The effects of microstructure on internal friction (strain amplitude for measurement≈1×10-4) and Young's modulus have been investigated for the heat-treated specimens of commercial 80kgf/mm2 grade high-tensile strength steel (HT 80).
It was found that the internal friction was strongly affected by the distribution of carbide particles in the interior of the grain. The internal friction abruptly decreased with a decrease of particle spacing below about 1×10-6m. This can be correlated with a decrease of magneto-mechanical histeresis loss. Young's modulus increased with an increase in the amount of carbides in the steel which resulted in a decrease in dissolved carbon content in the matrix.
It was revealed that the as-received steel (sorbite structure) had the largest Young's modulus and the smallest internal friction, while the annealed specimen (coarse sorbite) showed an excellent combination of large internal friction and large Young's modulus. The surface finishing also influenced the internal friction of specimens.
