Structural and phase transformations in Hadfield steel upon frictional loading in liquid nitrogen

Abstract

Structural transformations that occur in 110G13 steel (Hadfield) upon sliding friction in liquid nitrogen (–196°С) have been investigated by metallographic, electron-microscopic, and X-ray diffraction methods. The frictional action was performed through the reciprocating sliding of a cylindrical indenter of quenched 110G13 steel over a plate of the studied steel. A like friction pair was immersed into a bath with liquid nitrogen. It has been shown that the Hadfield steel quenched from 1100°С under the given temperature conditions of frictional loading retains the austenitic structure completely. The frictional action forms in a surface layer up to 10 μm thick the nanocrystalline structure with austenite grains 10–50 nm in size and a hardness 6 GPa. Upon subsequent low-temperature friction, the tempering of steel at 400°С (3 h) and at 600°С (5 min and 5 h) brings about the formation of a large amount (tens of vol %) of ε (hcp) martensite in steel. The formation of this phase under friction is supposedly a consequence of the reduction in the stacking fault energy of Hadfield steel, which is achieved due to the combined action of the following factors: low-temperature cooling, a decrease in the carbon content in the austenite upon tempering, and the presence of high compressive stresses in the friction-contact zone.