF

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Publication number
EP0305914A2
EP0305914A2 EP88113916A EP88113916A EP0305914A2 EP 0305914 A2 EP0305914 A2 EP 0305914A2 EP 88113916 A EP88113916 A EP 88113916A EP 88113916 A EP88113916 A EP 88113916A EP 0305914 A2 EP0305914 A2 EP 0305914A2
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EP
European Patent Office
Prior art keywords
rolled steel
coating
steel
rolling
water
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Granted
Application number
EP88113916A
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German (de)
French (fr)
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EP0305914A3 (en
EP0305914B1 (en
Inventor
Max Dipl.-Ing. Aicher
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Stahlwerk Annahuette Max Aicher & Co Kg GmbH
Stahlwerk Annahuette Max Aicher GmbH and Co KG
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Stahlwerk Annahuette Max Aicher & Co Kg GmbH
Stahlwerk Annahuette Max Aicher GmbH and Co KG
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Priority to AT88113916T priority Critical patent/ATE70568T1/en
Publication of EP0305914A2 publication Critical patent/EP0305914A2/en
Publication of EP0305914A3 publication Critical patent/EP0305914A3/en
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C4/00—Coating by spraying the coating material in the molten state, e.g. by flame, plasma or electric discharge
    • C23C4/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
    • B21B45/04—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing
    • B21B45/08—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing hydraulically
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • C21D8/08—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires for concrete reinforcement
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/38—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling sheets of limited length, e.g. folded sheets, superimposed sheets, pack rolling
    • B21B2001/383—Cladded or coated products

