Molybdenum Carbide in Tempered Martensite

S. Yamasaki and H.K.D.H. Bhadeshia



Crystal Structure of Mo2C

Molybdenum carbide (Mo2C) can occur in many crystalline forms, the most common of which is α-Mo2C and β-Mo2C. It is the latter phase which is stable at low temperatures and occurs in steels. β-Mo2C has a close-packed hexagonal crystal structure with the carbon atoms located in one half of the available octahedral interstices. The lattice parameters assumed for the diagrams below are a=0.3007 nm and c=0.4729 nm.

Mo2C
Projection of four unit cells. The numbers indicate the fractional coordinates along the z-axis. The black atoms are carbon and the blue molybdenum.
Mo2C_x
Two molybdenum and one carbon atom per unit cell.
Mo2C_y
octa_z
As the projection along the z-axis, but with most of the atoms removed to show carbon in an octahedral interstice.
octa
Carbon in an octahedral interstice.


Molybdenum carbide needles in tempered martensite

The following micrographs are taken from thin foil samples using a transmission electron microscope.

0055-01Mo-1-802
Tempered martensite in Fe-Mo-C alloy. Details in S. Yamasaki and H. K. D. H. Bhadeshia, Materials Science and Technology, 19 (2003) 723.
0060-01Mo-2-807
Tempered martensite in Fe-Mo-C alloy.
0065-01Mo-2-812n
Tempered martensite in Fe-Mo-C alloy.
0244-01Mo-2-419
Tempered martensite in Fe-Mo-C alloy.
0246-01Mo-2-421
Tempered martensite in Fe-Mo-C alloy.
0452-01Mo-2-830
Tempered martensite in Fe-Mo-C alloy.
0458-01Mo-3-836
Tempered martensite in Fe-Mo-C alloy. Details in S. Yamasaki and H. K. D. H. Bhadeshia, Materials Science and Technology, 19 (2003) 723.
0459-01Mo-3-837
Tempered martensite in Fe-Mo-C alloy. Details in S. Yamasaki and H. K. D. H. Bhadeshia, Materials Science and Technology, 19 (2003) 723.
0461-01Mo-3-839
Tempered martensite in Fe-Mo-C alloy.
0532-01Mo-2-418
Tempered martensite in Fe-Mo-C alloy.
0538-01Mo-2-424
Tempered martensite in Fe-Mo-C alloy.
0541-01Mo-2-427
Tempered martensite in Fe-Mo-C alloy.
0549-01Mo-4-246
Tempered martensite in Fe-Mo-C alloy.
0570-01Mo-4-267
Tempered martensite in Fe-Mo-C alloy.
0571-01Mo-4-268
Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.
0796-01Mo-5-301
Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.
0822-01Mo-5-327
Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.
0825-01Mo-5-330
Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.
1096-01Mo-6-204
Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.
1132-01Mo-6-241
Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.
1134-01Mo-6-243
Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.





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