C21D — Modifying THE Physical Structure OF Ferrous Metals

CPC subclass C21D — MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING — covers 6,851 US utility patents granted between 2015 and 2025 according to USPTO PatentsView records. This subclass sits within the broader CPC class C21 (METALLURGY OF IRON), one of roughly 250 top-level technology categories in the Cooperative Patent Classification system jointly maintained by the USPTO and the European Patent Office. At the subclass level, four-character codes like C21D give the most practical resolution for tracking a specific technology domain without losing sight of adjacent filings. Every grant here has been classified by a USPTO examiner based on the technical disclosure in the patent specification.

The competitive landscape in C21D is shaped by 20 distinct companies actively filing in this space. JFE Steel Corporation leads with 865 patents, followed by NIPPON STEEL CORPORATION at 1,289 grants and POSCO CO., LTD at 691. Concentration at the top of the leaderboard indicates whether this technology area is dominated by a handful of incumbents or fragmented across many filers — a useful signal for investors evaluating competitive moats and for product teams mapping freedom-to-operate risk.

Filing trajectory matters as much as static counts. The yearly series on this page plots grants from 2015 through 2025, highlighting whether innovation in C21D is accelerating, plateauing, or cooling. Technology areas with rising post-2020 activity often reflect emerging markets or new platform shifts, while declining filings can signal mature domains where incremental improvement has slowed. Researchers, licensing professionals, and competitive-intelligence teams use these patterns — together with the top-assignee distribution — to decide where to invest, where to license, and where to avoid entanglement. All counts on this page come directly from USPTO PatentsView and reflect US granted utility patents only.