# Retained Austenite Destabilization during Tempering of Low-Temperature Bainite
## 3 Results
### Dilatometric Study of the Microstructural Evolution during Tempering
\begin{table}
\begin{tabular}{c c c} \hline \hline
**State** & **Phases** & **Conditions (\(C_{i}\) (wt \%))** \\ \hline \multicolumn{3}{c}{Scenario 1} \\  & & \(\gamma\ (fcc)\rightarrow\ \alpha\ (bcc)+\theta\) \\ \hline Initial & \(\gamma\) & \(C_{\gamma}\) = 0.6–2.5 \\ \hline \multirow{2}{*}{Final} & \(\alpha\ (bcc)\) & \(C_{\alpha}\) = 0.03 \\ \cline{2-3}  & \(\theta\) & \(C_{\theta}\) = 6.67 \\ \hline \multicolumn{3}{c}{Scenario 2} \\  & & \(\gamma\ (fcc)\rightarrow\ \gamma^{-}\ (fcc)+\theta\) \\ \hline Initial & \(\gamma\) & \(C_{\gamma}\) = 0.91 \\ \hline \multirow{2}{*}{Final} & \(\gamma^{-}\) & \(C_{\gamma^{-}}\) = 0.9–0.7 \\ \cline{2-3}  & \(\theta\) & \(C_{\theta}\) = 6.67 \\ \hline \multicolumn{3}{c}{Scenario 3} \\  & & \(\alpha_{b}\ (bct)\rightarrow\ \alpha\ (bct/bcc)\ +\ \theta\) \\ \hline Initial & \(\alpha_{b}\ (bct)\) & \(C_{\alpha b}\) = 0.2 \\ \hline \multirow{2}{*}{Final} & \(\alpha\ (bct/bcc)\) & \(C_{\alpha}\) = 0.03 \\ \cline{2-3}  & \(\theta\) & \(C_{\theta}\) = 6.67 \\ \hline \multicolumn{3}{c}{Scenario 4} \\  & & \(\left(\gamma+\alpha_{b}\rightarrow\gamma^{+}+\alpha_{b}^{-}\right)\) \\ \hline \multirow{2}{*}{Initial} & \(\gamma\) & \(C_{\gamma}\) = 0.91 \\ \cline{2-3}  & \(\gamma\) & \(f_{\gamma}\) = 0.32 \\ \cline{2-3}  & \(\alpha_{b}\ (bct)\) & \(C_{\alpha_{b}}\) = 0.2 \\ \cline{2-3}  & \(f_{\alpha_{b}}\) = 1 – \(f_{\gamma}\) = 0.68 \\ \hline \multirow{2}{*}{Final} & \(\gamma^{+}\) & \(C_{\gamma^{+}}\ =\ \left[f_{\gamma}\left(C_{\gamma}-C_{\alpha_{b}}+C_{\alpha_{b}^{-}} \right)+\left(C_{\alpha_{b}}-C_{\alpha_{b}^{-}}\right)\right]/f_{\gamma}\) \\ \cline{2-3}  & \(f_{\gamma^{+}}\) = \(f_{\gamma}^{-}\) \\ \hline \end{tabular}
\end{table} 
Table 5: Conditions used to calculate by atomic volumes the relative change in length (RCL) and the fraction of the phases involved in the mentioned scenarios occurring during a tempering treatment. The signs – and + denotes more or less C as compared to the initial state, respectively. for these carbides is about 0.01%, they would not be easy to detect by XRD. On the other hand, due to the depletion of carbon content by carbide precipitation, the Ms of any retained austenite remaining in the material increases, so that it can transform into martensite on cooling. Table 5 presents a summary of the different conditions used in the described scenarios. In accordance with the procedures described in the previous sections, the chemical compositions of the 06C1 MoV steel and a tempering temperature of 550 \({}^{\circ}\)C were selected for the atomic volume calculations. The constraints given in Equation (1) were applied for scenarios 1, 2, and 3, while those of Equation (2) were applied for scenario 4. In both equations, the subscript \(i\) indicates the phase and \(f_{i}\) and \(C_{i}\) indicate its fraction and C content respectively, and the term \(ini\) and \(fin\) refers to the initial and the final state, as indicated in Table 5.  
\[ \begin{array}{c}1\;=\;\left(\sum f_{i}\right)_{fin}\\ \left(C_{i}\right)_{ini}\;=\;\left(\sum f_{i}C_{i}\right)_{fin}\end{array}  \tag{1}\]  
\[ \begin{array}{c}\left(f_{i}\right)_{ini}\;=\;\left(f_{i}\right)_{fin}\\ \left(\sum f_{i}C_{i}\right)_{ini}\;=\;\left(\sum f_{i}C_{i}\right)_{fin}\end{array}  \tag{2}\]  
A summary of the results thus obtained is given in Figure 5, where values of the RCL \(>\) 0 and RCL \(<\) 0 correspond to expansions and contractions, respectively. It should be noted according to the calculations shown in Figure 5a that the decomposition of austenite would produce for scenario 1 an expansion for a C content less than 1.1 wt %, while a contraction is expected for higher values of \(C_{\gamma}\), which agrees with previous observations [58; 59; 60].