Abstract
Effects of grain size, microstructure and cold work on the internal friction were investigated using a commercial high-tensile strength steel HT 80.
The internal friction increased with decreasing grain size in the heat-treated specimens for both ferrite-pearlite and sorbite structures, while it did not exhibit any detectable grain-size dependence in the cold worked and heat-treated (recrystallized) specimens. At small strain amplitudes, the internal friction was larger in the heat-treated specimens with ferrite-pearlite structure than those with sorbite structure, irrespective of grain size. But, the internal friction was larger in the latter specimens at larger strain amplitudes and at larger grain sizes. The internal friction of the high-tensile strength steel in this case was principally attributed to the magneto-mechanical hysteresis loss and the viscous flow at grain boundaries and ferrite-pearlite phase boundaries.
The internal friction and the hardness increased with increasing amount of cold work. The increase of internal friction was larger at larger amounts of cold work and at larger strain amplitudes.
