Arcelor Mittal France v. AK Steel Corp., No. 11-1638 (Fed. Cir. 2012)Annotate this Case
ArcelorMittal’s patent covers boron steel sheet with an aluminum-based coating applied after rolling the sheet to its final thickness. The steel is used for “hot-stamping:” rapidly heating the steel, stamping it into parts of the desired shape, and rapidly cooling them. The rapid heating and cooling alters the crystalline structure of the steel, converting it to austenite and then martensite. By altering the steel’s microstructure, hot-stamping produces particularly strong steel, but there are associated problems. The aluminum-based coating claimed in the patent prevents oxidation during hot-stamping, so that scale does not form and decarburization does not occur, making hot-stamping less costly, reducing environmental impact, and allowing its use in production of delicate parts. ArcelorMittal brought an infringement action, alleging that AK Steel’s aluminum coated steel sheet products infringe the patent. After construing the terms “a hot-rolled steel sheet coated with an aluminum or aluminum alloy coating” and “the steel sheet has a very high mechanical resistance after thermal treatment,” the district court found no infringement and held that the asserted claims were obvious and anticipated. The Federal Circuit upheld the claim construction in part, reversed in part, reversed the verdict of anticipation, and stated that a new trial is required on obviousness.