C1018 Carbon Steel Research Articles

Structural and mechanical properties of radiofrequency N2/H2cold plasma-nitrided C38 carbon steel

C38 carbon steel has been nitrided by radiofrequency cold plasma discharge with the aim to study the effect of gas composition on structural and mechanical properties of nitrided substrates. The plasma nitriding was carried out on unheated substrates, using two different gas mixtures (75% N 2 /25% H 2 and 25% N 2 /75% H 2 ) for 8 h of plasma treatment. Electron Probe Microanalysis (EPMA) showed that the nitrogen content and the nitride layer thickness mainly depend on the hydrogen content in the plasma. For 75% N 2 /25% H 2 mixtures, nitrided samples showed the formation of thicker nitride layer with high content of nitrogen compared to those formed in the case of 25% N 2 /75% H 2 or pure N2 . The thickness of the nitride layer formed is approximately 15 μm for 8 h of plasma with 75% N 2 /25% H 2 . X-ray photoelectron spectroscopy (XPS) was employed to obtain chemical-state information of the plasma- nitrided steel surfaces. The mechanical properties of plasma-nitrided C38 steel were investigated by Vickers microhardness measurements. The micromechanical results show the formation of a new hard layer on the surface after N 2 /H 2 treatment plasma and it reaches a maximum value of more than 2242 HV 0.005 for 75% N 2 /25% H 2 plasma-nitrided samples. However, a decrease in the hardness values with the applied load has been evidenced.

Radiofrequency cold plasma nitrided carbon steel: Microstructural and micromechanical characterizations

In this work, C38 carbon steel was plasma nitrided using a radiofrequency (rf) nitrogen plasma discharge on non-heated substrates. General characterizations were performed to compare the chemical compositions, the microstructures and hardness of the untreated and plasma treated surfaces. The plasma nitriding was carried out on non-heated substrates at a pressure of 16.8 Pa, using N 2 gas. Surface characterizations before and after N 2 plasma treatment were performed by means of the electron probe microanalysis (EPMA), X-ray photoelectron spectroscopy (XPS) and Vickers microhardness measurements. The morphological and chemical analysis showed the formation of a uniform structure on the surface of the nitrided sample with enrichment in nitrogen when compared to untreated sample. The thickness of the nitride layer formed depends on the treatment time duration and is approximately 14 μm for 10 h of plasma treatment. XPS was employed to obtain chemical-state information of the plasma nitrided steel surfaces. The micromechanical results show that the surface microhardness increases as the plasma-processing time increases to reach, 1487 HV 0.005 at a plasma processing time of 8 h.

Study of Temperature Effect on the Corrosion Inhibition of C38 Carbon Steel Using Amino-tris(Methylenephosphonic) Acid in Hydrochloric Acid Solution

Tafel polarization method was used to assess the corrosion inhibitive and adsorption behaviours of amino-tris(methylenephosphonic) acid (ATMP) for C38 carbon steel in 1 M HCl solution in the temperature range from 30 to . It was shown that the corrosion inhibition efficiency was found to increase with increase in ATMP concentration but decreased with temperature, which is suggestive of physical adsorption mechanism. The adsorption of the ATMP onto the C38 steel surface was found to follow Langmuir adsorption isotherm model. The corrosion inhibition mechanism was further corroborated by the values of kinetic and thermodynamic parameters obtained from the experimental data.

Study of corrosion resistance properties of nitrided carbon steel using radiofrequency N 2/H 2 cold plasma process

C38 carbon steel have been plasma-nitrided using a radiofrequency cold plasma discharge treatment in order to investigate the influence of gas composition on corrosion behaviour of nitrided substrates. The investigated C38 steel was nitrided by a RF plasma discharge treatment using two different gas mixtures (75% N 2/25% H 2 and 25% N 2/75% H 2) at different times of plasma-treatment on non-heated substrates. Electron Probe Microanalysis (EPMA) showed that the nitrided layer formed using 75% N 2/25% H 2 gas mixture was thicker compared to those formed in the case of 25% N 2/75% H 2 or pure N 2. The modifications of the corrosion resistance characteristics of plasma-nitrided C38 steel in 1 M HCl solution were investigated by weight loss measurements and ac impedance technique. The results obtained from these two evaluation methods were in good agreement. It was shown that the nitriding treatment in both cases (75% N 2/25% H 2 and 25% N 2/75% H 2) improves the corrosion resistance of investigated carbon steel, while the better performance is obtained for the 75% N 2/25% H 2 gas mixture. X-ray photoelectron spectroscopy (XPS) was carried out before and after immersion in corrosive medium in order to establish the mechanism of corrosion inhibition using N 2/H 2 cold plasma nitriding process.