Definitions

  • the invention relates to a method for treating rolled steel, in particular reinforcing steel, prestressing steel or the like to increase the corrosion resistance by applying a coating made of a non-ferrous metal, preferably zinc, the rolled steel being descaled from the rolling heat and then preventing scale from forming again on the hot rolled steel the coating is applied.
  • a coating made of a non-ferrous metal preferably zinc
  • Rolled steel products are used, among other things, in construction as structural steel, here primarily in the form of reinforcing steel, as prestressing steel for prestressed concrete and for anchoring for earth and rock anchors, etc.
  • an alkaline solution with a pH value of more than 12 is formed by dissolving the lime particles contained in the cement.
  • an iron oxide cover layer forms on the surface of the reinforcement elements, which passivates the steel surface and protects it from surface corrosion .
  • the reinforcement elements are usually located in the edge areas of the components, where they join certain minimum distance to the outer surface, the so-called concrete cover, must be observed. Due to air pollution, especially in bridge structures, due to the increasing use of de-icing salts for removing snow and ice, chlorides dissolved in these media, with insufficient, often sufficient, concrete cover, can penetrate to the steel where they destroy the passivation layer and so on can attack the steel directly. The same applies to the tension members of earth and rock anchors, where the corrosive influence of the steel is caused by soil moisture, water and acidic soil components. For this reason, there is a need for additional corrosion protection measures for such rolled steel products used in construction.
  • metals in particular ferrous metals
  • a thin zinc layer as rust protection.
  • Various methods are known for this.
  • hot or hot galvanizing the parts to be protected are immersed in a bath of molten zinc, which can also be alloyed with aluminum if necessary.
  • Acidic sulphate, sulphate chloride or cyanide-caustic baths are used for electrolytic or galvanizing.
  • metal coatings by spraying the metal in liquid form, the metal being fed to a spray gun in wire or powder form, melted by oxygen / fuel gas mixtures and atomized by compressed air.
  • the rolled material is passed through a closed chamber filled with a deoxidizing gas, preferably carbon monoxide, in which the carbon monoxide burns to carbon dioxide after leaving the rolling stand at a temperature of approximately 980 to 760 degrees C.
  • a deoxidizing gas preferably carbon monoxide
  • the rolling stock passes through another chamber, in which it e.g. is coated with zinc in the form of zinc powder, which melts as a result of the heat still inherent in the rolling stock. Since the coated rolling stock still has a temperature of approx. 700 to 600 degrees C when it leaves this chamber, it has to be cooled down immediately after coating in order to prevent the applied zinc powder from burning to zinc oxide, for example.
  • This process is also relatively complex. Keeping the descaled surface of the rolling stock clean by means of an atmosphere of deoxidizing gas requires not only its provision, supply and maintenance of a deoxidizing atmosphere in a correspondingly sealed chamber, but also the maintenance of a corresponding temperature before the rolling stock after the Coating is quickly cooled using other media.
  • the invention is based on the object of being able to coat rolled steel products in a continuous operation immediately following the rolling process, utilizing the rolling heat and thereby keeping the procedural and apparatus expenditure as low as possible.
  • this object is achieved in that the rolled steel is subjected to press water in a continuous continuation of the rolling process for descaling, that the steel surface immediately after the descaling to prevent the formation of new scale by application of water quickly to a temperature of below 600 degrees C. is cooled and that the coating is then applied.
  • the advantage of the invention is primarily to be seen in the fact that only one medium, namely water, is used both for descaling, as well as for preventing the formation of new scale and at the same time for cooling, whereby the cooling can be carried out in such a way that the rolling heat can be optimally used for the coating. It is thereby achieved that all process steps or treatment processes can be carried out in a continuous continuation of the rolling process, that is to say at the rolling speed, so that the finished coated product leaves the production line in an analogous manner to a normal, non-post-treated rolled product.
  • the phenomenon is exploited that the scale adhering to the rolled steel from the rolling process, that in the last roll stand deformation of the rolling stock, for example during a transition from an oval to a circular cross-section, has already been loosened relatively easily immediately after the rolling stock has left the rolling stand.
  • the pressure of the press water should be over 200 bar, preferably 300 to 400 bar; if necessary, it can be increased to around 1,000 bar. This requires only a very short treatment, namely the passage of the rolled steel through a spray nozzle, which only results in an insignificant reduction in the temperature of the rolled steel.
  • While descaling is carried out by press water from the rolling heat at a temperature of about 900 to 1,000 degrees C, according to the invention, in continuation of this water treatment, the cooling is carried out in a continuous pass by using the same medium in such a way that the scaling temperature of 600 degrees C is as rapid as possible is below that no new scale can form and temperatures are reached at which the coatings can be applied.
  • This can be done according to the invention in that the rolled steel is passed through a water bath or sprayed with water.
  • Suitable temperatures for applying corrosion-resistant coatings are, for example, a temperature of approximately 560 to 570 degrees C for pure aluminum and a temperature of approximately 415 degrees C for pure zinc; intermediate stages can be activated for alloys.
  • it is easily possible to use any desired alloy for the coating since, starting from the rolling heat until it is completely cooled, all temperature ranges are run through.
  • the coating can be applied in any way.
  • the non-ferrous metal forming the coating can be sprayed on in powder form, whereby it melts; the Rolled steel can also be passed through a bath with the liquid non-ferrous metal.
  • this treatment can also be carried out in the form of heat treatment known per se using water.
  • One such process is the process known, for example, for low-carbon and therefore weldable concrete steels under the name "Tempcore” process, in which the water treatment is carried out in such a way that an edge zone consisting of martensite and bainite is present in the rolled steel immediately after quenching, while that remaining in the steel core Heat content during the subsequent cooling does not cause the edge zone to temper beyond the bainite stage.
  • the water treatment is carried out in such a way that the steels are quenched from a final rolling temperature between 860 and 1,060 degrees C in such a way that the surface layer forms a completely martensitic structure and the temperature of the surface layer is compensated for by temperature compensation in the period between 2 to 6 seconds after the start of the quenching process is 400 to 500 degrees C.
  • the cooling to be carried out according to the invention can be used in a particularly advantageous manner to improve the strength of the steels.
  • a further advantage of the invention lies in the fact that all work steps are carried out in a continuous process immediately following the rolling process in individual treatment stations arranged after the last rolling stand. While the rolling process, which is inevitably discontinuous due to the rolling of billets, has largely evened out until the last rolling stand is left, the method according to the invention naturally also has particular advantages if the rolling process has previously been carried out by continuous welding of the billets. This is achieved in a particularly advantageous manner by the known flash butt welding of the billets in the area between leaving the furnace or leaving a trio mill stand and the first tapping of the fine rolling mill.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Organic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Plasma & Fusion (AREA)
  • Manufacturing & Machinery (AREA)
  • Metal Rolling (AREA)
  • Heat Treatment Of Steel (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
  • Coating With Molten Metal (AREA)
  • Preventing Corrosion Or Incrustation Of Metals (AREA)
  • Prevention Of Electric Corrosion (AREA)
  • Electric Cable Arrangement Between Relatively Moving Parts (AREA)
  • Heat Treatment Of Articles (AREA)
  • Pit Excavations, Shoring, Fill Or Stabilisation Of Slopes (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Excavating Of Shafts Or Tunnels (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Laminated Bodies (AREA)
  • Heat Treatments In General, Especially Conveying And Cooling (AREA)
  • Electroplating Methods And Accessories (AREA)
  • Reduction Rolling/Reduction Stand/Operation Of Reduction Machine (AREA)
  • Rolls And Other Rotary Bodies (AREA)

Abstract

To apply a coating of a non-ferrous metal such as, for example, zinc to the surface of rolled steel to increase the corrosion resistance, it is proposed to descale the rolled steel continuously downstream of the rolling step from the rolling pass by applying pressurised water and, immediately after descaling and while preventing a renewed formation of scale, to cool it by means of water rapidly to a temperature suitable for hot application of the coating and finally to apply the coating. One of the advantages of the invention is that, both for descaling and for preventing the renewed formation of scale and for simultaneous cooling, only a single medium, namely water, is used, and the cooling can be controlled in such a way that the rolling pass can be exploited in an optimised manner for the coating. The result is that all process steps or treatment processes can proceed as a continuous extension of the rolling step, i.e. at rolling speed, so that the finished coated end product leaves the production line analogously to a normal, not aftertreated rolled product.

