Cathodic Polarization Conditions Research Articles

高張力４３４０鋼ＳＣＣ破面近傍の残留応力分布に及ぼす電極電位の影響

Stress corrosion cracking tests were conducted by using the compact tension (CT) specimens of 200°C tempered AISI 4340 steel in a 3.5% NaCl solution environment under various electrode potentials. The distribution of the residual stress beneath the fracture surface was measured with the X-ray diffraction technique. The fracture surface and the crack morphology were also observed by scanning electron microscopy. The Effect of electrode potential on the growth kinetics of stress corrosion cracking was discussed on the bases of the results of X-ray observation and scanning microfractography. The results obtained are summarized as follows:(1) The residual stress measured on the fracture surface was tension under cathodic potential. It decreased with increasing potential, and changed to compression under anodic potential.(2) The relation between the plastic zone depth ωy and the stress intensity factor K can be approximated by the following fracture mechanics equation:ωy=α(K/σY)2where σY is the yield strength. The α value was 0.084 under the free corrosion condition and 0.053 under the cathodic polarization condition.

Influence of impurities and microalloying on the delayed failure resistance of steels

The mechanical properties and delayed failure resistance of high-strength bolts made of steels of different degrees of purity and microalloyed with additions of titanium, boron, and niobium were studied. Bolts made of 40Kh steel, 40Kh-PV steel, and 20Kh2NMTRB steel were used for the investigation. Three-point bend tests were conducted and fracture toughness and the work for crack origin and propagation were determined from the test results. Delayed failure tests were made under conditions of cathodic polarization and hydrogen impregnation. Results of the investigations were comparatively analyzed and relations between the failure resistance, structure, composition, and impurity content of the microalloyed steels were established.

Investigation of Transient Polarization Currents during the Corrosion Fatigue of Mild Steel in 3.5% NaCl Solution

Abstract The corrosion fatigue behavior of mild steel in aqueous 3.5% NaCl solution has been investigated. The corrosion fatigue crack growth rate and the variation of transient polarization currents have been studied simultaneously under anodic and cathodic polarization conditions and at open circuit potential (OCP).

Chloride pitting and water chemistry control in cooling or boiler circuits

The effect of different anions (bicarbonate, phosphate, sulphate, hydroxyl) on the pitting corrosion by chloride ions has been investigated for a number of ferritic or austenitic steels and nickel alloys at different temperatures up to 175°C. For most of the alloys the normal order of inhibition is PO 4 3 > SO 4 2- ⩾ HCO 3, but some anomalies have been encountered for stainless steels at lower temperatures (<100°C), where the inhibitive action of SO 4 2- maybe more pronounced that the inhibition which can be obtained by adding equal amounts of phosphate. In the absence of strongly passivating alloying elements, such as chromium, high SO 4 2 concentrations may have a deteriorative effect. The same result may also be found under cathodic polarization conditions, where SO 4 2- and HCO 3 seem to stimulate reductive dissolution of the protective surface layer and may even cause some kind of pitting-type attack.

Investigation of stress corrosion cracking of the cast and forged steel in water

The aqueous stress corrosion behavior of cast steel and forged steel of the same heat has been examined. It was shown that the activation energy of crack growth of both cast and forged steels was identical,i.e., Q = 5540 cal/mol, and was comparable with the apparent diffusion activation energy of hydrogen in the steel. Theda/dt for cast and forged steel increased under both cathodic and anodic polarization conditions. Correspondingly, the steady-state hydrogen permeation flux increased steeply with the increase of polarizing current under either cathodic or anodic polarization. The influences of the polarization upon theda/dt and the hydrogen permeation flux were similar. TheK ISCC of the cast steel was larger than that of the forged steel. This may be due to the observation that the steady-state permeation flux for the forged steel was twice as large as that of the cast steel. For both cast and forged steels the fracture modes were clearly dependent uponK I at the crack tip, and a transition from dimple to quasi-cleavage or intergranular was observed on the fracture surfaces with decreasingK I .

Corrosion and Electrochemical Behavior of Titanium in aqueous sulfidic solutions

AbstractThis paper summarizes the results of an investigation of the corrosion and electrochemical behavior, including cathodic hydrogen absorption, of titanium in acidic and alkaline sulfidic solutions. The effect of chloride and cyanide ions on the corrosion behaviour of titanium in sulfidic solutions was also studied. Titanium in acidic and alkaline sulfidic solutions exhibits a stable passive corrosion potential and negligible corrosion. Chloride and cyanide ions do not affect the corrosion behavior of titanium in sulfidic solutions. Cyanide ions under conditions of cathodic polarization tend to promote activation of titanium. Cathodic polarization at temperatures higher than 72 °C promotes hydrogen uptake in titanium and formation of titanium hydride. The rate of hydrogen uptake increases with decreasing pH and increasing temperature. Cyanide ions tend to promote the rate of hydrogen uptake, whereas chloride ions have essentially no effect.