Ac impedance, X-ray photoelectron spectroscopy and density functional theory studies of 3,5-bis( n-pyridyl)-1,2,4-oxadiazoles as efficient corrosion inhibitors for carbon steel surface in hydrochloric acid solution

The corrosion inhibition properties of a new class of oxadiazole derivatives, namely 3,5-bis( n-pyridyl)-1,2,4-oxadiazoles ( n-DPOX) for C38 carbon steel corrosion in 1 M HCl medium were analysed by electrochemical impedance spectroscopy (EIS). An adequate structural model of the interface was used and the values of the corresponding parameters were calculated and discussed. The experimental results showed that these compounds are excellent inhibitors for the C38 steel corrosion in acid solution and that the protection efficiency increased with increasing the inhibitors concentration. Electrochemical impedance data demonstrate that the addition of the n-DPOX derivatives in the corrosive solution decreases the charge capacitance and simultaneously increases the function of the charge/discharge of the interface, facilitating the formation of an adsorbed layer over the steel surface. Adsorption of these inhibitors on the steel surface obeys to the Langmuir adsorption isotherm. X-ray photoelectron spectroscopy (XPS) and the thermodynamic data of adsorption showed that inhibition of steel corrosion in normal hydrochloric solution by n-DPOX is due to the formation of a chemisorbed film on the steel surface. Quantum chemical calculations using the Density Functional Theory (DFT) and the Quantitative Structure Activity Relationship (QSAR) approach were performed on n-DPOX derivatives to determine the relationship between molecular structure and their inhibition efficiencies. The results of the quantum chemical calculations and experimental inhibition efficiency were subjected to correlation analysis and indicate that their inhibition effect is closely related to E HOMO, E LUMO, and dipole moment ( μ).

Evolution of dissolution processes at the interface of carbon steel corroding in a CO 2 environment studied by EIS

The evolution of interfacial phenomena during CO 2 corrosion of C1018 carbon steel was characterized by EIS (Electrochemical Spectroscopy Impedance) and LPR (Linear Polarization Resistance). Turbulent conditions were simulated by a channel flow cell with deoxygenated 3 wt.% NaCl solution at 80 °C and pH 6 during 158 h. EIS helped in the characterization of the dynamic mechanism during the formation of the unprotective porous Fe 3C layer, and subsequent precipitation of the protective FeCO 3 layer inside the cementite. The experimental response of the active states at the interface was characterized by electrical passive elements with constant phase parameter analogs showing good agreement with the experimental results.

Enhanced corrosion resistance of carbon steel in normal sulfuric acid medium by some macrocyclic polyether compounds containing a 1,3,4-thiadiazole moiety: AC impedance and computational studies

We report here the use of macrocyclic polyether compounds containing a 1,3,4-thiadiazole moiety ( n-MCTH) in the corrosion inhibition of C38 carbon steel in 0.5 M H 2SO 4 acid medium. ▪ The aim of this work is devoted to study the inhibition characteristics of these compounds for acid corrosion of C38 steel using electrochemical impedance spectroscopy (EIS). Data obtained from EIS show a frequency distribution and therefore a modeling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. The experimental results obtained revealed that these compounds inhibited the steel corrosion in acid solution and the protection efficiency increased with increasing inhibitors concentration. The difference in their inhibitive action can be explained on the basis of the number of oxygen atoms present in the polyether ring which contribute to the chemisorption strength through the donor acceptor bond between the non bonding electron pair and the vacant orbital of metal surface. Adsorption of n-MCTH was found to follow the Langmuir’s adsorption isotherm. The thermodynamic functions of adsorption process were calculated and the interpretation of the results is given. These results are complemented with quantum chemical study in order to provide an explanation of the differences between the probed inhibitors. Correlation between the inhibition efficiency and the structure of these compounds are presented.

