Nature of a Carburized Case

ASM Heat Treating Society                

Nature of a Carburized Case At a temperature of approximately 925°C (1700°F), a steel surface is extremely active, and if the carbon content of its environment is higher than that of the steel, the steel absorbs carbon to achieve equilibrium with the environment.

However, if the carbon potential of the environment is lower than that of the steel, the steel loses carbon to its environment (decarburization). However, equilibrium conditions prevail only at the steel surface, and as distance from the surface increases, carbon concentration decreases gradually to the original carbon content of the steel. The drop in carbon content below the surface is important, because finishing operations (grinding, for example) must be planned carefully because too much stock removal in finishing removes the most valuable part of the case. A general rule is to plan operations so no more than 10% (per side) of the case is removed during finishing.