The effects of thermal cyclic aging on mechanical properties and microstructure of maraging steel 250 were studied using hardness tester, tensile testing machine, impact tester, optical, scanning electron, and stereo microscopy. Samples were solution annealed at 1093 K for 1 h followed by air cooling to form bcc martensite. Cyclic aging treatments were carried out at 753 and 773 K for varying time periods. Increase in hardness and strength with corresponding decrease in ductility and impact strength was observed with increasing aging cycles. Reverted austenite was detected by x-ray diffraction technique formed as a result of cyclic aging. The presence of reverted c was also confirmed by EDX-SEM analysis and attributed to the formation of Mo- and Ni-rich regions which transformed to c on cooling. Heterogeneity in composition and amount of reverted c was found to increase with increase in aging cycles and aging time. Fractography reveals the change in fracture mode from ductile dimple-like to brittle cleavage with increase in hardnessand strength due to cyclic aging. |
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