Molybdenum Carbide in Tempered Martensite

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

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• Tempered Martensite
• Martensitic Transformations.

Crystal Structure of Mo₂C

Molybdenum carbide (Mo₂C) can occur in many crystalline forms, but that which precipitates in steels has a close-packed hexagonal crystal structure of metal atoms, with the carbon atoms located in one half of the available octahedral interstices (but the carbon atom locations are assumed). The lattice parameters assumed for the diagrams below are a=0.3007 nm and c=0.4729 nm.

Projection of four unit cells. The numbers indicate the fractional coordinates along the z-axis. The black atoms are carbon and the blue molybdenum.	Two molybdenum and one carbon atom per unit cell.
	As the projection along the z-axis, but with most of the atoms removed to show carbon in an octahedral interstice.
Carbon in an octahedral interstice.	Movie, structure rotated about z-axis Movie, structure rotated about y-axis Movie, structure rotated about x-axis Movie, octahedral interstice Crystalmaker file Crystalmaker file Crystalmaker file

Molybdenum carbide needles in tempered martensite

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

Tempered martensite in Fe-Mo-C alloy. Details in S. Yamasaki and H. K. D. H. Bhadeshia, Materials Science and Technology, 19 (2003) 723.	Tempered martensite in Fe-Mo-C alloy.	Tempered martensite in Fe-Mo-C alloy.
Tempered martensite in Fe-Mo-C alloy.	Tempered martensite in Fe-Mo-C alloy.	Tempered martensite in Fe-Mo-C alloy.
Tempered martensite in Fe-Mo-C alloy. Details in S. Yamasaki and H. K. D. H. Bhadeshia, Materials Science and Technology, 19 (2003) 723.	Tempered martensite in Fe-Mo-C alloy. Details in S. Yamasaki and H. K. D. H. Bhadeshia, Materials Science and Technology, 19 (2003) 723.	Tempered martensite in Fe-Mo-C alloy.
Tempered martensite in Fe-Mo-C alloy.	Tempered martensite in Fe-Mo-C alloy.	Tempered martensite in Fe-Mo-C alloy.
Tempered martensite in Fe-Mo-C alloy.	Tempered martensite in Fe-Mo-C alloy.	Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.
Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.	Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.	Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.
Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.	Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.	Tempered martensite in Fe-Mo-C alloy. Molybdenum carbide precipitation.