Plate and weld material of ASTM A533 Grade B, Class 1 steel furnished by the Heavy Section Steel Technology Program was characterized for irradiation strengthening and fracture embrittlement. Plane strain fracture toughness, K _Ic, in the longitudinal orientation was determined ftom specimens irradiated at 540 F (282 C) to neutron fluence levels of 2 and 8 × 10¹⁹ n/cm² (E > 1 MeV); longitudinal tension specimens were irradiated at 510 F (265 C) at 2, 4, 6, and 8 × 10¹⁹ n/cm² (E > 1 MeV). Yield strength was more sensitive to irradiation strengthening than the ultimate strength, and the yield strength increase (Δσ_ys, ksi) as a function of fluence (Ф) and temperature (T, deg. F) may be described by:

Δσys = 22 [1- exp (-Φ/5 × 1018)] + Φ/1019(4.3−0.0038T)

Irradiation levels of 2 and 8 × 10¹⁹ produced shifts of 185 F (103 C) and 275 F (153 C) in the 50-ksi√in K_Ic fracture toughness transition of A533 plate; the measured shifts agree closely with those predicted, 153 F (85 C) and 282 F (157 C), from a proposed correlation of shift in transition and change in yield strength. Fracture toughness K_Ic and tensile properties of plate material were independent of the orientation. The fracture toughness of ASTM A533-B submerged-arc weldment metal irradiated at 540 F (282 C) to a fluence of 3 × 10¹⁹ n/cm² (E > 1 MeV) exhibited a marked sensitivity for irradiation embrittlement; the indicated shift of the 50-ksi√in K_Ic fracture toughness transition level was approximately 390 F. The yield and ultimate tensile strengths of ASTM A533-B sub-arc weld were determined for 510 F (265 C) irradiations to fluences of 0.5 × 10¹⁹ n/cm² and 4.0 to 4.6 × 10¹⁹ n/cm² (E > 1 MeV). Irradiation strengthening of weld yield properties is slightly greater than the longitudinal base properties.