In Situ Photoelectron Spectroscopy for Characterizing the Chemical Evolution of a Carbon Steel Surface by Heat-Treatment

Abstract

The microstructure that governs the nature of carbon steel is determined by the combination of iron and carbon. Ferrite and austenite differ in their arrangements of iron atoms, and they differ from cementite with respect to iron and carbon bonding. In this work, we combine structural studies (X-ray diffraction, scanning electron microscopy, and atomic force microscopy) and synchrotron-based in-situ X-ray photoelectron spectroscopy (XPS) to demonstrate the behavior of the carbon in carbon steel using a thermal annealing process conducted from room temperature to 900 °C in an ultrahigh-vacuum chamber. In situ XPS experiments revealed not only that the chemical states varied depending on depth from the surface but also that the carbide changed into the C-solute phase at temperatures greater than 300 °C. In addition, the steel surface can be oxidized under the very low relative humidity condition (0.1 mbar of water at 550 °C). Our findings provide important insights into the subtle balance of interactions involving the properties of steel that differ between the surface and bulk phases, offering new opportunities to engineer the properties of carbon steel.

Keywords: carbon-steel, in-situ XPS, surface chemical states, Cr Ka2 X-ray source