The Influence of Hydrogen on the Low Cycle Fatigue Behavior of Medium Strength 3.5NiCrMoV Steel Studied Using Notched Specimens

The influence of hydrogen on low cycle fatigue (LCF) of 3.5NiCrMoV steel electrochemically hydrogen charged in the acidified pH 2 0.1 M Na₂SO₄ solution is studied. In the presence of hydrogen, the fatigue life decreases significantly by ≈70 to ≈80% by: (i) the crack initiation period is decreased; and (ii) the crack growth rate is accelerated. SEM observation indicates that in the presence of hydrogen, the fracture surface shows flat transgranular fracture with vague striations and some intergranular fracture at lower stresses. The fatigue crack growth rate increases with increasing cyclic stress amplitude and with hydrogen fugacity. Once the fatigue crack reaches a critical length, the specimen becomes mechanical unstable and fracture due to ductile overload occurs. The hydrogen contribution to the final fracture process is not significant.