Cast Iron Electrodes Research Articles

Electrofrictional Hardening of the 40Kh and 65G Steels

This study investigated the influence of electrofrictional treatment on the structure and hardness of the surface layers of the 40Kh and 65G steels. Based on the results of scanning electron microscopy, it was determined that during the electrofrictional hardening (EFH) of 40Kh steel, a hardened surface layer, with a microhardness of 873 ± 37 HV0.1, was formed. This layer consisted of two zones: a surface-quenched zone, with a structure of fine needle-like martensite and austenite; and a heat-affected zone (transition layer), with a structure of martensite and high-dispersion pearlite (troostite), smoothly transitioning into the original ferrite–pearlite structure. After EFH, a layer with a thickness of ~150 μm containing carbides in the martensite was formed on the surface of the 65G steel, which smoothly transitions into the heat-affected zone with a structure of needle-like martensite. The microhardness of the 65G steel in its initial state was 277 ± 20 HV0.1, and after EFH, it reached 811 ± 23 HV0.1. The results of the microstructure analysis of the 40Kh and 65G steels after EFH were consistent with the results of X-ray phase analysis. It was established that the phase composition of the 40Kh and 65G steels in their initial states consisted of an α-Fe phase with a body-centered cubic (BCC) lattice, and after EFH, both steels formed strengthening phases: residual austenite (γ-Fe) and martensite (α′-Fe). During EFH, under high temperature and pressure conditions, carbon from the cast iron electrode was alloyed with iron, contributing to the formation of cementite on the surface of the 65G steel. These obtained data allowed us to conclude that electrofrictional treatment is an effective method for the surface hardening of 40Kh and 65G steels.

Ductile Iron: A Low-Cost Optimal Anode Material for Electrochemical Generation of Ferrate(VI)

The effects of anode composition and temperature on anode electrochemical properties, the passivation layer’s structure, and ferrate(VI) generation in 14 M NaOH were investigated. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic polarization (GP) were used to analyze the electrochemical processes involving the electrosynthesis of ferrate using some low-cost anode materials: ductile iron, grey cast iron, and mild steel. The results proved that the presence of silicon and graphite with sphere form in the ductile iron anode significantly increased ferrate electro-generation. The optimal temperature for the electro-generation of ferrate was 30 °C–40 °C. The current efficiency using the ductile iron anode was constantly at least about 30% superior to that of the grey cast iron and mild steel electrodes. The ductile iron anode material was the most feasible option because it provides the highest ferrate concentration (1.58 g L−1) with the highest current efficiency of 74% and the lowest specific energy consumption of 1.2 kWh kg−1 ferrate.

EFFECT OF WELDING ELECTRODES AND POST-WELD HEAT TREATMENT ON SOME MECHANICAL PROPERTIES AND MICROSTRUCTURAL TRANSFORMATIONS OF MILD STEEL WELDMENT USING SMAW PROCESS

The current study investigates the effect of some welding electrodes and post-weld heat treatment (PWHT) on tensile strength, hardness, impact energy, and microstructural transformations of mild steel weldments, using the shielded metal arc welding (SMAW) technique. Four different electrode specifications were used in this study, these includes cast iron (AG4700), mild steel (E6014), stainless steel (E308L-16), and mild steel (E6013) electrodes. Eight (8) samples of mild steel plate of length 100mm and 5mm thickness were first sectioned and welded across the width using the four electrodes (2 samples per each). After welding, four of the welded plates with each of the four different electrode materials were then subjected to the post-weld heat treatment (Normalizing) at a temperature of 8000C, soaked for 50 mins, and then allowed to cool naturally in an open-air. Both the heat-treated and the as-welded samples were then subjected to various mechanical tests. The result obtained showed that the welds with mild steel electrodes (E6013 and E6014) possess higher tensile strength for both the heat-treated and untreated welds, while the AG4700 electrode gave the highest impact energy after thermal treatment as compared to other welds. The hardness values with all the four electrode materials were generally found to decrease after post-weld heat treatment. The microstructural results revealed the breaking of the original fine grain structures in the as-welded condition to more coarser structures after heat treatment for all the weldments, which appears to account for the lower hardness obtained in the post-treated steel welds. Based on the results obtained, it can be concluded that some electrode materials impart adequate mechanical properties in the as-welded condition, while some, depending on the type of mechanical properties to be improved, require post-weld heat treatment on the weldment.

