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

Abstract

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.

The effect of deep cryogenic treatments on the mechanical properties of an AISI H13 steel

“…These results are in accordance with the revised literature, since a reduction in the retained austenite content is usually reported when a cryogenic stage is applied [24][25][26][27][28][29].…”

Rejuvenation of metallic glasses by non-affine thermal strain

“…There are reports that under cyclic mechanical loading at room temperature, in the elastic regime, a Zr-based BMG can undergo some crystallization 44 . Deep cryogenic treatment of steels certainly induces phase changes 22,25 . In the present work, X-ray diffraction (Bragg-Brentano geometry, Bruker D8 instrument, Cu Ka radiation) was used to check that the samples remained fully glassy throughout, and especially after thermal cycling.…”

“…Across a range of metallic glass compositions, melt-spun and bulk, thermal cycling induces changes in properties. As the cycling is down to 77 K, these changes can be compared with the property improvements (hardness, wear resistance) obtained by deep cryogenic treatment (DCT) of steels 22 . DCT, however, works through phase changes (transformation of residual austenite, precipitation of fine carbides) on holding at low temperature.…”

Martensitic transformation in AISI D2 tool steel during continuous cooling to 173 K

“…The effect of cryogenic treatment on microstructure evolution, wear, and mechanical properties of Fe-C steel, tool steels, and specifically AISI D2 tool steel has been previously reported by many researchers [10][11][12][13][14][15][16][17][18][19][20][21]. The temperature ranges studied by researchers varies from 223K to 77K and depending on the investigated temperature interval, the denominations are different:…”

“…Preciado and Pellizzari [10], Olia et al [12], and Das et al [19,21] have presented the most recent studies on the influence of cryogenic treatment and subsequent tempering on the sequence of precipitation of temper carbides and the evolution of mechanical and wear properties. However, in spite of the extensive amount of work, little information is available on martensite's characteristics and the kinetics of martensitic transformation during direct cooling to 173 K (shallow cryogenic temperature).…”