Prior art can show what the claims would mean to those skilled in the art

| December 5, 2012

ArcelorMittal v. AK Steel Corp.

November 30, 2012

Panel: Dyk, Clevenger, and Wallach.  Opinion by Dyk.


The U.S. District Court for the District of Delaware held that defendants AK Steel did not infringe plaintiffs ArcelorMittal’s U.S. Patent No. 6,296,805 (the ‘805 patent), and that the asserted claims were invalid as anticipated and obvious based on a jury verdict.

ArcelorMittal appealed the district court’s decision.  On appeal, the CAFC upheld the district court’s claim construction in part and reverse it in part.  With regard to anticipation, the CAFC reversed the jury’s verdict of anticipation.  With regard to obviousness, the CAFC held that a new trial is required because the district court’s claim construction error prevented the jury from properly considering ArcelorMittal’s evidence of commercial success.

미국 델라웨어주 연방지방법원 (U.S. District Court for the District of Delaware)은 원고 (ArcelorMittal)가 피고 (AK Steel)를 상대로 낸 특허 침해 소송에서 원고의 특허 (U.S. Patent No. 6,296,805)가 예견가능성 (anticipation) 및 자명성 (obviousness) 기준을 통과하지 못하였다는 배심원의 판단을 바탕으로 피고가 원고의 특허를 침해하지 않았다고 판결하였다.

이에 불복하여 원고는 연방항소법원 (U.S. Court of Appeals for the Federal Circuit)에서 상고 (appeal) 하였으며, 연방항소법원은 지방법원의 청구항 해석 (claim construction)에 대해 일정 부분은 확인하였으나, 나머지 부분은 번복하였다.

예견가능성과 관련하여 연방항소법원은 배심원의 예견가능성 판단과 다른 결정을 내렸다.

자명성과 관련해서는 연방지방법원의 잘못된 청구항 해석으로 인하여 배심원이 원고의 상업적 성공 (commercial success) 증거를 고려하지 않았기때문에 재심 (new trial)이 필요하다고 판결하였다.


‘805 patent

The ‘805 patent is directed to the aluminum-based coating for preventing oxidation occurring during hot-stamping.  The aluminum-based coating is applied to boron steel sheet after rolling the sheet to its final thickness.  The steel is used for hot-stamping, a process that includes rapidly heating the steel, stamping it into parts of the desired shape, and rapidly cooling them.  As a result of the rapid heating and cooling processes, the microstructure of the steel is altered, thereby creating strong steel particularly suitable for the manufacture of automobile parts.  However, the high temperatures required for hot-stamping cause oxidation, forming “scale” on the steel’s surface.  Scale must be removed, but removing it requires expensive and environmentally harmful “shot-blasting” and “pickling” operations.

The ‘805 patent discloses the method of preventing oxidation occurring during hot-stamping, thereby making hot-stamping less costly, reducing the environmental impact, and allowing the steel to be used for the production of parts that are too delicate to survive “shot-blasting”.

The asserted claims of the ‘805 patent are independent claim 1 and dependent claims 2, 5, 7, and 16.  Independent claim 1 reads as follows:

1.  A hot-rolled coated steel sheet comprising a hot-rolled steel sheet coated with an aluminum or aluminum alloy coating, wherein the steel in the sheet comprises the following composition by weight:

0.0005%<boron<0.08%, the remainder being iron and impurities inherent in processing, and the steel sheet has a very high mechanical resistance after thermal treatment and the aluminum or aluminum alloy coating provides a high resistance to corrosion of the steel sheet.