Towards in situ electro-generation of ferrate for drinking water treatment: A comparison of three low-cost sacrificial iron electrodes

This work studied the mechanisms governing the electrode processes along with the structure and impact of the passivation layer on the electro-generation of ferrate using three low-cost sacrificial iron materials: mild steel (MS), grey cast iron (GCI) and white cast iron (WCI) electrodes in highly alkaline media. Cyclic voltammetry studies showed that the mechanisms controlling the electrode reactions depend on its alloy composition as it influences the iron species formed in the passivation layer. The presence of silicon in the GCI electrode reduced the stability of the latter, significantly enhancing the ferrate electro-generation due to the persistence of γ-FeOOH in the passivation layer. The instability/dissolution of this layer contributed to a 54%-higher generation of ferrate with GCI when compared to the other electrodes, reaching a maximum titre of 37 mM of ferrate in 10 M NaOH solution with a current efficiency of 45% and the lowest specific energy consumption of 8 kWh kg−1.

Study of Inhibition Performance of a Vapor Phase Inhibitor on Rusty Iron Coins

Immersion tests were used to study the inhibition effects of a complex vapor phase inhibitor on rusty iron coins. Electrochemical behaviors of simulated cast iron specimens in corrosion solution with or without inhibitor have been investigated by Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The rust composition structure of the cast iron coins after corrosion inhibition treatment was analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Scanning Electron Microscope (SEM) has been used to detect the morphology change before and after inhibition treatment. The results show that the vapor phase inhibitor has a good synergistic inhibition effect. The corrosion potentials of cast iron electrode were positive shift and passivation phenomenon has been tested. A steady deposit film containing Fe2O3 and α-FeOOH were formed on the surface of the specimen. A chemisorption was formed between the inhibitor and iron coin surface rust, and the rust changed compact. It increases the corrosion resistance of the rust layer.

Research and Proposal on Welding Technique for Longitudinal Crack Defect Welding

Manufacturing of intentional crack defect welding as designed and similar to realistic crack defects for researches of mechanical properties of welding and training of non-destructive testing (NDT) operator is a difficult and challenging work. Nowadays, methods for manufacturing of specimens of welding with cracking defect still exists some disadvantages such as difficulty in manufacturing, reactionless of the cracks to NDT techniques, the difference between the crack shape and that in nature, and high cost, etc. In this research, we propose a new approach to create welding crack with residual stress using cast iron electrodes. The process to create the welding cracks based on this technology using the SMAW combining with GTAW allows to create the welding with cracks similar to those in nature. Cracks are created with lateral deviation not more than ± 0.5 mm, well response to the phased array ultrasonic testing technique and have similar shape to natural shape of the crack defect.

Experimental Investigation on Weld Ability of Cast Iron

Welding cast iron is used in ships, bridges, pressure vessels, industrial machinery, automobile, rolling stock and many other fields. Problems associated with welding are common issues in these fields. A Study was conducted to investigate Weldability of grey cast iron, as grey cast iron contains graphite in flake form, carbon can readily be introduced into the weld pool, causing weld metal embrittlement and Grey cast iron welds are subject to the formation of porosity and the cold cracking susceptibility of welds. When we observed that gray cast iron is welded non uniform heating and cooling in weld metal and in base metal generates harder Heat Affected Zone (HAZ), cold crack susceptibility and residual stress in weldement. Different methods investigate experimentally to minimize above difficulties. Those methods for reducing the effects of above problems were, minimize base metal dilution, compensate for shrinkage stresses, and the use of low strength filler metals to reduce cracking without sacrificing overall joint strength. Main while the beast type of arc welding electrodes for welding of grey cast iron are nickel and nickel-iron types have been used with or without preheating and / or post weld heat treatment. At the same time Cast iron and steel electrodes must be used with high preheats (530°C) to prevent cracking and the formation of hard deposits. The other mechanisms to improve Weldability of gray cast iron are Pre heating and/or Post heating of the base metal was experimentally employed and investigated.

