Marine Steel Research Articles

Evaluation of the stress corrosion crack growth behaviour of high-strength marine steel based on model of crack tip mechano-electrochemical effect

Here, the stress corrosion crack growth behaviour of a high-strength low-alloy steel under anodic potential was investigated in artificial seawater. As applied potential shifts positively, the crack growth rate first increases and then decreases. The crack growth behaviour is controlled by the mechano-electrochemical effect at the crack tip. Even under anodic potential, hydrogen embrittlement (HE) occurs at the crack tip, and HE is the main factor of crack growth. A model of mechano-electrochemical effect at the crack tip is developed to study the phenomenon. It was found that applied potentials change the crack growth behaviour via involvement in HE and anodic dissolution at the crack tip. The critical value of applied potential affecting crack growth is the crack tip potential of –0.0591 pH.

Effect of different feedstocks on the microstructure and mechanical properties of HSLA steel repaired by underwater laser direct metal deposition

Underwater laser direct metal deposition (UDMD) technique shows great potential for the on-site repair of damaged structures in the ocean. In this study, aiming at the possibility of flexible feedstock substitution, two powders with different properties are employed to repair the preprepared HSLA steel plates using UDMD. The combined effects of alloy compositions and UDMD processing on the repair performance including microstructure, mechanical properties and corrosion behavior, are systematically studied. The results show that the localized laser melting/solidification and rapid underwater cooling effect significantly increase the cooling rates, and thus lead to the formation of fine-grained lath martensite and acicular ferrite. The high Ni content in the sample repaired with ultra-high strength (UHS) powder contributes to the interlath austenite. Compared with that of the sample repaired with high strength (HS) powder, the microhardness of the sample repaired with UHS powder is high due to the solid solution strengthening and grain boundary strengthening. In addition, the tensile properties of the UDMD samples exceed the marine steel requirement (yield strength ≥690 MPa). The acceptable impact toughness of the UDMD samples is due to the existence of acicular structures and high fraction HAGBs. Furthermore, the UDMD samples present a better corrosion resistance in comparison with the substrate. The experimental findings demonstrate the employment feasibility of powder substitution on the UDMD repair of complex steel structures in the ocean.

Laser Descaling Area Recognition Method Based on LabVIEW and Machine Vision

Abstract Automated laser descaling represents a crucial advancement in marine maintenance, particularly in localized corrosion treatment. This research utilizes AH32 marine steel for corrosion testing, applying color feature extraction and the OTSU thresholding method, refined with morphological processing, to accurately delineate descaling areas. We have engineered a laser descaling protocol with an impressive 97% recognition accuracy through the innovative application of LabVIEW technology combined with machine vision. Implementing this technology promises enhanced corrosion resistance for marine vessels, setting a new standard for maintenance efficiency and quality.

Study on adhesion mechanism of fouling organisms on marine steel surface based on inverted microscope

Marine stainless steel is immersed in seawater for a long time, and its surface will inevitably adhere layer by layer to form biofilm, which will lead to microbial corrosion of the material. Therefore, it is necessary to master the microbial adhesion mechanism to better control the occurrence of fouling. However, at present, the observation method is to dye by fluorescence microscope or fix the fouling organisms and then observe them by scanning electron microscope (SEM). These methods all damage the cell activity of algae, and only the results of algae attachment can be observed, which is not conducive to further study of algae attachment mechanism. Based on the inverted microscope platform, the observation of algae attached to the metal surface found that the thinner the substrate of the sample liquid, the clearer the image of algae attached to the metal surface, and further found that the dominant algae in the liquid could complete the attachment and aggregation behavior on the metal surface within 1 hour to 2 hours. The conclusions obtained in this paper will guide the study on the attachment mechanism of fouling organisms on metal surfaces and provide a preliminary basis for the design of prevention and control strategies and time points of fouling organisms.

Development of an Al-Zn-Bi alloy sacrificial anode for the protection of steel in artificial seawater: an electrochemical analysis

The Al-Zn sacrificial anodes are widely used for cathodic protection in marine steel structures. This study evaluates the impact of bismuth addition on the electrochemical properties of the Al-Zn sacrificial anode in artificial seawater. The microstructure analysis confirms the presence of uniformly distributed intermetallic β-AlFeSi and spherical Bi within the α-Al matrix. The open circuit potential (OCP) comparison between Al-Zn-Bi and carbon steel reveals a potential difference of approximately 400 mV, indicating sufficient cathodic protection for the steel. Electrochemical impedance measurements indicate the initial hindered dissolution of the anode due to surface film formation, which later dissociates due to the aggressive attack of Cl− species in the electrolyte. The sufficiently negative surface potential (−0.875 Vvs. Ag/AgCl) observed at 10 mA cm−2 demonstrates the suitability of anode for fulfilling the cathodic protection criteria of steel structures.

