Corrosion-damage behavior of 38CrMoAlA steel under alternating hot-humid/salt-fog conditions and its effect on mechanical properties for aircraft–engine applications

38CrMoAlA steel is widely used in critical components, such as blower drive shafts of aircraft engines, because of its remarkable mechanical properties and surface hardening potential. However, its performance in harsh marine environments, characterized by high temperatures, humidity, and salt spray, remains a notable concern. In such environments, the steel is highly susceptible to severe corrosion, which can undermine its structural integrity and operational reliability. This study systematically investigates the corrosion behavior and corrosion-induced mechanical degradation of 38CrMoAlA steel under simulated service conditions that imitate the extreme environmental exposure of an aircraft-engine blower drive shaft operating in marine settings. To replicate the harsh conditions, a multicycle accelerated corrosion test is designed, consisting of alternating exposure to wet heat and salt spray across a series of cycles. In particular, specimens were subjected to 7 d of wet heat followed by 4 d of neutral salt spray and then 3 d of acidic salt spray. A variety of evaluation methods were employed for the assessment of material degradation, including comparison of macroscopic surface morphologies at different stages of corrosion cycles, weight loss measurements to calculate corrosion rates, and mechanical testing to determine the effect of corrosion on tensile strength, fatigue life, and fracture toughness at room temperature. Scanning electron microscopy (SEM) was employed to gain insights into microstructural changes associated with corrosion products and fracture surfaces. The examination results revealed that corrosion pits induced by salt spray and wet heat exposure resulted in notable alterations at the microstructural level. The presence of corrosion pits not only contributed to localized material degradation but also facilitated crack initiation and propagation. Energy-dispersive spectroscopy was performed to analyze the elemental composition of the corrosion products, helping further elucidate the chemical mechanisms underlying the corrosion process. A laser confocal microscope was used to quantify the depth and distribution of corrosion pits, providing detailed data on the extent of localized corrosion damage. The results of this study revealed significant corrosion damage to 38CrMoAlA steel after exposure to accelerated wet heat and salt spray cycles. Corrosion pits were notably deep, particularly after the third test cycle, with the maximum pit depth measured to be ～506 μm. After completing five cycles, the corrosion rate reached a steady state at ～1.47 mm·a–1, indicating that corrosion occurred slowly as corrosion products accumulated on the steel surface. Despite this stabilization in corrosion rate, the mechanical properties of the steel showed severe degradation. Notably, the tensile strength decreased by 11%, the yield strength by 64%, the elongation at break by 12%, and the reduction of area by 30%. The mechanical degradation observed in this study can be primarily attributed to the stress concentration effects caused by corrosion pits, which notably reduced the effective load-bearing area of the steel. Moreover, corrosion pits served as initiation sites for cracks that propagated during loading, resulting in premature failure of the material. SEM imaging of the fracture surfaces revealed numerous intergranular cracks surrounding corrosion pits, with these cracks rapidly expanding under loading conditions. This progression of crack growth, combined with the loss of load-bearing capacity due to pitting, severely impaired the steel’s ability to withstand cyclic loading, further expediting the failure of the material. The findings of this study provide a comprehensive understanding of the corrosion mechanisms and associated mechanical degradation of 38CrMoAlA steel under marine environmental conditions. The observed deterioration underscores the importance of developing advanced protective strategies to (a) mitigate the effects of corrosion and (b) extend the operational life of critical components such as aircraft-engine blower drive shafts. The data from this investigation offer valuable insights that can inform future material selection and development of more effective protective coatings and corrosion-resistant treatments. Ultimately, these findings contribute to ensuring the long-term durability and reliability of aircraft components exposed to harsh and corrosive marine environments, enhancing their performance and safety in real-world applications.