250° C Internal Friction Peak in Iron

Abstract

WE read with interest the communication by Rosenfield¹ regarding the 250° C internal friction peak in iron, and would like the opportunity of commenting on the inferences and conclusions made in it. Previous work by Köster et al.², more recently confirmed by Petarra³, has established a unique relationship between the Snoek peak (43° C for ∼ 1 c/s) and the 250° C peak for the cases of dilute iron–nitrogen and dilute iron–carbon alloys. A dependence² of the 250° C peak height on the degree of deformation, and therefore on the dislocation density in the specimen, was also found for these alloys. Unpublished work in this Department on the 250° C peak has shown that either carbon or nitrogen or both elements are essential for the appearance of the peak. Furthermore, after a decarburization treatment, specimens of pure iron showed no evidence at all of a 250° C peak on subsequent testing. This treatment (moist hydrogen) could certainly have introduced oxygen into the specimens.