Enhanced corrosion resistance properties of radiofrequency cold plasma nitrided carbon steel: Gravimetric and electrochemical results

Cold plasma nitriding treatment was performed to improve the corrosion resistance of C38 carbon steel. Nitriding process was conducted using a radiofrequency nitrogen plasma discharge for different times of treatment on non-heated substrates. The modification of the corrosion resistance characteristic of the C38 steel due to the treatment in acid medium (1 M HCl) were investigated by gravimetric and electrochemical tests such as potentiodynamic polarisation curves and electrochemical impedance spectroscopy (EIS). It was shown that the plasma nitriding treatment improves the corrosion resistance. Indeed, in the gravimetric tests, nitrided samples showed lower weight loss and lower corrosion rate in comparison to untreated one. In the Tafel polarisation tests, the nitrided samples showed greatly reduced corrosion current densities, anodic dissolution and also retarded the hydrogen evolution reaction. Using EIS method, an adequate structural model of the interface was used and the values of the corresponding parameters were calculated and discussed. The results obtained from weight loss and electrochemical studies were in reasonable agreement. X-ray photoelectron spectroscopy (XPS) was carried out to establish the mechanism of corrosion inhibition of nitrided C38 steel in 1 M HCl medium. The enhancement of the corrosion resistance is believed to be related to the iron nitride compound layer formed on the C38 steel surface during plasma nitriding, which protected the underlying metal from corrosive attack in the aggressive solutions.

Effects of selection and fate of substrates supplied to anaerobic bacteria involved in the corrosion of pipe-line steel

The corrosion of AISI C1020 carbon steel in an anoxic, marine, sulphide-containing environment was examined as a function of bacterial physiology and consortial complexity. The carbon steel was exposed to three organism;Eubacterium limosum, Desulfovibrio sp. andDesulfobacter sp. which were provided with H2/CO2, butanol, glucose, and acetate as carbon and electron sources. A consortium of these bacteria utilizing hydrogen gave rise to relatively high corrosion rates (5.7×10−4 mhos cm−2) with respect to corrosion resulting from bacteria supplied with organic electron sources (0.6–1.6×10−4 mhos cm−2). Disproportionation of electrons between sulphate reduction and fermentation had a significant effect on the corrosion rate in the case ofDesulfovibrio. Surface examination using scanning electron microscopy coupled with electrochemical impedance spectroscopy supported the hypothesis that the corrosion rate was controlled by the relative intactness of a ferrous sulphide film in which the bacteria were embedded.

Multi-electrode probe for statistical evaluation of microbiologically influenced corrosion

Microbial biofilms increase the complexity and spatial variation of the interfacial chemistry occurring at metal surfaces and can facilitate corrosion. A multi-electrode probe was designed to replicate interfacial chemistry by providing multiple interfaces on a single probe. Electrochemical impedance spectroscopy (EIS) was used to examine the electrochemical properties of four-electrode probes containing 430 (USN430000) stainless steel coupons in test solutions. The EIS results obtained with the probe were compared to the ASTM G-106 standard method, and the probe was determined to be accurate. In addition, no interference or crosstalk between electrode channels was observed. In order to demonstrate the utility of the probe, four-electrode probes were used to investigate microbiologically influenced corrosion of C1020 carbon steel. Enrichments of aerobic, fermentative, and sulfate reducing bacteria from a corrosion tubercle were inoculated into the bulk phase of a corrosion cell and formed biofilms on the carbon steel electrodes. A five fold increase in the polarization admittance of carbon steel coupons exposed to biofilms relative to sterile medium was observed. The four-electrode probe provided the necessary degrees of freedom to show the statistically significant differences.

A study of carbon steel corrosion inhibition by phosphate ions and by an organic buffer using a scanning vibrating electrode

The scanning vibrating reference electrode technique (SVET) has been used to map anodic and cathodic currents in solutions over freely corroding type C1020 carbon steel. All solutions contained millimolar concentrations of chloride and were sterilized. The effect of phosphate and an organic buffer on the corrosion of carbon steel in liquid media were studied because they were added to promote bacterial growth. Phosphate acted as an anodic inhibitor in the media, causing initiated pits to repassivate. If initiated pits did not repassivate, for example in a stagnant medium or when crevice corrosion initiated adjacent to the sample coating, the corrosion rates increased and the corrosion remained localized. Increased anodic current resulted in a drop in the open circuit potential and a decrease in the polarization resistance. The results show that phosphate can lead to lower average corrosion rates, than uninhibited steel, but as an anodic inhibitor can also lead to rapid penetration at localized sites.