Description

Die Erfindung betrifft ein Verfahren zum Behandeln von Walzstahl, insbesondere Betonstahl, Spannstahl oder dergleichen zur Erhöhung der Korrosionsbeständigkeit durch Aufbringen eines Überzuges aus einem Nichteisenmetall, vorzugsweise Zink, wobei der Walzstahl aus der Walzhitze heraus zunächst entzundert und dann unter Verhinderung einer Neubildung von Zunder auf den heißen Walzstahl der Überzug aufgebracht wird.The invention relates to a method for treating rolled steel, in particular reinforcing steel, prestressing steel or the like to increase the corrosion resistance by applying a coating made of a non-ferrous metal, preferably zinc, the rolled steel being descaled from the rolling heat and then preventing scale from forming again on the hot rolled steel the coating is applied.

Walzstahlerzeugnisse werden unter anderem im Bauwesen als Baustahl, hier vor allem in Form von Betonstahl, als Spannstahl für Spannbeton sowie für Abspannungen für Erd- und Felsanker usw. verwendet.Rolled steel products are used, among other things, in construction as structural steel, here primarily in the form of reinforcing steel, as prestressing steel for prestressed concrete and for anchoring for earth and rock anchors, etc.

Bei Verwendung als Bewehrung für Bauteile aus Beton, sei es als schlaffe Bewehrung für Stahlbeton, als Spannbewehrung oder auch als Zugglied für einen Erd- oder Felsanker, besteht zwischen dem Bewehrungsstahl und dem Beton in aller Regel ein Verbund. Dieser entsteht bei Stahlbeton und bei Spannbeton mit sofortigem Verbund ohne weiteres dadurch, daß die Bewehrungselemente in den Beton eingebettet sind und von diesem dicht umhüllt werden, bei Spannbeton mit nachträglichem Verbund dadurch, daß die zur Erhaltung der Längsbeweglichkeit der Spannglieder erforderlichen Spannkanäle nachträglich mit Zementmörtel injiziert werden.When used as reinforcement for components made of concrete, be it as slack reinforcement for reinforced concrete, as tension reinforcement or as a tension member for an earth or rock anchor, there is usually a bond between the reinforcing steel and the concrete. For reinforced concrete and prestressed concrete with an immediate bond, this is easily achieved by the fact that the reinforcement elements are embedded in the concrete and are tightly encased by it, and in prestressed concrete with a subsequent bond, the prestressing channels required to maintain the longitudinal mobility of the tendons are subsequently injected with cement mortar will.

Bei der Herstellung von Beton entsteht durch Lösung der im Zement enthaltenen Kalkteilchen eine alkalische Lösung mit einem ph-Wert über 12. Dies hat zur Folge, daß sich auf der Oberfläche der Bewehrungselemente eine Deckschicht aus Eisenoxid bildet, welche die Stahloberfläche passiviert und vor Oberflächenkorrosion schützt. Aus statischen, aber auch aus konstruktiven Gründen liegen die Bewehrungselemente meist in den Randbereichen der Bauteile, wo sie einen gewissen Mindestabstand zur Außenfläche, die sogenannte Betonüberdeckung, einhalten müssen. Durch die Luftverschmutzung, bei Brückenbauwerken vor allem durch die zunehmende Verwendung von Auftausalzen für die Beseitigung von Schnee und Eis, haben in diesen Medien gelöste Chloride bei unzureichender, oft auch bei ausreichender Betonüberdeckung die Möglichkeit bis zum Stahl vorzudringen, wo sie die Passivierungsschicht zerstören und so den Stahl direkt angreifen können. Ähnliches gilt für die Zugglieder von Erd- und Felsankern, wo die korrosive Beeinflussung des Stahles durch Bodenfeuchte, Wasser und saure Bodenbestandteile hervorgerufen wird. Aus diesem Grund besteht ein Bedürfnis nach zusätzlichen Korrosionsschutzmaßnahmen für solche im Bauwesen verwendete Walzstahlerzeugnisse.In the production of concrete, an alkaline solution with a pH value of more than 12 is formed by dissolving the lime particles contained in the cement. This has the consequence that an iron oxide cover layer forms on the surface of the reinforcement elements, which passivates the steel surface and protects it from surface corrosion . For structural as well as structural reasons, the reinforcement elements are usually located in the edge areas of the components, where they join certain minimum distance to the outer surface, the so-called concrete cover, must be observed. Due to air pollution, especially in bridge structures, due to the increasing use of de-icing salts for removing snow and ice, chlorides dissolved in these media, with insufficient, often sufficient, concrete cover, can penetrate to the steel where they destroy the passivation layer and so on can attack the steel directly. The same applies to the tension members of earth and rock anchors, where the corrosive influence of the steel is caused by soil moisture, water and acidic soil components. For this reason, there is a need for additional corrosion protection measures for such rolled steel products used in construction.

