A method for producing a steel strip with improved strip edge quality

Abstract

The invention belongs to the field of twin roll strip casting and relates to the production of thin steel strip in a twin roll caster and downstream processing steps suitable for the final application. The invention discloses a method of producing a steel strip, the method comprising: casting a continuous thin steel strip from a steel melt in a twin roll caster with a thickness of less than 3 mm; cooling one or both edges of the steel strip; hot rolling the steel strip with the cooled edges in a hot rolling mill and reducing the thickness of the steel strip; cooling the steel strip in a cooling station; winding the steel strip on a coiler. The steel strip produced according to the method of the invention has a better edge quality.

Description

Technical Field

[0001] This invention relates to the manufacture of thin steel strips in the mid- and downstream processing steps of a twin-roll continuous casting machine, which are suitable for end applications. Background Technology

[0002] In a twin-roll continuous casting machine, molten metal, typically steel, is conveyed from a conveyor system to a casting pool supported on the casting surfaces of a pair of counter-rotating horizontal casting rolls. These rolls are internally water-cooled, causing a solidified metal shell to form on the moving roll surfaces. The metal shell is collected at the roll gap between them to produce a solidified strip of product conveyed downwards through the roll gap. The term "roll gap" as used herein refers to the general area closest to the casting rolls.

[0003] Molten metal can be poured from a ladle into smaller containers or a series of smaller containers, from which the molten metal flows through one or more metal conveying nozzles located above the roll gap to form a pool of molten metal supported on the casting surface of the casting roll, above the roll gap, and extending the length of the roll gap.

[0004] The casting pool is typically confined between side plates or side seals, which are held in a sliding engagement with the end portion of the casting roll to restrict flow out of the casting pool. The upper surface of the casting pool (often referred to as the "mensular height") is typically higher than the lower end of the delivery nozzle, such that the lower end of the delivery nozzle is submerged in the casting pool.

[0005] When steel strip is cast through a twin-roll continuous casting machine, the thin strip leaves the roll gap, passes through a guide table, through a pinch roll stand, and then through a hot rolling mill, where it is thinned to the desired thickness. The hot-rolled strip is then cooled to form a strip with the microstructure required for the final application. The cooled strip is then coiled, where a shear upstream of the coiler periodically cuts the strip to form the desired length in each coil.

[0006] Depending on the steel composition and casting conditions, strips produced through twin-roll casting, hot rolling, and cooling can be used for a variety of end applications.

[0007] One technical problem with twin-roll continuous casting of steel strip is that the edges of the strip after casting and hot rolling may be rough, and these rough edges must be trimmed to suit the customer. The edge trimming step is an additional step in the manufacturing process, thus increasing costs. Furthermore, the need to trim rough edges can have a significant impact on product yield. In some cases, the impact on yield can be as high as 5%. Summary of the Invention

[0008] This invention is based on the applicant's understanding that the quality of the side edges of steel strips can be significantly improved by controlling the temperature of the side edges before they enter the hot rolling mill, typically by cooling, usually by quenching.

[0009] This invention includes a twin-roll continuous casting method for producing steel strip, the method comprising: - Casting continuous thin steel strips with a thickness of less than 3 mm from molten steel in a twin-roll casting machine; - Cool one or both edges of the steel strip; - Hot rolling of steel strip with cooling edges in a hot rolling mill, reducing the strip thickness; - Cooling the steel strip in the cooling station; and - Wind the steel strip in the coiler.

[0010] The term "edge of the steel strip" is understood in this article to refer to a distance of up to 20 mm from the side edge of the steel strip.

[0011] The method may include cooling one or both edges of the steel strip by at least 40°C.

[0012] The method may include cooling one or both edges of the steel strip by at least 50°C.

[0013] The method may include cooling one or both edges of the steel strip to at least 80°C.

[0014] The method may include cooling one or both edges of the steel strip by at least 40°C and less than 150°C.

[0015] The method may include cooling one or both edges of the steel strip by at least 40°C and less than 220°C.

[0016] The method may include cooling one or both edges of the steel strip to less than 150°C.

