Question
Which one of the following crystal structure changes occurs during the transformation of mild steel from austenite to martensite?
The correct answer is
Face centered cubic to body centered tetragonal
Crystal Structure Change: Austenite to Martensite
The transformation of mild steel from austenite to martensite involves a specific change in crystal structure.
- Austenite Phase: The high-temperature austenite phase in steel has a Face-Centered Cubic (FCC) crystal structure.
- Martensite Formation: Martensite forms via a rapid, diffusionless transformation from austenite, typically during quenching. This process traps interstitial carbon atoms within the iron lattice.
- Martensite Structure: The trapped carbon atoms distort the lattice, changing the crystal structure from FCC to Body-Centered Tetragonal (BCT). The BCT structure is a slightly stretched version of the Body-Centered Cubic (BCC) structure along one axis.
Therefore, the transformation sequence is from FCC (Austenite) to BCT (Martensite).
The correct option describes this transformation as Face centered cubic to body centered tetragonal.
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Important Questions from Microstructure Ferrite Pearlite Cementite Fraction
- In optical microscopy, which one of the following combinations of wavelength ($\lambda$) and numerical aperture (NA) provides the best spatial resolution?
- A 0.2 wt.% plain carbon steel sheet is heated and equilibrated in the inter-critical region followed by instant water quenching. The microstructure of the quenched steel sheet consists of
Magnesium treatment is carried out to produce ______________ cast iron.
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- In a typical scanning electron microscope (SEM) image, information about topography and atomic contrast are obtained from ________.
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