MXPA96004877A - Process of continuous elaboration of a laminated sheet of stainless steel, and continuous line for the use of proc - Google Patents

Abstract

A production process is described on a line, in continuous form, of a strip of laminated sheet of stainless steel, which has an improved surface condition, characterized in that the hot-worked sheet is subjected to a treatment that includes at least: primary pickling that ensures the removal of the husk; - a cold rolling in at most three steps of rolling; - a final annealing, - a final pickling, and - a cold rolling of the "hardening rolling" type. It is possible to carry out before the primary pickling, a flattening or finishing lamination under traction, which produces a residual elongation of 1 to 5% to crack the oxide layer and flatten the cha

Description

PROCESS OF ELABORATION, CONTINUOUSLY, OF A BAND STAINLESS STEEL SHEET AND CONTINUOUS LINE FOR THE USE OF THE PROCESS The invention relates to a production process, on a line, in a continuous manner, of a strip of laminated sheet of stainless steel having an improved surface condition. Different processes for making a sheet of stainless steel sheet from a hot-worked sheet are known, processes which aim to obtain a sheet having an improved surface condition, characterized for example by a roughness Ra lower than 0.25 icometers. A method of making a sheet of stainless steel sheet is known, which comprises the operations of annealing the strip of hot-rolled sheet, and of pickling said strip, these operations being carried out on a first line. On a second line, the pickled veneer band is subjected to a cold rolling operation on a reversible laminator, the laminating operation being carried out in five steps, and in a general manner, in seven steps or more, at a rate of reduction that can vary from 50 to 80%. The sheet metal strip thus cold rolled is then wound and transported on a line to undergo annealing, followed by pickling. Finally, the strip of pickled sheet is subjected to a cold rolling operation of the "hardening rolling" type which can be followed by a finishing and shearing rolling operation. The drawback of this process is mainly due to the large number of installations in which the cold-processed sheet metal strip must be treated successively, with the consequences of treatment, training and personnel costs, numerous intermediate maintenance with risks of deterioration of the the sheet metal strip, metal loss by trimming, and treatment durations in general longer than a week, even two weeks or more, due to delays to each of the facilities, delays that need assortment of materials, storage surfaces , and corresponding storage costs. The purpose of the invention is the production, in a continuous manner, of a strip of stainless steel sheet which has certain characteristics of roughness and uniformity of appearance on the surface, the sheet metal strip obtained on a single industrial line, the manufacturing process which ensures a consistent reduction in the number of steps in the cold rolling operation, and which allows the whole of the operations necessary to obtain a sheet metal band having a defined surface quality to be carried out economically. The object of the invention is a process for producing on a line, continuously, a strip of laminated sheet of stainless steel having an improved surface condition, characterized in that the hot-worked sheet is subjected to a treatment that includes less: - a primary pickling that ensures the removal of the scale, - a cold rolling in at most three steps of rolling, - a final annealing, - a final pickling, and - a cold rolling of the type "hardening rolling " Preferably, the treatment also has, before the primary pickling, a finishing lamination under traction which produces a residual elongation of 1 to 5% to crack or crack the oxide layer and flatten the sheet. The other features of the invention are: -the sheet metal strip is, in addition, subject to an abrasion that can be carried out before, and / or after, and / or during the primary pickling operation, -the abrasion is carried out with at least a brush, - the strip of sheet is, after the lamination of hardening under traction, subjected to a pulverization or shot blasting to remove the scale, - for a strip of sheet of ferritic steel, the cold rolling of the strip is carried out with a reduction rate of less than 60%, -for a strip of austenitic steel sheet, the cold rolling of the strip is carried out with a reduction rate of less than 50% -the The sheet metal strip is subjected to a final annealing carried out under an oxidizing atmosphere at a temperature between 800 and 1200 ° C, - the sheet metal strip, after cold rolling and final annealing, is subjected to a cold rolling of the "lamination" type of hardening ", the cold rolling produces an elongation of the strip, comprised between 0.5 and 2% - the sheet metal strip is, on the other hand, after the final pickling and rolling of the" hardening lamination "type, subjected to a lamination Finisher, -the sheet metal strip is also subjected to a shearing operation to cut the edges. The invention also relates to an industrial line for manufacturing a strip of stainless steel sheet for the operation of the process characterized in that it comprises, in succession: a straightener under traction, a primary pickling station, a rolling device cold, continuously, non-reversible, -a final annealing device, -a final pickling device, -a cold rolling device of the type "hardening lamination". The other characteristics of the line are: -the line also includes a spray or shot blasting station, -the primary pickling station comprises a means that ensures a stop, in the line, of the pickling of the sheet metal strip, -the station of pickling comprises a container comprising an acid bath, provided with a device for extracting the bath from the sheet metal strip, immersed in the bath, - the pickling station is of the spray type, - the pickling station is electrolytic, - the container of the electrolytic pickling station contains an electrolyte chosen from a neutral salt, phosphoric acid or a mixture of both, - the line further comprises a means of abrasion which can be placed before, and / or after the pickling, and / or at the primary pickling station, -the abrasion medium is a brush, -the cold rolling device is composed of at most three cells of the multicilind type With the work rolls having a diameter of less than 180 m and preferably of less than 150 mm, the line also comprises at least one seasoning rolling station associated with the cold rolling device of the "hardening rolling" type, the line further comprises at least one shearing device of the edges of the band. The following description and the appended figures, all given by way of non-limiting example, will be to better understand the invention.