[0017] The method may include cooling one or both edges of the steel strip to less than 220°C.

[0018] The method may include cooling one or both edges of the steel strip by using water to cool the edges of the strip.

[0019] The method may include cooling one or both edges of the steel strip by water quenching the strip edges.

[0020] The method may include quenching the edges of the strip with water from a spray nozzle.

[0021] The steel melt can be any steel composition that can be processed in a twin-roll belt casting machine.

[0022] For example, steel may contain, by weight, C<0.6%, Si<0.3%, Mn<2.5%, Nb<0.1%, P<0.03%, S<0.0025%, sol Al<0.01%, N<0.005%, Cu<0.4%, with the remainder being iron, impurities and inclusions.

[0023] The term "impurity" refers to elements present in the melt as an unavoidable result of the steelmaking process or as a consequence of the raw materials used in steelmaking. These are often nonmetallic elements. Examples of impurities are N, P, S, and H.

[0024] The term "inclusion" refers to compounds formed during the steelmaking process. Examples of "inclusions" include AlN and MnS.

[0025] The method may include superheating the molten steel to a superheat temperature before transferring it to a twin-roll casting machine.

[0026] The method may include hot-rolled steel strip, wherein the cast strip enters the hot rolling mill at an average mill entry temperature of 1020-1150°C.

[0027] The method may include hot-rolled steel strip, wherein the cast strip enters the hot rolling mill at an average mill entry temperature of 1050-1120°C.

[0028] The method may include hot-rolled steel strip, wherein the cast strip enters the hot rolling mill at an average mill entry temperature of 1050-1080°C.

[0029] The method may include hot-rolled strip, wherein the strip enters the hot rolling mill at an average mill entry temperature that is 140-160°C higher than the average mill exit temperature.

[0030] This method may include casting continuous thin steel strips with a thickness of less than 2.5 mm in a twin-roll casting machine.

[0031] The present invention also provides an apparatus for producing steel strip, comprising: - Twin-roll continuous casting machine for forming continuous thin steel strips with a thickness of less than 3 mm from molten steel; - With edge cooling stations, used to cool one or both edges of the steel strip, giving the steel strip a cooled edge; - Hot rolling mill, used to reduce the thickness of steel strip; - Cooling station for cooling steel strip; and - A coiler used to form steel strip coils.

[0032] The edge cooling station can be configured to quench one or both edges of the steel strip at a temperature of at least 40°C.

[0033] The edge cooling station can be configured to quench one or both edges of the steel strip at a temperature of at least 50°C.

[0034] The method may include cooling one or both edges of the steel strip to at least 80°C.

[0035] The edge cooling station can be configured to quench one or both edges of the steel strip at a temperature of at least 40°C and less than 150°C.

[0036] The method may include cooling one or both edges of the steel strip by at least 40°C and less than 220°C.

[0037] The method may include cooling one or both edges of the steel strip to less than 150°C.

[0038] The method may include cooling one or both edges of the steel strip to less than 220°C.

[0039] The edge cooling station can be configured to quench the edge of the strip with water.

[0040] An edge cooling station may include spray nozzles for supplying water to quench the edge of the strip.

[0041] The edge cooling station may include a water spray assembly extending across the belt above and / or below the belt, the assembly including water spray nozzles for supplying water to quench the belt edge.

[0042] The equipment may include a pinch roll stand upstream of a hot rolling mill.

[0043] The edge cooling station can be located at any suitable location between the pinch roll stand and the hot rolling mill.

[0044] Typically, edge cooling stations are positioned as close as possible to the hot rolling mill.

[0045] The present invention also provides a twin-roll cast and hot-rolled steel strip with a thickness of less than 3 mm produced by the above method.

[0046] The present invention also provides a twin-roll steel strip with a thickness of less than 3 mm produced by the above-described equipment through casting and hot rolling.

[0047] Twin-roll cast and hot-rolled steel strips may have at least one side edge, which, in the form of casting and hot rolling, has a straight edge that does not require side trimming.

[0048] Twin-roll steel strips, both cast and hot-rolled, can have a width spanning both the cast and hot-rolled strips and a microstructure that is at least substantially uniform along their length, without requiring side trimming.

