The effects of titanium and boron on the microstructure of a low alloyed Cr-Mo steel with 0.6 wt-%C have been investigated by comparison with a steel containing only titanium and a steel free from both titanium and boron. Each of the steels was subjected to thermomechanical treatment and annealed at 700°C, resulting in small grains of size a few micrometres. The steel containing both titanium and boron possessed the smallest ferrite grains and M3C carbides of the three examined. This is attributed to a fine dispersion of borides (TiB2) and borocarbides (Ti(C,B)) of size 10 nm in the ferrite matrix through the pinning effect. At the grain boundaries small carbide particles were present which were effective in inhibiting grain boundary migration. The extremely fine borides and/or borocarbides were useful in suppressing intragranular deformation of ferrite grains due to precipitation hardening. This may have assisted in promoting grain boundary sliding, resulting in superior superplastic elongation.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanics of Materials
- Mechanical Engineering