EFFECTS OF TITANIUM AND NIOBIUM ON MICROSTRUCTURE AND MECHANICAL ADHESION OF THERMAL OXIDE SCALES ON HOT-ROLLED LOW CARBON STEEL

Improvement in strengthening steel without losing its ductility is the main development in the steel industry. The presence of a small amount of Ti and Nb concentrations significantly increases the strength of hot-rolled low carbon steel. In order to attain the finishing temperature of the hot-rolling process, the alloys are processed under 900 degrees C in 17.2% steam mixed with an oxygen atmosphere and pure oxygen atmosphere for 1 min and 5 mins, respectively. The small amount of Ti/Nb additions influences the grain size and scale adhesion. The grain size was reduced by 16% in the Ti/Nb addition sample resulting in better strength properties by means of grain refinement. The Ti/Nb addition sample is less sensitive to the water vapour content than the base metal in an oxidizing atmosphere. The oxide scale in the Ti/Nb sample was found to have a Ti- doped magnetite phase. In both oxidizing atmospheres, the Ti/Nb addition sample showed lower strain initiating at the first spallation than that of the base metal sample, resulting in a weaker oxide scale adhesion.