Patent Application
20090107648
The invention concerns a roll for metal production and/or metal processing, especially a continuous casting roll, which has a roll body made of metal and a coating of wear-resistant material applied on the roll body, where the coating contains electrodeposited nickel and where the surface of the coating forms the working surface of the roll.
The strand guide rolls have a great deal to do with the satisfactory operation of a continuous casting plant as well as with the quality of the cast product and the economy of the plant. The function of the strand guide rolls is to support, guide, bend, and convey the solidified strand after it has left the mold. In this connection, the roll bodies and the bearings of the segmented rolls are subject to high thermal, mechanical, and corrosive chemical stresses.
The thermal stress arises from direct contact of the surface of the roll body with the cast strand, which has a temperature of 800° C. to 1,200° C. The mechanical stress is the result of ferrostatic forces, bending and straightening forces, and drive forces that must be transferred from the roll to the strand. In addition, the rolls are subject to wear due to friction with the strand. Due to the large amounts of cooling water that are needed and the high temperatures in combination with aggressive chemical compounds, which are introduced, for example, by the use of casting flux, it is also necessary to take into account the corrosion characteristics and the corrosion protection of the materials and parts used for the roll.
It is well known that the rolls of a continuous casting plant can be produced from a heat-treatable steel as the base material (e.g., 21 CrMoV 511 V, 16 CrMo 44, 24 CrMo 5, and S 355), which is capable of absorbing the high mechanical stresses. However, this steel is usually less well suited for permanently withstanding the thermal and corrosive chemical stresses. To realize adequate resistance to high temperatures and corrosive chemical effects as well, it is known that buildup welding can be used to cover the surface of the roll body with a soft martensitic material. However, this technique is relatively cost-intensive.
A roll of this general type is known from EP 1 555 074 A1 and EP 1 468 761 A1. EP 1 582 279 A1 describes a similar solution. WO 96/02340 describes a casting roll that is furnished with an outer wear-resistant coating.
DE 40 27 225 C2 discloses a method for producing a continuous casting roll that consists of a core of iron material covered with a jacket of wear-resistant material. A layer of copper or copper alloy is provided between the outer jacket and the core of iron material. To optimize the thermal conductivity of the roll, a nickel coating is electrodeposited on the layer of copper. This intermediate nickel coating is then covered with a wear-resistant cover layer of a nickel-chromium-boron alloy by buildup welding.
U.S. Pat. No. 5,161,306 also proposes the application of a wear-resistant layer on a roll body that is coated with intermediate layers; in this case, the wear-resistant layer consists of chromium oxides (Cr2O3).
US 2002/0056539 A1 also proposes the application of a wear-resistant layer on a continuous casting roll; in this case, the wear-resistant layer is based on nickel and contains carbon, chromium, and molybdenum.
Other rolls with various wear-resistant coating materials are disclosed by JP62-183950 A1, JP62-230462 A, JP63-086856 A, JP60-030560 A, JP59-129754 A, and JP62-207549 A.
The objective of the invention is to remedy the disadvantages described above and to create a roll, especially a continuous casting roll, which has sufficient strength and at the same time is capable of withstanding the thermal, abrasive mechanical, and corrosive chemical stresses that arise during the operation of the roll, with it being possible to operate the roll for the longest time possible and with little or no geometric change in the roll. At the same time, it must be possible to produce the roll at low cost. A further objective of the invention is to propose a corresponding method for producing a roll of this description.
The solution to this problem by the invention is characterized by the fact that, besides electrodeposited nickel as the base material, the coating contains ceramic particles, which are carbides of titanium (Ti), tantalum (Ta), tungsten (W), zirconium (Zr), boron (B), chromium (Cr), and/or silicon (Si), or oxides of aluminum (Al), chromium (Cr), silicon (Si), beryllium (Be), or zirconium (Zr), where the amount of ceramic particles in the nickel or nickel alloy is 15-40 vol. %, and preferably 25-30 vol. %.
The invention is thus novel in relation to previously known solutions by virtue of the fact that the wear-resistant coating, whose surface forms the working surface of the roll, is applied by a galvanic, i.e., electrolytic, method.
The thickness of the coating applied by the galvanic or electrolytic process is preferably 0.01 mm to 10 mm, and especially 0.05 mm to 2 mm.
In one embodiment of the invention, the coating consists of pure nickel. However, it is preferred that the coating contain other constituents besides nickel. Specifically, these other constituents besides nickel can be, for example, one or more of the constituents cobalt (Co), phosphorus (P), iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), and chromium (Cr).
In this connection, in a preferred embodiment, the coating consists of a nickel-cobalt alloy in which ceramic particles of silicon carbide are incorporated.
