# Study of the Rotary Bending Fatigue Resistance of 30 MnB5, 41 CrS4 and 30 MnVS6 Steels
## 2 Materials and Methods
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Steel** & **\% wt** & **C** & **Si** & **Mn** & **P** & **S** & **Cr** & **Mo** & **Cu** & **B** & **N** & **V** \\ \hline \multirow{2}{*}{30 MnB5} & min & 0.27 & - & 1.15 & - & - & - & - & - & 0.0008 & - & - \\  & max & 0.33 & 0.40 & 1.45 & 0.025 & 0.035 & - & - & 0.40 & 0.0050 & - & - \\ \hline \multirow{2}{*}{41 Cr54} & min & 0.38 & 0.10 & 0.60 & - & 0.02 & 0.90 & - & - & - & - \\  & max & 0.45 & 0.40 & 0.90 & 0.025 & 0.04 & 1.20 & - & - & - & - \\ \hline \multirow{2}{*}{30 MnVS6} & min & 0.26 & 0.15 & 1.20 & 0.025 & 0.02 & - & - & - & - & 0.01 & 0.08 \\  & max & 0.33 & 0.80 & 1.60 & 0.05 & 0.06 & 0.30 & 0.08 & - & - & 0.02 & 0.20 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Composition of the steels used according to the corresponding standards. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Steel** & **Key** & **C** & **Si** & **Mn** & **P** & **S** & **Cr** & **Mo** & **B** & **N** & **V** \\ \hline \multirow{2}{*}{30 MnB5} & B1/B2 & 0.325 & 0.275 & 1.5 & 0.02 & 0.0275 & - & - & 0.0025 & - & - \\ \hline \multirow{2}{*}{41 Cr54} & EC & 0.395 & 0.40 & 0.80 & 0.035 & 0.035 & 1.0 & - & - & - & - \\ \hline \multirow{2}{*}{30 MnVS6} & MV & 0.36 & 0.62 & 1.4 & 0.022 & 0.057 & 0.19 & 0.03 & - & 0.13 & 0.09 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Chemical composition of the four evaluated steels. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Steel** & **Key** & **C** & **Si** & **Mn** & **P** & **S** & **Cr** & **Mo** & **B** & **N** & **V** \\ \hline \multirow{2}{*}{30 MnB5} & B1/B2 & 0.325 & 0.275 & 1.5 & 0.02 & 0.0275 & - & - & 0.0025 & - & - \\  & max & 0.395 & 0.40 & 0.80 & 0.035 & 0.035 & 1.0 & - & - & - & - \\ \hline \multirow{2}{*}{30 MnVS6} & MV & 0.36 & 0.62 & 1.4 & 0.022 & 0.057 & 0.19 & 0.03 & - & 0.13 & 0.09 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Mechanical properties of the four types of steel evaluated. In order to evaluate the fatigue behavior of the two steels considered in the study, the rotary-bending fatigue test was used, following the corresponding standard [27]. Figure 1 shows the device used for the fatigue tests and a detailed image of the clamping of the specimen. In this type of test, the stress is applied to the specimen in the form of a bending moment generated by applying a load to one of the ends of the specimen. In this way, the specimen, at a given moment, has an induced tensile stress on the upper surface, while the lower surface is subjected to compression (Figure 2). This situation is reversed when the specimen is rotated, establishing a complete cycle in each rotation [35,36]. Under these alternating stress conditions, the load ratio is R = \(-1\). The geometry of the tested specimens corresponds to the type 3 set forth in the standard (Hourglass specimen--Single-point loading), The dimensions of the specimens are shown in Figure 3a. The assembly scheme of the specimen in the test equipment is shown in Figure 3b. As can be seen in the figure, the specimens have a cylindrical section of 4 mm (d) in the test area and 9 mm (D) in the clamping area. The samples have been carefully machined,  
Figure 1: Device used for the test (**a**) A more detailed view of the same device (**b**). In the figure, A is axis of rotation linked to the motor at the far left of the figure, B the force transducer, C the masses, D the sample and E the load axis at the end of the specimen. Figure 3: Shape and dimensions of the tested specimens (**a**) Assembly of the specimen in the test device (**b**). Figure 2: Stresses on the specimen at a given instant of the test (tension in the upper part and compression in the lower part). maintaining an average roughness, Ra, less than 0.2 \(\upmu\)m as recommended in the standard and in other previously published studies [27,37].