CPC technology class · C21

C21C - Processing Of Pig-iron

Processing of pig-iron, e.g. refining, manufacture of wrought-iron or steel; treatment in molten state of ferrous alloys. 716 US utility patents granted 2015–2025, with the leading assignees and year-by-year grant trajectory.

Compiled by PlainPatent · May 15, 2026

716
US patents granted: #2/3
in C21: 8.6%
C21 class share: -10%
5-yr velocity

The verdict

According to USPTO PatentsView, Processing Of Pig-iron ranks #496 of 670 CPC technology areas - 716 US patents granted since 2015, with recorded grant volume down 10% over five years.

#496
of 670 CPC technology areas: 716
US patents granted, 2015–2025: Jfe Steel
leading assignee (37): -10%
grant velocity, last 5 yrs

How C21C's grant cadence moved

Between 2020–2024, C21C recorded 283 grants versus 316 in 2015–2019 (-10% equal-window velocity). Across complete years, output peaked in 2017 at 78 grants and bottomed in 2021 at 43 (+81% peak-over-trough). Lead assignee Carbon Technology Holdings, LLC holds 3.2% of the class ; the top three share 8.0%.

Leaderboard read

C21C concentration, lead at 3.2%

Carbon Technology Holdings, LLC leads this historical grant record at 3.2% of C21C - foreign corporation assignees hold 69% of class grants (235 of 342). Figures describe granted US utility patents in this CPC subclass, not current investment or legal strength.

Leader's share: 3.2%
Top three share: 8.0%
Lead over #2: 2

Where C21C sits inside C21

Among 3 subclasses in C21 (Metallurgy OF Iron), C21C ranks #2 and holds 8.6% of the parent class's 8,280 recorded grants. Sibling chips below are the other subclasses in the same parent class, not the nationwide volume/lead-share peers further down.

C21D 6,851 C21B 713

Rising assignees active in C21C

Company-wide grant multiples (2022–2024 vs 2019–2021) among assignees with ≥5 patents in this subclass. Growth is company-wide; class patent counts are subclass-specific.

#1 University of Science and Technology Beijing 2.44x 25 → 61 company-wide · 13 in C21C
#2 Carbon Technology Holdings, LLC 2.33x 12 → 28 company-wide · 23 in C21C
#3 Elkem ASA 1.71x 7 → 12 company-wide · 11 in C21C
#4 KW Associates LLC 1.67x 3 → 5 company-wide · 8 in C21C
#5 Chemtreat, Inc. 1.50x 14 → 21 company-wide · 5 in C21C

C21C grants by year, peak 2017 (78)

US utility-patent grants per year in C21C, 2015–2025 - recent five years are down 10% versus 2015–2019.

Carbon Technology…

23
Danieli & C Officine…

21
University of Science…

13
Refractory Intellectua…

12
Sms group

11
Heraeus Electro-nite…

11
Elkem Asa

11
Primetals Austria

10
Tata Steel

10
Arcelormittal

9
Technological…

9
Paul Wurth

9

What this shows Jfe Steel is the most active filer in C21C, holding 37 of the 716 patents in this class. Concentration at the top signals how contestable this technology area is for new entrants.

View data table

Top patent holders in CPC subclass C21C
Rank	Company	Patents in C21C
#1	Carbon Technology Holdings, LLC	23
#2	Danieli & C. Officine Meccaniche S.P.A.	21
#3	University of Science and Technology Beijing	13
#4	Refractory Intellectual Property GMBH & Co. KG	12
#5	SMS group GmbH	11
#6	Heraeus Electro-Nite International N.V.	11
#7	Elkem ASA	11
#8	Primetals Technologies Austria GmbH	10
#9	Tata Steel Limited	10
#10	ArcelorMittal	9
#11	Technological Resources PTY Limited	9
#12	Paul Wurth S.A.	9
#13	KW Associates LLC	8
#14	Novelis Inc.	7
#15	Outotec (FINLAND) OY	7
#16	Baoshan Iron & Steel Co., Ltd.	6
#17	Suncoke Technology AND Development LLC	6
#18	Outotec Oyj	6
#19	Tenova S.P.A.	6
#20	Berry Metal Company	6

Footprint here vs. claim strategy

Each dot is a leading C21C assignee, placed by how many patents it holds in this class (horizontal) against its company-wide average claims per patent (vertical) - a read on whether the class is led by broad-but-shallow filers or focused deep-claim players.

Top 14 C21C assignees by class footprint. Bubble size = patents in C21C. Source: USPTO PatentsView (claim depth is company-wide across all classes).

Classes near C21C's 716-grant footprint

Nationwide nearest neighbors for C21C (#496 of 670 by volume ; lead share 5.2%) - not the C21 parent-class siblings above.

Nearest by grant volume

C21B 713 B09C 712 C05D 707 C23G 703

Nearest by lead-assignee share

H10F 5.2% F15D 5.2% H01P 5.1% Y02E 5.1%

Questions about C21C

Which company holds the most patents in C21C?

JFE Steel Corporation leads C21C with 37 patents (3.2% of the subclass). By PatentsView assignee type, foreign corporations account for 69% of class grants.

Which C21C assignees grew fastest recently?

Among assignees with ≥5 grants in C21C, University of Science and Technology Beijing shows the highest company-wide grant multiple (2.44x: 25 grants in 2019–2021 → 61 in 2022–2024) while holding 13 patents in this subclass. Growth is company-wide, not class-only.

How does C21C compare inside parent class C21?

Inside C21 (Metallurgy OF Iron), C21C ranks #2 of 3 subclasses by grant volume and holds 8.6% of the parent class total. The largest sibling is C21D (6,851 grants).

What to do with this data

C21C in context - here's where to go next.

Carbon Technology Holdings, LLC leads C21C with 23 grants in this class. See full portfolio
C21C ranks #496 of 670 by grant volume among all tracked CPC technology areas. See the ranking
Inside parent class C21, the largest sibling subclass is C21D with 6,851 grants. Explore C21D

Figures reflect USPTO PatentsView grant data through 2026-05-15; pending applications not yet granted are not counted.

Methodology - C21C figures are USPTO PatentsView granted-utility totals for this subclass (716 grants in the tracked window).

Every figure on PlainPatent is rendered directly from USPTO source data, no number is typed in by an editor. This page draws directly on USPTO source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.