[0049] Twin-roll steel strips, both cast and hot-rolled, can have a width spanning both the cast and hot-rolled strips and a yield stress that is at least substantially uniform along their length, without requiring side trimming.

[0050] The thickness of twin-roll cast and hot-rolled steel strips can be less than 3 mm.

[0051] The thickness of twin-roll cast and hot-rolled steel strips can be less than 2.5 mm.

[0052] The steel strip can have any suitable microstructure. Attached Figure Description

[0053] To describe the invention in more detail, some illustrative examples will be given with reference to the accompanying drawings, in which: Figure 1 This is a schematic side view of an embodiment of the twin-roll continuous casting machine of the present invention; Figure 2 yes Figure 1 An enlarged partial cross-sectional view of a part of a twin-roll continuous casting machine; Figure 3 yes Figure 1 A partial schematic side view of the outlet end of a twin-roll continuous casting machine; Figure 4 These are two images of steel strip produced in a standard twin-roll belt casting machine; Figure 5 These are two images of a steel strip segment produced in a twin-roll belt casting apparatus according to the present invention; Figure 6A These are three images comparing a steel strip segment produced in the twin-roll belt casting apparatus according to the invention and a steel strip segment produced in a standard twin-roll belt casting apparatus, indicating the edge temperature of the two steel strip segments. Figure 6B It is a color chart, representing the different temperature ranges corresponding to different colors. Detailed Implementation

[0054] The following description of embodiments of steel strip produced by the twin-roll belt casting method is not the only embodiment of the present invention.

[0055] Furthermore, the following description of embodiments of the twin-roll casting machine is not the only embodiment applicable to the production of steel strips according to the present invention.

[0056] All other embodiments obtained by those skilled in the art based on the embodiments described in this invention without any inventive effort fall within the protection scope of this invention.

[0057] Unless otherwise defined, the technical or scientific terms used in this disclosure should be understood in the sense that would be commonly understood by one of ordinary skill in the art to which this invention pertains.

[0058] Now for reference Figure 1 and Figure 2The diagram illustrates a twin-roll continuous casting machine comprising a main machine frame 10 erected from the plant floor and supporting a pair of counter-rotating casting rolls 12 mounted in a module of a roll box 11. The casting rolls 12 are mounted in the roll box 11 to facilitate operation and movement as described below. The roll box 11 facilitates the rapid movement of the casting rolls 12, ready for continuous casting, from their set position to their operating casting position as a unit within the continuous casting machine, and allows for easy removal of the casting rolls 12 from their casting position when they need to be replaced. There is no particular desired construction for the roll box 11, as long as it performs the functions described herein that facilitate the movement and positioning of the casting rolls 12.

[0059] A twin-roll continuous casting machine includes a pair of counter-rotating casting rolls 12, each roll having a laterally positioned casting surface 12A to form a roll gap 18 between them. Molten metal, more specifically molten steel, which will be further described below, is supplied from a ladle 13 via a metal conveying system to a metal conveying nozzle 17 (core nozzle) located between the casting rolls 12 and above the roll gap 18. The molten metal thus conveyed forms a pool 19 of molten metal above the roll gap 18, which is supported on the casting surface 12A of the casting rolls 12. The pool 19 is confined within the casting area at the ends of the casting rolls 12 by a pair of side-sealing plates or side-sealing plates 20. The upper surface of the pool 19 (commonly referred to as the “mensular” height) can rise above the lower end of the conveying nozzle 17, such that the lower end of the conveying nozzle 17 is immersed in the pool 19. The casting area includes the addition of a protective atmosphere above the pool 19 to inhibit oxidation of the molten metal within the casting area.

[0060] The ladle 13 is typically of a conventional structure, supported on a rotating turret 40. For metal conveying, the ladle 13 is positioned above a movable tundish 14 in the casting position to fill the tundish 14 with molten metal. The movable tundish 14 can be positioned on a tundish cart 66, which is capable of transferring the tundish 14 from a heating station (not shown) to the casting position, where the tundish 14 is heated to near the casting temperature.

