Marine applications often involve metallic materials, including steel, that must endure harsh conditions such as cavitation erosion (CE). This study investigates the CE behavior of 42CrMo4 steel, both in its original state and after pre-corrosion in a 3.5% NaCl solution for 120 days, simulating a simplified marine environment. Cavitation testing was conducted using an ultrasonic vibratory setup with a stationary sample, at intervals of 10 and 30 min, with a total testing time of 150 min. Mass loss (ML), mass loss rate (MLR), mean depth of erosion (MDE), and level of degradation (LoD) were calculated, while surface roughness (Rz) was measured using a TR200 tester. Surface changes were analyzed through field emission scanning electron microscopy (FESEM) and image analysis techniques. Morphological parameters such as the number of pits, average diameter, and total pit area were used to quantify surface damage. Results showed that pre-corroded samples exhibited a significantly higher erosion rate than non-corroded ones. Pre-corrosion introduced microcracks and surface defects that served as initiation sites for cavitation damage. These imperfections increased surface roughness and created favorable conditions for pit formation, leading to faster and deeper material loss. Image and FESEM analyses confirmed the presence of larger and deeper pits in pre-corroded samples compared to the smaller and shallower pits in non-corroded specimens. This study highlights the impact of pre-corrosion on the cavitation resistance of 42CrMo4 steel and demonstrates the effectiveness of combining mass loss data with morphological and surface analyses for evaluating cavitation damage under marine-like conditions.

This study focuses on the susceptibility and surface degradation of low-alloy carbon steel 42CrMo4 to corrosion and cavitation erosion, as this steel is widely used in marine environments with aggressive chemical species and harsh conditions. Due to its high strength and fatigue resistance, 42CrMo4 steel is often employed in offshore mechanical components such as shafts and fasteners as well as crane parts in ports and harbors. Various experimental methods, including corrosion and cavitation tests, were used to assess the steel’s surface integrity under extreme conditions. Surface changes were monitored using modern analytical tools for precise assessments, including image and morphological analyses, to quantify degradation levels and specific parameters of defects induced by corrosion and cavitation. Non-destructive techniques such as optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and image analysis software were employed for the quantitative assessment of morphological parameters and elemental analysis. EDS analysis revealed changes in elemental composition, indicating corrosion products that caused significant mass loss and defect formation, with degradation increasing over time. The average corrosion rate of 42CrMo4 steel in a 3.5% NaCl solution reached a peak value of 0.846 mm/year after 120 days of exposure. Cavitation erosion behavior was measured based on mass loss, indicating the occurrence of different cavitation periods, with the steady-state period achieved after 60 min. The number of formed pits increased until 120 min, after which it decreased slightly. This indicates that a time frame of 120 min was identified as significant for changes in the mechanism of pit formation. Specifically, up to 120 min, pit formation was the dominant mechanism of cavitation erosion, while after that, as the number of pits slightly declined, the growth and merging of formed pits became the dominant mechanism. The cavitation erosion tests showed mass loss and mechanical damage, characterized by the formation of pits and cavities. The findings indicate that the levels of surface degradation were higher for corrosion than for cavitation. The presented approach also provides an assessment of the degradation mechanisms of 42CrMo4 steel exposed to corrosive and cavitation conditions.

The choice of steel depends on environmental factors like temperature, pressure, and chemical exposure. Steel components in machinery often face varying conditions that can lead to damage, such as cavitation erosion. In this study, steel 42CrMo4 samples were chosen to represent a common and widely used steel. Application of this type of steel is often related to the statically and dynamically stressed components for vehicles, engines, and machines, where corrosion or cavitation can occur. The behavior of steel samples under conditions of cavitation erosion in distilled water was the focus of this paper. Testing was performed using a standard cavitation vibratory setup using a stationary specimen, according to the ASTM G-32 procedure. Image and morphological analyses were implemented to quantify the level of sample degradation caused by cavitation. The observed changes in the monitored parameters during testing are linked to the degradation mechanism of cavitation erosion. The results showed that pits began forming within 60 minutes, and afterward, the growth and merging of these pits significantly impacted the degradation process.

Many steels are used in specific environments, while one of these is maritime applications. High-strength 42CrMo4 steel finds numerous applications in the marine industry, including shaft parts, crankshafts, connecting rods, drilling joints, pump parts, steam turbines, and salvage equipment. In order to provide performance reliability in the marine environment, it is essential to study the corrosion resistance of surfaces of 42CrMo4 steel components and parts. The steel's behavior is typically evaluated in a synthetic NaCl solution, which is prepared as a standard substitute for seawater. This paper is focused on the behavior of the steel samples under corrosion conditions in NaCl solution. The level of sample surface degradation which is caused by the corrosion over a 4-month exposure period was evaluated using SEM/EDS analysis. The mass loss increased during the testing period, following an almost linear model in all time periods.

Specific environmental conditions, such as marine environments, often influence steel applications in marine industries. These conditions are commonly simulated using a NaCl solution to simplify the study and eliminate the complexities of seawater's chemical and biological variability. In this study, 42CrMo4 steel samples, a widely utilized material in components subjected to static and dynamic stresses found in vehicles, engines, and machinery, were selected for analysis due to their susceptibility to various forms of corrosion. The corrosion behavior of the samples was monitored using mass loss and corrosion rate. The results were then correlated with changes in mechanical properties, including tensile strength and Brinell hardness. The study provides insight into how corrosion impacts the degradation of mechanical properties.

Corrosion of high-chromium tool steels in marine environments is a major concern for structural materials, as chloride-rich conditions accelerate material degradation and reduce service life. The corrosion process involves complex interactions among passive film degradation, localized pitting, and surface defect evolution. This study investigates the corrosion progression of X210Cr12 tool steel immersed in a 3.5 wt.% NaCl solution, representing a marine-like chloride environment. Corrosion progression was monitored by combining mass loss measurements, SEM/EDS characterization, quantitative image analysis, and principal component analysis (PCA). The results reveal three distinct stages of surface degradation: initial pit nucleation, pit propagation accompanied by formation of new defects and growth of already existing ones, and pit coalescence with accelerated mass loss after 90 days of exposure, which can be associated with pronounced chromium depletion and degradation of the protective surface layer. The cumulative mass loss increased from 0.024 g after 30 days to 0.153 g after 120 days, while the calculated corrosion rate increased from 0.067 to 0.107 mm/year. Image analysis showed an increase in the degraded surface area from 0.089% to 13.34% at 120 days. EDS measurements indicated a pronounced decrease in surface chromium content accompanied by increasing oxygen content in corroded regions. PCA identified the most informative morphological descriptors, showing that size-related parameters dominated in the early stages of corrosion, while shape-related descriptors became more important during advanced stages of degradation. The proposed methodology provides a data-driven approach for monitoring corrosion progression and identifying morphological parameters associated with different stages of surface degradation under marine-like chloride conditions.