13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- near specimen surface are seen. The fatigue crack length near the specimen surface can be evaluated in Fig. 9b, approximately 20µm owing to plastic compressive deformations. Figure 8. SEM photos of fracture surface of PH-42 Supra steel non-nitrided fatigue test specimen in rotating bending test: a) rupture by brittle fracture and b) detail of beginning of fatigue crack at specimen surface. Figure 9. SEM photos of fracture surface of PH-42 Supra steel plasma nitrided fatigue test specimen in rotating bending test: a) rupture by brittle fracture and b) detail of fatigue crack growth at specimen surface. 4. Conclusions From the experimental results of PH-42 Supra steel (Schmolz + Bickenbach do Brasil) plasma nitrided, nitriding layer of 0.3mm, and as received (non-nitrided) specimens tested in tensile test, Vickers micro-hardness and rotating bending fatigue testing and analysis of fracture surface by SEM, the following conclusion can be drawn, a) Fatigue limit stress of PH-42 Supra steel plasma nitrided was 710 MPa which is much higher a b a b
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