Figure 1 represents an outline of the principle that materializes, in a cold rolling operation, the evolution of the surface condition of a sheet metal strip, from the point of view of roughness, as a function of the number of steps and the rate of cold rolling reduction.

Figure 2 shows a curve of the rolling forces as a function of the cold rolling reduction rate, for two grades of rolling oil used.

Figure 3 is a diagram of the rolling line according to the invention.

Figure 4 is another diagram of the rolling line according to the invention.

The invention relates to an in-line production process, continuously, of a laminated sheet of stainless steel having an improved surface condition 2B, characterized by a roughness Ra less than 0.25 microns, even less than 0.25 microns in the longitudinal sense and in the transversal sense, the process does not generate change of apparent dye, halo or traces of oxide. According to the process of the invention, a strip of hot-worked sheet is subjected, first, to a finishing lamination under traction. The purpose of the traction finishing lamination is to cause, by means of the traction that generates a residual elongation of 1 to 5% of the sheet metal strip, a chipping of the oxide layer of said strip. The finishing lamination associated with the traction ensures in this state of the process, an improvement of the flatness of the sheet metal strip, improvement that influences the following operations such as spraying. After the operation of the finishing lamination under traction, the sheet metal strip is subjected to a pickling, which ensures an improved surface state of the sheet metal strip, comparatively to a conventional method of manufacturing a sheet metal strip, as described above. in the prior art. In figure 1, curves A and B present a scheme of the principle that materializes, in a cold rolling operation, the evolution of the surface condition of a sheet metal strip, from the point of view of roughness, depending on the number of steps and the reduction rate. The evolution of the surface state in the classical process is signaled by the curve A, that of the invention is indicated by the curve B. As shown in the curves A and B of figure 1, the variation of the roughness of a band of sheet metal is decreasing depending, on the one hand, on the rate of reduction of the band at the time of cold rolling, and on the other hand on the number of steps in cold rolling. The number of steps P is embodied in the curves of Figure 1 by a figure contained in a circle.

The classic process, in which the sheet metal strip has undergone, before cold rolling, an annealing followed by blasting or pulverization and pickling, allows to obtain a sheet metal strip having a roughness Rt of 25 to 40 micrometers and Ra of 2.5 to 4 micrometers. In the process according to the invention, the band before cold rolling has a roughness Rt of 10 to 20 micrometers and a Ra of 2 micrometers. The band is also completely free of rust. Preferably, and in order to improve the state of the surface of the sheet metal strip flattened under tension, the sheet metal strip is subjected to an abrasion, for example an abrasive brush, the brushing being carried out before, after or during the primary pickling operation. Likewise, in order to improve the state of the sheet metal surface before the cold rolling and pickling operation, the sheet metal strip can be subjected to a blasting or spraying operation which facilitates the removal of the scale without disturbing the excessive way the surface of the sheet. In fact, the strip of sheet made in hot and not annealed, has high mechanical characteristics that, associated with the conditions of shot blasting or soft pulverization, allow blasting or spraying without damaging disturbance of the surface of the sheet metal strip. When it is recognized that the state of the surface of a sheet metal strip, in particular, is improved by the fact that the sheet metal strip is subjected to a large number of steps in the cold rolling operation, the applicant has remarked that The quality of the surface condition of the sheet metal strip, from the roughness point of view, is due, in large part, to the quality of the surface condition of the sheet metal strip before the cold rolling operation . The cold rolling despite a large number of steps does not erase more than very gradually the roughness that appears at the time of the treatment of the sheet metal strip before the cold rolling. According to the invention, the operations of lamination finishing under traction and associated pickling, aim to ensure to the surface of the sheet metal band a roughness such that it allows to consistently reduce the number of steps in the operation of cold rolled. This is materialized by curve B of figure 1.