[0061] The movable tundish 14 may be fitted with a sliding door 25 actuated by a servo mechanism to allow molten metal to flow from the tundish 14 through the sliding door 25 at the casting position, and then through the refractory outlet shroud 15 to the transition piece or distributor 16. The molten metal flows from the distributor 16 to the conveying nozzle 17 located between the casting rolls 12 and above the roll gap 18.

[0062] The side sealing plate 20 may be made of a refractory material, such as zirconia graphite, graphite alumina, boron nitride, boron nitride zirconia, or other suitable composite materials. The side sealing plate 20 has a surface capable of physical contact with the molten metal in the casting roll 12 and the casting pool 19. The side sealing plate 20 is mounted in a side sealing plate holder (not shown), which can be moved by a side sealing plate actuator (not shown), such as a hydraulic or pneumatic cylinder, servo mechanism, or other actuator, to engage the side sealing plate 20 with the end of the casting roll 12. Furthermore, the side sealing plate actuator is capable of positioning the side sealing plate 20 during casting. During the casting operation, the side sealing plate 20 forms an end closure for the molten metal pool on the casting roll 12.

[0063] Figure 1 A twin-roll continuous casting machine for producing thin strip 21 is shown. The strip initially moves downwards and then upwards around a hot box to a guide table 30 containing a controlled protective atmosphere, such as nitrogen, to minimize strip oxidation. The strip then moves through the guide table 30 to a pinch roll frame 31 that includes pinch rolls 31A.

[0064] As described below, the casting roll 12 is internally water-cooled, so that as the casting roll 12 rotates in the reverse direction, with each rotation of the casting roll 12, the casting surface 12A moves to contact and pass through the casting pool 19, and a shell solidifies on the casting surface 12A. The shell gathers together at the roll gap 18 between the casting rolls 12 to produce a thin casting strip product 21 conveyed downward from the roll gap 18. The thin casting strip product 21 is formed by the shell at the roll gap 18 between the casting rolls 12 and is conveyed downward and moved downstream.

[0065] As the thin-cast strip 21 exits the pinch roll frame 31, it passes through the strip edge cooling station 40, which cools the strip edge, i.e. the portion within 20 mm of the edge, by at least 40°C and less than 220°C, as further described below.

[0066] After passing through the edge cooling station 40, the thin cast strip 21 passes through a hot rolling mill 32, which includes a pair of work rolls 32A and a support roll 32B, forming a gap capable of hot rolling the thin cast strip 21 conveyed from the casting rolls 12. In the hot rolling mill 32, the thin cast strip 21 is hot rolled to reduce the strip to a desired thickness, improve the strip surface, and enhance strip flatness. The work rolls 32A have working surfaces associated with the desired strip profile across the entire length of the work rolls 32A. Typically, the steel strip enters the hot rolling mill at an average mill entry temperature of 1020-1150°C and exits the hot rolling mill at an average mill exit temperature 140-160°C lower than the average mill entry temperature.

[0067] The edge cooling station 40 can be located at any suitable position between the pinch roll 31A and the hot rolling mill 32.

[0068] Typically, the edge cooling station 40 is positioned as close as possible to the hot rolling mill 32.

[0069] The edge cooling station 40 can be any suitable structure.

[0070] The edge cooling station 40 can be configured to utilize water (in the direction of spray nozzles directed towards the edge of the strip) delivered by spray nozzles as the strip moves from the pinch roll stand 31 to the hot rolling mill 32. Figure 1 and Figure 3 The edge of the strip is cooled (schematically shown above and / or below the strip by reference numeral 40), typically with the side edges quenched. While the spray nozzle atomizes the coolant to generate a spray, in any embodiment, any other coolant outlet may be used instead of the spray nozzle. Besides generating a spray, other types of coolant outlets can discharge a non-atomized coolant stream.

[0071] During operation, the strip exits the roll gap at a temperature of approximately 1400°C or higher. To prevent oxidation and scale formation on the strip, the metal strip is cast downwards into a housing 27, which supports a protective atmosphere directly beneath the casting rolls in the casting position. The housing 27 extends along the path of the thin-cast strip to the first pinch roll stand 31 and further along the path to the hot rolling mill 32 to reduce oxidation and scale formation.

