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Abstract:
Maraging steels are precipitation-hardened steels that show an improvement in nearly 80 pct of strength when aged to temperatures of 500 °C, but on aging to temperature higher than this, they rapidly start to lose their strength due to the formation of large fractions of reverted austenite. In this study, 70 pct cold-rolling deformation is induced prior to aging to increase the density of dislocation interfaces. Consequently, the material also develops a dual {111} (67 pct) and {100} (33 pct) micro-texture, which suppresses the formation of reverted austenite, even upon aging to temperatures of 540 °C. Therefore, the strength of the material is retained. On the other hand, cold rolling also leads to an increase in the density of defect interfaces, which allows for the nucleation of precipitates to be accelerated. The coherent precipitate formed during peak-aging conditions contains more Fe and does not re-dissolve into the matrix when aged at 540 °C, unlike in the hot-rolled counterpart. The lack of dissolution of a significant fraction of Ni-rich precipitates prevents local Ni enrichment required for the nucleation of austenite. At the peak-aged condition, there is a 60 pct increase in strength, 50 pct decrease in strain to failure, and a 40 pct increase in initiation fracture toughness as compared to the as-solutionized cold-rolled condition, a condition that is challenging to achieve considering the strength–ductility trade-off. However, with predominantly coherent precipitates in place, planar slip continues to be the preferred mode of deformation. This is reflected in the form of crack branching in fracture tests and leading to rising fracture resistance with crack growth, improving the overall fracture toughness of the material.
