The mechanical strengths of Fe-C steels are intimately related to their microstructures which in turn are controlled through the details of their processing and heat treatment. The key factor responsible for the diversity of their mechanical response is the phase transformation of Iron from a close packed face centered cubic (FCC) structure to a less densely packed body centered cubic (BCC) form. While the more densely packed FCC form of Iron accommodates significant solubility of Carbon atoms in the octahedral interstices, Carbon is essentially insoluble in the more open BCC structure.
To resolve the apparent paradox in two solubilities, this video, presented at a level accessible to a beginning materials science undergraduate, explains why the interstitial sites in BCC metals are much smaller than their FCC counterparts.
Негізгі бет Fe-C Steels: (Part 1: Why is Carbon Unstable in the BCC Form of Iron?)
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