1987 Volume 73 Issue 8 Pages 1049-1056
The present work deals with the resistance to deep drawing-induced brittleness. The materials used in this study are 4045 kgf/mm2 grade extra-low-carbon high strength steel sheets containing P and Si as strengthening elements.
Though the resistance to the brittleness is improved by B addition in any steel, it is more remarkable in Nb and Ti containing steel than in Nb or Ti containing one.
The difference of the effects of B between Nb and Ti containing steel and Nb containing one is attributable to the difference of existing state of B. In Nb and Ti containing steel, B exists as solute atom because N is precipitated as TiN, thus acting to inhibit the segregation of P to grain boundaries. Solute B also en0hances the grain boundary strength by itself. On the other hand, solute B content is quite small because a considerable portion of B precipitates as BN in Nb containing steel.
The reason why Nb and Ti containing steel is superior to Ti containing steel in resistance to the brittleness is that a small amount of solute C coexists with B only in the former. Solute C also inhibits the segregation of P to grain boundaries and enhances the grain boundary strength.