Understanding Acoustic Emission Testing- Reading 1 Part B-A

The properties of different steels are determined by their crystal lattice
structures, that is the spatial arrangement of their atoms. Adding alloying
elements makes certain crystal structures more likely to form which allows the
properties of the steel to be fine-tuned. It is concluded from thermodynamic
calculations that a combination of manganese, silicon and aluminum would
probably be suitable for the development of the new lightweight construction
steel. These elements are lighter than iron and they force the crystal lattice
into certain structures: iron can switch between different crystal lattices, or
iron atoms can switch their positions and form different arrangements in the
crystal lattices.
There is, for example, an FCC.: face-centered cubic arrangement, known as
"austenite". In this case, the iron atoms sit on the corners of the crystal lattice
cube with an atom in the center of each face of the cube. Then there is the
BCC.: body-centered cubic layout. Again, the iron atoms are arranged on the
corners, but with another one in the cube's center. There is also a type in
which the iron atoms are distributed in a hexagonal arrangement. The bodycentered
cubic and the hexagonal forms are both traditionally referred to as
martensite. The crystal lattice changes, and with it, the character of the steel,
depending on the alloy element content (the alien atoms in the crystal lattice).
Charlie Chong/ Fion Zhang
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