Surface decarburization is a loss of carbon in the skin
of the material. Favoring factors are high temperatures and larger quantities
of oxygen in the atmosphere.
In the following some characteristics for a decarburization
are listed :
1. Increased amount of ferrite
2. Reduction of the amount at carbides
3. Lamellar pearlite at annealed hypereutectoid
4. Worse etchenability at higher alloyed
5. Various amounts of the different microstructures
These details have to be understood as a change in proportion
to the basic structure. You measure up to an imaginary line after which the
carbide distribution or the composition of the microstructure doesn't change
any more. Smaller fluctuations, which represent a natural irregularity at the
carbon distribution, are not considered.
The links listed below lead you to some examples of different
heat treatment conditions at various steel grades. The measured depth of the
decarburization are marked in the pictures. The represented surface decarburizations
and the measurings have been confirmed in this form, also in the conversation
with other metallograher. 0,01 - 0,02 mm have to be described as normal differences
in the assessment.