CS245345B1 - A method of thermo-chemical treatment of the surface of transport furnace rollers made of heat resistant aluminum-nickel alloy - Google Patents

Abstract

The solution relates to a method of thermo-chemical treatment of the surface of transport furnace cylinders of heat-resistant chromium-nickel alloy containing at least 2 percent of aluminum by annealing in an oxidizing and subsequent protective atmosphere after incorporation into a working furnace. The cylinders are annealed in the first stage under the exclusive presence of air from 200 to 500 ° C with a duration of 2 to 3 hours at every 100 QC. In the second stage, from 501 to 800 ° C, they are annealed with a similar duration of 1 to 4 hours and at 800 ° C for 3 to 4 hours. The second stage is carried out in the presence of nitrogen sequentially added from its 0 to 100% fraction with simultaneous air extrusion.

Description

245345 3 4

BACKGROUND OF THE INVENTION The present invention relates to a method of thermo-chemical treatment of the surface of transport furnace furnaces of a chromium-nickel alloy with a content of at least 2% of the core and to solve the problem of preventing increments and sticking. pick-ups on their surface and thereby improve the quality of the metal-sheet belts, especially of electrical steels.

During the continuous heat treatment, in particular of electrotechnical steels, the surface of the transport rollers in the furnace is subjected to the processing temperatures for the gradual formation of increments and glues, which cause so-called bruising in the deformation pattern, which results in a reduction of the final quality of the sheet. Growths, the so-called pick-ups, arise mainly from naval chrome-nickel alloys that are most widely used for this purpose. The resulting chromium oxides, nickel oxides and optionally other alloying elements formed on the surface of the cylinder react and bind at least the lower iron melting point iron formed on the treated belt, which causes the formation of stickers, so-called oxygenated eutectics. . There are various pieces to solve the problem of limiting the occurrence of anarastation of the oxygen eutectics at the surface of the rollers. For example, in conventional chromium-nickel steel cylinders for the processing of high-silica sheets, the solution according to AO CSSR No. 175 079 is known according to which a layer of exclusively iron oxide is to be formed therein by the known process of annealing of cylinders to The solution assumes that they are bonded to silicon oxides formed on the sheet metal strip. However, the test has shown a low rate of iron oxide formation on the cylinder and, in practice, the solution failed because it did not solve the formation of chemically stable oxides on the cylinder, whereas oxide formation was needed iron on it. A further attempt to form such chemically stable oxides on the surface of the roll is according to AO CSSR No. 204 755, which consists in additionally spraying the metallization coating from the cylinder and subsequent di-fusion annealing, which presupposes binding by spraying and the cylinder body of chromium-nickel steel. This experiment also failed to over-bind. The problem of the successful development of the basic material according to AOČSRR 231 947, namely an alloy based on chromium-nickel alloyed with aluminum in the range of 2.3 to 4.0%, while suppressing the sulfur and phosphorus content of ammonium. However, this alloy must also be thermo-chemically treated for this purpose.

It is also known to provide a heat-chemical treatment of chromium-nickel steel rolls, but without the presence of aluminum as a alloy for the processing of high-silicon transformer sheets. At this time, the 4 hour form of the cylinder is heated to 800 degrees Celsius while maintaining the air and then the protective atmosphere is gradually added until a temperature of 850 ° C is reached. In this way, a protective layer in the form of oxide-chromium and nickel in the range of 20 to 55% and iron oxides in the remaining proportion should be provided. The need for this is similar to that of AO No. 175 079 and can be effective for processing other types of sheet metal.

Moreover, known solutions to the problem are based on the use of various types of material and construction of transport rollers, ie, in addition to the above-mentioned heat-resistant chromium-nickel steels, ceramic or other refractory materials in combination with metallic support elements, for example in AO CSSR no. However, these materials with advantageous surface properties cannot be used for the production problems of peeling and cracking of the material and the difficulty in attaching to said metal bearing elements due to insufficient adhesion, thermal gradients or insufficient resistance to mechanical shocks. .

The above-mentioned drawbacks are solved by the problem of thermal chemical treatment of the surface of transport furnace rollers made of chromium-nickel alloy with a content of at least 2 percent of aluminum, and by ironing in an oxidizing and subsequent protective atmosphere after incorporation into the process according to the invention. The essence of the invention is that the cylinders are annealed in the first stage under the exclusive presence of oxygen from 200 to 500 ° C. At this first stage, it is annealed with a duration of 2 to 3 hours every 100 ° C of gradual increase in temperature. Next, the cylinders are annealed immediately to the second stage in the range of from 501 to 800 ° C and the presence of nitrogen at a dew point of at most -30 ° C in a working atmosphere added in the range of from 0 to 100% with air extrusion. annealing at 1 to 4 hours for each 100 ° C of gradual temperature rise. Finally, at 800 [deg.] C., the presence of nitrogen is allowed to calculate for 3-4 hours. In particular, the advantages of the process according to the invention are that chromium oxide, nickel oxide and mainly aluminum oxide are still formed on the surface of the rolls, which is the alloying of the basic material, ie with thermal and chemical resistance to the oxides and metal particles located thermally. the treated strips and thus prevent the formation of stickers and increases in our surface and thereby the bruising and deformation of the processed sheet. This extends the life of the rollers without the need to renovate their surface. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT: The basic equipment of 100 furnace rollers, for example 120 x 2100 mm, is incorporated into the recrystallization furnace by refinishing worksheets

Claims (1)

Method of thermo-chemical treatment of the surface of transport furnace cylinders of a refractory chromium-nickel alloy containing at least 2 percent aluminum by annealing in an oxidizing and subsequent protective atmosphere after installation in a working furnace, characterized in that the cylinders are annealed in the first stage oxygen from air in the range of 200 to 500 ° C with a hold time of 2 to 3 hours at every 100 ° C of gradual temperature increase, then in the second stage in the presence of nitrogen with a dew point up to -30 ° C gradually added in a proportion of up to 100 % in a working atmosphere with simultaneous expulsion of air, ranging from 501 to 800 ° C with a hold time of 1 to 4 hours at 100 ° C incremental temperature rise, whereas at 800 ° C in the exclusive presence of nitrogen anneal with a hold time of 3 to 4 4 hours.