Low cost grain refined steels as alternative to conventional maraging grades

摘要

It is proposed that Fe-12 percent Ni steels alloyed with 1 or 2 percent AI, and 1 percent Mo for pitting resistance, may offer a steel competitive with 18Ni (300) maraging steel in strength and toughness, but at one-third of the alloy cost. Previous alloy development research with a similar objective based on Fe-Cu alloys is reviewed. Although aging binary iron alloys containing up to 6 percent Cu at 485 deg C leads to considerable increase in hardness, impact energies are very low owing to intergranular failure. Alloys containing 4 percent Cu alloyed with 9 percent Ni to increase hardenability, hot workability and impact toughness showed no edge cracking on forging to 1 in (25 mm) plate at 1050 deg C. Grain refining the same alloy with 0.24 percent Nb and 0.04 percent C resulted in a ductile-brittle transition temperature below -100 deg C in the aged condition. The balancing of Nb and C contents for grain refinement in martensitic steels is discussed. To increase hardness, additions of 0.9 percent AI and 1.6 percent AI were made to the grain refined steel containing 4 percent Cu and 9 percent Ni. This resulted in considerable increments in hardness on aging at 450 deg C, but the alloys are no longer commercially viable owing to the high cost of Cu. Work on the proposed cost competitive Fe-12Ni-( 1-2)Al-1 Mo grain refined steel is continuing.