Abstract
Low-and high-cycle fatigue properties of quenched and tempered SCM435 steel were investigated at R=-1 in 0.7 MPa H_2 gas, 0.1 MPa N_2 gas and air using round specimens with a small artificial hole (d=100 μm). At σ_a=500 MPa (low-cycle fatigue), N_f at 2 Hz in N_2 and air was almost the same. N_f at 2 Hz and 0.2 Hz in H_2 was shorter than N_f at 2 Hz in N_2 and air. However, N_f at 0.02 Hz in H_2 was almost the same as N_f in N_2 and air. That is, N_f is the shortest at f=0.2 Hz in H_2. At σ_a=300 MPa〜400 MPa (high-cycle fatigue), N_f at 20 Hz in H_2 and N_2 was longer than N_f at 20 Hz in air. In addition, calculating strain intensity factor range ΔK_ε by cyclic stress-strain curve, the da/dN-ΔK_ε curve for short crack obtained by round bar specimens with a small artificial hole at σ_a=500 MPa was coincident with the da/dN-ΔK_ε for long crack obtained by CT specimens.
