A Study of the Growth Mechanism of Lenticular Carbides in Cyclically Stressed 52100 Steel

Abstract

The deformation bands which form in cyclically stressed AISI 52100 steel inner rings (during rolling contact) are studied by transmission electron microscopy. These deformation bands are regions where the temper carbides have dissolved and a well-developed cell structure has formed. Many of the deformation bands are bordered by lenticular-shaped carbides which form after prolonged cyclic stressing. The deformation bands were tempered in the electron microscope and most were found to be free of excess carbon since no precipitation of carbides occurred at normal tempering temperatures. In one specimen there was profuse precipitation of carbides at the cell walls indicating that an excess of free carbon had segregated around dislocations. It is concluded the regions free of excess carbon are due to the nucleation and growth of a lenticular carbide while no lenticular carbide formed at the deformation band which was supersaturated with carbon.