Influence of deep cryogenic treatment on the thermal decomposition of Fe–C martensite

• Published in: Journal of materials science Vol. 49; no. 23; pp. 8183 - 8191
• Main Authors: Preciado, M., Pellizzari, M.
• Format: Journal Article
• Language: English
• Published: Boston Springer US 01.12.2014; Springer; Springer Nature B.V
• Subjects: Activation energy; Annealing; Calorimetry; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Cryogenic effects; Cryogenic engineering; Cryogenic temperature; Cryogenic treatment; Crystallography and Scattering Methods; Dilatometry; Dislocation density; Heat treatment; Martensite; Martensitic transformations; Materials Science; Mechanical properties; Metallurgical analysis; Original Paper; Polymer Sciences; Quenching and tempering; Retained austenite; Segregation process; Solid Mechanics; Steel; Thermal decomposition; Cryogenic Treatment; Dilatometry; Martensite; Cementite; Austenite
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-014-8527-2

The beneficial effects of deep cryogenic treatment (DCT) at temperatures close to −180 °C on certain mechanical properties of steels are well known, although the metallurgical base mechanism of DCT still needs further clarification. In this study, the thermal decomposition of steel martensite (100Cr6) subjected to low-temperature soaking over different periods (SDCT = 5 min at −180 °C, LDCT = 24 h at −180 °C) is investigated by means of differential scanning calorimetry and dilatometry. The results were compared with those for the same conventionally quenched and tempered steel. Isochronal annealing experiments at different heating rates were performed, in order to highlight the main tempering stages and to obtain their relevant activation energies. DCT was clearly shown to lower the Ea of the pre-precipitation process more intensely than in the quenched steel. This result may probably be ascribed to an increased dislocation density and to the activation of the carbon segregation process in larger amounts of martensite. The precipitation of transition carbides was also enhanced by the low-temperature conditioning of martensite. As expected, DCT transformed the retained austenite, so that the corresponding peaks almost disappeared from both the dilatometric and the DSC patterns.