Ganz allgemein ist es bekannt, Metalle, insbesondere Eisenmetalle, als Rostschutz mit einer dünnen Zinkschicht zu überziehen. Hierzu kennt man verschiedene Verfahren. Zur Feuer- oder Heißverzinkung werden die zu schützenden Teile in ein Bad aus geschmolzenem Zink getaucht, das gegebenenfalls auch mit Aluminium legiert sein kann. Für das elektrolytische oder galvanische Verzinken benutzt man saure Sulfat-, Sulfatchlorid- oder zyankalisch-ätzkalische Bäder. Es ist auch bekannt, Metallüberzüge durch Aufspritzen des Metalls in flüssiger Form aufzubringen, wobei das Metall einer Spritzpistole in Draht- oder Pulverform zugeführt, durch Sauerstoff-Brenngasgemische geschmolzen und durch Druckluft zerstäubt wird. All diese Verfahren sind aufwendig, vor allem aber für die Behandlung von in einem kontinuierlichen Arbeitsgang hergestellten Massenprodukten großer Länge, wie Betonstähle oder Spannstähle, nicht oder nur mit großem Arbeits- und Kostenaufwand einzusetzen. Dazu kommt, daß die zu überziehenden Erzeugnisse natürlich vor dem Aufbringen eines solchen Überzuges gereinigt, Walzstahlerzeugnisse insbesondere von der ihnen schon vom Walzvorgang her anhaftenden Zunderschicht befreit werden müssen; dies geschieht üblicherweise durch Sandstrahlen, Beizen oder ähnliche Behandlungen.It is very generally known to coat metals, in particular ferrous metals, with a thin zinc layer as rust protection. Various methods are known for this. For hot or hot galvanizing, the parts to be protected are immersed in a bath of molten zinc, which can also be alloyed with aluminum if necessary. Acidic sulphate, sulphate chloride or cyanide-caustic baths are used for electrolytic or galvanizing. It is also known to apply metal coatings by spraying the metal in liquid form, the metal being fed to a spray gun in wire or powder form, melted by oxygen / fuel gas mixtures and atomized by compressed air. All of these processes are complex, but above all they cannot be used for the treatment of mass products of great length, such as reinforcing steel or prestressing steel, which are produced in a continuous operation, or only with great effort and expense. In addition, the products to be coated are of course cleaned before the application of such a coating, rolled steel products in particular from those already supplied by them Rolling ago adhering scale layer must be freed; this is usually done by sandblasting, pickling or similar treatments.

Bei in einem kontinuierlichen Verfahren hergestellten Walzstahlerzeugnissen ist es auch schon bekannt geworden, das Walzgut im unmittelbaren Anschluß an den Walzvorgang zu entzundern und unter Verhinderung einer Neubildung von Zunder sowie unter Ausnützung der Walzhitze mit einem korrosionsbeständigen Überzug, z.B. aus Zink, zu versehen (US-PS 2 442 485). Die Entzunderung erfolgt dabei im letzten Walzgerüst als Folge einer starken, mit einer Streckung verbundenen Verringerung des Querschnitts des Walzgutes, wodurch der spröde Zunder aufbricht, so daß das Walzgut das Walzgerüst im wesentlichen zunderfrei verläßt. Um diesen Zustand zu erhalten, wird das Walzgut nach Verlassen des Walzgerüstes mit einer Temperatur von ca. 980 bis 760 Grad C durch eine geschlossene, mit einem desoxidierenden Gas, vorzugsweise Kohlenmonoxid, gefüllte Kammer geführt, in der das Kohlenmonoxid zu Kohlendioxid verbrennt. Unmittelbar danach durchläuft das Walzgut eine weitere Kammer, in der es z.B. mit Zink in Form von Zinkpulver beschichtet wird, das infolge der dem Walzgut noch innewohnenden Hitze aufschmilzt. Da das beschichtete Walzgut beim Verlassen dieser Kammer aber noch immer eine Temperatur von ca. 700 bis 600 Grad C hat, muß es unmittelbar nach der Beschichtung schnell abgekühlt werden, um zu verhindern, daß das aufgebrachte Zinkpulver etwa zu Zinkoxid verbrennt.In the case of rolled steel products produced in a continuous process, it has also become known to descale the rolling stock immediately after the rolling process and to prevent scale from forming again and to use the rolling heat with a corrosion-resistant coating, e.g. made of zinc, to be provided (US Pat. No. 2,442,485). Descaling takes place in the last roll stand as a result of a strong reduction in the cross section of the rolling stock associated with stretching, as a result of which the brittle scale breaks up, so that the rolling stock leaves the rolling stand essentially free of scale. In order to maintain this state, the rolled material is passed through a closed chamber filled with a deoxidizing gas, preferably carbon monoxide, in which the carbon monoxide burns to carbon dioxide after leaving the rolling stand at a temperature of approximately 980 to 760 degrees C. Immediately afterwards, the rolling stock passes through another chamber, in which it e.g. is coated with zinc in the form of zinc powder, which melts as a result of the heat still inherent in the rolling stock. Since the coated rolling stock still has a temperature of approx. 700 to 600 degrees C when it leaves this chamber, it has to be cooled down immediately after coating in order to prevent the applied zinc powder from burning to zinc oxide, for example.

