EFFECT OF INTERNAL HYDROGEN ON THE FATIGUE CRACK-GROWTH OF A 12CR-1MO STEEL

Internal hydrogen concentration of 4 appm were found to have a significant effect on the fatigue crack growth rate of a 12Cr-1Mo steel tested at 25°C. This effect was most pronounced at ΔK values lower than about 15 MPa√m for tests conducted at a load ratio of 0.5. Hydrogen induced an intergranular fracture mode that increased in percentage of the total fracture with decreasing crack velocities at decreasing ΔK values. Hydrogen has been shown to induce intergranular fracture in this steel in percharged and dynamic tensile tests and in subcritical crack growth tests at cathodic potentials. The fatigue crack growth rate of both the hydrogen-charged and uncharged material was a function of the cyclic frequency between frequencies of 0.2 and 5 Hz; the fatigue crack growth rate increased with decreasing frequencies or increasing period. There is some evidence that the as-received hydrogen concentration of 1 appm affected the crack growth rate.