AbstractFor low carbon acicular ferrite steels, niobium in solution may contribute to a low austenite to ferrite transformation temperature. Hot rolling schedules and steel compositions which could minimise the precipitation of niobium from the austenite as carbonitride are investigated. It is found that rather large quantities of niobium may be kept in solution under rolling conditions which favour rapid recrystallisation of austenite. Carbonitride precipitation in deformed austenite appears to be proportional to the precipitation potential at the deformation temperature which can be calculated by appropriate solubility equations taking into account actual compositions of steels. No precipitation of carbonitride during or after the austenite to ferrite transformation is observed in those specimens which exhibit acicular ferrite microstructures after air cooling.MST/805