Research is under progress for developing fuel-cell vehicles that use hydrogen as a fuel to travel, and deploying hydrogen stations that supply hydrogen to such fuel-cell vehicles. Stainless steel is one of the candidate materials that can be used for such applications. However, in a high-pressure hydrogen gas environment, even stainless steel may be embrittled by hydrogen gas (hydrogen-environment embrittlement). The standards for pressurized-hydrogen containers for automobiles specified by the High-Pressure Gas Safety Law permit the use of SUS316L as a stainless steel that does not suffer from hydrogen-environment embrittlement.
However, in order to achieve light-weight fuel-cell vehicles and compact hydrogen stations and address the necessity of high-pressure operation of hydrogen stations, it is desired that a stainless steel for use in a container or joint or piping do not suffer from hydrogen-environment embrittlement in a hydrogen-gas environment and have a high strength not lower than SUS316L, as is conventional. In recent years, high-strength steels have been proposed that have a high N content and use the resulting solute strengthening and fine-particle nitrides, as disclosed in WO 2004/111285, WO 2004/083477, WO 2004/083476, and Japanese Patent No. 5131794.