Slag Engineering Patents: Who Leads, Where the Gaps Are 2026
- 53.4% of all 640 records sit with just five assignees — filing here means competing directly against entrenched claim positions, not carving out open ground.
- Filings grew 13% from 2021 to 2024 (8 to 9 in the trend series), a modest recovery after the 2018 peak of 43 rather than a fading field.
- Japan received 211 filings more than the EPO, India, US, China and Australia combined receiving-office counts shown for this dataset, marking where enforcement risk concentrates.
Filing growth compares 2021 (8 records) with 2024 (9) — a three-year span. 2024 is the most recent year we treat as complete: publication lags filing by roughly 18 months, so 2025 onwards are still filling in and any growth rate that ends there would understate the field. Top-5 share is the combined record count of the five largest assignees divided by all 640 records in scope (CR5), not by the ranked leaders only.
What this landscape covers
Slag engineering sits at the intersection of process metallurgy and refractory chemistry: how steelmakers manage dephosphorization, slag basicity, magnesia saturation and slag foaming to protect furnace linings and control melt chemistry. The 640 records in scope span carbon injection practice, slag conditioning agents, and slag splashing techniques used to extend refractory life in both basic oxygen furnaces and electric arc furnaces.
The search combines steelmaking and EAF slag terminology with the specific process levers — basicity, saturation, splashing, carbon injection, refractory protection — that separate routine slag disposal patents from process-control claims. Because publication lags filing by roughly 18 months, the 2025-2026 counts in the trend chart are still filling in and should not be read as a decline.
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Filing trends and technology composition
Two views of the same 640-record dataset: how filing activity has moved year over year, and which IPC subclasses carry the claim volume.
Filing activity, 2017-2026
Filings peaked at 43 in 2018, cooled through the early 2020s, then rose 13% from 8 in 2021 to 9 in 2024 — the last year the dataset treats as complete. 2025 and 2026 counts (down to 1 by 2026) reflect publication lag, not a retreat from the technology.
Technology composition by IPC subclass
C21C (steelmaking) covers 52.7% of the 640 records, with C21B (blast furnace iron production) and C04B (ceramics, cement and refractories) each present in roughly a quarter of filings — evidence that slag chemistry claims routinely cross from furnace process into refractory material composition. Shares sum past 100% because records carry multiple IPC classes.
Shares are the percentage of the 640 records in scope. A patent can carry several IPC classes, so the shares add up to more than 100%.
Go deeper on Slag Engineering in Steelmaking with Eureka
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Steelmaking slag repurposed as fertilizer raw material
The representative record specifies a steelmaking slag composition bounded by mass-percent ranges for P2O5, MnO, boron, total iron, CaO, SiO2, sulfur, MgO and Al2O3, aimed at qualifying furnace slag as fertilizer feedstock rather than waste. Filed by Nippon Steel, it illustrates how slag composition claims now extend beyond the furnace into downstream valorisation.Filed 2019-01-17 · AU2018282390A1
View full record| # | Publication no. | Patent title | Citations |
|---|---|---|---|
| 1 | US5397379A | Process and additive for the ladle refining of steel | 108 |
| 2 | US20110165400A1 | Production of a mainly carbonate bonded article by carbonation of alkaline materials | 68 |
| 3 | WO2009133120A2 | Production of a mainly carbonate bonded article by carbonation of alkaline materials | 57 |
| 4 | US6383251B1 | Direct iron and steelmaking | 55 |
| 5 | JP1985261501A | Dephosphorization of iron ore | 40 |
| 6 | JP1979083603A | Removing method for phosphorus from ore | 34 |
| 7 | US5630862A | Method of providing fuel for an iron making process | 32 |
| 8 | JP2001048605A | Treatment of steelmaking slag for cement | 27 |
| 9 | JP2011208277A | Method for recovering iron and phosphorus from steelmaking slag and raw material for phosphatic fertilizer | 26 |
| 10 | JP2012007189A | Method for recovering iron and phosphorus from steelmaking slag, blast furnace slag fine powder or blast furn… | 26 |
Citation counts inside this corpus favour older filings and should be read as a signal of influence, not current relevance — several of the most-cited records date from the 1990s to early 2010s.
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Reading the concentration, receiving-office and citation figures together points to a field with an entrenched core and specific open edges.
Claim space is crowded at the top
With five assignees holding 342 of 640 records, new entrants filing standard dephosphorization or basicity-control claims are filing into occupied territory. The gap between fifth place (26) and tenth place (13) shows a steep drop-off rather than a smooth tail.
Enforcement risk clusters in Japan
Japan's receiving-office count outweighs the EPO, India, US, China and Australia figures given here, consistent with the Japanese steelmakers' historical dominance of the assignee ranking. Freedom-to-operate work should start there before assuming US or EU art is representative.
A modest rebound, not a rush
Filings grew from 8 in 2021 to 9 in 2024, a real but small recovery after the 2018 peak of 43. Recent-year momentum by individual assignee is mostly flat or negative, so the rebound is broad rather than led by one filer ramping up.
Foundational ladle-refining art still anchors the field
The most-cited record in the dataset, on ladle refining additives, sits well ahead of the next most-cited documents. Its age means it functions as a citation anchor for examiners rather than a live competitive threat.
Eureka can read the same corpus for gaps instead of for coverage: under-claimed branches adjacent to slag engineering in steelmaking, with the prior art for and against each one.
