A stainless steel is a ferritic alloy, in general, with a low carbon content and a Cr content equal to or greater than 10.5%. To study the phase transformations and heat treatments undergone by these steels, a phase diagram is used, as shown in the following figure:

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In this diagram, there is a sigma phase of tetragonal structure, whose occurrence I have read should be avoided. But, in the notes I am reading, the reason does not appear. Why should the sigma phase be avoided?

  • $\begingroup$ Not an expert in this, but this site suggests that the sigma phase is less corrosion resistant and more brittle than the surrounding phases. I don't know if you are looking for more detail than what's given there. $\endgroup$
    – Tyberius
    Mar 27, 2022 at 15:34
  • $\begingroup$ Was the comment by Tyberius helpful? Please let us know if you've found an answer or learned anything new about this in the last 5+ months! $\endgroup$ Sep 7, 2022 at 14:19
  • $\begingroup$ This post appears to be abandoned. It can be reopened if someone would like to answer or if OP addresses suggestions/questions from the comments. $\endgroup$
    – Tyberius
    Oct 26, 2022 at 13:16


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