Effect of residual stresses and strain hardening on changing in corrosion cyclic crack resistance of vessel steels

An attempt is made to establish regularities of near the threshold development of corrosion-fatigue cracks in vessel steels, depending on the level of residual stress (RS) and cold hardening, conditioned by sheet straigthening taking into account crack closing (CC). Two chromium-nickel-molybdenum steels with the sorbite structure, yield strength of which constituted aproximately 800 and 1000 MPa, were investigated. During tests in the air the effect of technological treatment on cyclic crack resistance of steels by the change in CC. A satisfactory correlation between the level and sign of RS, localized in near the surface layers of the material, as well as in the change of CC and ΔKth (constituent value of crack development threshold) as a result of the straightening is obtained. It testifies to the determining role of RS in the formation of cyclic crack resistance thresholds. The role of cold hardening of the material in the formation of crack resistance thresholds in the air is insignificant, however, it increases considerably under the effect of corrosive medium. Cold hardening suppresses the positive effect of aqueous medium, i.e. it weakens CC and decreases fatigue crack growth resistance due to increase in the material tendency for hydrogen emrittlement