Process effects on white layer formation in hard turning

This paper discusses surface microstructural alterations in hard turned steels. A metallurgically unetchable structure, called "white layer", followed by a dark etching layer has been found on AISI 52100 steel surfaces machined in a hardened state (60 Rc). The scale of this white layer depends upon cutting process parameters, specially tool wear and cutting speed. White layer depth was measured using image processing on samples prepared by standard metallographic techniques. White layer depth increases with flank wear. It also increases with cutting speed, but reaches an asymptote at high speeds. On the other hand, depth of cut shows almost no effect on white layer depth; and increasing feed rate only makes the white layer slightly deeper. White layer formation is discussed in the context of phase transformations, and its influence on machined surface structures is considered for future work.