Surface Structure of Grade-U8 Steel after Processing by Deforming Cutting

The structure of grade-U8 steel after high speed processing by deforming cutting is studied. The phase composition and structural features of a hardened surface layer comprised of separate areas (so called ribs) in close with each other are established. While applying the methods of optical and electron microscopy in the near-tool bit area of the rib, the following features are detected: nonequilibrium ferrite and coarse acicular martensite with crystal sizes of about 100 nm, parquet martensite-like structures with plate widths of tens of nanometers, as well as cementite crystals of various sizes from 10 to 100 nm. Such a heterogeneous structural state occurs in the rib area in contact with the tool bit during processing by deforming cutting. The structure of the opposite rib area is cardinally different and comprised of equiaxed ferrite grains with a size of ~500 nm and with fine boundary depositions (presumably carbides) with a size of 10–20 nm.