Abstract
To understand the microstructural evolution of a pearlitic rail steel during rolling–sliding contact friction, phase structure and mechanical properties of deformed layers, from top surface to inner matrix, were investigated gradually by scanning electron microscopy, electron probe microanalysis (EPMA), X-ray diffraction, transmission electron microscopy (TEM) and nano-hardness indentation. Focused ion beam method was used to prepare site-specific TEM specimens to study the thickness-dependent deformed microstructure. After the deformation, a white etching layer (WEL), was formed on the top surface, which appeared in white color under an optical microscope. Quantitative EPMA analysis revealed slightly lower carbon concentration, inhomogeneously distributed within the WEL. According to high-resolution TEM observation and quantitative electron diffraction analysis, it was found that the WEL was indeed composed of uniform nano-grains of martensite and ferrite, where no cementite and austenite were found. All the results supported that the WEL was formed by severe plastic deformation, and the hardness value of WEL reached 12 GPa by nano-hardness indentation.
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