# Study of the Rotary Bending Fatigue Resistance of 30 MnB5, 41 CrS4 and 30 MnVS6 Steels
## 2 Materials and Methods  
Four different types of steels have been used for this study. The first two are boron-alloyed quenching and tempering steels, designated 30 MnB5, complying with the requirements of the standard UNE-EN ISO 683-2: 2019 Heat-treatable steels, alloy steels and free-cutting steels--Part 2: Alloy steels for quenching and tempering [28]. This type of steel is normally oil quenched. In the present study, it will be evaluated whether a quenching in water, which entails a modification in the mechanical properties and the fatigue behavior, is beneficial compared to the reference material quenched in oil. Oil-quenched boron steel will be called 30 MnB5 (B1) and water-quenched 30 MnB5 (B2). Steel B1 was subjected to a quenching treatment with an austenitization temperature of 800 \({}^{\circ}\)C and subsequent cooling in oil for a period of 8 min. Steel B2 was treated in the same way, but by modifying the cooling in oil by water and keeping the rest of the parameters. In both cases, after the hardening treatment, tempering was carried out. For this, a treatment temperature of 550 \({}^{\circ}\)C was used and the cooling was in the air. With this sequence, both present tempered martensite in their microstructure [14; 15; 16; 29]. As an alternative to these two options, the use of another steel for quenching and tempering is proposed, 41 CrS4 (according to the same standard [28]) and a microalloyed steel, 30 MnVS6, which meets the requirements established in the standard UNE-EN 10,267:1998 Ferritic-pearlitic steels for precipitation hardening from hot working temperatures [20; 24; 30; 31; 32]. The first (41 CrS4) was subjected to a quenching and tempering treatment to obtain a tempered Martesite structure with the following parameters: austenization temperature of 850 \({}^{\circ}\)C and cooling in water for 10 min; tempering temperature of 540 \({}^{\circ}\)C and air cooling. Microalloyed steel is a pearlitic-ferrritic steel that hardens by precipitation during the hot-forming process. It was tested without heat treatment since an alternative is sought that, avoiding this process, is competitive [33]. Table 1 shows the compositions, in percent by weight, indicated in the respective standards for the steels used in the study, and Table 2 indicates the required mechanical properties. For quenched and tempered steels, minimum values are established for the yield strength (R\({}_{\text{e}}\)), elongation (\(\epsilon\)), structure (\(Z\)) and Charpy impact resistance measured with a V-notch (Charpy V-Notch, CVN), and a range of values for the tensile strength  
(R\({}_{\text{m}}\)). The same benchmarks are set for microalloyed steel, but there is no requirement for toughness. Tables 3 and 4 show the chemical composition and the mechanical properties determined for the steels used in the present research. As can be seen in the values shown in Table 4, the tensile strength and the yield strength of boron steel tempered in water (B2) are higher than the values shown for traditional steel tempered in oil (B1). The steel hardened and annealed with chromium (EC) presents higher values than the previous two, while the microalloyed steel (MV) reaches lower values. It is also observed that the R\({}_{\text{e}}\)/R\({}_{\text{m}}\) ratio for B1, B2 and EC steels is similar: 0.90, 0.91 and 0.93 respectively. For MV steel this ratio is significantly reduced to 0.69. [PERSON] et al. (2018) state that the majority of combustion engine vehicle axle failures are due to fatigue failures related to bending stresses. Therefore, the evaluation of the fatigue resistance of alternative steels is essential to establish whether the reference steel--30 SnB5 (B1)--can be substituted for them.