Epsilon carbide precipitation during tempering of plain carbon martensite |
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Authors: | Yasuya Ohmori Imao Tamura |
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Affiliation: | (1) Department of Materials Science and Engineering, Ehime University, 790 Matsuyama, Japan;(2) Research Institute for Applied Sciences, Kyoto University, 606 Kyoto, Japan |
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Abstract: | Epsilon carbide precipitation in steel martensite has been investigated by means of transmission electron microscopy. The
first stage of tempering initiates with the nucleation of very fine ε-carbide particles on the closely spaced parallel line
defects, the morphology being so-called “cross-hatched” ε-carbide needles. The ε-carbide particles which produce the well-defined
dif-fraction patterns are related to the martensite matrix with a Pitsch and Schrader orientation relationship.32] These particles subsequently grow into rods elongated in the direction parallel to the
within the matrix. The final reaction in the first stage is the rearrangement of ε-carbide rods into a disklike morphology.
The e-carbide rods elongated in the 〈100〉ε di-rections coalesce on
planes in a raftlike manner, as in the case of those formed in the quench-aged low-carbon ferrite, the tetragonality of martensite
being completely lost. Although the deviation from hexagonal symmetry about the 0001]ε axis exists, no evidence of orthorhombic η-carbide formation was obtained. |
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