Metallurgical aspects and closure maps of fatigue crack growth of alloy steels part I : Effect of second phase on crack closure

The role of second phase in AISI 4330 steel on the fatigue crack closure has been investigated. The mixed microstructure of upper bainite-martensite shows a better fatigue crack growth (FCG) resistance in the near threshold region than the fully martensitic structure steel due to increase in roughness induced closure stress.