Environmentally Induced Crack Growth of High-Strength Steels under Dynamic Loading Conditions and Hydrogen Evolution Behavior

摘要

The influences of dynamic loading conditions on the environmentally induced cracking under dynamic loading were investigated in two kinds of 1500 MPa grade high-strength steels, a vanadium-added steel (V content: 0.3 percent, 15LA steel) and a vanadium free steel (Vfree steel). The corrosive environment used was a 3 percent Nad + 3g/L NH_4SCN solution at 25deg C. The tests were conducted at the cathodically charged condition with a constant cathodic current density of 3 mA/cm~2. The threshold stress intensity factor of the dynamic SCC, K_(DSCC), under a small vibratory loads superimposed on a sustained load, became lower than K_(ISCC) with larger decrease in 15LA steel than in Vfree steel. The crack growth rate of both steels under low-frequency varying load at a stress ratio R of 0.1 and a stress cycle frequency of 0.1 Hz was enhanced compared with that in dry air due to cyclic stress corrosion cracking, with lower threshold than K_(ISCC)-Similarly to the case of dynamic SCC, the effect of low-frequency varying load was larger in 1 SLA steel than in Vfree steel; a decrease of threshold value, K_(DSCC), from K_(ISCC) was larger in 1 SLA steel. The hydrogen evolution rate obtained by gas chromatograph with heating system was increased by the cathodic charging, with a lower temperature peak. The noticeable difference in the hydrogen evolution behavior between the two steels was that the hydrogen evolution rate increased over 80t in 15LA steel, but did not in the Vfree steel.