According to the invention, the reduction of the number of steps in cold rolling imposes rolling conditions that ensure a reduction in the roughness of the sheet metal strip. The total reduction in the thickness of the sheet metal strip is optimized so as not to exceed a rolling force of 800 tons per meter of width, exerted on the rolls of the rolling mills. Beyond this limit, there is the formation of a thick and rough transfer layer on the working cylinders, which print the strip of laminated sheet to confer a high roughness, corresponding to a Ra of approximately 1 micrometer. The diameter of the rollers of the rolling mill is less than 180 mm, and preferably less than 150 mm, to allow high reductions in the thickness of the strip, with rolling forces of less than 800 tons per meter of width. Such cylinders ensure an improvement of the roughness in the course of cold rolling. The cylinders of the last cell must be polished to have a very weak roughness, and preferably less than 0.1 micrometer. To achieve thickness reductions of the sheet metal strip with reduction rates of less than 60%, it is preferable to use paraffinic laminate oils, which contain one or the friction reducing additives, the additives preferably being one or several esters, where the concentration total in the oil is greater than or equal to 10%. The rolling oils used allow the reduction rates described above to be carried out in an even smaller number of steps, two steps for example, without increasing the rolling forces. For example, the use of a paraffinic oil containing at least 10% ester allows, at an identical rolling stress, a reduction in the thickness of the sheet metal strip of 35%, compared to the reduction of 25% obtained by a Classic oil that contains no more than 1% ester. Figure 2 shows two curves a and b corresponding to the rolling forces authorized as a function of the different reduction rates of the laminate, for two ester concentrations of a rolling oil. In order to improve the surface condition of the strip made of hot-rolled sheet, flattened under tension, the strip is subjected to brushing which can be abrasive, the brushing being carried out before, after or during the chemical pickling operation.

For the same purpose, the strip of hot rolled sheet, flattened under tension, can be, before pickling and / or brushing, subjected to a blasting or spraying, which facilitates the shedding of the scale. The sheet metal strip produced by the process according to the invention has a surface quality corresponding to a roughness Ra less than 0.25 micrometers, and can reach a roughness Ra less than 0.15 micrometers. The invention also relates, as shown in FIG. 3, to an industrial line 1 for the start-up of the process, an industrial line comprising, in an associated manner, a straightener 2 under traction, and a primary pickling station 3, ensuring a stop of the online pickling operation, simultaneously with the stoppage of the cold rolling device. In addition, a very important reduction in the duration of the steel pickling treatment is imposed, in order to avoid an accumulation of the strip between the different devices of the line. Such a production line, continuously, has the advantage of reducing intermediate maintenance and storage.

