Removal of carbon from the surface layer when steel is heated in an atmosphere that oxidizes carbon, such as air, wet endothermic gas or a leaking furnace. Partial decarb lowers surface hardness and fatigue strength; complete decarb leaves a layer of pure ferrite. It is measured by microhardness traverse or metallography and usually capped on drawings. Bar stock arrives with mill decarb that must be machined off before hardening.
Springs are four points low at the surface and the mount shows 0.004 of decarburization, the atmosphere was wet.
If the surface reads soft and a light grind brings the number up, it is decarb, not a bad quench.
Also heard as
- decarb
- decarbed
- decarburized
Related terms
Carbon potential
The carbon content a furnace atmosphere would give the surface of plain steel at equilibrium.
Dew point
The temperature at which water vapor in a furnace atmosphere condenses, used as a gauge of carbon potential.
Scale
The oxide crust that forms on steel heated in air or in an oxidizing atmosphere.
File hard
Hard enough that a sharp file skates across the surface without biting, roughly 58 HRC and up.
Rockwell hardness
The standard shop hardness test that presses a diamond or ball into a part and reads depth as a number.