TY - JFULL U1 - Zeitschrift (Einzelnes Zeitschriftenheft) A1 - Giertler, Alexander A1 - Koschella, Kevin A1 - Krupp, Ulrich ED - Beretta, Stefano T1 - Investigation of changing failure mechanisms in the VHCF regime caused by different strengths of a martensitic steel T2 - Procedia Structural Integrity N2 - The present study gives an overview of recent investigations dealing with the fatigue behaviour of the tempered martensitic steel 50CrMo4 (Fe-0.5wt%C-1wt%Cr) in the HCF and VHCF regime by taking into account a variation in material strength, by modifying the heat treatment parameters. The parameters for the tempering treatment were adapted to receive two material conditions with 37HRC and 57HRC, respectively. Subsequently, fatigue specimens were machined from the heat-treated bars for fatigue tests in an ultrasonic (f=20000Hz) and a resonance (f=95Hz) fatigue testing machine under fully reversed loading (R=-1) at laboratory air atmosphere. It was found that the dominant fatigue and fracture mechanisms change with increasing material strength. For 37HRC moderate-strength specimens crack initiation was shown to occur on the specimen surface within Cr depleted bands (segregation bands) as the dominant fatigue damage mechanism. Contrary to that, only internal crack initiation at non-metallic inclusions was observed for the high strength 57HRC condition. Furthermore, the completely different crack initiation mechanisms of the two heat treatment conditions were assessed by applying the Murakami approach relating the fatigue limit with the size of non-metallic inclusions. KW - Materialermüdung Y1 - 2017 UR - https://www.sciencedirect.com/science/article/pii/S2452321617304511 SN - 2452-3216 SS - 2452-3216 VL - 7 SP - 321 EP - 326 S1 - 6 PB - Elsevier CY - Amsterdam ER -