Who holds the ground, and where it opens up
The assignee ranking is the full 100-company list the dataset returns, not a curated top tier — concentration figures below are drawn from within it.
A single filer well ahead of the pack
The leading assignee's 110 records outpace fifth place (26) by more than 4x, indicating a long-running, deliberate filing programme rather than opportunistic patenting.
Corporate restructuring shows up in the pairs
The strongest co-assignee link (11 shared records) connects entities tied to Nippon Steel's later corporate name, a pattern typical of a group filing under both a legacy and current registration.
Established filers have gone quiet recently
Several of the historically largest assignees show zero filings in the latest tracked year, and the one still active is down 50% year over year. That is consistent with publication lag rather than an exit from the field.
| Assignee | Recent year | YoY |
|---|---|---|
| JFE Steel Corp | 1 | -50% |
| Nippon Steel Corporation | 0 | — |
| Nu Iron Technology LLC | 0 | — |
| NIPPON STEEL & SUMITOMO METAL CORP | 0 | — |
| Sumitomo Metal Industries, Ltd. | 0 | — |
| Nihon Jiriyoku Senko Co., Ltd. | 0 | — |
| Nippon Kokan KK | 0 | — |
| Carbstone Innovation | 0 | — |
Where to take this analysis
The landscape narrows down to specific questions once you know where the claim density sits.
Map freedom-to-operate against the leader's portfolio
With one assignee holding 110 of 640 records, any new filing in dephosphorization or basicity control needs a claim chart against that portfolio before drafting begins.
Run a portfolio comparison in EurekaTest claim language against the under-claimed branches
Sub-areas like carbonate-bonded slag valorisation and sensor-driven foaming control carry lighter filing density inside the broader C21C and C04B classes.
Draft and stress-test claims in EurekaTrack the post-2024 filings as they publish
2025-2026 counts are still filling in due to publication lag; re-running this search in six months will surface filings currently invisible to citation-based tools.
Set up monitoring in EurekaCommon questions on slag engineering patents
The assignee ranking in this dataset is led by a single company with 110 of the 640 records in scope, well ahead of the fifth-ranked assignee at 26. The top five assignees combined account for 53.4% of all 640 records, and the top ten for 67.0%, so the field is concentrated rather than fragmented. Japanese steelmakers and their corporate successors appear repeatedly in the ranking, reflecting decades of continuous filing on dephosphorization and basicity control.
Filing peaked in 2018 at 43 records and declined afterward, but the picture from 2021 to 2024 shows a 13% increase, from 8 to 9 filings. Counts for 2025 and 2026 appear lower, but that reflects the roughly 18-month lag between filing and publication rather than a real drop in activity. Treat 2024 as the most recent year with a complete picture and expect the 2025-2026 figures to rise as more applications publish.
Slag basicity is the ratio of basic oxides (like CaO) to acidic oxides (like SiO2) in furnace slag, and it governs how effectively a heat removes phosphorus and sulfur while protecting refractory linings from chemical attack. Because basicity control interacts with dephosphorization, magnesia saturation and refractory wear simultaneously, it sits at the centre of the C21C steelmaking subclass, which covers 52.7% of the 640 records in this dataset. Patent activity clusters here because small changes in basicity targets translate directly into measurable yield and refractory-life gains, making the claims commercially valuable to defend.
C21C (steelmaking) is the dominant subclass, present in 52.7% of the 640 records, followed by C21B (blast furnace iron production) at 27.2% and C04B (ceramics, cement and refractories) at 24.4%. C22B (metal extraction and refining) and F27D (furnace details and accessories) also appear meaningfully. Because a single record can carry several IPC codes, these shares add up to more than 100%, and a thorough search needs to combine at least the steelmaking and refractory-material classes rather than relying on C21C alone.
The clearest gaps sit in branches that touch the core IPC classes but appear thinly in the ranked assignee filings, such as carbonate-bonded slag valorisation, boron control in slag-derived fertiliser, and sensor-driven feedback for EAF slag foaming. These areas draw on C04B and C05D classes that individually cover under a quarter of the 640 records, well below the 52.7% concentration in core C21C steelmaking claims. A freedom-to-operate review focused on these specific sub-areas, rather than the crowded core basicity and dephosphorization claims, is more likely to surface open filing room.
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Disclaimer. This page is generated from Patsnap Eureka data drawn from a limited snapshot of global patent and scientific-literature records, and is provided for general information and reference only.
Patent data carries inherent limitations: recent filings (typically the most recent 18–24 months) are under-counted due to standard publication lag; counts may be reported at either a patent-family or a patent-record basis and are not always directly comparable; classification, applicant-name, and citation data may contain errors, duplicates, or omissions; and the underlying search query defines and constrains the scope shown. As a result, the analysis may be incomplete or inaccurate and may not reflect the full technology landscape.
Nothing on this page constitutes an exhaustive prior-art, novelty, freedom-to-operate, or validity search, nor does it constitute legal, financial, investment, or professional advice, and it should not be relied upon as such. Any patent, commercial, or strategic decision should be verified independently and reviewed with qualified patent, legal, and domain professionals. Patsnap makes no warranties, express or implied, as to the accuracy, completeness, or fitness for any particular purpose of the information presented.
Machine translation. Assignee and organisation names originally recorded in Chinese, Japanese or Korean have been rendered into English by an AI translation step so that the tables stay readable. These renderings are best-effort and may not match a company’s registered English name; the original name is what the underlying patent record carries, and it is what any Eureka query launched from this page uses.