[0072] Following the hot rolling mill 32, the hot-rolled strip enters a cooling station 97, where it is cooled by water delivered by spray nozzles 90 from a multi-row water spray assembly extending through the output platform 33 as it moves along the platform. While the spray nozzles atomize the coolant to generate a spray, in any embodiment, any other coolant outlet may be used instead of the spray nozzles. Other types of coolant outlets, besides generating a spray, can discharge a non-atomized coolant stream. The cooling station 97 cools the hot-rolled strip to any suitable temperature, taking into account the steel composition and microstructure required for the final application of the strip.

[0073] The cooled hot-rolled thin strip 21 passes through a second pinch roll stand 91, which has a pair of rolls 91A that provide tension to the thin strip 21 during shearing.

[0074] exist Figure 3 In the exemplary embodiment shown, the cooling station 97 extends along a path 99 between the hot rolling mill 32 and the second pinch roll stand 91, and a plurality of spray nozzles 90 in a multi-row water spray assembly are arranged between the hot rolling mill 32 and the second pinch roll stand 91. Although in Figure 3 It is not discernible in the depicted view, but the rows of spray nozzles 90 are arranged in the width direction, extending substantially across the width of the strip or the width of the cooling station, and are spaced apart along the length of the cooling station.

[0075] Finally, the cooled hot-rolled thin strip 21 is wound and periodically cut upstream of the coiler by a shear at shearing station 98 to form the required length of strip for each roll.

[0076] about Figure 1-3 Further details of the twin-roll continuous casting machine described herein can be found in the specification of Chinese Patent Application No. 201780029304.2 filed in the name of the applicant, and the disclosure of that specification is incorporated herein by cross-reference.

[0077] The above-described embodiments of the twin-roll continuous casting machine and method are applicable to the production of steel strips with a thickness of less than 3 mm, typically less than 2.5 mm, from molten steel melt comprising, by weight: C < 0.6%, Si < 0.3%, Mn < 2.5%, Nb < 0.1%, P < 0.03%, S < 0.0025%, sol Al < 0.01%, N < 0.005%, Cu < 0.4%, with the remainder being iron, impurities, and inclusions. The term "impurity" refers to elements present in the melt as an unavoidable result of the steelmaking operation or as a consequence of the steelmaking raw materials. These are often non-metallic elements. Examples of impurities are N, P, S, and H. The term "inclusion" refers to compounds formed during the steelmaking process. Examples of "inclusions" include AlN and MnS.

[0078] As described above, the purpose of the edge cooling station 40 is to reduce the temperature of one or both edges of the steel strip. In the described embodiment, this is achieved using water.

[0079] The applicant has discovered that the quality of the side edges of the steel strip can be significantly improved by controlling the temperature of the side edges before they enter the hot rolling mill 32.

[0080] In particular, the applicant has discovered that the quality of the side edges of the steel strip can be significantly improved by controlling the temperature of the side edge strip by cooling (typically quenching) the side edge before it enters the hot rolling mill 32.

[0081] Figure 4 These are two images of steel strip produced in a standard twin-roll belt casting machine. The standard strip has uneven edges, which requires significant side trimming, typically about 20 to 25 mm per side, resulting in a yield loss of about 5%. It is clearly visible from these images that there are obvious quality problems with the side edges.

[0082] Figure 5These are two images of a steel strip section produced in an experiment according to an embodiment of the method of the present invention, using a twin-roll belt casting apparatus. These images show the cross-section of the steel strip after it has been hot-rolled and cooled. It is clearly visible from these images that the quality of the side edges has been significantly improved, to the point that edge trimming is no longer required.

[0083] The test was conducted on a Q235 belt using a work roll bite-type sprayer (1345 mm [1307 mm cold] / ~5 rolls) to supply water to the belt. For the purposes of the test, the intermediate nozzles of the nozzles that were otherwise open were closed, and water was supplied only through the two edge nozzles on each grade.