Auch dieses Verfahren ist relativ aufwendig. Die Reinhaltung der entzunderten Oberfläche des Walzgutes durch eine Atmosphäre von desoxidierendem Gas bedingt nicht nur dessen Vorhaltung, Zuführung und die Aufrechterhaltung einer desoxidierenden Atmosphäre in einer in entsprechender Weise abgedichteten Kammer, sondern auch die Aufrechterhaltung einer entsprechenden Temperatur, bevor das Walzgut nach der Beschichtung unter Anwendung anderer Medien schnell abgekühlt wird.This process is also relatively complex. Keeping the descaled surface of the rolling stock clean by means of an atmosphere of deoxidizing gas requires not only its provision, supply and maintenance of a deoxidizing atmosphere in a correspondingly sealed chamber, but also the maintenance of a corresponding temperature before the rolling stock after the Coating is quickly cooled using other media.

Vor diesem Hintergrund liegt der Erfindung die Aufgabe zugrunde, Walzstahlerzeugnisse in einem unmittelbar an den Walzvorgang anschließenden, kontinuierlichen Arbeitsgang unter Ausnützung der Walzhitze beschichten zu können und dabei den verfahrensmäßigen und apparativen Aufwand möglichst gering zu halten.Against this background, the invention is based on the object of being able to coat rolled steel products in a continuous operation immediately following the rolling process, utilizing the rolling heat and thereby keeping the procedural and apparatus expenditure as low as possible.

Nach der Erfindung wird diese Aufgabe dadurch gelöst, daß der Walzstahl in kontinuierlicher Fortsetzung des Walzvorganges zur Entzunderung mit Preßwasser beaufschlagt wird, daß die Stahloberfläche unmittelbar nach der Entzunderung zur Verhinderung der Neubildung von Zunder durch Anwendung von Wasser schnell auf eine Temperatur von unter 600 Grad C abgekühlt wird und daß danach der Überzug aufgebracht wird.According to the invention, this object is achieved in that the rolled steel is subjected to press water in a continuous continuation of the rolling process for descaling, that the steel surface immediately after the descaling to prevent the formation of new scale by application of water quickly to a temperature of below 600 degrees C. is cooled and that the coating is then applied.

Der Vorteil der Erfindung ist vor allem darin zu sehen, daß sowohl zur Entzunderung, wie auch zur Verhinderung der Neubildung von Zunder und zugleich zur Abkühlung nur ein einziges Medium, nämlich Wasser, verwendet wird, wodurch die Abkühlung so geführt werden kann, daß die Walzhitze in optimaler Weise für die Beschichtung ausnützbar ist. Dadurch wird erreicht, daß alle Verfahrensschritte bzw. Behandlungsvorgänge in kontinuierlicher Fortsetzung des Walzvorganges, also bei Walzgeschwindigkeit ablaufen können, so daß das fertig beschichtete Endprodukt in analoger Weise die Produktionsstraße verläßt wie ein normales, nicht nachbehandeltes Walzprodukt.The advantage of the invention is primarily to be seen in the fact that only one medium, namely water, is used both for descaling, as well as for preventing the formation of new scale and at the same time for cooling, whereby the cooling can be carried out in such a way that the rolling heat can be optimally used for the coating. It is thereby achieved that all process steps or treatment processes can be carried out in a continuous continuation of the rolling process, that is to say at the rolling speed, so that the finished coated product leaves the production line in an analogous manner to a normal, non-post-treated rolled product.

