Carburising is the process of saturating the surface layer of low carbon steels at 850° - 950°C with carbon from a carbonaceous source capable of giving up its carbon to the metal.
There are following methods of carburizing:
In this process, components are packed in an environment with high carbon content.
A reducing agent (carbon monoxide) is introduced when heated. Due to high temperatures, carbon monoxide starts to release carbon to be diffuse into the steel surface.
The materials are then hardened due to carbon absorption. The case depth is approximately 0.1 – 1.5 mm. Pack carburizing requires high skilled labor, due to the temperature which is hard to uniform.
Gas Carburising is almost similar to Pack Carburising except for the part where the supply of carbon monoxide gas to the heated furnace and carbon decomposition.
The carbon monoxide gases are contained safely and the components are enclosed in a carbon filed enclosure that is replenished continuously to maintain high carbon content which results in a high production rate in comparison to pack carburizing.
A lot of problems that are faced in Pack Carburising are solved by using this process.
This method can be used in mass production.
For this process, the steel components are immersed in a liquefied carbon-rich environment (cyanide). Another method is by using molten salt.
The molten salt can also introduce carbon into the metal. The metal is then undergone rapid quenching. The quality produced is similar to the ones in Gas Carburising, but with low nitrogen and high carbon content.
Solid powder carburizing:
In this method, the carburizing compound is a solid carburized, usually charcoal of 3 to 10 mm size (fines are screened off), or coke, semi-coke, or coal.
To accelerate the carburizing activator, or energizer normally BaCO3 and/or Na2CO3 in amounts 10-30% of charcoal is added.