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 (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)
Description
C21D encompasses heat treatment processes and equipment that alter the physical and mechanical properties of ferrous metals and alloys through controlled thermal cycles, including annealing, tempering, hardening, normalizing, and stress relief. The class also covers general-purpose heat treatment apparatus applicable to both ferrous and non-ferrous metals, as well as specific processes for improving workability such as decarburization and softening treatments. This classification excludes specialized surface treatment methods (covered under C21C) and specific alloy composition modifications, focusing instead on structural transformation achieved via temperature control and cooling regimens.
Filing statistics
CPC subclass C21D recorded 112,271 patent applications worldwide between 2013 and 2023. Annual filings grew from 6,047 in 2013 to 10,554 in 2023 (+75%), peaking at 12,689 applications in 2020. The most active applicants in class C21 are JFE STEEL (8,270 applications), NIPPON STEEL CORPORATION (5,222 applications) and POSCO (POHANG IRON AND STEEL COMPANY) (4,824 applications).
Source: EPO PATSTAT, worldwide filings
16 direct subcodes
Child Classifications
Navigate with arrow keys, Enter to open
- C21D 1/00 General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D 10/00 Modifying the physical properties by methods other than heat treatment or deformation
- C21D 11/00 Process control or regulation for heat treatments
- C21D 2201/00 Treatment for obtaining particular effects
- C21D 2211/00 Microstructure comprising significant phases
- C21D 2221/00 Treating localised areas of an article
- C21D 2241/00 Treatments in a special environment
- C21D 2251/00 Treating composite or clad material
- C21D 2261/00 Machining or cutting being involved
- C21D 2281/00 Making use of special physico-chemical means
- C21D 3/00 Diffusion processes for extraction of non-metals; Furnaces therefor (local protective coatings C21D1/72)
- C21D 5/00 Heat treatments of cast-iron
- C21D 6/00 Heat treatment of ferrous alloys
- C21D 7/00 Modifying the physical properties of iron or steel by deformation (apparatus for mechanical working of metal B21, B23, B24)
- C21D 8/00 Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02)
- C21D 9/00 Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
Top Applicants
Top 10 applicants by patent filingsfor class C21, 2013–2023, worldwide · Source: EPO PATSTAT
- JFE STEEL JP 8,270
- NIPPON STEEL CORPORATION JP 5,222
- POSCO (POHANG IRON AND STEEL COMPANY) KR 4,824
- JFE STEEL 3,311
- ARCELORMITTAL LU 3,239
- NSSMC (NIPPON STEEL & SUMITOMO METAL) JP 2,659
- HYUNDAI STEEL COMPANY KR 1,492
- ANGANG STEEL COMPANY 1,318
- BAOSHAN IRON & STEEL COMPANY 1,233
- KOBE STEEL JP 1,228