Method for controlling a continuous strip steel casting process based on customer-specified requirements

#The present invention relates generally to systems and methods for providing steel strip to order, and more specifically to systems and methods for converting customer-specified steel strip requirements to process operating parameters for controlling a continuous strip casting process operable to produce the customer-specified steel strip product.

#The conventional steel industry process for fulfilling a customer's order for a steel product with particular mechanical, dimensional and finish properties is complicated and time-consuming, and may typically require 10 or more weeks to accomplish. Referring to FIG. 1, for example, a flowchart is shown illustrating a flow of one conventional process 10 for producing a customer-ordered steel strip product, wherein the term “strip” as used herein is to be understood to mean a product of 5 mm thickness or less.

#Process 10 begins at step 12 where the steel manufacturer receives the customer order, typically set forth in terms of mechanical (e.g., yield strength), dimensional and finish requirements for the steel strip product as well as a desired quantity. Thereafter at step 14, the steel manufacturer determines from the customer order the particular steel chemistry requirements for achieving the product's specified properties. The chemistry requirements are selected from a large recipe list of steel chemistries that is available (and in many cases dates back to ingot casting/hot rolling technology where chemistry was the prime determinant of mechanical and finish properties). Thereafter at step 16, the steel manufacturer determines casting parameters corresponding to operating parameters and/or set points for a steel casting process that will be used to produce steel slabs from molten steel formed in accordance with the steel chemistry requirements. At step 18, the steel manufacturer determines downstream slab processing requirements, initially focusing on achieving the customer's dimensional requirements such as thickness etc and then working through additional downstream processing steps that may be required to achieve the final product properties. Such downstream slab processing requirements may include, for example, any one or combination of (a) slab reheat parameters corresponding to hot mill furnace operating parameters and/or set points for hot strip mill processing, (b) hot rolling parameters corresponding to mill rolling operating parameters and/or set points for hot strip mill processing, (c) cold rolling parameters corresponding to pickling and cold rolling operating parameters and/or set points for cold mill processing, and (d) heat treatment parameters corresponding to heat treatment operating parameters and/or set points for heat treatment.

#FIG. 1 is a flowchart illustrating a conventional steel strip production process.

#FIG. 2 is a diagrammatic illustration of one preferred embodiment of a continuous steel strip casting apparatus, in accordance with the present invention.

#FIG. 3 is a diagrammatic illustration showing some of the details of the twin roll strip caster of the apparatus of FIG. 1.

#For the purposes of promoting an understanding of the principles of the invention, reference will now be made to a preferred embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated embodiment, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

#The present invention is based on producing steel strip in a continuous strip caster. It is based on extensive research and development work in the field of casting steel strip in a continuous strip caster in the form of a twin roll caster. In general terms, casting steel strip continuously in a twin roll caster involves introducing molten steel between a pair of contra-rotated horizontal casting rolls which are internally water-cooled so that metal shells solidify on the moving rolls surfaces and are brought together at the nip between them to produce a solidified strip delivered downwardly from the nip between the rolls, the term “nip” being used to refer to the general region at which the rolls are closest together. The molten metal may be poured from a ladle into a smaller vessel from which it flows through a metal delivery nozzle located above the nip so as to direct it into the nip between the rolls, so forming a casting pool of molten metal supported on the casting surfaces of the rolls immediately above the nip and extending along the length of the nip. This casting pool is usually confined between side plates or dams held in sliding engagement adjacent the ends of the rolls so as to dam the two ends of the casting pool against outflow, although alternative means such as electromagnetic barriers have also been proposed. The casting of steel strip in twin roll casters of this kind is for example described in U.S. Pat. Nos. 5,184,668, 5,277,243 and 5,934,359, all of which are expressly incorporated herein by reference. Additional details relating to continuous steel strip processing of this type are described in co-pending U.S. patent application Ser. Nos. 09/967,105; 09/967,163; 09/967,166; and 09/966,184; each filed Sep. 28, 2001, and all of which are assigned to the assignee of the present invention and the disclosures of which are each expressly incorporated herein by reference.

#It has been determined that it is possible to produce steel strip of a given composition that has a wide range of microstructures, and therefore a wide range of mechanical properties, by continuously casting the strip and thereafter selectively varying downstream strip processing parameters. For example, it has been determined from work carried out on low carbon steel, including plain carbon steel that has been silicon/manganese killed, that selecting cooling rates in the range of 0.01° C./s to greater than 100° C./s to transform the strip from austenite to ferrite can produce steel strip that has yield strengths that range from 200 MPa to greater than 700 MPa. One example of the flexibility of continuous strip casting that has thus been recognized is that a production run of a continuous strip caster that is casting steel strip of a given composition can be controlled such that the cast strip can be selectively subjected to different cooling rates through the austenite to ferrite transition, with the result that the strip can be produced so as to have any selection of a range of different microstructures and therefore mechanical properties (e.g., yield strength).