Simulated textile dye wastewater treatment by electrochemical oxidation: application of response surface methodology (RSM)

One of the main problems linked with wastewater from textile industries is colour. Reactive dyes in industrial discharge are difficult to manage as they are not readily amenable to biological treatment. The present study employs an electrochemical method using cast iron electrodes and sodium chloride (NaCl) as electrolyte to decolourize synthetic wastewater containing reactive red dye (Cibacron Red CR). Response surface methodology was employed to assess individual and interactive effects of operational parameters; electrolyte concentration (0.6–1.0 g/l), current density (1–3 mA/cm2), reaction time (20–60 min) and initial dye concentration (20–100 mg/l) on dye degradation. The range of NaCl concentrations studied did not show any effect on dye removal indicating that the concentrations were higher than the optimum level required. Under optimum process conditions (NaCl concentration 0.6 g/l, current density 1.4 mA/cm2 and reaction time 60 min), initial dye concentration of 100 mg/l could be almost completely removed (≥99%).

Voltammetric and impedance study of the influence of the anode composition on the electrochemical ferrate(VI) production in molten NaOH

Three typical anode materials: pure iron (Fe), silicon-rich steel (FeSi) and white cast iron (FeC) electrodes were used in the process of electrochemical ferrate(VI) synthesis in the molten sodium hydroxide. The voltammetric peak current densities corresponding to the first and second step of the anode dissolution in the case of FeC as well as FeSi electrode are higher compared to the pure iron electrode. After passivity region subsequently the transpassive iron dissolution, including ferrate(VI) formation together with an oxygen evolution occurs and the current shoulder is visible for all electrodes used. Measured electrochemical impedance spectra confirm the physical model of the polarized surface based on the concept of two macrohomogeneous surface layers. In all cases the resistance of both inner and outer layer decrease with increasing applied potential. With increasing temperature the resistance of inner and outer layer decreases. The capacity of inner and outer layer increases with increasing potential. This is in agreement with decrease of the resistances of both layers: layers are getting thinner or more disintegrated by oxygen evolution or strong anodic dissolution. The number of exchanged electrons calculated from a static polarization curve at the potentials in ferrate(VI) formation region is z=3 for all electrode materials used.

Post‐Treatment of Coking Industry Wastewater by the Electro‐Fenton Process

Effluents of the coking industry cannot be effectively treated in biological treatment units because of non-biodegradable organic matters and phenolic compounds present in the wastewater. In this study, post-treatment of biologically treated coking wastewater via the electro-Fenton process was investigated to minimize the effects of discharge of this kind of wastewater on the environment. The electro-Fenton experiments were performed using cast iron electrodes. Chemical oxygen demand (COD) and phenol were selected as the target parameters. The optimum operating conditions were as follows: reaction time = 10 minutes, pH = 3.0, electrical current = 1.0 A, and [H2O2] = 2000 mg/L. Under these conditions, COD and phenol removal efficiencies were 67.8% and 98.0%, respectively. In addition, it was determined that COD removal followed first-order reaction kinetics. Consequently, the electro-Fenton process was determined as an effective alternative post-treatment method for coking industry effluents.

Electrochemical peroxidation of contaminated aqueous leachate

The landfill process for disposal of domestic waste produces a large volume of contaminated aqueous leachate. This study was aimed at investigating the feasibility of using electrochemical peroxidation (ECP) for the treatment of this leachate. ECP is a process by which aqueous, or suspended organic matter, is oxidised by the action of hydroxyl free radicals, produced using hydrogen peroxide and cast iron or mild steel electrodes. The effectiveness of the ECP process was quantified by measuring reductions in leachate biological oxygen demand (BOD) and chemical oxygen demand (COD) as a result of treatment. Optimisation of the process was carried out by varying electrode voltage, polarity switching rate, leachate pH and hydrogen peroxide concentration. This resulted in an observed BOD reduction of 36% and COD reduction of 52%, which was achieved by adjusting the pH to 4.0, applying an electrode voltage of 1.9V and switching speed of 5 cycles per minute. The optimum hydrogen peroxide concentration was found to be 100ppm. In addition to reductions in BOD and COD, reductions in chloride and ammonium levels were measured and found to be 15% and 18% respectively. The results of the investigation indicate that the ECP process is effective in the treatment of landfill leachate, and suggest that with further optimisation, ECP may serve as an attractive alternative to current biological leachate treatment methods.

