This paper describes the development of two new grades of Fe-3Cr-3W(Mo) alloys at the Oak Ridge National Laboratory. The two grades are designated as A and B. The higher strength Grade B differs from Grade A in that it contains 0.10 wt % Ta. Both grades, when tested in normalized and tempered conditions, show a good combination of tensile strength and Charpy impact properties. Tensile properties of both A and B are over 150 MPa (20 ksi) higher than the highest strength commercial alloy T23. Grade B has higher creep-rupture strength than the T23 steel for the entire temperature range from 540 to 650°C. Grade B also exceeds creep-rupture strength of modified 9Cr-1Mo alloy (Grade 91) up to 615°C. Grade A exceeds the creep-rupture strength of T23 steel up to 600°C and match its values at the higher temperatures. Both grades have been scaled up to 50-ton-size commercial heats and processed into forgings and hot-rolled plates and bars.

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