Fatigue strength of an ultra-high strength low alloy steel fabricated via laser powder bed fusion

Abstract

High strength low alloy (HSLA) steels are important metallic materials especially in the defense and military sectors due to their superior mechanical properties and cost-effectiveness compared to superalloys. This study investigates monotonic tension/compression strength and fatigue strength, including both the low cyclic fatigue (LCF) and high cyclic fatigue (HCF), of a HSLA steel produced using laser powder bed fusion (LPBF) additive manufacturing (AM). The LCF tests were strain-controlled (from 0.45% to 1.2% strain amplitudes) achieving a constant strain rate of 0.0005/s, while the HCF tests were stress-controlled (from 467 MPa to 1007 MPa stress range), all carried out at room temperature. Specimens of the alloy were manufactured in two build orientations to evaluate anisotropy. Moreover, a set of rolled plate and as-cast specimens were tested to facilitate comparisons. The alloy exhibited excellent performance confirming the potential of LPBF AM to manufacture HSLA steels with significant performance gains over as-cast counterparts. Nevertheless, the rolled material exhibited the highest performances. Details pertaining to the processing along with the testing results and characterization of microstructural origins of the high strength are presented and discussed in this paper.