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April 16 (Bloomberg) -- ArcelorMittal USA LLC, part of the world’s biggest steelmaker, sued a unit of AK Steel Holding Corp. for infringing a patent for automotive quality cold-rolled sheet steel.

The U.S. arm of Luxembourg-based ArcelorMittal contends West Chester, Ohio-based AK is wrongly using the high-tensile-strength aluminum-boron technology for stamped auto parts, according to a complaint filed today in federal court in Wilmington, Delaware.

“ArcelorMittal has been damaged by such infringement and will continue to be damaged by such infringement,” unless it’s stopped by a court, according to the complaint, which seeks a jury trial, damages and court costs.

In a similar case filed in 2010, a judge in the same court ruled that the patent was invalid and not infringed. An appeals court last year sent the case back for review. Meanwhile, the owner made changes to the old patent, had it reissued with a different number and is using it in this case.

Barry L. Racey, an AK spokesman, didn’t immediately return e-mail and voice-mail messages seeking comment on the lawsuit after business hours.

The new case is ArcelorMittal v. AK Steel, U.S. District Court, District of Delaware (Wilmington). The old case is ArcelorMittal v. AK Steel, 10-cv-00050, U.S. District Court, District of Delaware (Wilmington).

To see the patent in the new lawsuit, click: RE153. The older patent: 6,296,805.

To contact the reporter on this story: Phil Milford at

To contact the editor responsible for this story: Michael Hytha at

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