Topic summary
Martensitic transformation
Extracted from the Wikipedia article Diffusionless transformation.
Iron-carbon martensitic transformation
The distinction between austenitic and martensitic steels is subtle in nature. Austenite exhibits a face-centered cubic (FCC) unit cell, whereas the transformation to martensite entails a distortion of this cube into a body-centered tetragonal shape (BCT). This transformation occurs due to a displacive process, where interstitial carbon atoms lack the time to diffuse out. Consequently, the unit cell undergoes a slight elongation in one dimension and contraction in the other two. Despite differences in the symmetry of the crystal structures, the chemical bonding between them remains similar.