Quenching heat treatment process| Codere

Quenching is the final and critical step of the hardening process.

After heating above the AC3 critical temperature, parts are rapidly cooled below the martensitic finish temperature (Ms). This transformation of austenite into martensite leads to a significant increase in hardness and mechanical strength.

Quenching can be performed in various media—gas, salt, oil, water or air—each offering a specific cooling rate and operating window. Selecting the right quenching medium is essential to obtain a fully martensitic structure while avoiding undesirable mixed phases such as pearlite or bainite.

Cooling Media

Quenching media are classified from slowest to fastest cooling rate:

Air cooling
Gas cooling
Salt cooling
Oil cooling
Water cooling

Technical principles of martensitic hardening

Quenching aims to achieve a fully martensitic microstructure without forming intermediate phases that degrade mechanical performance.

The chosen cooling medium affects hardness, distortion and microstructure
Distortion tendency is inversely related to quenching severity
Water quenching generates the highest distortion; air quenching the lowest
Salt and oil offer a balance between performance and dimensional stability

During transfer from furnace to quench tank, protective gases are used to minimize decarburization, IGO/IGA and surface discoloration.

Air

Slowest medium
Risk of oxidation
Used when minimal quench severity is required

Gas

Clean process with limited oxidation
Moderate exchange rate
Nitrogen commonly used as protective gas

Salt

Operating range: 180 °C to 400 °C
Suitable for martensitic and bainitic hardening
Excellent heat transfer, easily washable

Oil

Most common medium
Operating typically between 50 °C and 100 °C
High cooling rate

Water

Fastest and harshest cooling medium
Vapor blanket formation may reduce uniformity
Highest distortion risk

Codere expertise in quenching

Codere develops high-performance quenching systems designed to limit deformation, protect surfaces and ensure reliable and repeatable metallurgical results.