MICROSTRUCTURAL EFFECTS ON FATIGUE AT INTERMEDIATE AND HIGH CRACK GROWTH-RATES IN A LOW-ALLOY STEEL

A commercial 0.5Cr0.5Mo0.25V steel has been heat treated to produce a wide range of microstructures (ferrite, bainite and martensite), yield stresses (285-834 MPa) and toughnesses. The fatigue properties have been investigated at intermediate and high fatigue crack growth rates. The ferritic microstructures have the lowest toughness and fractography reveals the isolated incidence of a cleavage static mode which gives a slight increase in the growth rate. The exponent m in the Paris law is found to decrease with increasing yield strength and toughness, the change being greatest at the lower load ratio. The exponent m is found to be greater for R = 0.1 than for R = 0.4 over the whole range of microstructures. © 1979.