Mossbauer study of the annealing effect on low-alloyed steels

Structural analyses of Fe-Cr and Fe-Cr-Ni low-alloyed steels before and after annealing at 600 degreesC using Mossbauer spectrometry, X-ray diffraction and scanning electron microscopy are reported. At the received state, the two steels present a fine bainitic microstructure with equal hardness. From Mossbauer analysis, two iron sites are identified as substitutional by Cr, Mo, Ni atoms and as insertional by carbon in bainitic ferrite. Both sites are locally deformed by residual stresses. The presence of small quantities of retained austenite and epsilon carbide has been observed. Annealing for one hour at 600 degreesC causes a decrease in hardness for both steels with a decrease of retained austenite. After longer time of annealing, precipitation of (Fe,Ni)(23)C-6 occurs in the Fe-Cr-Ni steel and increases hardness.