Surface hardening method

Heating and quenching

Also called flame or induced hardening. As the name suggests, this metal case hardening process involves a flame or heat. In this step, high carbon steel parts are heated to extreme temperatures by oxygen flame or induction heating, and then the heated carbon steel parts are rapidly cooled by a coolant (usually water). This fire hardening works well on steel or iron with sufficient carbon content. Carbon content should be 0.3-0.6 wt%. For steels with carbon content lower than this value, there are other steps such as nitriding and carburizing.

Nitriding

Nitriding is another form of case hardening technology. In this step, iron is heated to 84-621°C in an ammonia atmosphere to decompose ammonia. The depth of the hardened surface depends on how long the steel component has been exposed to the ammonia environment. This method must use chromium, molybdenum, aluminum and other elements to form chromium nitride to solidify the steel surface. Increased nitrogen and exposure to nitrogen promotes nitride formation. This process only works if the metal is solidified together with the elements that form chromium nitride (chromium, molybdenum, etc.). Nitriding generally requires lower temperatures than heating and quenching and does not require a quenching step, thus reducing distortion.

carburization

Carburization is another form of case hardening that is widely used to improve the mechanical properties of steel substrates. During the carburizing process, the steel alloy is heated to high temperatures and large amounts of carbon are exposed on the surface. Depending on the application requirements, the external carbon source can be a gas, liquid, or solid. The large amount of external carbon then forms carbides with other elements on the steel surface. These carbides provide greater hardness and wear resistance. Similar to nitriding, heating conditions are generally lower and may result in smaller deformations.

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