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)

Introduced: September 1968

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.

Title

Titles differ between systems:

IPC: 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

CPC: 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)

Full Title

Full titles differ between systems:

IPC:

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

CPC:

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)

Additional Content IPC

Glossary

Cast-iron cast-irons Ferrous alloy which solidifies with an eutectic, with C 2.1 - 4%. Sub-critical annealing/Stress relief annealing Heat treatment for relieving or dissipating stresses in weldaments, heavily machined parts, castings, forgings by heating them, uniformly heated through, and air cooled/slow cooled with subsequent finishing or heat treatment. Oil-hardening Process of hardening a ferrous alloy by heating within or above the transformation range and quenching in oil Decarburisation Subjecting the steel to high temperatures and heat treating in a media containing air, oxygen or hydrogen to remove carbon at the surface. Recrystallization After all metal crystals have been dissolved by heating enough to lose its structural strength, the metal temperature then falls, allowing the crystals to re-form Spheroidizing Heating the carbon steel to approximately 700 °C for over 30 hours to form spheroidite, to soften higher carbon steels and allow more formability. Aging (or ageing) A process in which the hardness or strength of a metal alloy having a constituent in supersaturated solid solution is increased over time as the constituent precipitates out as a secondary phase containing the constituent. When occurring at room temperature the process is termed "natural aging", while a process that occurs when subjecting the metal alloy to elevated temperature is termed "artificial aging". Aging for a longer time than that corresponding to maximum strength or hardness at the particular temperature is termed "over-ageing". Hardening The increase in resistance to deformation Precipitation hardening As the quenched alloy ages, a new material precipitates out of the metallic crystal lattice, filling in abutting spaces, and increasing hardness Normalizing A process of heating metallic material above its critical temperature and cooling in air thereby establishing a fine uniform grain size and improving the microstructural uniformity Quenching The rapid cooling of metallic material either from elevated temperature to room temperature or cooling of metal to sub-ambient temperature, at a specific rate, with a given medium. Tempering Heating of a previously quenched or normalized metallic material to an elevated temperature, and then cooling under suitable conditions to obtain the desired mechanical properties. Martempering Heat treatment of steel involving austenitisation of steel followed by quenching in heat extracting medium (e.g. salt), at a rate fast enough to avoid the formation of ferrite, pearlite or bainite to a temperature slightly above the martensite start (Ms) point Austempering Isothermal heat treatment applied to steel and cast iron, involves holding the metallic material at the quenching temperature for an extended period of time in order to produce a lower bainite microstructure for steels and a structure of acicular ferrite and high carbon, stabilized austenite known as ausferrite for cast-irons. Case Hardening Heat treatment or combination of heat treatments of surface hardening involving a change in the composition of the outer layer of an iron-base alloy in which the surface is made harder by inward diffusion of a gas or liquid followed by appropiate thermal treatment.

Limiting references

Apparatus for mechanical working of metal without essentially removing material; Punching metal Apparatus for mechanical working of metal not otherwise provided for, e.g. turning, boring Apparatus for grinding or polishing of metal Mechanical descaling , Cooling-beds for metal rolling Cold coilers Chemical descaling Cementation by diffusion processes Surface treatment of metallic material involving at least one process provided for in class and at least one process covered by Electrolytic descaling Unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid material

Application references

Apparatus for heat treatment of railway trains on the spot

Of 16 combined children, 9 exist in both systems.

7 codes are CPC-only extensions.

Note: 7 CPC extensions are marked as secondary classification only.

4 shared codes have differing titles between IPC and CPC.

Child Classifications

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C21D 1/00 General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering IPC+CPC Available in IPC and CPC
C21D 10/00 Modifying the physical properties by methods other than heat treatment or deformation since 1980 +1 CPC IPC+CPC Available in IPC and CPC
C21D 11/00 Process control or regulation for heat treatments since 1974 +1 CPC IPC+CPC Available in IPC and CPC
C21D 2201/00 Treatment for obtaining particular effects 2nd only +5 CPC CPC only CPC only
C21D 2211/00 Microstructure comprising significant phases 2nd only +9 CPC CPC only CPC only
C21D 2221/00 Treating localised areas of an article 2nd only +3 CPC CPC only CPC only
C21D 2241/00 Treatments in a special environment 2nd only +2 CPC CPC only CPC only
C21D 2251/00 Treating composite or clad material 2nd only +2 CPC CPC only CPC only
C21D 2261/00 Machining or cutting being involved 2nd only CPC only CPC only
C21D 2281/00 Making use of special physico-chemical means 2nd only +2 CPC CPC only CPC only
C21D 3/00 Diffusion processes for extraction of non-metals; Furnaces therefor (local protective coatings C21D1/72) IPC+CPC Available in IPC and CPC
C21D 5/00 Heat treatments of cast-iron IPC+CPC Available in IPC and CPC
C21D 6/00 Heat treatment of ferrous alloys since 1974 +6 CPC IPC+CPC Available in IPC and CPC
C21D 7/00 Modifying the physical properties of iron or steel by deformation (apparatus for mechanical working of metal B21, B23, B24) IPC+CPC Available in IPC and CPC
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) since 1980 IPC+CPC Available in IPC and CPC
C21D 9/00 Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor +12 CPC IPC+CPC Available in IPC and CPC

Top Applicants

Top Applicants (IPC)

Class C21,2013–2023, worldwide · Source: EPO PATSTAT

JFE STEEL JP 7,470
POSCO (POHANG IRON AND STEEL COMPANY) KR 4,615
JFE STEEL 4,538
NIPPON STEEL CORPORATION JP 4,536
ARCELORMITTAL LU 2,597
NSSMC (NIPPON STEEL & SUMITOMO METAL) JP 2,241
ANGANG STEEL COMPANY 2,126
NSSMC (NIPPON STEEL & SUMITOMO METAL) 1,783
BAOSHAN IRON & STEEL COMPANY 1,620
HYUNDAI STEEL COMPANY KR 1,545

Top Applicants (CPC)

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