Structure and phase composition of surface zones of carburized and carbonitrided layers

Abstract

1. Mossbauer spectroscopy makes it possible to detect the following iron-containing phases in the surface layers of carburized and carbonitrided samples: martensite, austenite, cementite, and iron oxides. 2. The quantities of these phases depend on the conditions of the chemicothermal treatment and can be used to judge the quality of the treatment with the proper correction factor. 3. The layer nearest the surface is most sensitive to the quality of the chemicothermal treatment (a layer ∼0.1 μ deep) in which the spectra of iron oxides are observed along with those of compounds characteristic of the Fe-C system. 4. With chemicothermal treatment in an endothermal atmosphere, a high concentration of iron oxides is observed in surface zones as thick as 1 μ. The higher the concentration of alloying elements with a large affinity for oxygen in the solid solution, the larger the total concentration of oxides. 5. No oxides are observed on the surface of samples carburized in an atmosphere of methane at a pressure of 10−3 mm Hg.