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Medium-temperature steels used for pressure vessels include Mo steel, Cr-Mo steel, and Cr-Mo-V steel, with a service temperature range of 400–600°C. In pressure vessels used in the petroleum and chemical industries, the media often contain hydrogen, and under certain temperatures and hydrogen partial pressures, this can cause hydrogen corrosion of the steel. The above-mentioned medium-temperature steels containing Mo, Cr, and V all possess a certain degree of resistance to hydrogen corrosion; therefore, they are also used as hydrogen-resistant steels in pressure vessels in the petroleum and chemical industries. The specific material to be chosen should be determined based on the medium temperature and hydrogen partial pressure, following the Nelson curve. Commonly used steel grades for medium-temperature applications abroad include 0.5Mo, 0.5Mo-0.5Cr, 0.5Mo-1Cr, 0.5Mo-1.25Cr, and 1Mo-2.25Cr; these grades are classified based on their alloy element content and hydrogen resistance. The main domestic equivalent and similar steel grades are as follows. (1) Steel plates: 15CrMoR, 14Cr1MoR, 12Cr2Mo1R, 12Cr1MoVR, 12Cr2Mo1VR. (2) Steel pipes: 12CrMo, 15CrMo, 12Cr2Mo1, 1Cr5Mo, 12Cr2MoVG. (3) Forgings: 35CrMo, 15CrMo, 14Cr1Mo, 12Cr2Mo1, 12Cr1MoV, 12Cr2Mo1V, 12Cr3Mo1V, 1Cr5Mo. (4) Bolts: 30CrMoA, 35CrMoA, 35CrMoVA, 25Cr2MoVA, 40CrNiMoA, 1Cr5Mo (new grade S45110).