BEHAVIOUR OF BORON IN CARBONIZED AND CARBONITRIDED CASE AND CASE-HARDENABILITY OF BORON STEEL

The B is obviously redistributed in B steel within the whole carbonized and carbonitrided case because of the interaction between B with N and C during carbonizing and carbonitriding. The most of all behaviour of B observed in the carbonized case is the enrichment into the surface layer and the depletion from the sub-layer beneath surface, and in the earbonitrided case is the formation of abundant BN in the wide region from surface and the extension of depleted solution B into deep zone. The redistribution of B is remarkably influenced on the hardenability of the case. The carbonized case hardenability is affected not only by the carbon changed in content and influenced on B hardenability effect, but also by the B depletion in sub-layer. The abundant BN particles with solution B depletion deeply into the interior formed in carbonitrided ease is very harmful to the hardenability.