Effect of aging on microstructure and mechanical properties of cobalt free 18%Ni (250 grade) maraging steel

Microstructure and mechanical properties of a 2000 MPa grade co-free maraging steel

“…[20,21] To date, research on Co-free maraging steels has concentrated on T-250 and other grades with 1800 MPa strength level. [2,14,16,[22][23][24][25] Discrepancy among the results exists similar to that for 18Ni Co-containing maraging steels. For example, Vanderwalker believed that in T-250, austenite nucleated first in martensite, followed by nucleation of Ni 3 Ti from the austenite site, [22] contrary to Vasudevan et al's work showing Ni 3 Ti to be the only precipitation phase.…”

“…[3,15] Many authors observed reverted austenite of different morphology under overaging or special treatment, its orientation relationship with martensite varying in the range of Nishiyama-Wassermann (N-W) [3,16,17] and Kudjumov-Sachs (K-S) [3,6,17,18] types. In terms of mechanical properties, Rack and Kalish [19] and Zhu et al [20] found embrittlement in 18Ni (350 ksi grade) maraging steels after low-temperature aging at 673 to 723 K. Overaging decreases strength, ductility, and toughness, [14,19] but there were also reports of improved strength and toughness due to reverted austenite. [20,21] To date, research on Co-free maraging steels has concentrated on T-250 and other grades with 1800 MPa strength level.…”

“…Different precipitation phases have also been identified, including ␥-Ni 3 Mo, [1,3,[6][7][8] -Ni 3 Ti, [1][2][3][4]6,[8][9][10][11] Laves-Fe 2 Mo, [1][2][3]6,9] -FeMo, [1] -Fe 7 Mo 6 , [1,4] FeTi, [1,7] Fe 2 Ti, [1] , [11,12,13] and dispersion austenite, [10] either singly or simultaneously occurring. Moving on to precipitation strengthening mechanisms, there are a dislocation looping mechanism [2,14] and a shearing mechanism. [3,15] Many authors observed reverted austenite of different morphology under overaging or special treatment, its orientation relationship with martensite varying in the range of Nishiyama-Wassermann (N-W) [3,16,17] and Kudjumov-Sachs (K-S) [3,6,17,18] types.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Dense, fine, and complex microstructures form in maraging steels during aging treatment, with precipitation having complicated diffraction patterns. These, coupled with compositional variations of different steels, have resulted in differing opinions among the research literature.…”

Observation of Precipitation Evolution in Fe-Ni-Mn-Ti-Al Maraging Steel by Atom Probe Tomography

“…These elements make these steels rather expensive, [1][2][3] and, as a result, a new class of Co-free maraging steels has emerged that contain Fe, Ni, Mo, and Ti. [4][5][6][7][8] The improved properties achieved in these newer steels are associated with the formation of Ni 3 Ti and Fe 2 (Mo,Ti) precipitates, which strengthen the alloys through the operation of Orowan-type mechanisms. The morphology of the Ni 3 Ti particles was found to be needle-like, [7,[9][10][11][12] plate-like, [11] or rod-like.…”