Stress-assisted corrosion mechanism of 3Ni steel by using gradient boosting decision tree machining learning method

Traditional 3Ni weathering steel cannot completely meet the requirements for offshore engineering development,resulting in the design of novel 3Ni steel with the addition of microalloy elements such as Mn or Nb for strength enhancement becoming a trend.The stress-assisted corrosion behavior of a novel designed high-strength 3Ni steel was investigated in the current study using the corrosion big data method.The information on the corrosion process was recorded using the galvanic corrosion current monitoring method.The gradi-ent boosting decision tree(GBDT)machine learning method was used to mine the corrosion mechanism,and the importance of the struc-ture factor was investigated.Field exposure tests were conducted to verify the calculated results using the GBDT method.Results indic-ated that the GBDT method can be effectively used to study the influence of structural factors on the corrosion process of 3Ni steel.Dif-ferent mechanisms for the addition of Mn and Cu to the stress-assisted corrosion of 3Ni steel suggested that Mn and Cu have no obvious effect on the corrosion rate of non-stressed 3Ni steel during the early stage of corrosion.When the corrosion reached a stable state,the in-crease in Mn element content increased the corrosion rate of 3Ni steel,while Cu reduced this rate.In the presence of stress,the increase in Mn element content and Cu addition can inhibit the corrosion process.The corrosion law of outdoor-exposed 3Ni steel is consistent with the law based on corrosion big data technology,verifying the reliability of the big data evaluation method and data prediction model selection.

Data-mining and atmospheric corrosion resistance evaluation of Sn-and Sb-additional low alloy steel based on big data technology

Machine-learning and big data are among the latest approaches in corrosion research.The biggest challenge in corrosion research is to accurately predict how materials will degrade in a given environment.Corrosion big data is the application of mathematical methods to huge amounts of data to find correlations and infer probabilities.It is possible to use corrosion big data method to distinguish the influence of the minimal changes of alloying elements and small differences in microstructure on corrosion resistance of low alloy steels.In this research,corrosion big data evaluation methods and machine learning were used to study the effect of Sb and Sn,as well as environmental factors on the corrosion behavior of low alloy steels.Results depict corrosion big data method can accurately identify the influence of various factors on corrosion resistance of low alloy and is an effective and promising way in corrosion research.

Mechanical properties and corrosion behavior of selective laser melted 316L stainless steel after different heat treatment processes

Irregular grains, high interfacial stresses and anisotropic properties widely exist in 3D-printed metallic materials, and this paper investigated the effects of heat treatment on the microstructural, mechanical and corrosion properties of 316 L stainless steel fabricated by selective laser melting. Sub-grains and low-angle boundaries exist in the as-received selective laser melted(SLMed) 316 L stainless steel. After heat treatment at 1050℃, the sub-grains and low-angle boundaries changed slightly, and the stress state and strength decreased to some extent due to the decrease of dislocation density. After heat treatment at 1200℃, the grains became uniform, and the dislocation cells vanished, which led to a sharp decline in the hardness and strength. However, the ductility was improved after recrystallization heat treatment.The passive film thickness and corrosion potential of the SLMed 316 L stainless steel decreased after heat treatment, and the pitting potential also decreased due to the accelerated transition from metastable to steady-state pitting;this accelerated transition was caused by the presence of weak passive films at the enlarged pores after heat treatment, especially for an adequate solid solution treatment.

A new understanding of the effect of Cr on the corrosion resistance evolution of weathering steel based on big data technology

In this work,we studied the effect of Cr element on the corrosion resistance evolution of weathering steel based on corrosion big data technology.It suggested that corrosion big data technology is suitable for evaluation of the effect of microalloying Cr element on the corrosion evolution behavior of weathering steel.New understandings prove that the effect of Cr on the corrosion process is dynamic rather than static,the processes is affected by both of the environmental factors and the electrochemical or chemical reactions in the rust layer.Besides,Cr element has both beneficial effect and detrimental effect on the corrosion resistance of weathering steel.The beneficial effect is that the general corrosion resistance of Cr-additional steel is better than that of Cr-free steel,while the detrimental effect is that localized corrosion is intensified as the increase of Cr content in the Cr-additional steel.

