For through-hardening grades – whether a martensitic or bainitic structure is desired – decarburization, added carburization and intergranular oxidation (IGO) are not acceptable. Small amounts may be ground off, but these undesired properties can add to the risk of cracking upon quenching. In most cases, through-hardening microstructures are stress neutral to tensile at the surface and are prone to cracking.
Case-carburized components must also control IGO and decarburization to less than grind stock. Compressive stresses are the rule with case-carburized parts, which typically prevent cracking unless the situation is severe.
This means that a furnace must have a proper atmosphere and be reasonably sealed, especially in the case of through-hardening grades.