Surface integrity, corrosion resistance, and low-temperature impact property of FH36 marine steel subjected to ultrasonic surface rolling process

Surface integrity, corrosion resistance, and low-temperature impact property of FH36 marine steel subjected to ultrasonic surface rolling process

Corrosion mechanism and microstructure evolution of yttrium-doped marine steel

The effects of Yttrium dosage and heat treatment process on the microstructure, inclusions, and corrosion resistance of marine steel, as well as the electrochemical parameters on corrosion behavior were studied in this work. The results show that Yttrium mainly exists in Yttrium oxide and Yttrium sulfide. In the process of the optimal heat treatment temperature (800°C-5h), the movement of grain boundaries is hindered by the nailing action of Y2O3, which makes the grain size refined. Yttrium can refine the corrosion products and improve the adhesion ability between the corrosion layer and the substrate, which can effectively improve the corrosion resistance of marine steel. The electrochemical parameters mainly affect the proportion and structure of α-FeOOH and α-Fe2O3 in the corrosion layer by affecting the ion diffusion rate or oxygen content, thus affecting the corrosion resistance property. With the increase of temperature, the diffusion coefficient of oxygen in solution increases, and the limiting current density also increases, which is not conducive to the formation of dense corrosion layer and will lead to faster corrosion speed.

Effect of microstructures tuning on mechanical properties of an ultra-high strength marine steel via the TRIP effect

Effect of microstructures tuning on mechanical properties of an ultra-high strength marine steel via the TRIP effect

Stress Distribution of EH40 with Defects Considering Solid-State Phase Transformation

Residual stress of laser-welded marine steel EH40 was experimentally and numerically analyzed considering weld defects (collapse, hump, and unfitness) and solid-state phase transformation (SSPT). A double-cylindrical source model was used to simulate the temperature distribution. The mean prediction errors of the model without and with weld defects along the plate thickness were 9.2 and 3.5%. Based on the thermodynamics of SSPT, microstructure fractions were computed and verified by weld hardness test results. Under the effect of SSPT, residual stress changed from compressive stress to tensile stress with the increase of the distance from the weld center. Weld defects have an influence on the value of residual stress, and this effect was greater when SSPT was considered. The affected zone extended from the vicinity of weld defects to the whole weld. The variations of longitudinal residual stress (LRS) and transverse residual stress (TRS) caused by weld defects and SSPT both exceeded 150 MPa. LRS was mainly affected by the loss and increase of metal, while TRS was affected by the stress concentration caused by shape geometry changes. Thus, the influence of weld defects on TRS was greater than that on LRS. The proposed finite element model considering weld defects and SSPT can be used to accurately predict residual stress in laser welding of marine steel EH40 and provide a theoretical basis to reduce welding stress.

An intelligent framework for forecasting and investigating corrosion in marine conditions using time sensor data

Corrosion of marine steel structures can be regarded as a time-dependent process that might result in critical strength loss and, eventually, failures. The availability of reliable forecasting models for corrosion would be useful, enabling intelligent maintenance program management, and increasing marine structure safety, while lowering in-service expenses. In this study, an intelligent framework based on a data-driven model is developed that employs a group method of data handling (GMDH) type neural network to forecast free atmospheric corrosion as time-series problem. Therefore, data from sensor data with a 30-min interval over a 110 day period that includes free atmospheric corrosion as well as environmental factors are used. In addition, the Shapley additive explanations (SHAP) technique is used to investigate the impact of the surrounding environmental factors on free atmospheric corrosion. For the performance evaluation of the proposed intelligent framework, selected comparative metrics are used. Findings demonstrate the high accuracy and efficiency of the time series data-driven framework for tackling free atmospheric corrosion progression in marine environments.