Electrochemical Pretreatment of Wastewater from Color Photograph Processing Unit

Wastewater emanating from color photograph processing units is usually in small quantities (5–20 L per day) and contains high concentrations of recalcitrant organic compounds. Disposal of such highly recalcitrant wastewater into a public sewer may result in an inhibiting effect on biological treatment system of a sewage treatment plant and thus these persistent organics can escape to receiving water bodies. A continuous full-scale treatment unit for such a small quantity of wastewater is not a viable option, economically and technically. In this study, a small batch type of an electrochemical reactor has been utilized to investigate the feasibility of electrochemical treatment of wastewater from a color photograph processing unit. The treatability studies were conducted using cast iron electrode. It was found that the cast iron electrode was efficient in removing both chemical oxygen demand and biochemical oxygen demand to the levels that meet the standards for discharge to surface water and public sewer. The energy consumption to meet the standards for sewer disposal was less compared to that of surface water disposal. The electrochemical reactor was found to be cost effective in both installation and operation for meeting the sewer disposal standards. It was concluded that the wastewater could be partially treated (pretreatment) electrochemically to meet the standard for sewer disposal rather than that of surface water disposal.

Rapid comparative wear evaluation of oilseed screw press maintenance materials in Nigeria

In Nigeria, the performance of refurbished oilseed screw presses has been severely limited by the arbitrary use of locally available materials for maintenance. To improve the future performance of such presses, a comparative study of the wear characteristics of four different locally available materials, namely mild steel, hardfacing, cast-iron and stainless steel electrode fills, was carried out using a low cost wear testing rig. Mild steel electrode fill deposit proved to have the lowest wear resistance. Whereas cast-iron electrode fill performed best at relatively low operating speed (40 rpm) and pressure (13.7 MPa), stainless steel electrode fill proved to have the highest wear resistance at higher operating speed (85 rpm) and pressure (19.7 MPa). This study provides a scientific basis for future selections of appropriate materials for refurbishing worms and cage linings of worn out oilseed screw presses in Nigeria.

Electrochemical treatment of cigarette industry wastewater: feasibility study

The electrochemical treatability of wastewater from the cigarette industry has been investigated in this paper using cast iron electrode. The treatment efficiency was monitored in terms of COD, BOD and suspended solids concentration. The cast iron anode was found effective in treatment of the above-mentioned wastewater. About 56% of COD and 84% of BOD removal was observed at 3.5 A current for 5 h of electrolysis. The effect of increase in surface area of anode reduces electrolysis time and also energy consumption per kg of COD removal. The treated effluent was subjected to chemical coagulation studies using Ca(OH) 2 as coagulant. The final treated effluent was found to confirm the stipulated standards for safe disposal into surface water bodies (Indian Standards). It was concluded that the electrochemical treatment followed by chemical coagulation could be opted as an alternate treatment scheme for the present industry.

A wear testing rig for rapid comparative evaluation of maintenance materials for some oilseed screw press components

The frequent wear of worms and cage linings and the arbitrary refurbishment of these components using any of the locally available welding electrodes has limited the general performance of oilseed screw presses in Nigeria. A low cost rig, which consists of a sample-bearing piston unit, a cylinder unit and a pressure-sensing unit, was designed and developed for carrying out rapid, inexpensive comparative evaluations of the wear performance of locally available electrode fill materials, for use in the maintenance of worn-out screw press components. In addition to demonstrating the potential value of the rig for comparative wear evaluations, preliminary tests on cast iron electrode fill samples, with a palm kernel fruit oilseed meal, showed that for the same operating pressure of 13.7 MPa, increasing the test operating speed from 40 to 85 rpm led to a 12-fold increase in the wear rate of the samples.

