PSI - Issue 23

Golta Khatibi et al. / Procedia Structural Integrity 23 (2019) 475–480 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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obtained under fully reversed conditions at a frequency range of 0.1-11 Hz shows a fatigue resistance equivalent to about 630 MPa at 1e8 cycles (matdat.com). Typical fracture surfaces of the failed samples are presented in Fig. 6b-e showing the crack initiation sites near or at the surface, crack propagation region and the final overload area. As expected, fatigue cracks always initiated at the location of stress concentration in the root of the notch, where presence of larger carbide particles near or at the surface were found to be responsible for lower cycles to failure at the given stress amplitude. The final rupture area in both cases showed characteristics of a ductile type fracture with a dimple morphology. Since the hardness and wear properties of the both weld overlays are not considerably different, the improved fatigue properties of C-series samples are most probably related to their microstructure containing a higher amount of austenite. The higher proportion of the hard and brittle martensitic phase of E-series together with the presence of larger carbide particle leads to a reduced resistance to fatigue crack propagation in this material. The positive effect of the retained austenite on the fatigue resistance of high strength steel weldments in the near the threshold region has been reported by (Ritchie 1978). In this research it could be shown that the applied ultrasonic fatigue testing method is a proper and fast tool to predict the wear behavior of weld overlay materials exposed to fatigue and impact loads. The results could be confirmed by a cyclic impeller tumbler wear test and they were additionally underlined by metallographic investigations showing differences in overall homogeneity of the microstructure, especially in retained austenite and the distribution and size of hard phases in the as welded overlay of the two tested welding wires. Even though the chemical composition of a welding consumable is one of the key criteria for selecting hardfacing solutions against wear, other factors such as the raw materials and ingredients used for composing the cored welding wire are of high importance with regard to the specific microstructure and material properties obtained after welding. Based on the presented investigations further ultrasonic fatigue tests series are planned in order to get a better understanding for the relation between the chemical setup of more complex alloyed welding consumables and the resulting microstructure after welding and their behavior under dynamic load. In parallel the ultrasonic fatigue test method will be developed into a standardized tool for categorizing weld overlay materials. Acknowledgements The financial support by the Austrian Federal Ministry for Digital and Economic Affairs and the National Foundation for Research, Technology and Development is gratefully acknowledged. The authors are also grateful to B. Larsson for his support in preparing the welded samples as well as Dipl.-Ing. C. Katsich and the Austrian Center of Competence for Tribology in performing the impact abrasion wear tests. References Badisch, E., Kirchgaßner, M., “ Influence of welding parameters on microstructure and wear behaviour of a typical NiCrBSi hardfacing alloy reinforced with tungsten carbide ,” Surf. Coat. Technol. (2008) 202, 6016-6022 Franek, F., Badisch, E. Kirchgaßner M. “ Advanced Methods for Characterization of Abrasion/Erosion Resistance of Wear Protection Materials ,” FME Transactions (2009) 37, 61-70 Hawk, J. A. and Wilson, R. D., “Tribology of Earthmoving, Mining, and Minerals Processing,” in Modern Tribology Handbook, Vol. 2, Bhushan, B. (ed.), CRC Press, Boca Raton, (2000). https://www.matdat.com/ Kirchgaßner M., Badisch, E., Franek, F, “ Behaviour of iron-based hardfacing alloys under a brasion and impact”, Wear (2008) 265, 772 -779 Peterson R. E., Stress Concentration Factor, John Wiley & Sons, New York (1974) Roth, L. D. Ultrasonic fatigue testing. Metals Handbook. Vol 8 9 th ed. Mechanical testing, ASM International, (1985) 240-258 Puškár A ., “ Ultrasonic fatigue testing equipment and new procedures for complex material evaluation ” , Ultrasonics (1993) 31, 61-67 Ritchie, R.O., Chang, V.A., Paton, N.E., “ Influence of Retained Austenite on Fatigue Crack Propagation in HP 9-4-20 High Strength Alloy Steel ,” Fatigue of Engineering Materials and Structures (1979) 1, 107-121 Sun Z.D., Bathias, C., Baudry G., “Fretting fatigue of 42CrMo4 steel at ultrasonic frequenc y, ” International Journal of Fatigue (2001) 23, 449 – 453 4. Conclusion