Origin of low-temperature shoulder internal friction peak of Snoek-Köster peak in a medium carbon high alloyed steel

• The LTS-SK internal friction peak was found as the steel aged at temperatures below 373 K.
• The evolution of the LTS-SK peak is accompanied by the decrease of solid dissolved carbon content.
• The origin is attributed to the interaction between carbon atoms and twin boundaries in martensite.

A distinct internal friction peak located at the low-temperature shoulder of Snoek-Köster peak (LTS-SK) was found in Fe–0.39C–9.8Ni–1.56Si–2.0Mn steel and its evolution with respect to various aging treatments was investigated. The LTS-SK internal friction peak was found to occur when aged below 373 K. TEM observation confirmed that the ε-carbide precipitated beyond 373 K, providing an evidence that the LTS-SK peak cannot be caused by ε-carbide precipitation. The corresponding evolution on the S-K peak and thermoelectric power (TEP) illustrated that the carbon content in the solid solution decreases due to carbon atoms segregation on the surrounding dislocations during low-temperature aging. The origin of the LTS-SK peak is likely attributed to the interaction between the carbon atoms and twin boundaries in martensite.