In this dataset, it is a patent family that combines an alloy or heat-treatment claim under codes like C22C38/00 or C21D with an explicit durability test or mechanism claim — corrosion resistance, hydrogen embrittlement resistance, or stress corrosion cracking under codes such as C23F11 or G01N17. That combination matters because many AHSS patents claim strength or formability without ever testing or claiming a durability result, so a pure composition search would pull in far more noise. The 1,136 families here all make a durability claim explicitly, not just an alloy claim.

Filing activity concentrates among a small set of integrated steelmakers including Nippon Steel, JFE Steel, Kobe Steel and POSCO, with POSCO's own research institute appearing as a frequent co-assignee. Momentum has cooled across the board: Nippon Steel's latest-year filings fell 50% year on year, and several other frequent filers show a full year-on-year drop to zero filings. That pattern points to a maturing claim space rather than an actively expanding one.

Filings ran at 73 in 2017, rose to a peak of 85 in 2018, and had fallen to 49 by the 2022 midpoint. This is consistent with early, broad alloy and heat-treatment claims being filed quickly once the core durability mechanisms — hydrogen trapping, coating adhesion, corrosion-resistant compositions — were established, leaving less open ground for follow-on filers. Note that the most recent one to two years in any patent trend are understated because publication lags filing by roughly 18 months, so the apparent decline at the very end of the window should be read cautiously.

US20110268600A1, filed by Nippon Steel, claims steel with hydrogen embrittlement resistance at 1200 MPa or greater strength, achieved through hydrogen-trap deposits of oxides, carbides or nitrides held within specific size, density and aspect-ratio ranges. A later filer working on hydrogen-trap-site engineering at comparable strength levels and similar microstructural parameter ranges is the one most likely to run into this claim. It does not block composition-only claims that do not rely on engineered trap-site geometry, nor does it cover surface-coating routes to corrosion resistance, which sit in a different part of this landscape.

Filing density is heavily weighted toward bulk alloy composition (C22C, 1,112 records) and heat treatment (C21D, 954 records), while surface-engineering routes are comparatively thin: electrolytic cleaning and hydrogen-trap removal (C25F) sits at 70 records, and electroplating-based corrosion barriers (C25D) at 52. Laminate and clad durability structures (B32B, 118) and cold-drawn wire durability (B21C, 30) are similarly under-claimed relative to the core alloy space. A first claim in these narrower branches faces less crowded prior art than a new bulk-composition claim would.