Durch die Beaufschlagung der Stahloberfläche mit Preßwasser mit hohem Druck zur Entzunderung wird die Erscheinung ausgenützt, daß der dem Walzstahl vom Walzvorgang her anhaftende Zunder, der bei der im letzten Walzgerüst erfolgenden Verformung des Walzgutes, z.B. bei einem Übergang von einem ovalen auf einen Kreisquerschnitt schon gelockert wurde, unmittelbar nachdem das Walzgut das Walzgerüst verlassen hat, relativ leicht vollständig beseitigt werden kann. Der Druck des Preßwassers sollte über 200 bar, vorzugsweise bei 300 bis 400 bar liegen; er kann, wenn erforderlich, bis auf etwa 1.000 bar gesteigert werden. Dies erfordert nur eine sehr kurze Behandlung, nämlich den Durchlauf des Walzstahles durch eine Spritzdüse, was nur eine unwesentliche Verminderung der Temperatur des Walzstahles zur Folge hat.By applying pressurized water to the steel surface with high pressure for descaling, the phenomenon is exploited that the scale adhering to the rolled steel from the rolling process, that in the last roll stand deformation of the rolling stock, for example during a transition from an oval to a circular cross-section, has already been loosened relatively easily immediately after the rolling stock has left the rolling stand. The pressure of the press water should be over 200 bar, preferably 300 to 400 bar; if necessary, it can be increased to around 1,000 bar. This requires only a very short treatment, namely the passage of the rolled steel through a spray nozzle, which only results in an insignificant reduction in the temperature of the rolled steel.

Während das Entzundern durch Preßwasser aus der Walzhitze heraus bei einer Temperatur von etwa 900 bis 1.000 Grad C erfolgt, wird nach der Erfindung in Fortsetzung dieser Wasserbehandlung im kontinuierlichen Durchlauf durch Anwendung desselben Mediums die Abkühlung so geführt, daß die Zunderungstemperatur von 600 Grad C möglichst rasch unterschritten wird, daß sich also kein neuer Zunder mehr bilden kann, und Temperaturen erreicht werden, bei denen die Überzüge aufgebracht werden können. Dies kann nach der Erfindung dadurch geschehen, daß der Walzstahl durch ein Wasserbad geführt oder mit Wasser besprüht wird. Geeignete Temperaturen zum Aufbringen korrosionsbeständiger Überzüge sind bei reinem Aluminium beispielsweise eine Temperatur von ca. 560 bis 570 Grad C und bei reinem Zink eine Temperatur von ca. 415 Grad C; bei Legierungen können Zwischenstufen eingeschaltet werden. So ist es nach der Erfindung ohne weiteres möglich, jede gewünschte Legierung für den Überzug zu verwenden, da, ausgehend von der Walzhitze bis zur vollständigen Abkühlung, alle Temperaturbereiche durchlaufen werden.While descaling is carried out by press water from the rolling heat at a temperature of about 900 to 1,000 degrees C, according to the invention, in continuation of this water treatment, the cooling is carried out in a continuous pass by using the same medium in such a way that the scaling temperature of 600 degrees C is as rapid as possible is below that no new scale can form and temperatures are reached at which the coatings can be applied. This can be done according to the invention in that the rolled steel is passed through a water bath or sprayed with water. Suitable temperatures for applying corrosion-resistant coatings are, for example, a temperature of approximately 560 to 570 degrees C for pure aluminum and a temperature of approximately 415 degrees C for pure zinc; intermediate stages can be activated for alloys. Thus, according to the invention, it is easily possible to use any desired alloy for the coating, since, starting from the rolling heat until it is completely cooled, all temperature ranges are run through.

Das Aufbringen des Überzuges kann auf beliebige Weise erfolgen. Das den Überzug bildende Nichteisenmetall kann in Pulverform aufgespritzt werden, wobei es aufschmilzt; der Walzstahl kann aber auch durch ein Bad mit dem flüssigen Nichteisenmetall geführt werden.The coating can be applied in any way. The non-ferrous metal forming the coating can be sprayed on in powder form, whereby it melts; the Rolled steel can also be passed through a bath with the liquid non-ferrous metal.

Während der Walzstahl nach der Entzunderung durch die Wasserbehandlung vor neuer Zunderbildung geschützt wird, besorgt diesen Schutz nach Aufbringen des Überzuges bis zur vollständigen Abkühlung des Walzstahles eben dieser Überzug. In manchen Fällen ist es angebracht, auf den Überzug z.B. aus Zink als zusätzlichen Schutz noch eine Schicht aus einem Kunstharz, z.B. Epoxyharz, aufzutragen. Auch ein solcher Arbeitsgang kann ohne weiteres in das erfindungsgemäße Verfahren unter Ausnützung der Restwärme integriert werden.While the rolled steel is protected against new scale formation by descaling by water treatment, this protection provides this coating after the coating has been applied until the rolled steel has completely cooled. In some cases it is appropriate to apply e.g. a layer of synthetic resin, e.g. Epoxy resin to apply. Such an operation can also be easily integrated into the method according to the invention using the residual heat.

