Yield stress elevations (Δσ^y) in pressure vessel steels irradiated at intermediate flux and fluence systematically decreased with increasing temperature and decreasing copper and nickel content. Lower stress relief temperature also decreased Δσ^y at bulk copper concentrations greater than about 0.3%. The dependence of Δσ^y on irradiation temperature between 260 and 316°C increased with copper and nickel content and decreased with phosphorous content. When normalized by the average Δσ^y, the fractional temperature dependence correlates with a simple empirical chemistry factor of copper and phosphorous. The correlation predicts data on the irradiation temperature dependence of Δσ^y found in the literature within a standard error of about 0.3 MPa/°C and is consistent with current understanding of hardening mechanisms. However, questions remain about the effects at very low flux and finer scale variations over smaller temperature intervals.