Fatigue Fracture of Steel with a Ferrite-Martensite Composite Structure

In this paper, we present results of fatigue tests a natural steel composite material for cyclic bending by zero-loading cycle. Natural ferrite-martensitic (NFMC) has structure alternating layers ductile ferrite and strong martensite, which causes special mechanism crack retardation under loading. The cycle assumes the presence tensile forces directed only in one direction, makes it possible to avoid hardening edges during its growth. Using obtained data on kinetics development rate growth, diagram failure was constructed depending number vibration cycles. Test samples from chemical composition are compared. case, traditional heat treatment carried out tempering sorbitol. other layered ferrite-martensite quenching initial line ferrite-pearlite intercritical temperature range. These materials had same hardness, but difference structural organization determined advantage with NFMC terms fracture resistance When approaches martensite-ferrite interface, delamination occurs due stresses parallel plane. growth stops until additional energy formation new conditions close uniaxial stress state is supplied. A technique determining characteristics loading, recommended testing steels alloys load changes, presented.