Effect of isothermal temper embrittlement and subsequent hydrogen embrittlement on tensile properties of 2.25Cr–1Mo–0.25V base metal and welded metal

2.25Cr–1Mo–0.25V base metal (BM) and welded metal (WM) with different temper embrittlement states were obtained by isothermal temper embrittlement test. The ductile–brittle transition temperature and the carbide size of temper embrittled 2.25Cr–1Mo–0.25V BM and WM increased with the isothermal tempering time. The increase in temper embrittlement time leads to a decrease in yield strength (YS) and ultimate tensile strength (UTS). Hydrogen embrittlement (HE) can decrease the ductility and increase YS and UTS of the material. The hydrogen embrittlement sensitivity and microstructure analysis both show a combined effect of HE and temper embrittlement. The deeper the temper embrittlement, the more sensitive the material to HE. When the hydrogen content in the material is low, the WM is less susceptible to HE due to its welding defects.