Effects of Mo and W Contents on Creep Rupture Strength and Toughness of a 10% Cr Heat Resistant Steel

Abstract

With the Mo equivalents (wt%Mo+1/2 wt%W) being within the range of 1.2-1.6%, the effects of Mo and W contents on creep rupture strength and toughness have been investigated for a 10 Cr heat resistant steel.
(1) With the Mo equivalent being a constant of 1.2, variation in W and Mo contents shows little effect on the toughness and on the creep rupture properties at under 600°C as well as on the short-term side of higher temperatures, but the steel containing more W shows higher creep rupture strength on the long-term side of 700°C.
(2) The steels containing more Mo or W show lower toughness when heated at 600°C, but increased creep rupture strength at 600°C as well as on the short-term side of higher temperatures. The change is related to the fact that the increase in Mo or W content enhances both solution hardening and precipitation hardening under the conditions mentioned above. However, the increase in Mo or W content has no any beneficial effect on the long-term creep rupture strength at above 650°C. The increased coarsening tendecy of precipitates resulting from the increase in Mo or W content was considered the factor detrimental to the creep rupture strength on the long-term side at above 650°C.
(3) The steels developed in this study show a extrapolated 10⁵ h creep rupture strength of as high as 15-20 kgf/mm² at 600°C and 7-9 kgf/mm²at 650°C. It is evaluated that these steels would be applicable at up to 621°Cas the rotor material.