A study was made of defect mobility in a high-C martensitic tool steel. Mechanical spectroscopic investigations are performed at 80 to 700K. Torsion-pendulum (1Hz) and flexural vibrating-reed (3kHz) techniques were used, and the results were compared in order to obtain thermal activation parameters. Differential scanning calorimetry measurements are also performed over the same temperature range in order to detect structural transformations. The internal-friction spectra, as a function of temperature, exhibited 4 peaks. The physical mechanisms which were responsible for peak formation were analyzed on the basis of the peak activation energies, the effect of cold work and tempering on the internal-friction spectra, and a comparison with differential scanning calorimetry data. The conclusions were supported by published information on similar materials. It was found that the above peaks were all of relaxation type, and were related to dislocation movement in the martensite and to their interaction with solute atoms. One peak was the maximum of an internal friction spectrum which was related to a transformation of the material, and probably involved carbide-forming reactions. This transformation coincided with a hardness decrease which marked the first stage of tempering.

Internal Friction in a Martensitic High-Carbon Steel. R.Bagramov, D.Mari, W.Benoit: Philosophical Magazine A, 2001, 81[12], 2797-808