EXPERIMENTAL INVESTIGATION OF SEGREGATION OF CARBON ATOMS DUE TO SUB-ZERO CRYOGENIC TREATMENT IN COLD WORK TOOL STEEL BY MECHANICAL SPECTROSCOPY AND ATOM PROBE TOMOGRAPHY

摘要

In this work, we present mechanical spectroscopy of cold work tool steel subjected to sub-zero cryogenic soaking treatment to reveal the carbon segregation and the subsequent carbides refinement. The maximum of Snoek-Koster (SK) peak height was obtained in the sample subjected to soaking 1h at -130 degrees C cryogenic treatment. The SK peak height is reduced with prolonging the soaking time. The results indicate that an increase in the height of SK peak is connected with an increase in dislocation density and the number of segregated carbon atoms in the vicinity of dislocations or twin planes after martensite transformation at -130 degrees C which is confirmed by corresponding TEM and atom probe tomography measurement. Hence, it is suggested that the isothermal martensite, formed during the cryogenic soaking treatment decreases (APT) the height of SK peak.