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The effect of residual and stabilizing elements on toughness has been investigated for a series of 18Cr-2Mo ferritic stainless steels which contained 0.015C and 0.015N. The residual elements varied were sulfur, manganese, and silicon. The stabilization variables were niobium, titanium, (Nb + Ti), and (Nb + Al).
The impact transition temperature was determined in the base metal and weld deposit for all steels. Crack opening displacement (COD) measurements were made on selected steels in the welded condition and a COD transition temperature was determined for these.
Over the ranges investigated, sulfur, manganese, and silicon had only minor effects on the base metal and welded impact toughness.
The best base metal impact toughness was achieved with a combination of (Nb + Al) stabilization. A niobium-stabilized steel to which 0.5 percent aluminum had been added exhibited a FATT50 (fracture appearance transition temperature) of -60°C. Niobium stabilization and (Nb + Ti) stabilization gave transition temperatures intermediate between (Nb + Al) combination and titanium-stabilization.
The (Nb + Al) stabilizer combination also gave the best weld metal impact toughness with a FATT50 of approximately 25 °C; however, the steel had limited weld ductility. The niobium-stabilized steels had higher weld impact transition temperatures than the titanium-stabilized steel, with the mixed (Nb + Ti) combination being intermediate between them.
The (Nb + Ti) stabilized steel had the best COD fracture toughness and seems to be the best stabilizer choice for a combination of base metal and welded toughness and ductility.
ferritic stainless steels, 18Cr-2Mo stainless steel, impact toughness, crack opening displacement (cod), fracture toughness, transition temperature
Manager, Stainless Steel Development, Climax Molybdenum Co., Pittsburgh, Pa.