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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.

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The Small Punch Test (SPT) is a miniaturized test to characterize the mechanical properties of the materials. The load-displacement curve obtained by this test does not directly provide the material parameters, and linear correlations between data obtained from SPT curve and each mechanical property are necessary. The main difficulty of these correlation methods is the high level of scattering showed when analyzing a wide set of materials in the same study.In this paper, a finite element analysis focused on steel alloys was performed to understand the specimen behavior in the early stages of the SPT. Present methods to correlate the material yield strength with the data obtained from the SPT curve were also analyzed via this FEM study to discover the meaning of the current correlation scattering for this mechanical property. This numerical research also proved the accuracy of the proposed correlation method for the yield strength via the SPT. The maximum slope of zone I (Slope ini ) of the SPT curve showed an accurate correlation with this mechanical property.Focusing on steel alloys, experimental tensile tests and SPT's were performed to validate the numerical analysis and to demonstrate the suitability of the proposed Slope ini versus yield strength correlation method.

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