PlainPatent

CPC technology class · C21

C21D - Modifying THE Physical Structure OF Ferrous Metals

Modifying the physical structure of ferrous metals; general devices for heat treatment of ferrous or non-ferrous metals or alloys; making metal malleable, e.g. by decarburisation or tempering. 6,851 US utility patents granted 2015–2025, with the leading assignees and year-by-year filing trajectory.

6,851
US patents granted
C21
Parent CPC class
20
Active assignees
+41%
5-yr velocity

The verdict

Modifying THE Physical Structure OF Ferrous Metals ranks #211 of 670 CPC technology areas - 6,851 US patents granted since 2015, with filing up 41% over five years.

#211
of 670 CPC technology areas
6,851
US patents granted, 2015–2025
Jfe Steel
leading assignee (865)
+41%
filing velocity, last 5 yrs
Top assignee: JFE Steel Corporation (865 patents)

CPC subclass C21D - MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING - covers 6,851 US utility patents granted between 2015 and 2025 according to USPTO PatentsView records, within the broader CPC class C21 (METALLURGY OF IRON). See our CPC classification guide for how the system works.

The competitive landscape in C21D is shaped by 20 distinct companies actively filing in this space. JFE Steel Corporation leads with 865 patents, followed by Nippon Steel Corporation at 616 grants and Posco Co., Ltd at 400.

Filing activity in C21D is up 41% over the past five years versus 2015-2019, a sharp acceleration suggesting an emerging or fast-moving technology area. All counts come directly from USPTO PatentsView and reflect US granted utility patents only.

Is C21D innovation accelerating?

US utility-patent grants per year in C21D, 2015–2025 - recent five years are up 41% versus 2015–2019.

300400500600700800 20152016201720182019202020212022202320242025 515

Who leads C21D?

The 12 most active assignees in MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING - wider bars mean more grants

patents

What this shows Jfe Steel is the most active filer in C21D, holding 865 of the 6,851 patents in this class. Concentration at the top signals how contestable this technology area is for new entrants.

Source USPTO PatentsView, granted utility patents As of 2015–2025 grant years
View data table
Top patent holders in CPC subclass C21D
Rank Company Patents in C21D
#1 JFE Steel Corporation 865
#2 Nippon Steel Corporation 616
#3 Posco Co., Ltd 400
#4 Nippon Steel & Sumitomo Metal Corporation 357
#5 Arcelormittal 197
#6 Baoshan IRON & Steel Co., Ltd. 116
#7 KOBE Steel Ltd. 109
#8 Thyssenkrupp Steel Europe Ag 76
#9 NTN Corporation 52
#10 Hyundai Steel Company 44
#11 NHK Spring Co., Ltd. 39
#12 Thyssenkrupp Ag 38
#13 Nippon Steel & Sumikin Stainless Steel Corporation 37
#14 ATI Properties Llc 34
#15 Daido Steel Co., Ltd. 34
#16 Aktiebolaget SKF 33
#17 Voestalpine Stahl Gmbh 31
#18 Nucor Corporation 29
#19 Nisshin Steel Co., Ltd. 29
#20 SMS Group Gmbh 27

About This Class

CPC subclass C21D belongs to class C21.

6,851 patents were granted in this class between 2015 and 2025.

20 companies actively patent in this space.

Classification System

Cooperative Patent Classification (CPC) is a hierarchical patent classification system used by the USPTO and EPO.

← All Technology Classes Technology Rankings →

Footprint here vs. claim strategy

Each dot is a leading C21D 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 C21D assignees by class footprint. Bubble size = patents in C21D. Source: USPTO PatentsView (claim depth is company-wide across all classes).

Top 14 C21D assignees by class footprint. Bubble size = patents in C21D. Source: USPTO PatentsView (claim depth is company-wide across all classes). Scatter plot of 14 data points (bubble-sized by third dimension). 51015202530 -20002004006008001000 Patents in C21D Avg claims / patent (company-wide) Jfe SteelNippon SteelPoscoNippon Steel & Sumito…ArcelormittalBaoshan Iron & SteelKobe SteelThyssenkrupp Steel Eu…NtnHyundai SteelNhk SpringthyssenkruppNippon Steel & Sumiki…Ati Properties
Top 14 C21D assignees by class footprint. Bubble size = patents in C21D. Source: USPTO PatentsView (claim depth is company-wide across all classes).

Frequently Asked Questions

What is CPC class C21D?
CPC subclass C21D covers MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING. It belongs to CPC class C21 (METALLURGY OF IRON), with 6,851 US utility patents granted since 2015.
How many patents have been filed in C21D?
6,851 US utility patents were granted in CPC subclass C21D between 2015 and 2025, based on USPTO PatentsView data.
Which company holds the most patents in C21D?
JFE Steel Corporation leads C21D with 865 patents, making it the most active assignee in this technology area.
How is patent data for C21D collected?
Patent data comes from USPTO PatentsView, a public research dataset maintained by the United States Patent and Trademark Office. It covers all US granted utility patents and assigns CPC codes based on the technology described in each patent.
What is the difference between CPC class and subclass?
A CPC class (e.g., C21) is a broad technology category. Subclasses like C21D provide finer granularity within that category. PlainPatent organizes data at the subclass level (4-character codes) for the most useful view of technology domains.

Read our methodology - how this data is sourced, computed, and verified.

Data sourced from USPTO PatentsView - official U.S. government patent data. See our methodology for computation details. Retrieved and formatted by PlainPatent Editorial

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.