Abstract
Abstract This paper presents a study on defect mobility in a high-carbon martensitic tool steel. Mechanical spectroscopy investigations are performed in the temperature range 80–700 K. Torsion pendulum (about 1 Hz) and flexural vibrating-reed (about 3 kHz) techniques are used and compared in order to obtain thermal activation parameters. Differential scanning calorimetry (DSC) measurements are also performed in the same temperature range in order to detect structure transformations. The internal-friction spectra obtained as a function of temperature show four peaks P1, P2, P3 and P4. The physical mechanisms responsible for the peak formation are analysed on the basis of the peak activation energies, the influence of cold work and tempering on the internal-friction spectra and the comparison with DSC. The conclusions are supported by present information available on similar materials. It is found that P1, P2 and P4 are all relaxation peaks and are related to dislocation movement in the martensite and to their interaction with solute atoms. P3 should be considered as a maximum in the internal-friction spectrum related to a transformation of the material, probably leading to carbide-forming reactions. This transformation coincides with a hardness decrease, which marks the first step of steel tempering.
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