The effect of postweld heat treatment on the susceptibility to temper embrittlement of 2¼Cr-1Mo steel forgings which have various silicon contents has been investigated. Then, to verify the validity of low-silicon 2¼Cr-1Mo steel for an actual forging, the mechanical properties and the susceptibility to temper embrittlement of a 296-mm (11.7-in.)-thick forged ring made from a 100-ton ingot with silicon content reduced to below 0.10 percent by the vacuum carbon deoxidation (VCD) process have been tested. The results are as follows: (1) the through-thickness mechanical properties of the forging meet the requirements of ASME SA-336, F22; (2) silicon content has no significant effect on the creep-rupture strength at least to 15 000 h at 550°C (1022°F) and 600°C (1112°F); and (3) the susceptibility to embrittlement is very low, as the shift in 50 percent fracture appearance transition temperature is 14°C (25°F) for step cooling and 22°C (40°F) for isothermal treatment at 475°C (887°F) for 5000 h.