## 4 Discussion  
Comparative testing of 38 CrNi3 MoV steel samples treated under different modes showed high wear resistance of 38 CrNi3 MoV steel samples after experimental treatment and its increase during cryogenic treatment (Table 3). The basic mode of hardening (quenching with low tempering) provided a high hardness of 38 CrNi3 MoV steel with the lowest wear resistance. Thus, the increased hardness of alloyed steel is not a guarantee of its high wear resistance. Isothermal hardening, according to experimental modes from temperatures of 850 \({}^{\circ}\)C and 750 \({}^{\circ}\)C, resulted in higher wear resistance, by 29% and 48%, respectively, of 38 CrNi3 MoV steel as compared to the usual hardening mode. Experimental mode of hardening from the two-phase area and DCT within 1 h provided a significant 58% increase in the wear resistance of 38 CrNi3 MoV steel. Hence, this mode can be the most efficiently applied for the heat treatment of critical parts of 38 CrNi3 MoV steel. In the samples of investigated steel, DCT for 10 min led to the transformation of soft austenite into hard martensite, which resulted in higher hardness (Table 3). In these samples, decreases in block sizes and increases in microdistortions of the crystal lattice in steel were found (Table 4) after DCT. First, this was caused by the volume change of the newly formed martensite, which led to the multiplication of dislocations and an increase in stresses. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No** & **Treatment Modes** & **Parameter a110, Å** & **Size of Blocks D, nm** & \
\begin{tabular}{c} **Magnitude** \\ \(\Delta a/a\times 10^{-3}\) \\ \end{tabular} &
\begin{tabular}{c} **Density** \\ \(\rho\times 10^{12}\), cm\({}^{-2}\) \\ \end{tabular} \\ \hline
1 & Basic mode & 2.8609 & 11.3 & 2.1 & 3.9 \\
2 & Basic mode + DCT 10 min & 2.8645 & 8.6 & 3.9 & 6.7 \\
3 & Basic mode + DCT 1 h & 2.8668 & 5.2 & 3.3 & 8.4 \\
4 & Basic mode + DCT 22 h & 2.8652 & 4.1 & 3.0 & 10.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Effect of DCT holding time on the parameters of fine structure and crystal lattice in 38 CrNi3 MoV steel. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Points** & **V** & **Cr** & **Mn** & **Si** & **Ni** & **Mo** & **Fe** \\ \hline
1 & 0.00 & 1.01 & 0.47 & 0.31 & 3.01 & 0.34 & 94.86 \\
2 & 0.00 & 1.22 & 0.49 & 0.35 & 3.22 & 0.52 & 94.20 \\
3 & 0.01 & 0.99 & 0.19 & 0.26 & 2.74 & 0.37 & 95.44 \\
4 & 0.08 & 0.88 & 0.21 & 0.23 & 3.21 & 0.46 & 94.93 \\
5 & 0.00 & 0.85 & 0.41 & 0.39 & 2.87 & 0.41 & 95.07 \\
6 & 0.00 & 0.98 & 0.44 & 0.45 & 2.64 & 0.54 & 94.95 \\
7 & 0.00 & 0.85 & 0.58 & 0.52 & 2.75 & 0.61 & 94.69 \\
8 & 0.17 & 0.92 & 0.61 & 0.47 & 3.09 & 0.18 & 94.56 \\
9 & 0.00 & 0.84 & 0.66 & 0.49 & 2.77 & 0.62 & 94.62 \\
10 & 0.11 & 1.10 & 0.28 & 0.38 & 3.07 & 0.39 & 94.67 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Values of chemical element contents for the different points in Figure 9. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No** & **Treatment Modes** & **Hardness, HRC** & **Retained Austenite, \%** & **Wear, \%** \\ \hline
1 & 850 \({}^{\circ}\)C, oil quenching, tempering at 230 \({}^{\circ}\)C, 2 h & 47.5 & 7.7 & 0.159 \\
2 & 850 \({}^{\circ}\)C, isothermal hardening at 230 \({}^{\circ}\)C, 2 h & 46.0 & 9.5 & 0.112 \\
3 & 750 \({}^{\circ}\)C, cooling to 400 \({}^{\circ}\)C, 20 min, air cooling & 36.3 & 10.8 & 0.083 \\  & (basic mode) & & & \\
4 & Basic mode + DCT 10 min & 41.5 & 2.6 & 0.078 \\
5 & Basic mode + DCT 1 h & 43.3 & 1.2 & 0.066 \\
6 & Basic mode + DCT 22 h & 45.7 & 0.3 & 0.072 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Effect of treatment type on hardness RA content and wear of 38 CrNi3 MoV steel. The second possible mechanism may be related to local thermal stresses. The atomic probe tomography of quenched steel performed in [34] showed that there are local clusters enriched in carbon, which agrees with our electron microscopy data.