ANALYSIS OF RESIDUAL STRESS BY X-RAY DIFFRACTION AND STUDY OF MICROSTRUCTURE IN WELDED JOINT OF ASTM A-36 MARINE STEEL

ASTM A-36 marine steel is one of the most used and classified as a medium strength carbon steel. Its characteristics and purpose are in common applications and in metallic structures in general, sawmills, walkways, agricultural machinery and implements, road, rail and oil implements. It is used in angles, round, flat and square bars and I, U and T profiles. In this work, 10 mm sheets, with a V chamfer, were welded using the MIG/MAG process and X-Ray Diffraction measurements were carried out to study of residual stresses caused by the welding process. Then samples were taken for metallography and microscopy in the Scanning Electron Microscope (SEM). They were also performed in the three regions of the weld: base metal (MB); thermally affected zone (ZTA) and in the molten zone (ZF) Brinell hardness tests, to determine the energy stored in the regions of the weld bead. Vickers Microhardness measurements were also made at the ZTA, as it is a very narrow range, to give more precision to the hardness measurements. The X-Ray Diffraction test showed that the air-cooled samples are compressive and the water-cooled samples are tensile. The micrographs of the samples, in the region of the weld, showed that the ferritic phase prevailed in the molten zone. It was also observed the precipitation of carbides and alloying elements, in addition to the presence of martensite. It is concluded, therefore, that the results for the MIG/MAG welding were satisfactory and recommended for the welding of ASTM A-36 Steel.

Influence of grain size and crystallographic orientation on microbially influenced corrosion of low-carbon steel in artificial seawater

How the microstructure of steel affects a material’s response to microbially influenced corrosion (MIC) in marine applications remains largely unclear, partly because of the challenge in mapping local structure–property relationships. Focusing on sulphate-reducing bacteria, the onset and rate of MIC on low-carbon marine steel samples were analysed with a wide range of grain size and as a function of the local surface crystallography using a combination of optical and electron microscopy, mass loss measurements, and electrochemical testing. It is shown that the alloy’s resistance to MIC decreases with increasing in grain size. A significant effect of the local crystallographic orientation on the material’s dissolution rate is also recorded, which is lowest along the 〈100〉 crystallographic orientation in this steel when exposed to artificial seawater. These findings outline a clear relationship between the microstructure and the susceptibility to MIC in marine steel, which may be used to design alloys with enhanced resistance to MIC in marine applications.

Mechanism of the Interaction Between Hydrogen, Microstructure, and Mechanical Properties in Low-Alloy High-Strength Marine Steel

Mechanism of the Interaction Between Hydrogen, Microstructure, and Mechanical Properties in Low-Alloy High-Strength Marine Steel

Corrosion Performance of Welded Joints for E40 Marine Steel

Marine steel requires excellent toughness and corrosion resistance in a low-temperature seawater environment. In this study, corrosion tests on E40 steel were performed, including electrochemical testing of the weld metal and heat-affected zone, dynamic corrosion testing in a simulated seawater environment, and the analysis and comparison of results obtained using different methods. The corrosion resistance of E40 was determined by measuring the saturation current density of the anodic dissolution of the steel in a corrosive medium by an electrochemical method. Under laboratory conditions, the corrosion resistance was investigated under simulated seawater. The results showed that regions with uneven microhardness corresponded to the inhomogeneity of the corrosion potential, with measured fluctuations of up to 40 mV. Nanoscale corrosive–aggressive non-metallic inclusions served as a substrate for the deposition of titanium and niobium carbonitrides, thereby weakening the corrosion resistance. The corrosion rate of the base metal was 1.16–1.64 mm/year, which was slightly higher than that of the heat-affected zone. The influence of deposition on the corrosion performance of welded joints under different deoxygenation processes was studied, and the deposition composition was controlled by a deoxygenation process to improve the corrosion resistance of the steel plate.

Electrode array probe designed for visualising and monitoring multiple localised corrosion processes and mechanisms simultaneously occurring on marine structures

An electrode array probe has been specially designed and demonstrated for in situ monitoring and visualising multiple localised corrosion processes and mechanisms, including crevice, weldment and pitting corrosion, occurring simultaneously on marine steel structures. It enabled the probing of time-dependent development of multiple localised corrosion processes, mechanisms and kinetics, thereby facilitating more in-depth understanding of the initiation, propagation and kinetics of localised corrosion of steel marine structures.

Effect of Mg-Ce Treatment on Inclusion Characteristics and Pitting Corrosion Behavior in EH420 Marine Steel

Reasonable regulation of nonmetallic inclusions in steel can significantly improve its strength, toughness, and corrosion resistance. In this paper, EH420 marine steel was treated with Mg, Ce, and Mg-Ce to modify the inclusions. The effects of different treatments on the morphology, composition, size distribution, induced intragranular ferrite (IGF) nucleation, and pitting resistance of inclusions were systematically analyzed using various methods. The results show that the Mg-Ce composite treatment can modify irregular MgAl2O4 inclusions into spherical Mg-Ce-O composite inclusions and MgO-dominated inclusions. The density of inclusions is increased from 74.8/mm2 to 186.0/mm2, and the average size of inclusions is decreased from 2.60 μm to 1.07 μm. The Mg-Ce-O composite inclusions are effective inclusions for inducing IGF. Furthermore, the pitting potential is increased from −503 mV to −487 mV, and the corrosion rate is decreased. The order of average electronic work function is ΦMgO < ΦCe2O3 < Φα-Fe < ΦAl2O3. Ce2O3 is hard to induce pitting corrosion due to its similar electronic work function to the steel matrix. Thus, the Mg-Ce composite treatment is better than that for Mg and Ce treatment alone, and has better application prospects.

