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The technology of microalloyed steels is expanding beyond its original emphasis on low-carbon, severely contro/-roI/ed stripand plate products. A lltIriefy of economical, highstrength, tough , as-rolled or as-forged microalloyed products are replacing more expensive heat-treated steels. Recrystallization-controlled rolling is being utilized to produce very fine ferrite grain sizes and good toughness in strip, plate and bar products processed with relatively high rolling temperatures. High-strength microalloyed long products such as railroad joint bars, truck frame rails and flat bars for truck trailer construcl ion are replacing heat -/ reated ~rls. Microalloyed, medium-carbon forging steels are used extensively for automobile engilzc and suspension components. Fully pear/We high-carbon rods are being microalloyed to £llhanee the properties of wire and springs.

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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