Abstract
This report deals with the effect of Nb carbonitride precipitation on deep drawability of cold rolledannealed sheets.
The maximum Lankford value was obtained when Nb/C was 8-12 for the vacuum melted steel sheet.
The solution and precipitation of Nb carbonitride were examined by chemical analysis; it was found that the carbonitride dissolved in austenite at 1 200-1 300° in only a few minutes in the case of extrmely low-C Nb-steel (C 0.006%, Nb 0.18%), but some part of it remained in the case of low -C Nb-steel (C 0.03%, Nb 0.32%).
Lankford values after cold rolling and annealing were examined for the both types of specimens. The extremely low-C Nb-steels were not affected by hot rolling conditions but low-C Nb-steel shewed a lower Lankford value when soaking and finishing temperatures were high. This was attributed to the precipitation of fine carbonitride.
