Effects of atomic hydrogen and flaking on mechanical properties of wheel steel

The effects of atomic hydrogen and flaking on the strength, plasticity, fracture toughness, and hydrogen-induced delayed cracking (HIDC) of a wheel steel were investigated. The results showed that the critical diffusible (C*(0)) or total (C*(T)) hydrogen concentration for forming flaking were C*(0) = 1.3 ppm and C*(T) = 3.7 ppm, respectively. There was no effect of flaking on the strength, plasticity, and fracture toughness if the amount of flaking was low, e.g., diffusible hydrogen concentration C-0 <= 3.9 ppm. Atomic hydrogen had no effect on the fracture toughness and the mechanical properties extended with normal strain rate. Atomic hydrogen, however, had the effect of reducing the plasticity during slow strain rate tests and induced delayed failure under constant displacement. The threshold stress intensity factor of HIDC, K-1H, decreased linearly with the diffusible hydrogen concentration C-0, i.e., K-1H(MPam(1/2)) = K-IC - 3.6C(0) (ppm) (0.2 <= C-0 <= 03.9). The HIDC Could be partly attributed to hydrogen-induced additive stress. There was no effect of flaking on HIDC.