Effect of stress relief temperature and cooling rate on pressure vessel steel welds

The compositions of the matrices of welds in a pressure vessel steel have been determined by atom probe tomography after a series of stress relief treatments. The weld had a bulk composition of Fe–0.29 at.% Cu–1.69 at.% Mn–0.54 at.% Ni–0.69 at.% Si–0.25 at.% Mo–0.08 at.% Cr–0.38 at.% C–0.022 at.% P–0.017 at.% S and was characterized in the as-welded state, after stress relief treatments of 24 h at 650 °C, 24 h at 610 °C, and 100 h at 580 °C followed by slow cooling to room temperature and after 24 h at 650 °C and 24 h at 610 °C followed by fast cooling to room temperature. Lower stress relief temperatures and slower cooling of the material from the stress relief temperature to room temperature both reduce the copper level in the matrix and should lead to less embrittlement during service in a nuclear reactor.