Microstructure evolution during hot rolling depends on several processing variables.These are the furnace soaking temperature and,for each pass in the schedule,the temperatures,the strains,the strain rates.Finally the cooling rate during transformation is also of importance.These variables will determine the amount of Nb in solution prior to rolling,the condition of the austenite during processing,the amount of accumulated strain in the austenite prior to transformation to ferrite and the room temperature microstructure.The phases and constituents present at room temperature will largely define the mechanical properties of the products.