Effect of deep cryogenic treatment on surface chemistry and microstructure of selected high-speed steels

Abstract

The purpose of this study is to provide a systematic, complementary research of deep cryogenically treated (DCT) steels AISI M2, M3:2 and M35 including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD) and X-ray photoelectron spectroscopy (XPS). The DCT effect on selected steels was analyzed through modification of microstructure, chemical composition, phase change and chemical state of the present elements, when comparing conventional heat-treated (CHT) and DCT samples. The XPS results provide input into the understanding of oxidation dynamics of DCT samples and DCT influence on the microstructure using EBSD, as the major interpretation tool. It is confirmed, that martensitic laths are sharper, smaller and generally more oriented along specific crystal directions of prior austenite grains within DCT samples compared to CHT counterparts. A first-time evaluation of oxidation states and oxygen absorbance of the surface of selected high-speed steels is conducted with XPS, which is correlated with the microstructural changes induced by DCT. Depth profile XPS analysis of CHT and DCT samples was also conducted that shows the oxidation layer thickness and elemental gradients. These results provide further understanding of DCT dynamic on the overall microstructure and the corresponding surface behavior of the selected steels.