In accordance with a preferred embodiment, the particle size of the ceramic particles is 1-5 μm. In another embodiment, the ceramic particles are much smaller, namely, 10 nm to 1,000 nm.
In accordance with an advantageous embodiment of the invention, not the least of the advantages realized in this way is that the hardness of the surface of the coating is 300-500 HV1 (Vickers hardness), and preferably 350-450 HV1.
A method for producing a roll for metal production and/or metal processing, especially a continuous casting roll, involves the following steps:
(a) production of a metal roll body;
(b) immersion of the roll body in an electrodeposition bath;
(c) electrodeposition of a coating on at least part of the surface of the roll body, where the coating consists at least partly of nickel, and the surface of the coating forms the working surface of the roll.
The proposal of the invention is thus no longer aimed at providing the base material of the strand guide roll with a soft martensitic surface layer that is welded on, as in the prior-art methods, but rather at applying a coating of nickel or a nickel alloy by electrodeposition.
In this connection, it is advantageous if a large number of rolls can be simultaneously coated in electrodeposition baths, so that the product costs per roll remain low. In addition, the thickness of the applied coating can be easily defined and varied by the residence time of the rolls in the electrodeposition bath.
The electrodeposited coating is thin and effectively protects the base material of the roll from corrosive attack. At the same time, the coating is very hard and has good resistance to high temperatures and good resistance to scaling. The wear resistance of the continuous casting roll is reliably and inexpensively improved in this way. The proposed rolls thus have a longer service life, which results in a corresponding reduction of costs for the operator of a continuous casting plant.
The drawings illustrate a specific embodiment of the invention.
The coating 3 has a coating thickness D, which can be, for example, 0.05 mm to 2.0 mm. The essential feature is that the surface 4 of the coating 3 is the working surface of the roll 1. In the case of a continuous casting roll, the working surface has contact with the continuously cast strand, which is still hot, and is thus subject to high thermal, mechanical, and corrosive chemical stress.
The coating 3 consists of nickel or a nickel alloy, which is applied to the roll body 2 galvanically (electrolytically) (in this connection, see
To increase especially the mechanical and thermal resistance of the surface 4 of the roll 1, the surface is provided with a considerable proportion of ceramic particles 5 with a mean particle diameter d, which in one embodiment of the invention can vary within the range of 1-5 μm. However, an alternative embodiment provides for the use of nanoparticles, i.e., the diameter d in this case is within the range of 10 nm to 1,000 nm.
When the current flows, a metallic precipitate that consists of nickel is electrochemically deposited on the (uncovered) surface of the rolls 1. The electric current removes metal ions from the consumable electrode 7 and deposits them on the surface of the rolls 1 by reduction. This causes the roll 1 to be coated uniformly and on all sides with nickel. The longer the rolls 1 remain in the bath 6, the thicker the coating 3 of nickel on the roll body 2 becomes.
The ceramic particles introduced in the coating make it possible to optimize the mechanical/technological properties of the nickel or nickel alloy coating for the each intended application. In the present situation, it is desired that a continuous casting roll be provided with a coating that is chemically resistant and stable at high temperatures and has very low wear rates when subjected to abrasive stress, but at the same time can be economically processed during its manufacture. For example, nickel compounds can be produced that have an average hardness of 350-450 HV1 at room temperature and can thus be worked with an acceptable degree of effort and at the same time have low wear rates even at higher temperatures.
Electrolytically produced metal alloy dispersions based on nickel/cobalt, in which ceramic particles (preferably silicon carbide) with a particle size of 1-5 μm or ceramic nanoparticles with a size of 10 to 1,000 nm are incorporated, are especially well suited for the proposed application.
The nickel that is used is preferably high-purity nickel that has been compressively prestressed.
Preferably, therefore, an electrolytic surface treatment of the roll body is carried out, in which a high concentration of hard solid particles is incorporated in a ductile nickel matrix. This combination imparts very good wear resistance to the part to be protected, for the cast strand then no longer runs directly on the metal of the metal matrix but rather on the ceramic particles that protrude from the base contour of the roll surface. This greatly reduces the abrasion of the nickel and makes it possible to achieve the goal of coating strand guide rolls for a long service life, i.e., for at least 10 years of use.
In this regard, it is also conceivable that several coatings can be electrodeposited on the roll body, and it is possible to apply the same coating material each time or to use different coating materials.
The continuous casting rolls can be used for all known applications, i.e., especially in plants for the continuous casting of carbon steel and stainless steel grades in ingots, round bars, sections, slabs, and thin slabs. The roll diameter (final diameter including the surface coating) of the strand guide roll is usually in the range of 80-350 mm.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 200600110384.5 | Mar 2006 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2007/000740 | 1/29/2007 | WO | 00 | 9/3/2008 |
