Effect of the defects occurring during WAAM process on fatigue strength of 08CrMoV and 30CrMnSi steels

At the moment, there are very few studies on fatigue failure of the products obtained by additive manufacturing, especially when fatigue failure occurs due to various types of defects. The importance of this topic is due to the potential for premature components damage under cyclic loading, especially in critical applications such as aviation and energy, where WAAM (wire arc additive manufacturing) can save significant manufacturing time by up to 40 – 60 %. The study evaluates the impact of technological defects on the fatigue strength of 08CrMoV and 30CrMnSi steels produced by WAAM. The authors used different surfacing modes to generate various types of defects, including macrodefects such as pores, lack of fusion, and surface concentrators, as well as microstructural defects like Widmannstetten structures and grain diversity. Defect-free samples were also produced. The authors performed metallographic analysis to investigate the metals microstructure, distribution and nature of any possible defects. Samples were etched using a 4 % aqueous HNO₃ solution. Fatigue tests were conducted on a specialized machine with sample loading following the cantilever bending method. Defect-free samples of both steels exhibited the highest fatigue strength. The presence of any type of defect, whether microstructural or macrostructural, resulted in a decrease in fatigue strength. Macrostructural defects, such as large pores and lack of fusion, had a stronger impact on the material fatigue strength compared to microstructural defects. Additionally, it was found that the presence of a surface concentrator had a greater influence on initiation of a primary fatigue crack than the presence of large non-melted regions in the sample central part.

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