Abstract
Fatigue crack growth properties under freely corroding and cathodic protection in 3%NaCl aqueous solution were studied under very-low cycling for HT80 high tensile and SUS304 stainless steels. The crack growth rate in 3%NaCl solution was accelerated as compared with that in air. The acceleration was dependent on material, environment, ΔK-level and frequency, and the following three types of acceleration was observed.
(1) The CF type acceleration was inherent to corrosion fatigue in free corroding and the rate was accelerated about twice at frequencies lower than 0.3Hz independently of material and ΔK level.
(2) The HE(IG) type was related to the intergranular cracking due to hydrogen embrittlement and appeared in the range of ΔK from 4 to 20MPa·m1/2 and at frequencies from 10-3 to 102Hz only for HT80 steel. The maximum acceleration rate became about five times at ΔK=10MPa·m1/2 and f=0.3Hz.
(3) The HE(TG) type was related to the transgranular and brittle fracture due to hydrogen embrittlement and the rate became constant at frequencies lower than 0.03Hz. This type was also dependent on material, environment and ΔK level. The maximum acceleration rate was nearly thirty and ten times for TH80 and SUS304 steels, respectively.
