The fracture toughness and the fatigue crack growth properties of heat treated SNCM439 steel were investigated under high pressure of hydrogen up to 9.9MPa at room temperature.
The results obtained are as follows;
(1) The fracture toughness, KQ value, of the steel in hydrogen was smaller than that in argon independent of heat treatments. KQ values of the quenched and the tempered steel were smaller than that of the annealed steel in hydrogen. On the fracture surface of these steels, the streched zone was not observed in hydrogen but in argon.
(2) The fatigue crack growth rate of the steel in hydrogen was larger than that in argon, and KFc of the steel in hydrogen was smaller than that in argon independent of heat treatments. The order to hydrogen susceptibility of fatigue crack growth properties increased from the annealed to the quenched and then to the tempered steel.
(3) The quasi-cleavage fracture did not occur in argon but in hydrogen on the fatigue fracture surface of the annealed steel. Both the amount of the intergranular fracture and the surface roughness of the transgranular fracture in hydrogen were larger than those in argon on the fatigue fracture surface of the quenched and the tempered steels.