In the field of cold rolling of stainless steel sheet strips, the treatment of the rollers of the rolling mill, must give the cylinders a resistance to wear, sufficient to maintain the quality of its surface during the rolling of a band winding of 30 tons. The cylinders used are made of high-speed steel, vanadium over-carbonaceous or even sintered, and they must be changed practically in each laminated coil. Then there is a need to stop the line in a regular way, at each change of work cylinders. The use of a pickling bath upstream of the cold rolling device imposes the problem of frequent shutdowns of the laminator controlling the passage time of the strip in the pickling bath. In effect, the different stoppages or stops of the sheet metal strip on a single line impose band reservation management by means of band accumulators placed between the different stations and devices. According to the invention, the primary pickling station 3 is followed by a cold rolling device 4. The pickling station 3 comprises a container containing an acid bath, provided with an extraction device for the strip of sheet in immersion . Preferably, and to ensure frequent stoppages of the line, without deterioration of the band by an uncontrolled chemical attack, the pickling station 3 is of the spray type. The spray picking station authorizes an instant pickling stop by stopping the spray simultaneously with the stoppage of the rolling mill. In another embodiment, the primary pickling station 3 can be an electrolytic pickling station, which has a container for example of neutral salt, the station being stopped by stopping the electrical supply of the electrolytic cell, the pickling station 3, provided with an etching stop means, allows to reduce the volume or to suppress the band accumulator 13 generally placed between the pickling station 3 and the cold rolling device 4. Line 1 possesses, after the non-reversible cold rolling device 4 comprising at most three cells 5, an annealing device 6 of the hardened sheet metal strip, a final pickling station 7, and a cold rolling device of the "hardening lamination" type "8.

Line 1 according to the invention can also include, after the straightening machine under tension 2, as shown in FIG. 4, a blasting or spraying station 9 and / or brushing means 10 which can be abrasive, they contribute to fine-tune the surface quality of the sheet metal strip before cold rolling, to obtain an improved surface state of the sheet metal strip after said cold rolling, of a reduced number of steps. The line can also have, after the cold rolling device of the type "finishing lamination", a straightener 11 associated with a shear 12. A second shear 12 can be placed after the straightener under tension 2. In an example of embodiment, A strip of austenitic hot-rolled steel sheet, having a thickness of 2 mm, is subjected to a finishing or flattening lamination under traction, which produces a residual elongation of 3.5%. The sheet metal strip is then pickled in two H2S0 sulfuric acid baths. In this state of the process, the sheet metal strip has a roughness of less than 1.5 micrometers. The sheet metal strip is then subjected to cold rolling in three steps on a Sendzimir cold rolling mill of the ZHi type. The sheet metal strip is cold rolled with a 50% reduction rate. The sheet metal strip is then annealed and then pickled. This presents, after these short operations of cold rolling, annealing and pickling, a roughness Ra less than 0.25 micrometers. The sheet metal strip is subjected to an operation, in one step, of cold rolling of the "hardening lamination" type which produces an elongation of 0.8%. The sheet metal strip then has a roughness Ra less than 0.1 micrometer. In another embodiment, a strip of ferritic steel sheet stabilized with titanium, hot-rolled and having a thickness of 3 mm, is subjected to flattening or finishing lamination under traction, which produces a residual elongation of 4%. The sheet metal strip is then pickled in a bath of sulfuric acid and then in a bath of nitric acid HNC. In this state of the process the sheet metal band has a roughness Ra less than 2 micrometers. The sheet metal strip is then subjected to cold rolling in two steps, at a 50% reduction rate on Sendzimir type ZHi mills, and then annealed and pickled. This presents, after these brief operations of cold rolling, annealing and pickling, a roughness Ra less than 0.25 micrometers. The sheet metal strip is then subjected to a cold rolling operation in a step of the "hardening lamination" type, which produces a band elongation of 0.8%. The sheet metal strip then has a roughness of less than 0.15 micrometers. It is imposed, on this line, the problem of pickling and in particular of a pickling in a short imposed time, to avoid, imperatively, an accumulation of the band treated between the different devices placed successively on the line of production of the band continuously. In yet another example, the strip of stainless steel sheet is pickled by an aqueous pickling solution consisting of hydrochloric acid and ferrous ions and pickling ferrous, in solution, in order to preserve a constant heat-removing ability of the aqueous acid solution hydrochloric, and to maintain the concentration of FeJ + ions, by reoxidation of the Fe ions t t generated at the time of pickling, the REDOX potential being maintained at a value between 0 and 800 mV, measured between a platinum electrode and an electrode of Ag / AgCi reference placed in the solution The pickling operations before rolling, in continuous line, ensure an optimum quality of the surface condition of the strip.The effectiveness of the pickling can allow, depending on the quality of the band of sheet metal, the suppression of the mechanical treatments of the flattened type or lamination finisher under traction, shot blasting or spraying, brushing, produced consistently in the industrial line for the manufacture of the sheet steel strip. According to the process of the invention, the reduction of the number of steps in cold rolling, allows the placement of a line in a continuous manner, comprising a cold rolling device, reduced, which generates an economy on investment, for the obtaining of a quality sheet, and also an important economy on the maintenance costs of the line and of the personnel. The line in continuous generates in this way a very important reduction of the duration of the treatment, therefore of the storages of products were finished and a suppression of the intermediate maintenance generating defects and loss of metal.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the contents of the following are claimed as property: "

