Fracture toughness and fatigue crack growth of AISI 4340 steel in high pressure hydrogen at room temperature

摘要

The fracture toughness and the fatigue crack growth properties of the annealed, quenched and quenched-tempered AISI 4340 steel were investigated in high pressure hydrogen up to 9.9 MPa at room temperature. The effect of gaseous inhibitors addedto hydrogen atmosphere on the fatigue crack growth of the steel to prevent hydrogen assisted fatigue crack growth was also examined. The following conclusions were drawn from the results:(1) The fracture toughness of the quenched steel both in argon and in hydrogen were almost constant at the stress intensity rate range tested. In all conditions of heat treatment the fracture toughness in hydrogen was smaller than that in argon anddecreased with increasing hydrogen pressure.(2) The fatigue crack growth of the steel in hydrogen was higher than that in argon in all conditions of heat treatment. The order of hydrogen susceptibility of the heat treated steal was as follows; the annealed steel < the quenched one < thequenched-tempered one.(3) Carbon monoxide, oxygen or sulfur dioxide has much effect on preventing hydrogen assisted fatigue crack growth, hut carbon dioxide, methane, water vapor or methyl mercaptan had little effect. On the other hand, hydrogen sulfide accelerated thefatigue crack growth.