Ownership in this dataset is concentrated among a small group of steel producers and heavy-industry manufacturers, with the leading assignee holding 483 records and the top five combined accounting for 27.0% of all 7,446 records in scope. Beyond the top ten, who together hold 40.7% of records, filings spread across a long tail of smaller and single-filing entrants. This pattern is typical of a mature metallurgy field where a handful of integrated producers file continuously while newer entrants file narrowly around specific alloy grades or test methods.

Filings peaked at 153 in 2018 and have eased since, with the most reliable comparable window showing a 10% decline from 108 filings in 2021 to 97 in 2024. That is a moderate pull-back rather than a collapse, and it should not be read as the field going quiet. Counts for 2025 and 2026 are still incomplete because patent publication typically lags filing by around 18 months, so recent-year totals will continue to rise as more applications publish.

Alloys, IPC subclass C22C, is by far the largest single classification, appearing in 50.6% of the 7,446 records in this dataset. Heat treatment of metals (C21D) follows at 20.0% and non-ferrous metal treatment (C22F) at 13.0%, with nuclear reactor and nuclear power plant classes forming a smaller but distinct cluster tied to reactor-water cracking. Because a single record can carry multiple IPC codes, these percentages overlap rather than sum to 100%.

US9995669B2, assigned to JFE Steel Corporation and published in 2018, claims a specific round bar tensile test specimen geometry for sulfide stress corrosion cracking testing, defined by precise radius-of-curvature and length relationships tied to load stress. It is a test-method and specimen-design patent, not a material composition patent, so it does not block alloy formulations directly. Anyone developing a competing sulfide stress corrosion cracking test specimen needs to check whether their shoulder-section geometry falls inside the claimed radius and length formulas before assuming freedom to operate.

The classification data shows corrosion & metal removal (C23F) at only 4.9% of records, notably thin given how central corrosion mechanisms are to the topic, which suggests corrosion-protection-specific claims are less crowded than alloy composition claims. Welding, soldering & brazing (B23K) sits at a moderate 8.3%, leaving room around joint-specific cracking resistance claims that are not simply alloy substitutions. Any white-space assessment should be paired with a freedom-to-operate check against the dominant C22C alloy claims, since a new claim in an adjacent class can still be blocked by a broad composition patent.