On May 12, 2015, the Federal Circuit held in ArcelorMittal v. AK Steel that an unamended claim whose scope is expanded during reissue based upon prosecution history will be seen as broadened, and thus invalid, if the reissue application was filed more than two years after issuance.
In a prior infringement litigation, the patent-in-suit claimed a steel sheet having a “very high mechanical resistance,” which was given was given a narrow claim construction, namely that the “very high mechanical resistance” was greater than 1500 MPa. The patentee filed a reissue application with the USPTO that added a new dependent claim stating that the resistance is “in excess of 1000 MPa,” which would suggest a broader scope for the “very high mechanical resistance.”
The Court noted that, "The only relevant change is the addition of a dependent claim which has the practical effect of expanding the scope of claim 1 to cover claim scope expressly rejected by a previous claim construction ruling."
Thus, the Court held that the broadened scope was improper because the reissue application had been filed more than two years after the original patent's issuance.