INVESTIGATIONS ON FATIGUE CRACK GROWTH RATE OF MEDIUM MANGANESE STEEL

Abstract

Behaviour of medium manganese steel, widely used in rail-road manufacturing, has been studied under cyclic type of loading. It is found that threshold stress intensity factor is very high as compared to other steels. A pivot point is observed about which crack growth lines seem to rotate. The pivot point is given as ( AK =38 MPa/m, da/dN =4x10-4 mm/cycle). Crack growth data for small specimen were fitted by three growth laws, namely, Paris, Forman and Modified Forman. Out of these, Modified Forman, equation was most fitting, but otherwise differences were not very large. Crack growth points for component fall on one side (left side) of scatter-band of crack growth data for small specimen. Fractography reveals the extremely brittle. nature of medium manganese steel, pointing to its low fracture toughness.