# Study of the Rotary Bending Fatigue Resistance of 30 MnB5, 41 CrS4 and 30 MnVS6 Steels
## 1 Introduction  
The automotive industry is undoubtedly one of the most important industries today. This industry has a vital influence on the internal economy of both European and Asian countries, constituting an important factor in increasing employability [1, 2]. In this industry great importance is attached to the selection of the materials used, determining this point both the production, use and maintenance costs, as well as the durability of the product [3, 4]. A proper selection of materials used in the manufacture of components such as shafts, pistons and pumps can significantly reduce failures in service. The aforementioned components need to have important reliability characteristics. For this reason, it is required that they be made with materials that possess adequate mechanical properties of strength, rigidity and hardness, and a sufficiently high resistance to fatigue to avoid component failure [5]. Low and medium carbon quench and tempered steels are frequently used in the automotive industry for the manufacture of these components due to their high yield strength and mechanical strength. These steels contain alloying elements such as Mn, Cr, Mo and B, among others, which increase the hardness of the steel when it undergoes a quenching and tempering treatment [6]. Boron steel is a generic term for a family of low-alloy tempered and annealed steels. The study of these steels began during the Second World War and experienced a remarkable boost in the 1950s. As a result of the war, it was critical to find quality elements and it became necessary to find elements that would constitute an alternative to the more expensive binders. After a long experimental phase, boron steels only began to take hold in the 1970s and 1980s, due to the appearance of advanced steel technologies. Today they occupy a prominent position in the market for tempered and annealed steels. Boron steel alloys allow them superior strength after hardening by heat treatment. Boron is generally added to medium-carbon alloy steels to improve performance and to achieve similar performance compared to high carbon, and other costly alloyed steels. It is preferred to use this route rather than increasing the carbon and manganese content or adding chromium and molybdenum as this could reduce ductility during the manufacturing process. Boron steels, although they have other alloying elements, have boron as one of the main constituents. They are hypoeutectoid steels, with a ferritic matrix and with pearlite in their constitution, with about 0.25% carbon by mass. The presence of boron in this type of steels is very important for hardenability. Boron increases the hardenability of hypoeutectoid steels by retarding the nucleation of proeutectoid ferrite in the austenitic grain limits, and to a lesser extent, the transformation of higher bainite, which is nucleated by ferrite, without appreciably affecting the growth rate of these compounds [7]. A small amount of boron has a powerful effect on hardenability, increasing the hardening of the steel [8; 9]. The influence on hardenability varies substantially with the carbon content in the composite. Boron is an interstitial element and has a very low solubility in \(\alpha\)-solid solution (\(<\)0.003%) [10; 11]. Boron steels coalesce at very high temperatures, and these steels combine wear resistance with high resistance at medium and high temperatures [12]. There are other factors that influence the effectiveness of boron, such as: the influence of nitrogen content, the influence of deoxidizers and the negative effect of high austenitizing temperature on the effect of boron on hardenability [13]. One of these boron steels is 30 MnB5 (1.5531) steel, which is frequently used in the automotive industry to manufacture the front axles of industrial vehicles [14; 15]. It is a steel alloyed with chromium and molybdenum and acquires its final mechanical properties after being subjected to a quenching and tempering treatment.