Claim construction: “Hot-rolled steel sheet”

The CAFC agreed with ArcelorMittal, which argued that the district court erroneously construed the term “hot-rolled steel sheet” to exclude the steel sheet that has been cold-rolled to its final thickness after initial hot-rolling.  The CAFC noted that the transition “comprising” in claim 1 expressly contemplates additional, unstated steps such as cold-rolling.  In addition, the CAFC stated that although the ordinary meaning of “hot-rolled steel sheet” in the industry refers to steel sheet that has not been cold-rolled, the specification makes clear that the term “hot-rolled steel sheet” does not preclude a cold-rolling step by citing the following parts of the specification:

1)      Col. 2, lines 37-40: “[t]he sheet according to the invention…may be cold-rerolled again depending on the final thickness desired”

2)      Col. 1, lines 37-38: the claimed invention’s purpose includes the production of “cold-rolled steel sheet”

3)      Col. 4, lines 8-9: “having a thickness of approximately 1 mm” (that thickness, at the time of the invention, could only have been achieved by cold-rolling, and even AK Steel conceded this point)

Therefore, the CAFC concluded that the district court erred by interpreting the claim term “hot-rolled steel sheet” to exclude steel sheet subsequently cold-rolled, and the correct construction is “a steel sheet that has been hot-rolled during its production.”

Claim construction: “Very high mechanical resistance”

This time, the CAFC disagreed with ArcelorMittal and affirmed the district court’s interpretation of the term “very high mechanical resistance.”  Once again, the CAFC relied on the specification, which states that a “high” and “substantial” mechanical resistance “may exceed 1500 MPa”, to interpret the term “very high mechanical resistance” to mean that it must be at least 1500 MPa.

With regard to extrinsic evidence, the CAFC relied on an article (“Bano”) on heat-treated boron steel written by one of the inventors of the ‘805 patent before the patent was filed.  The Bano article, which is prior art, describes steel with “high mechanical characteristic (UTS > 1500 MPa and YS > 1100 MPa)” after heat treatment.  The CAFC stated that prior art can “help demonstrate how a disputed term is used by those skill in the art,” (Vitronics Corp., 90 F.3d at 1584) and when an inventor’s understanding of a claim term is expressed in the prior art, it can be evidence of how those skilled in the art would have understood that term at the time of the invention (Markman, 52 F.3d at 991).  Consequently, the CAFC concluded that by defining “high” mechanical resistance as greater than 1500 MPa, the prior art suggests that “very high” mechanical resistance would be understood to be at least that high.


The CAFC reversed the jury’s finding of anticipation that was based on the Bano article.  The CAFC found that Bano does not even explicitly disclose coating with metals, and that the only specific coating it refers to is “phosphatization…followed by cataphoresis”, which refers to coating with paint, not metal.  In addition, the CAFC held that even if paint and metal were part of the same general formula, the Bano article does not support a finding that there is a “definite and limited class” of coating for steel sheet.

Therefore, since there is not “an explicit disclosure of aluminum coating or substantial evidence that aluminum belonged to a sufficiently definite and limited class of possible coating”, the CAFC concluded that the jury verdict of anticipation should be reversed.


The CAFC affirmed the jury’s finding of obviousness that the asserted claims of the ‘805 patent are obvious in view of Bano in combination with a French Patent No. 1,297,906 (French ‘906 patent).  The French ‘906 patent discloses coating steel with aluminum to protect against oxidation during hot forging.

With regard to the final issue (whether the district court’s erroneous claim construction of “hot-rolled steel sheet” requires a new trial on obviousness), the CAFC emphasized that the required consideration of commercial success includes a threshold determination of whether the commercial success has the necessary nexus with the claimed invention (In re Kao, 639 F.3d at 1068-69).  The CAFC held that this is not a case where the prima facie case of obviousness so strong that, as a matter of law, it would overcome ArcelorMittal’s commercial success evidence.

Therefore, the CAFC concluded that the district court’s claim construction prejudiced ArcelorMittal with respect to obviousness, and remanded for a new trial addressing only the commercial success aspect of obvious and infringement under the correct claim construction.


Applicants should use relative adjectives in a way that more definitively limits their interpretation and carefully review the specification whether they are coherently described in the specification.  Applicants can also add dependent claims to further limit relative adjectives.  In addition, if applicants’ understanding of claim terms are expressed in the prior art, the prior art could be a useful source for determining how disputed terms are used by those skilled in the art.

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