Report on Investigation Results of Exposure Durability of Titanium-Coated Marine Steel Structures

Report on Investigation Results of Exposure Durability of Titanium-Coated Marine Steel Structures

Influence of available chlorine on corrosion behaviour of low alloy marine steel in natural seawater

ABSTRACT Available chlorine is known to play a significant role in metal corrosion due to its oxidising properties. In this paper, the effect of available chlorine concentration on corrosion behaviour of the low alloy marine steel was investigated by electrochemical and immersion tests. Experimental results show that the corrosion rate of low alloy marine steel is accelerated with the increase of available chlorine concentration in seawater. The localised electrochemical dissolution of the steel is more active with the concentration of available chlorine increasing. Energy dispersive spectroscopy (EDS) was performed to understand the composition of the corrosion products that the large enrichment of Cl element occurred for the high available chlorine concentration (100 ppm) after 720 h exposure to seawater. The influence of available chlorine concentration on mechanical property of low alloy marine steel indicatesthe less impact on the tensile and yield strength of the low alloy marine steel.

Hybrid Zinc Coatings with Chitosan/Alginate Encapsulated CuO-Nanoparticles for Anticorrosion and Antifouling Protection of Mild Steel

The construction of anticorrosion coatings containing antifouling agents is an effective way to ensure the long-term durability of marine steel infrastructures. In this work, an innovative hybrid coating was prepared by introducing biocide CuO nanoparticles in ordinary zinc coating to improve its protective ability for steel in aggressive salt water environments. The CuO nanoparticles were embedded inside the matrix of chitosan/alginate complexes to prevent spontaneous copper leaching during corrosive attacks. Two procedures were applied for the electrodeposition of hybrid/composite zinc-based coatings on low-carbon steel substrates (DC current): first—the co-electrodeposition of encapsulated CuO nanoparticles with zinc on a cathode (steel) electrode from a sulfate electrolyte with a relatively low pH value of about 4.5–5.0 and second—the encapsulated CuO nanoparticles were electrodeposited from aqueous solution as an intermediate layer between two zinc deposits. The particles size and stability of suspensions were evaluated using dynamic light scattering. Both hybrid coatings were compared in terms of surface morphology and hydrophilicity (SEM and AFM analysis, contact angle measurement) and corrosion resistance (potentiodynamic polarization curves, polarization resistance). The protective characteristics of the coatings were compared in a 3.5% NaCl solution and artificial sea water. The hybrid coating showed 2–4 times higher polarization resistance than the bare zinc coating during a 30 day immersion in artificial sea water, indicating that this coating has the necessary characteristics to be used in a marine environment.

Application of Multi-Cylinder Synchronous Control for Telescopic Mechanism of Marine Steel Pile Cleaning Equipment

In order to clean up marine fouling attached to marine steel pile, this paper proposed an innovative configuration scheme of the marine steel pile cleaning equipment by the scraping method and its telescopic mechanism by applying a multi-cylinder synchronous control strategy to the cleaning equipment, and produced a test prototype of the cleaning equipment that could solve the problem of cleaning equipment eccentricity and tilt in the field of ocean engineering. Based on the MATLAB Simulink module, a simulation model of the operation process of the telescopic mechanism of the marine steel pile cleaning equipment was established to complete the evaluation of the multi-cylinder synchronous control performance under multiple working conditions. Through the test, the synchronous working performance of the telescopic mechanism of the cleaning equipment under the no-load condition was preliminarily verified. The test results showed that under the no-load condition, the relative errors between the three cylinders and the target displacement were 0.8%, 0.4%, and 0.2%, respectively, and the cleaning equipment could reach the specified working position at the given working speed. The displacement synchronization error between each cylinder was 0.7 mm, 0.7 mm, and 0.6 mm, respectively, and the displacement synchronization error was controlled within 1 mm. The telescopic mechanism had good synchronization, which can ensure the stability and prevent the eccentricity and tilt during the cleaning equipment operation as well as provide a valuable reference for the manufacturing of cleaning equipment.