The precipitation of epsilon-carbide in twinned martensite

Tempering of martensite has been investigated by means of thin foil electron microscopy in a high carbon steel, a high nickel steel, and a silicon steel. ε carbide has been unambiguously identified in each steel. It was found that the carbide was precipitated with the Jack orientation relationship: $$\begin{gathered} \left( {0001} \right)_\varepsilon \parallel \left( {011} \right)_{\alpha '} \hfill \\ \left( {10\bar 10} \right)_\varepsilon \parallel \left( {2\bar 11} \right)_{\alpha '} \hfill \\ \end{gathered} $$ In the silicon steel the ε carbide precipitated in the form of needles which grew with a \(\left {01\bar 10} \right]_\varepsilon \) close to \(\left {21\bar 1} \right]_{\alpha '} \) . This growth direction minimizes the surface energy of the needles, yet allows growth in a direction of low mismatch.