Cast iron deterioration with time in various aqueous salt solutions

The changes with time in the corrosion rate and corrosion current density on a cast iron electrode in various aqueous salt solutions have been carried out using total immersion test and potentiostatic polarization curves. The concentration of salts taken is expected to be present in potable water. The relative behaviour of these salts towards corrosion has also been studied, which is found to be different from previous studies. The total immersion test parameters viz. weight loss, corrosion rate as well as potentiostatic parameters, open circuit potential,I corr, Tafel slopes, corrosion rate, have been calculated by standard methods. Besides these the relative increase in corrosion rate with time as well as the percentage to which corrosion rate should be decreased so as to provide protection towards corrosion have also been calculated. It was found that KCl and NaCl are major contributors than MnSO4, Pb(NO3)2, KI and KBr. The relative increase in corrosion is high in KBr, KI, NaNO3, CaCl2, and less in Pb(NO3)2, NaHCO3 and CaCO3 test solutions. For the reliability of results the data has been statistically analysed.

Dynamic aspects of the electroreduction of chromic acid solutions

Potentiodynamic and impedance spectroscopy measurements were performed on ARMCO iron, steels (C30, C40, C50), cast iron and graphite electrodes in a bath of industrial composition: CrO3 250 g dm−3, H2SO4 2.5 g dm−3. Attention focused on the electrochemical reactions occurring before the start of the chromium deposition. The electrochemical evidence is markedly affected by the chemical nature of the cathode. This is rationalized by proposing a reaction mechanism involving the formation, depending on the chemical nature of the substrate, of a passive adsorbed film consisting of mixed chromium and iron oxides. Moreover, the proposed overall scheme accounts for the presence of periodic current oscillations observed both in potentiodynamic and potentiostatic curves. In close agreement, impedance spectra show negative loops when measured at the corresponding potentials.

Influence of Electrolyte Hydrodynamics on Current Yield in Ferrate(VI) Production by Anodic Iron Dissolution

The dependence of current efficiency for ferrate(VI) synthesis on the superimposed electrolyte flow rate was determined using 14 M NaOH solution and a white cast iron electrode. The electrolyte mean velocity in the cell ranged from 0.4 to 2.9 cm s-1 and current density from 1.4 to 35.3 mA cm-2. It was found that current efficiency was influenced by electrolyte velocity only at current densities lower than 7 mA cm-2. This is explained in terms of the removal of intermediate products from the anode surface by the electrolyte convection. This factor becomes negligible at higher current densities in comparison to mass transfer induced by oxygen evolution on the anode surface.

Electrochemical production of ferrate(VI) using sinusoidal alternating current superimposed on direct current: grey and white cast iron electrodesThis paper is dedicated to the memory of Professor Ivo Roušar.

The current yield during the electrochemical production of ferrate(VI) in a batch cell was measured using grey and white cast iron as working electrode materials. Sinusoidal alternating current superimposed on the direct current with a frequency varying in the range 0.1 mHz to 5 kHz was used. The amplitude (peak to peak) of the alternating current component varied from 39.8 to 91.1 mA cm −2 in the case of grey cast iron and 37.0 to 86.0 mA cm −2 in the case of white cast iron. The direct current density was maintained at a constant value of 16.0 mA cm −2 in both cases. A 14 M NaOH solution was used as electrolyte and the temperature range of 10–50°C was studied. The current yield for ferrate(VI) synthesis exhibited a maximum at frequencies varying from 0.5 mHz to 0.5 Hz and 0.5 to 5 Hz depending on the alternating current amplitude for the grey and white cast iron electrode, respectively.

Nodular iron joint welded with nickel-iron electrodes: Hybrid/mixed finite element analysis

Nickel-iron type cast iron electrodes are widely used in welding QT600–3 nodular iron. In order to obtain the total field displacement, strain, and stress distribution of these welded joints under the critical fracture condition, a highly accurate elasto-plastic hybrid/mixed finite element method has been presented in this paper. Also, the corresponding plane stress element model has been given. In addition, this paper describes macro-imitation of the brittle structure in the welded joints. The calculated displacement results are in good agreement with the experimental measurement by using the Moiré fringe method. The reasons of fracture under the lower tensile stress are also discussed.