Graphitization

the formation (deposition) of graphite in iron, nickel, cobalt, and other metal alloys in which carbon is contained in the form of unstable chemical compounds, carbides. At high temperatures the carbide is completely replaced by graphite. The rate of graphitization increases upon a rise in temperature, as well as upon preliminary hardening, deformation, and irradiation.

Graphitization of steel usually adversely affects the mechanical properties of steel (it reduces the strength and plasticity). At the same time the graphite, which has lubricating properties, increases the durability of the articles. The graphitization of iron alloys is used in producing articles from cast iron and graphitic bearing and die steel. Silicon, or less frequently aluminum, is introduced into steel or iron to accelerate graphitization. The graphitization of a number of alloys (tool-cutting, spring, boiler, and other steels) reduces their operating quality and is undesirable. Graphitization can be arrested by introducing additives (chromium or manganese), which increase the stability of the carbides. The term “graphitization” is sometimes used to designate the formation of graphite in iron-carbon alloys that do not contain carbides. Graphite is separated from alloys that are supersaturated with carbon upon their solidification and subsequent cooling.