The Mossbauer Spectroscopy Studies of Cementite Precipitations during Continuous Heating from As-Quenched State of High Carbon Cr-Mn-Mo Steel

This work complements the knowledge concerning the kinetics of cementite precipitation during tempering. Investigations were performed on 120MnCrMoV8-6-4-2 steel. The samples of investigated steel were austen- itized at the temperature of 900±C and quenched in oil. Then four of five samples were tempered. Tempering consisted of heating the samples up to chosen temperatures at the heating rate of 0.05±C/s and fast cooling after reaching desired temperature. This work presents the results of investigations performed carried out using the Mossbauer spectroscopy technique and their interpretation concerning cementite nucleation and growth during tempering. The values of hyperfine magnetic field on 57Fe atomic nuclei, determined for the third component of the Mossbauer spectrum as regards to its intensity, indicate that these are the components coming from ferro- magnetic carbides. Big differences in hyperfine magnetic fields coming from Fe atoms existing in the structure of carbides, measured on samples heated up to the temperatures of 80±C and 210±C, in comparison with values for 57Fe atoms precipitated from carbides during heating up to the temperaturę of 350±C and 470±C, allow to state that these are the carbides of different crystal structure. The influence of hardened steel heating temperature on cementite precipitation was determined. The Mossbauer spectroscopy was applied not only for magnetic hyperfine fileld studies, but also to analyze the values of quadrupole splitting and isomeric shift, which resulted in significant conclusions concerning the changes in cementite precipitations morphology, chemical composition and the level of stresses being present in this research