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ection II: Phase Diagram Evaluations

C-Cr-Fe-Mo-V (Carbon-Chromium-Iron-MolybdenumVanadium) V. Raghavan

Cr-Mo-V steels are technologically important for creepresistant applications. [2001Kro] assessed the phase equilibria of this quinary system and computed five isothermal sections for Fe-rich alloys and compared them with the available experimental results.

Binary Systems For brief descriptions of the C-Cr, C-Fe, C-Mo, Cr-Fe, Cr-Mo, and Fe-Mo binary systems, see the C-Cr-Fe-Mo update in this issue. For descriptions of the C-V, Cr-V, and Fe-V binaries, see the C-Cr-Fe-V update in this issue. In the Mo-V system, a continuous body-centered cubic solid solution exists between Mo and V.

Ternary Systems The C-Cr-Fe, C-Cr-Mo, C-Fe-Mo, and Cr-Fe-Mo ternary systems are briefly described in the C-Cr-Fe-Mo update in this issue. For the Fe-Mo-V system, [1992Rag] presented a schematic liquidus projection and two isothermal sections at 1297 and 897 °C. See [1995Vil] for data on the other ternary systems.

Quaternary Systems Updates on the C-Cr-Fe-Mo and C-Cr-Fe-V systems appear in this issue. There appear to be no data on the C-CrMo-V, C-Fe-Mo-V, and Cr-Fe-Mo-V systems.

Quinary Phase Equilibria [1972And] prepared more than 150 compositions of three groups of steels, containing Cr-Mo, Cr-V, and Cr-Mo-V, respectively. All steels contained a constant (nominal) amount of 0.12 wt.% C and residual elements of 0.5 wt.% Mn and 0.5 wt.% Si. The samples were annealed at 650 and 700 °C up to 1000 h. Phase identification was done by x-ray diffraction of residues obtained by electrolytic extraction. The alloy carbides identified include Fe3C, Cr7C3-based M7C3, Cr23C6-based M23C6, V4C3-based M4C3 (this is denoted as VC-based MC in this review), Fe2MoC ðnÞ; (Fe,Mo)6C-based M6C, and Mo2C-based M2C. The

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approximate composition of the metallic elements in the extracted carbides was obtained by x-ray fluorescence analysis. The ratios of the partitioning of the alloying elements between matrix and carbide were estimated and listed. For the Cr-Mo-V steels, four isothermal sections were constructed as a function of Cr and Mo at 700 and 650 °C and at 0.5 and 1.0 wt.% V. Additional isothermal sections were constructed as a function of Cr and V at 700 °C and at constant Mo contents of 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, and 2 wt.% Mo, respectively. [1998Vyr] vacuum-melted four Cr-Mo-V steels containing in weight percent: 0.09-0.12 C, 2.40-2.62 Cr, 0.70-0.95 Mo, and 0.02-0.34 V. Residual Mn and Si contents were about 0.7 and 0.3 wt.%, respectively. The steels were quenched from 1250 °C to produce a martensitic structure and then annealed (tempered) between 500 and 720 °C up to 1000 h. Extracted carbide particles were analyzed by electron diffraction and energy dispersive x-ray spectroscopy. The alloy carbides found were M3C, M23C6, M2C, M7C3, MC, and M6C. The carbides identified after each annealing treatment were listed along with those predicted from equilibrium calculations for all the four steels. Timetemperature diagrams were constructed to illustr