An internal friction study of a vanadium microalloyed steel by a dynamic mechanical thermal analyser

The internal friction of a C-Mn-Al-V-N steel was investigated using a dynamic mechanical thermal analyser (DMTA) under different austenitisation time, cooling and tempering conditions. Internal friction measurements using a DMTA instrument showed energy loss peaks at different temperatures for a frequency of 1 Hz. For example, as well as the normal nitrogen peak, other broader loss peaks were observed centred on 100°C in the case of air-cooled samples austenitised at 900°C for 1 h. This is most probably due to carbon or nitrogen atom jumps associated with Fe-N-V sites, since the energy barrier which must be overcome for a carbon or nitrogen atom to break away from the foreign atom such as vanadium will be larger than that in a normal interstice. In addition, this abnormal damping peak disappeared after tempering at 450°C for 72 h. This indicates the precipitation of carbon and/or nitrogen.