HYDROGEN FATIGUE RESISTANT FERRITE STEEL AND MANUFACTURING METHOD THEREOF

A ferritic steel having tensile properties and fatigue properties capable of withstanding use in a hydrogen environment and a method of manufacture thereof are provided. By adding one or more element selected from among vanadium (V), titanium (Ti) and niobium (Nb) so that the steel includes, together with at least ferrite grains in the structure, a carbide or carbides of one or more element selected from among V, Ti and Nb, the reduction of area and the fatigue crack propagation rate of the ferritic steel in a hydrogen environment are improved. The advantages of the invention were confirmed in cases where the ferrite grains are small grains of 1 µm or less in size, and in cases where the ferrite grains are coarse grains from several micrometers to 20 µm in size, and moreover in cases where the ferrite grains are coarse grains from several micrometers to 60 µm in size.