Question: We are currently carburizing AISI 1010 low-carbon steel. We are not sure what surface hardness to expect after the carburizing procedure.

Answer: The surface hardness will be dependent on the following:

•    Austenitizing temperature
•    Quench medium
•    Quench medium temperature
•    Surface carbon potential
•    Speed of transfer from the austenitizing furnace to the quench medium

The method of hardness testing should be as light a load as possible in relation to the case depth. The ideal and most accurate method to use when measuring surface hardness is by a transverse microhardness survey. This should be done across a representative sample cut at right angles to the diameter of the steel bar using a 200-gram load and employing either a Vickers or Knoop indentor traversed across the formed case and into the core.

The ISO definition of the effective case is: the surface hardness down to 513 Vickers or approximately 50 Hardness Rockwell C scale.

The definition of core hardness is: core hardness of the material plus 50 hardness Vickers points or 5 HRC points above core hardness.