Effect of W on Creep Properties of 9Cr-3W-3Co-Nd-B Steel Weld Metals

ASME Gr. 93 steel is a heat-resistant steel, in which creep strength is increased by adding elements such as W and B to the conventional 9% Cr ferritic heat-resistant steel. An investigation has been conducted on the effects of W addition on the creep rupture time and metallographic structure of weld metals for Gr.93 steel. The results of the creep rupture test on weld metals with varying additions of W show that creep rupture time increases with the increasing amount of W. Observations of specimens thermally aged at 650℃ have confirmed the presence of the Laves phase, suggesting that the increase in creep rupture time is attributable to particle dispersion strengthening by the Laves phase. Increasing the additive amount of W increases the number density of the Laves phase and, furthermore, suppresses the coarsening of the Laves phase during thermal aging. The coarsening rate of the Laves phase during thermal aging has been in good agreement with the calculated value obtained from the theoretical equation for Ostwald ripening. Like M23C6, the Laves phase may contribute to the creep strengthening by suppressing the coarsening of the lath size. © 2023 Kobe Steel Ltd. All rights reserved.