The Mössbauer Spectroscopy Studies of ϵ to Cementite Carbides Transformation during Isothermal Heating from As-Quenched State οf High Carbon Tool Steel

Abstract

This work presents results of investigations using the Mössbauer spectroscopy technique and their interpretation concerning transformation of to cementite carbides during tempering in relation to the previously conducted dilatometric, microscopic and mechanical investigations. Investigations were performed on 120MnCrMoV8-6-4-2 steel. The influence of the tempering time on nucleation and solubility of carbides, and on cementite nucleation and growth, was determined. The analysis of phase transformations during various periods of tempering using the Mössbauer spectroscopy technique made possible to reveal fine details connected with the processes.

Mössbauer spectroscopic investigation of retained-austenite content of high-carbon tool steel during isothermal tempering of as-quenched samples

“…On the basis of the results obtained by us and presented in paper [26], one can conclude that most probably the increased stability of retained austenite results from dissolution of ε carbides in the martensitic matrix. This leads to an increase in carbon concentration in martensite, resulting in a decrease in driving force of carbon diffusion from austenite to austenite-martensite boundaries.…”

“…Analyzing the obtained Mössbauer spectra ( Fig. 1 and [26]) one can notice that when the tempering time increases, the amount of retained austenite in structure of the examined steel also increases (double peak). In Fig.…”

“…1. Further spectra were published in paper [26]. It has been shown [1,2] that during continuous tempering from quenched state, cementite (Fe 3 C) nucleates independently at lath boundaries and twin boundaries of martensite.…”

“…Analyzing the changes in isomeric shift with tempering time, one may note that after 1 h of tempering, stresses in austenite decrease slightly, in comparison with tempering for 0.5 h. This results from the precipitation of ε carbides from martensite, leading to a decrease in its volume, therefore also in stresses exerted on austenite located between martensite laths. Renewed minimal increase in isomeric shift after 1.5 h should be attributed to start of ε carbides dissolution and cementite precipitation [26]. That is why carbon concentration in martensite has increased again, leading to chemical stability of retained austenite (no driving force for diffusion of carbon from retained austenite to martensite).…”

“…Many works [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] showed that Mössbauer spectroscopy gives a possibility to obtain new data, which may help more detailed interpretation of the phenomena connected with phase transformations during tempering. This paper presents the results of investigations using Mössbauer spectroscopy and their interpretation concerning retained austenite transformation during isothermal heating from as-quenched state in relation to previously conducted dilatometric and microscopic investigations [1,2].…”