13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- In metal fatigue, tensile stresses act to open crack tip and promotes crack growth. However, compressible stresses can increase the fatigue limit or have little or no contribution to crack generation and propagation. In this context, it is important to study the fatigue limit of machined steel components of high hardness and steel components with plasma nitriding surface treatment which increase even more the surface hardness. Figure 1. Fatigue limit of various steel grades versus hardness [2]. Hence, the main goal of this work is to present and compare the experimental results of rotating bending fatigue tests of PH-42 Supra steel plasma nitrided and non-nitrided which is low carbon steel and are employed to fabricate plastic injection molds and inserts. 2. Material and Experimental Procedure Fatigue tests were performed using specimens of PH-42 Supra steel delivered by Schmolz + Bickenbach of Brazil. According to the steel supplier, the material had limit strength of 1250 MPa, elasticity modulus of 206 GPa and Rockwell hardness of 40HRC [4]. For the plasma nitrided steel specimens the attained surface hardness was 60HRC. The material chemical composition is shown in Table 1. Table 1. Chemical composition of PH-42 Supra steel, according to supplier [5]. C % Mg % Ni % Cu % Al % 0.15 1.5 3.0 1.0 1.0
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