This dataset identifies 388 published records filed or published between 2015 and mid-2026 that match gas nitriding, plasma nitriding and nitrocarburizing claim language tied to compound layer thickness, white layer porosity, diffusion zone hardness, distortion minimization or corrosion resistance. That figure counts patent families in the assignee ranking, which is the fairer unit than raw document counts since it neutralises multi-jurisdiction refiling. It is not the entire universe of surface-hardening patents, since the search string targets a specific technical vocabulary.

The ranked leaders come mainly from bearing, driveline and industrial coating backgrounds, with the top assignee holding 17 records against a field of 100 ranked companies. The top 5 combined account for 18.6% of all 388 records and the top 10 for 30.9%, meaning leadership is real but far from exclusive — most of the field sits in a long tail of few-filing entrants. Any competitive read should treat this as a moderately concentrated field rather than one dominated by a single player.

Filings grew from 15 in 2021 to 22 in 2024, a 47% increase, and 2024 is the most recent year with complete publication data. The lower counts shown for 2025 and 2026 reflect the roughly 18-month lag between filing and publication rather than an actual decline in activity. Anyone tracking this space should expect the 2025–2026 figures to rise as later publications come through.

US5810947A, held by National Science Council and granted in 1998, claims a specific sequence: nitriding SKD 61 tool steel (via nitrocarburizing, gas nitriding or plasma nitriding), repolishing the surface through a defined series of SiC grits, then depositing a chromium nitride film by cathodic arc ion plating at 200°C. It protects that particular process combination and its adhesion/hardness benefit, not nitriding or CrN coating in general. Work using different repolishing steps, different coating deposition methods, or different substrate steels would sit outside its literal claim scope, though a full freedom-to-operate check should still map its exact claim language.

The IPC composition shows heavy concentration in C23C coating claims (75.0% of records) and C21D heat treatment (29.1%), while application-specific classes like E21B drilling equipment, B23K welding, C25D electroplating and F16C bearings each sit at only 3.6-3.9% of records. That gap suggests narrower claims combining nitriding with these downstream applications — distortion control for thin-wall parts, or porosity-controlled nitrocarburizing sequenced with electroplating — face less crowded prior art than general coating or heat-treatment claims.