電解鉄の変形応力におよぼす固溶水素と水素析出の影響

Recently much interest has been focused on the role of hydrogen-dislocation interactions in relation to the susceptibility of materials to hydrogen embrittlement. By using electrolytic iron as a specimen, tensile tests were carried out under conditions of concurrent cathodic polarization to maintain a concentration of dissolved hydrogen in a dynamic steady state. Since cathodic hydrogen charging causes internal damage and dynamic interactions of dissolved hydrogen with moving dislocations, tensile stress shows various changes with charging conditions. In the present study the influence of the dissolved hydrogen on the flow stress was distinguished from that of the hydrogen damage by selection of the charging and tensile conditions. While the dissolved hydrogen increases flow stress by a dynamic interaction with moving dislocations, the precipitation of hydrogen produces a number of cracks and deformation, and decreases flow stress.The gas pressure produced by hydrogen damage, such as cracks or voids, was estimated by using the apparent hydrogen solubility deduced from a trapping model and the equation proposed by de Kazinczy. The gas pressure thus estimated was comparable to the tensile strength of the iron specimen. The relation between the applied stress and the internal stress resulting from hydrogen precipitation was also studied by measuring the stress changes caused by heavy hydrogen charging during stress relaxation. The stress relaxation caused by the heavy hydrogen charging was mainly due to the high stress caused by the precipitation of hydrogen.

Mutual Occurrence of Cathodic and Anodic Cracking in Iron

Abstract Experimental evidence is presented which supports the contention that anodic dissolution can occur in iron under strong cathodic polarization conditions. This evidence takes the form of metallographic observations of surface nucleated macrocracks, as well as the presence of ferrous ions in that part of the electrolyte in contact with such cracks. The implications of the presence of these cracks on material integrity and the efficacy of cathodic protection are briefly discussed.

Photopotential measurements in the study of surface layers in metal corrosion, inhibition and passivation phenomena

Photopotential measurements have been used to investigate the semiconducting characteristics of surface layers on metallic materials in different electrolytic environments. The photopotential data are measured by a pulse technique, the duration of the light pulse being 0.2–1 × 10 -3 sec and the ratio of light to dark time 1–2.5 × 10 -2. The oscillographic recording of the photopotentials allows the determination of the p- or n-type semiconducting properties of the surface layers. Photopotential recording is possible on free corroding metals or under galvanostatic anodic and cathodic polarization conditions. By using this technique, the surface layers formed in the following experimental conditions have been examined: 1. (1) free corroding or polarized copper electrodes in chloride solutions, in the presence or absence of different organic corrosion inhibitors; 2. (2) free corroding or polarized nickel electrodes in sulphate solution. In some cases the results are compared with those obtained by different techniques. A relationship between the semiconducting characteristics (the sign and time constant of the photopotential) and the protecting efficiency of the surface layers is examined.

The effects of polarization on the failure in acids of cold-worked 18Cr [sbnd]10Ni steels

The fracture of tensile specimens of heavily cold-worked 18Cr 10Ni austenitic stainless steels subjected to a low strain-rate at room temperature has been examined by optical microscopy. Experiments were performed in air and in both H 2SO 4 and HCl + NaCl (a) under open circuit conditions and (b) polarized galvanostatically, cathodic and anodic at c.ds. up to 100mA/cm 2. Two types of fracture were induced by the environment: (i) s.c.c. occurred in HCl + NaCl under conditions of anodic polarization (this was associated with the prior occurrence of pitting and crevice attack and fracture did not always occur across the narrowest section of a specimen), (ii) embrittlement under conditions of cathodic polarization in both solutions (this was associated with blister formation which occurred more readily in H 2SO 4 and appeared to be promoted by plastic deformation). Experiments on pre-pitted specimens indicated that the effect of pitting was chemical rather than metallurgical.

Galvanic coatings on titanium alloys

1. In the cathodic polarization of a titanium electrode in acid and alkaline solutions, the hydrogen evolved interacts with the metal of the cathode. The composition and structure of the compounds of titanium with hydrogen formed, depend upon the electrode potential, the nature of the electrolyte, the current density, and the time of treatment. 2. Under certain conditions of cathodic polarization, simultaneously with the formation of titanium hydrides, a breakdown of them is observed. The ratio of the rates of formation and decomposition of the hydrides depends upon the electrode potential and the nature of the electrolyte. 3. The evolution of cathodic hydrogen on the surface of titanium, freed of oxides, occurs at high negative potentials. With increasing saturation of the surface of the titanium electrode with hydrogen, its potential is shifted in the direction of electropositive values.

Effect of cathodic protection on the corrosion-fatigue strength of steels of various hardness in sea water

1. Steels 20, 40 and 45KhNMFA of widely different hardnesses were shown to have a qualitatively similar dependence of their corrosion-fatigue strength in a 3% NaCl solution (simulating sea water) on the cathodic current density: the effectiveness of cathodic protection increases as the current density increases to a certain critical value, and beyond it decreases. 2. Under optimum cathodic polarization conditions, the corrosion-fatigue limit of steel 20 practically reaches, and that of steel 40 exceeds, the corresponding fatigue limits in air. The maximum corrosion-fatigue limit of steel 45KhNMFA at the optimum cathodic current density is 20% lower than the fatigue limit in air. 3. A reduction in effectiveness of cathodic protection at current densities higher than the optimum is observed for all steels, but is particularly large for hard steels. 4. The character of the dependence of corrosion-fatigue strength on cathodic current density is explained as being a result of the interaction of two factors producing opposite effects. The “positive” factor is the protective action of cathodic polarization and the “negative,” the reduction in fatigue strength by absorbed hydrogen.