[0084] Figure 6A There are three images comparing a steel strip segment produced in a twin-roll belt casting apparatus according to the invention with a steel strip segment produced in a standard twin-roll belt casting apparatus. These images indicate the edge temperature and side edge condition of the two steel strip segments after leaving the hot rolling mill. Figure 6B This is a color chart, representing different temperature ranges corresponding to different colors. It's clear from the colors of the temperature-indicating sections that one section has a lower strip edge temperature, while another has a higher strip edge temperature. As mentioned above, the lower strip edge temperature section is produced by cooling the section with water at the hot rolling mill inlet. It's evident from the image that the section with the lower strip edge temperature has a better quality edge than the section with the higher strip edge temperature. This edge quality eliminates the need for edge trimming in the production of commercial products. The section with the lower strip edge temperature was found to have a substantially uniform microstructure and yield stress across the width and length of the section after hot rolling, and on this basis, it exhibits better quality.

[0085] Many modifications can be made to the above embodiments without departing from the spirit and scope of the invention.

[0086] For example, although this embodiment uses water delivered by a water sprayer to cool the side edges of the steel strip, the invention is not limited to using water as a coolant and using a sprayer as a delivery option.

Claims

1. A method for producing steel strip, the method comprising: - Casting continuous thin steel strips with a thickness of less than 3 mm from molten steel in a twin-roll casting machine; - Cool one or both edges of the steel strip by at least 40°C and less than 220°C before it enters the hot rolling mill; - The steel strip with cooled edges is hot-rolled in a hot rolling mill, and the thickness of the steel strip is reduced; - Cool the steel strip in a cooling station; and - The steel strip is wound on a coiler.

2. The method of claim 1, comprising cooling one or both edges of the steel strip by at least 50°C and less than 220°C.

3. The method according to claim 1 or 2, comprising cooling one or both edges of the steel strip with water.

4. The method of claim 3, further comprising cooling the edge of the strip with water from a sprinkler nozzle.

5. The method according to claim 1 or 2, comprising hot-rolling the steel strip, wherein, The steel strip enters the hot rolling mill at an average mill entry temperature of 1020-1150°C.

6. The method according to claim 1 or 2, comprising hot-rolling the steel strip, wherein, The steel strip enters the hot rolling mill at an average mill entry temperature that is 140-160°C higher than the average mill exit temperature.

7. An apparatus for producing steel strip, comprising: - Twin-roll continuous casting machine for forming continuous thin steel strips with a thickness of less than 3 mm from molten steel; - An edge cooling station for cooling one or both edges of the steel strip by at least 40°C and less than 220°C before the steel strip enters the hot rolling mill; - Hot rolling mill, used to reduce the thickness of steel strip with cooled edges; - A cooling station for cooling the steel strip; and - A coiler for forming a coil of the steel strip.

8. The device according to claim 7, wherein, The edge cooling station is configured to cool one or both edges of the steel strip by at least 50°C and less than 220°C.

9. The device according to claim 7, wherein, The edge cooling station is configured to cool one or both edges of the steel strip by at least 40°C and less than 150°C.

10. The device according to any one of claims 7 to 9, wherein, The edge cooling station is configured to cool the edge of the strip with water.

11. The device according to any one of claims 7 to 9, wherein, The edge cooling station includes water spray nozzles for supplying water to cool the edge of the strip.

12. The device according to any one of claims 7 to 9, wherein, The belt edge cooling station includes a water spraying assembly located above and / or below the belt, wherein the water spraying assembly includes water spray nozzles for supplying water to cool the belt edge.

13. The equipment according to any one of claims 7 to 9, comprising a pinch roll stand upstream of the hot rolling mill.

14. The device according to claim 13, wherein, The edge cooling station is located between the pinch roll stand and the hot rolling mill.

15. A twin-roll cast and hot-rolled steel strip, less than 3 mm thick, produced by the method according to any one of claims 1 to 6.

16. A twin-roll steel strip, cast and hot-rolled, with a thickness of less than 3 mm, produced by the equipment according to any one of claims 7 to 14.

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