Da der Walzstahl erfindungsgemäß nach der Entzunderung durch Behandlung mit Wasser abgekühlt wird, kann diese Behandlung auch in Form an sich bekannter Vergütungsverfahren unter Anwendung von Wasser erfolgen. Ein solches ist das z.B. bei kohlenstoffarmen und daher schweißgeeigneten Betonstählen unter der Bezeichnung "Tempcore"-Verfahren bekannte Verfahren, bei dem die Wasserbehandlung so erfolgt, daß in dem Walzstahl unmittelbar nach der Abschreckung eine Randzone aus Martensit und Bainit vorliegt, während der im Stahlkern verbliebene Wärmeinhalt während der nachfolgenden Abkühlung ein Anlassen der Randzone nicht über die Bainit-Stufe hinaus bewirkt. Bei kohlenstoffreichen, als Spannstahl geeigneten Stählen wird die Wasserbehandlung so geführt, daß die Stähle von einer Endwalztemperatur zwischen 860 und 1.060 Grad C so abgeschreckt werden, daß in der Randschicht sich vollständig martensitisches Gefüge ausbildet und die Temperatur der Randschicht durch Temperaturausgleich im Zeitraum zwischen 2 bis 6 Sekunden nach Beginn des Abschreckvorganges 400 bis 500 Grad C beträgt. Auf diese Weise läßt sich die nach der Erfindung vorzunehmende Abkühlung noch in besonders vorteilhafter Weise zu einer Verbesserung der Festigkeit der Stähle nutzen.Since the rolled steel is cooled according to the invention after descaling by treatment with water, this treatment can also be carried out in the form of heat treatment known per se using water. One such process is the process known, for example, for low-carbon and therefore weldable concrete steels under the name "Tempcore" process, in which the water treatment is carried out in such a way that an edge zone consisting of martensite and bainite is present in the rolled steel immediately after quenching, while that remaining in the steel core Heat content during the subsequent cooling does not cause the edge zone to temper beyond the bainite stage. In the case of carbon-rich steels suitable as prestressing steel, the water treatment is carried out in such a way that the steels are quenched from a final rolling temperature between 860 and 1,060 degrees C in such a way that the surface layer forms a completely martensitic structure and the temperature of the surface layer is compensated for by temperature compensation in the period between 2 to 6 seconds after the start of the quenching process is 400 to 500 degrees C. In this way, the cooling to be carried out according to the invention can be used in a particularly advantageous manner to improve the strength of the steels.

Ein weiterer Vorteil der Erfindung liegt schließlich darin, daß alle Arbeitsgänge in einem kontinuierlich durchlaufenden, unmittelbar an den Walzvorgang anschließenden Verfahren in einzelnen, dem letzten Walzgerüst nachgeordneten Behandlungsstationen durchgeführt werden. Während der bedingt durch das Walzen von Knüppeln zwangsläufig diskontinuierliche Walzvorgang sich bis zum Verlassen des letzten Walzgerüstes schon weitgehend vergleichmäßigt hat, entfaltet natürlich auch das erfindungsgemäße Verfahren besondere Vorteile dann, wenn zuvor schon durch ein Verschweißen der Knüppel der Walzvorgang zu einem Endloswalzen gemacht wird. Dies gelingt in besonders vorteilhafter Weise durch das an sich bekannte fliegende Abbrenn-Stumpfschweißen der Knüppel in dem Bereich zwischen dem Verlassen des Ofens bzw. dem Verlassen eines Trio-Walzgerüsts und dem ersten Anstich der Feinwalzstraße.Finally, a further advantage of the invention lies in the fact that all work steps are carried out in a continuous process immediately following the rolling process in individual treatment stations arranged after the last rolling stand. While the rolling process, which is inevitably discontinuous due to the rolling of billets, has largely evened out until the last rolling stand is left, the method according to the invention naturally also has particular advantages if the rolling process has previously been carried out by continuous welding of the billets. This is achieved in a particularly advantageous manner by the known flash butt welding of the billets in the area between leaving the furnace or leaving a trio mill stand and the first tapping of the fine rolling mill.