Understanding environmental impacts on initial atmospheric corrosion based on corrosion monitoring sensors

Atmospheric corrosion monitoring(ACM)sensors were employed to study the initial atmospheric corrosion of carbon steels over a one-month period in six outdoor dynamic atmospheric environments in China.Based on the~250,000 corrosion data sets collected,the environmental impacts of relative humidity,temperature and rainfall on the initial corrosion behavior of carbon steels were investigated.The results showed that rainfall was the strongest environmental factor influencing the initial atmospheric corrosion rate.Relative humidity significantly influenced the corrosion of carbon steels in low-precipitation environments and non-rainfall period.

Corrosion Mechanism of Corrosion-Resistant Steel Developed for Bottom Plate of Cargo Oil Tanks

A new type of corrosion-resistant steel consisting of ferrite and bainite phases was developed for cargo oil tanks of crude oil tankers. The corrosion rate of this new steel was 0.22 mm/a, which was equivalent to ca. 1/5 of the criterion（≤1 mm/a） for corrosion-resistant steels. The composition and element distribution of the corrosion products were investigated by micro-Raman spectrometry and energy dispersive spectrometer. The results demonstrated that the corrosion product wascomposed of α-FeOOH, Fe3O4 and a continuous Cu enrichment layer. This kind of corrosion product was protective to the steel matrix and accounted for the enhancement of the corrosion resistance of the new developed steel.

Interaction between austein-ferrite phases on passive performance of2205 duplex stainless steel

The passive behavior of 2205 duplex stainless steel（DSS） and its individual phases（α-phase, γ-phase） in neutral 3.5% NaCl solution was investigated by various electrochemical methods. The results indicated that galvanic effect between α and γ phases cannot deteriorate local corrosion, but favors the enhancement of the passive film. Under the galvanic effect, the diffusion of the dissolved passive cations would be promoted in a short distance between α and γ zones, leading to modifications of the chemical composition and semiconductive property of the passive film and therefore the enhancement of the corrosion resistance of DSS 2205.

Effect of Microstructures on Corrosion Behavior of Nickel Coatings:(Ⅱ) Competitive Effect of Grain Size and Twins Density on Corrosion Behavior

Nanocrystalline nickel coatings with grain size of 50 nm were annealed in vacuum at 200 ℃ and 400 ℃ for 10 min, Their microstructures were investigated by transmission electron microscopy （TEM）. And their corrosion behaviors were studied by means of polarization and electrochemical impedance spectroscopy （EIS）, The results showed that their grain size grew up to about 60 nm （200 ℃） and 500 nm （400 ℃）, respectively, The specimen annealed at 200 ℃ possessed higher density of twins in compared with the counterparts of as-deposited and annealed at 400 ℃, The normal grain size effect on the corrosion behavior was not observed, However, it was found that the corrosion resistance of the coating linearly changed with the density of twins.

Effect of chloride ions on 316L stainless steel in cyclic cooling water

The effect of Cl^- on the 316L stainless steel in simulated cooling water has been studied using polarization curves, electrochemical impedance spectroscopy （EIS）, Mott- Schottky plot and scanning electron microscopy （SEM） techniques. Cl^- concentrations vary from 200 to 900 mg/L. Results reveal that the corrosion resistance increases with the decrease of Cl^- concentration in simulated cooling water. The increase of Cl^- concentration leads to the shift of the corrosion potential towards the positive direction. Mott-Schottky curves show that in the passive film, Cr2Oa and FeO at the inner layer exhibit P-type but Fe2O3 and CrOa （CrO4^2-） N-type semiconductive properties. The SEM/EDX data demonstrate that elements such as Fe, O, C, Si and Cl as well as the presence of calcium and aluminum are presented on the surface of the metal.

