In the present investigation, high carbon steel and Nb microalloyed steel have been subjected to hot rolling (～80% hot deformation) by varying the finish rolling temperature (FRT) followed by air cooling to room temperature. The specimens were austenitised at 1200°C for 1 h and then subjected to hot deformation with two FRTs of 800°C and 1000°C. The deformation at a higher temperature results in a continuous grain boundary network structure with apparent evidence of recrystallisation whereas, finer grains at lower deformation temperature has been observed. The volumetric percentage of ferrite has been found to be more in case of Nb microalloyed steel at a lower FRT whereas, more volume percentage of pearlite has been observed when cooled from higher deformation temperature. On the other hand, deformation at a lower temperature (800°C FRT) results in more amount of ferrite formation in the Nb microalloyed steel. The average hardness value has been found to be higher (≈270 HV30/20) for the Nb microalloyed steels at higher deformation temperature (1000°C FRT) which is attributed to the finer interlamellar spacing (≤ 100 nm). Subsequent air cooling to room temperature from a higher deformation temperature increases the ultimate tensile strength (UTS) of high carbon steel marginally but improve the UTS of Nb microalloyed steel significantly. The tensile fracture morphology reveals the abundant presence of dimples at a lower deformation temperature, indicating a ductile fracture. The fracture surface of the Nb microalloyed steel subjected to higher deformation temperature exhibits a typical river-like pattern indicating cleavage fracture. Finally, a correlation between microstructure and properties have been established.
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