Claims (8)

1. Verfahren zum Behandeln von Walzstahl, insbesondere Betonstahl, Spannstahl oder dergleichen zur Erhöhung der Korrosionsbeständigkeit durch Aufbringen eines Überzuges aus einem Nichteisenmetall, vorzugsweise Zink, wobei der Walzstahl aus der Walzhitze heraus zunächst entzundert und dann unter Verhinderung einer Neubildung von Zunder auf den heißen Walzstahl der Überzug aufgebracht wird, dadurch gekennzeichnet, daß der Walzstahl in kontinuierlicher Fortsetzung des Walzvorganges zur Entzunderung mit Preßwasser beaufschlagt wird, daß die Stahloberfläche unmittelbar nach der Entzunderung zur Verhinderung der Neubildung von Zunder durch Anwendung von Wasser schnell auf eine Temperatur von unter 600 Grad C abgekühlt wird und daß danach der Überzug aufgebracht wird.1. A method for treating rolled steel, in particular reinforcing steel, prestressing steel or the like to increase the corrosion resistance by applying a coating made of a non-ferrous metal, preferably zinc, the rolled steel first being descaled out of the rolling heat and then preventing scale from forming again on the hot rolled steel the coating is applied, characterized in that the rolling steel is subjected to pressurized water in a continuous continuation of the rolling process for descaling, that the steel surface is cooled immediately after the descaling to prevent the new formation of scale by application of water to a temperature of below 600 degrees C. and that the coating is then applied. 2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß das Preßwasser mit einem Druck von über 200 bis zu etwa 1.000 bar, vorzugsweise zwischen 300 und 400 bar aufgebracht wird.2. The method according to claim 1, characterized in that the press water is applied at a pressure of over 200 to about 1,000 bar, preferably between 300 and 400 bar. 3. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß der Walzstahl durch ein Wasserbad geführt wird.3. The method according to claim 1 or 2, characterized in that the rolled steel is passed through a water bath. 4. Verfahren nach Anspruch 1 oder 2, dadurch gekennzeichnet, daß der Walzstahl mit Wasser besprüht wird.4. The method according to claim 1 or 2, characterized in that the rolled steel is sprayed with water. 5. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß der Überzug durch Aufspritzen des Nichteisenmetalls in Pulverform aufgetragen wird.5. The method according to any one of claims 1 to 4, characterized in that the coating is applied by spraying the non-ferrous metal in powder form. 6. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß der Walzstahl zum Aufbringen des Überzuges durch ein Bad mit dem geschmolzenen Nichteisenmetall geführt wird.6. The method according to any one of claims 1 to 4, characterized in that the rolled steel for applying the coating through a bath with the molten Non-ferrous metal is guided. 7. Verfahren nach einem der Ansprüche 1 bis 6, dadurch gekennzeichnet, daß auf den Überzug noch eine Schicht aus einem Kunstharz, z.B. Epoxyharz, aufgetragen wird.7. The method according to any one of claims 1 to 6, characterized in that a layer of a synthetic resin, e.g. Epoxy resin is applied. 8. Verfahren nach einem der Ansprüche 1 bis 4, dadurch gekennzeichnet, daß die Abkühlung des Walzstahles in Form einer Abschreckung derart erfolgt, daß in dem Walzstahl unmittelbar nach der Abschreckung eine Randzone aus Martensit und Bainit vorliegt, während der im Stahlkern verbliebene Wärmeinhalt während des nachfolgenden Abkühlens ein Anlassen der Randzone bewirkt.8. The method according to any one of claims 1 to 4, characterized in that the cooling of the rolled steel takes place in the form of a quench in such a way that an edge zone of martensite and bainite is present in the rolled steel immediately after the quenching, while the heat content remaining in the steel core during subsequent cooling causes the edge zone to temper.
EP88113916A 1987-09-01 1988-08-26 Process for the treatment of rolled steel for increasing corrosion resistance Expired - Lifetime EP0305914B1 (en)

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AT88113916T ATE70568T1 (en) 1987-09-01 1988-08-26 METHOD OF TREATMENT OF ROLLED STEEL TO INCREASE CORROSION RESISTANCE.

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DE3729177A DE3729177C1 (en) 1987-09-01 1987-09-01 Process for treating rolled steel to increase resistance to corrosion
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EP0305914A3 (en) 1989-08-09
DK460688A (en) 1989-03-02
HU203586B (en) 1991-08-28
DE3729177C1 (en) 1989-01-05
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CA1306391C (en) 1992-08-18
PT88371B (en) 1993-02-26
NO176578C (en) 1995-04-26
DK460688D0 (en) 1988-08-17
NO883781L (en) 1989-03-02
EP0305914B1 (en) 1991-12-18
NO176578B (en) 1995-01-16
PL158408B1 (en) 1992-08-31
DE3866998D1 (en) 1992-01-30
NO883781D0 (en) 1988-08-24
PT88371A (en) 1989-07-31
JPH0445591B2 (en) 1992-07-27
PL274389A1 (en) 1989-04-17
JPS6475692A (en) 1989-03-22
ATE70568T1 (en) 1992-01-15
CN1031724A (en) 1989-03-15
ES2028964T3 (en) 1992-07-16
HUT52178A (en) 1990-06-28
DD282246A5 (en) 1990-09-05
SU1674689A3 (en) 1991-08-30

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