Simultaneously Improving Mechanical Properties and Stress Corrosion Cracking Resistance of High-Strength Low-Alloy Steel via Finish Rolling within Non-recrystallization Temperature

The effect of hot rolling process on microstructure evolution,mechanical properties and stress corrosion cracking(SCC)resistance of high-strength low-alloy(HSLA)steels was investigated by varying the finish rolling temperature(FRT)and total rolling reduction.The results revealed granular bainite with large equiaxed grains was obtained by a total rolling reduction of60%with the FRT of 950℃(within recrystallization temperature T_(r)).The larger grain size and much less grain boundaries should account for the relatively lower strength and SCC resistance.A larger rolling reduction of 80% under the same FRT resulted in the formation of massive martensite-austenite(M/A)constituents and resultant low ductility and SCC resistance.In contrast,a good combination of strength,ductility and SCC resistance was obtained via 80% rolling reduction with the FRT of 860℃(within non-recrystallization temperature T_(nr)),probably because of the fine grain size and M/A constituents,as well as a high density of grain boundary network.

Effect of Microstructures on Corrosion Behavior of Nickel Coatings:(Ⅰ) Abnormal Grain Size Effect on Corrosion Behavior

Nickel coatings with different microstructures were synthesized by pulse jet electrodeposition technique.Their morphology and microstructure were investigated by scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The corrosion property of the coatings was studied by using polarization,electrochemical impedance spectroscopy（EIS）,potential of zero free charge（PZFC） measurements and Mott-Schottky（M-S） relationship.The results showed that the coating with grain size of 50 nm possessed higher corrosion resistance than that with grain size of 10 nm.This abnormal behavior may be related to the existence of nanoscale twins in the coatings and the lower concentration of acceptor in the passive films.

Role of Martensite Structural Characteristics on Corrosion Features in Ni-Advanced Dual-Phase Low-Alloy Steels

The relationship between the corrosion resistance and martensite structure of Ni-advanced dual-phase weathering steel was studied using transmission electron microscopy,scanning electron microscopy,electrochemical analysis,and atomic force microscopy.The investigations indicate that the final microstructure of the dual-phase weathering steel was composed of a large amount of low-carbon lath martensite distributed in the ferrite matrix.The potential of the martensite phase is higher than that of ferrite,which acts as a microcathode.As the martensite volume fraction in the Ni-advanced dual-phase weathering steel increased,the corrosion rate increased owing to the greater galvanic couple formed between the ferrite and martensite from the increasing ratio of the cathode area to the anode area.In addition,this work provides a method to obtain advanced weathering steel with improved mechanical properties and corrosion resistance.

Recent Advances on the Corrosion Resistance of Low-Density Steel:A Review

This paper reviews the previous literature on the alloy composition design of low-density steel(LDS),focusing on the eff ect of Al,Mn,Ni,and other alloy elements on the formation of the steel matrix and second phase,and provides classifi cation.The microstructure of LDS after processing includes the matrix structure,к-carbide,and B2(FeAl,NiAl,or MnAl)phase of ferritic LDS,austenitic LDS,and dual-phase LDS.The infl uence of alloy elements on the corrosion resistance of LDS is derived from the addition of Al and Mn for metallurgy.Additionally,the infl uence of Cr and Mo addition on the corrosion resistance improvement was studied.The electrochemical properties of the corrosion process in LDS are discussed.Further,the microstructure of LDS aff ects the corrosion resistance properties including pitting corrosion,hydrogen embrittlement,and SCC(stress corrosion cracking).Finally,future research directions are proposed.

Effects of Carbon Content and Microstructure on Corrosion Property of New Developed Steels in Acidic Salt Solutions

New steels with different carbon contents were self-developed by thermo-mechanical controlled processing. The effects of the carbon content and the microstructure on the corrosion properties of new steels were investigated by immersion test and SEM. The results indicated that the ferrite phase （both the proeutectoid and eutectoid ferrite） dissolved preferentially. Cementite reserved and accumulated on the surface. As carbon content increased, the content of ferrite decreased and cathode/anode area ratio increased. Therefore, the corrosion rate of new steels increased from 0.30 to 0.90 mm/years when the carbon content rose from 0.05 to 0.13 wt%. The corrosion process of new steels was studied using electrochemical impedance spectroscopy experiments during 72 h. It indicated that the impedance modulus IZlo.ol nz of the new steels reduces with the increase of the immersion time. While the corrosion process of the new steel with 0.11 wt% C developed faster than that with 0.07 wt% C, although their IZlo.ol nz was similar at the initial stage.