Claims (23)

1. A continuous production process on a line of a sheet of stainless steel laminated sheet having an improved surface condition, characterized in the process, because the hot-worked sheet is subjected to a treatment that includes at least: - a pickling primary that assures the removal of the scale, -a cold rolling in at most three steps of rolling, -an final annealing, -a final pickling, and-a cold rolling of the "hardening rolling" type.

2. The process according to claim 1, characterized in that it also includes, before the primary pickling of the strip, a finishing or flattening lamination under tension, which produces a residual elongation of 1 to 5% to crack the oxide layer and flatten the sheet.

3. The process according to any of claims 1 and 2, characterized in that the sheet metal strip is further subjected to an abrasion that can be carried out before, and / or after, and / or during the primary pickling operation.

4. The process according to claim 3, characterized in that the abrasion is carried out with at least one brush.

5. The process according to any of claims 1 to 4, characterized in that the sheet metal strip is, after flattening under tension, subjected to a shot peening or pulverization to eliminate the scale.

6. The process according to any of claims 1 to 5, characterized in that for a strip of ferritic sheet steel, the cold rolling of the strip is carried out with a reduction rate of less than or equal to 60%.

7. The process according to any of claims 1 to 5, characterized in that for an austenitic sheet steel strip, the cold rolling of the strip is carried out with a reduction rate of less than or equal to 50%.

8. The process according to any of claims 1 to 7, characterized in that the sheet metal strip is subjected to a final annealing carried out under an oxidizing atmosphere, at a temperature comprised between 800 and 1200 ° C.

9. The process according to any of claims 1 to 8, characterized in that the sheet metal strip, after the cold rolling and final annealing, is subjected to a cold rolling of the "hardening lamination" type, producing the cold rolling an elongation of the band, comprised between 0.5 and 2%.

10. The process according to any of claims 1 to 9, characterized in that the sheet metal strip is subjected to a flattening or finishing lamination after the final and laminated pickling of the "hardening lamination" type.

11. The process according to any of claims 1 to 10, characterized in that the sheet metal strip is further subjected to a shearing operation to trim the edges.

12. The industrial line for manufacturing a strip of stainless steel sheet for the operation of the process according to claims 1 to 11, characterized the line because it comprises successively: a straightener under traction, a primary pickling station , - a continuous cold rolling device, non-reversible, - a final annealing device, - a final pickling device, - a cold rolling device of the "hardening rolling" type.

13. The line according to claim 12, characterized in that it also comprises a blasting or spraying station.

14. The line according to any of claims 12 and 13, characterized in that the primary pickling station comprises a means that ensures a stop or stop, in the line, of the pickling of the sheet metal strip.

15. The line according to any of claims 12 to 14, characterized in that the pickling station comprises a container containing an acid bath provided with a device for extracting the bath from the sheet metal strip in immersion in the bath.

16. The line according to any of claims 12 to 14, characterized in that the pickling station is of the spray type.

17. The line according to any of claims 12 to 14, characterized in that the pickling station is electrolytic.

18. The line according to claim 17, characterized in that the cell of the electrolytic pickling station contains an electrolyte chosen from a neutral salt, phosphoric acid or a mixture of both.

19. The line according to any of claims 12 to 18, characterized in that the line further comprises an abrasion means that can be placed before, and / or after the pickling extraction, and / or at the primary pickling station.

20. The line according to claim 19, characterized in that the abrasion means is a brush.

21. The line according to any of claims 12 to 20, characterized in that the cold rolling device is composed of more than three cells of the multi-cylinder type, the working cylinders having a diameter of less than 180 mm and preferably less than 150 mm.

22. The line according to any of claims 12 to 21, characterized in that the line also comprises at least one finishing or rolling finishing station associated with the cold rolling device of the "hardening lamination" type.

23. The line according to any of claims 12 to 22, characterized in that the line further comprises at least one shearing device of the edges of the strip.