Electrical steel processing without a post cold-rolling intermediate anneal

Abstract

Embodiments of the present invention comprise; annealing steel sheets (e.g., hot rolled steel sheets or thin cast strip steel); cold rolling the sheets in one or more cold rolling steps (e.g., with annealing steps between multiple cold rolling steps); and performing one or more of tension leveling, a rough rolling, or a coating process on the sheets after cold rolling, without an intermediate annealing step between the final cold rolling step and the tension leveling, the rough rolling, or the coating process, or the customer stamping or final customer annealing. In order to achieve the desired properties for the steel sheet, stamping and final annealing is performed by the customer. The new process provides an electrical steel with the similar, same, or better magnetic properties than an electrical steel manufactured using the traditional processing that utilizes an intermediate annealing step after cold rolling and before the stamping and final annealing.

Description

RELATED APPLICATIONS AND PRIORITY CLAIM[0001]This application is a continuation-in-part of, and claims priority to U.S. patent application Ser. No. 14 / 334,239 entitled “Electrical Steel Processing Without A Post-Cold Rolling Intermediate Anneal,” filed on Jul. 17, 2014, which is a continuation-in-part application, and claims priority to U.S. patent application Ser. No. 13 / 739,184 entitled “Electrical Steel Processing Without A Post-Cold Rolling Intermediate Anneal,” filed on Jan. 11, 2013, which claims priority to Provisional Application No. 61 / 586,010 filed Jan. 12, 2012, and which are all assigned to the assignee hereof and hereby expressly incorporated by reference herein.BACKGROUND[0002]This invention relates generally to the field of semi-processed electrical steel sheet manufacturing, and more particularly embodiments of the invention relate to achieving electrical steel sheet products with the desired final magnetic properties after they have been annealed at the customer. Se...

AI Technical Summary

Benefits of technology

[0005]The saturation of the electrical steel is an indication of the highest induction that the steel can achieve. The permeability of the electrical steel is the measure of the ability of the steel to support the formation of a magnetic field within itself and is expressed as the ratio of the magnetic flux to the field of strength. Electrical steel with high permeability allows for an increased induction for a given magnetic field, and thus, with respect to motor applications, reduces the need for copper windings, which results in lower copper costs. The core loss is the energy wasted in the electrical steel. Low core loss in electrical steels results in a higher efficiency in the end products, such as motors, generators, ballasts, and the like. Therefore, it may be desirable in many products to use electrical steels with a high ability to support a magnetic field and a high efficiency (e.g., high permeability and low core loss) if it is not detrimental to the cost of manufacturing or other desirable steel properties.

[0008]During the hot rolling step (or between multiple hot rolling steps the electrical steel sheet may be maintained at a temperature above the recrystallization temperature, which is a temperature at which deformed grains are replaced by a new set of undeformed grains. Recrystallization is usually accompanied by a reduction in the strength and hardness of a material and a simultaneous increase in the ductility. The hot rolling process reduces the thickness of the steel sheet and controls the grain structure of the electrical steel. After the hot rolling stage(s) the steel is potentially pickled in a bath (e.g., sulfuric, nitric, hydrochloric, other acids, or combinations of these, etc.) in order to remove scale on the surface of the steel from oxidization. Thereafter, the electrical steel sheet is annealed to change the magnetic properties of the steel. During annealing the steel is heated, and thereafter cooled, to coarsen the structure of the steel, and improve cold working properties. The electrical steel sheet is then cold rolled after annealing, which comprises rolling the electrical steel sheet below the recrystallization temperature. Cold rolling may begin at room temperatures; however, the temperature of the steel sheet may be elevated at the beginning of the cold rolling process, or otherwise rise during cold rolling due to the cold rolling process itself. The cold rolling process increases the strength of the steel, improves the surface finish, and rolls the steel sheet to the desired thickness.

[0010]Temper rolling, in the case of semi-processed steels, may be performed after annealing in order to improve the surface finish of the electrical steel sheet, enhance the stamping characteristics, and provide improved magnetic properties after the customer has stamped (e.g., punched, or the like) the electrical steel sheet and performed a final customer annealing step (e.g., heating the stamped part).

[0013]In the present invention, as is the case with traditional electrical steel processing, scrap steel and / or iron is melted into molten steel or molten steel is produced from iron ore; the molten steel is sent for decarburization and for alloy additions; the steel is poured into ladles and cast into slabs (or continuously cast in some embodiments described later); and the slabs are hot rolled, pickled, annealed (e.g., batch annealed or continuously annealed), and cold rolled into sheets. However, unlike traditional electrical steel processing, in the present invention, the intermediate annealing step (e.g., the batch annealing step, or alternatively, the continuous annealing step) after cold rolling is not performed. Instead, in the present invention, after cold rolling a tension leveling step may be performed or a coating may be applied to the semi-processed electrical steel sheet before it is sent to the customer. At the customer locations, as is the case with the traditional method for manufacturing semi-processed electrical steels, the customers stamp the electrical steel sheets into the desired shapes, and thereafter, perform a customer annealing step to remove distortions created by the stamping and to maximize the magnetic properties of the electrical steel.

Problems solved by technology

The core loss is the energy wasted in the electrical steel.

Improving one property may come at the detriment of another.

For example, when increasing the permeability a higher core loss may result (and vice versa).

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