Steel carburizing is a thermal treatment that involves changing the surface layer of the processed material. This process is applied to low-carbon steels (up to 0.25% carbon content). The carbon content in the carburizing site increases to 1-1.3%, and the carburizing depth most often oscillates between 0.5 and 2 mm. Diffusion carburizing of parts for reduction gear changes their technical parameters – first of all, it increases hardness. This treatment increases the strength of the element while maintaining the appropriate softness of its core. Steel elements subjected to carburization become resistant to abrasion, and thus, perfectly fulfill their functions in mechanical systems.
There are two steps in the carburizing process: absorption (absorption of carbon in atomic form by the surface of the steel) and the penetration of carbon into the material.
Steel carburizing – methods
- in powders: the element is placed in a box with powdered charcoal and carburizing accelerators, e.g. barium carbonate, sodium carbonate. Such carburizing is performed at a temperature of about 900–950 ° C. The carburized part is most often surface hardened.
- gaseous: the element is usually placed in an atmosphere of natural gas or other gas resulting from the decomposition of petroleum products. This process is carried out at the temperature of 850–950 ° C. Constant gas circulation must be maintained in special muffle furnaces. Gas carburizing is more complicated as it requires proper installations. It is also more accurate and much faster.
- in liquid media: performed at about 850 ° C. The carburizing substance is a mixture of salt with the addition of SiC carborundum.
- in fluidized beds: the element is immersed in the fluidized bed. They are formed by particles of alumina or sand, carried by hot saturating gas flowing through the bed from below.
- vacuum: performed under reduced pressure in an atmosphere of methane or other gases. Good absorption and low gas consumption are the advantages of this method.
- ionization: based on heating in a vacuum furnace in a hydrocarbon atmosphere. When a voltage is applied, a plasma is produced followed by carbon ions which bombard the metal surface.
Currently, after the carburizing treatment, further heat treatment is performed. Namely core temperature quench, surface specific quench and low temper. Failure to do so is considered a technological error.