Influence of peening on the corrosion properties of AISI 304 stainless steel

The effects of peening treatment on the microstructure and corrosion behavior of AISI 304SS were investigated. Shot and ultrasonic peening were performed on the austenitic stainless steel, and peened specimens were compared in terms of microstructure, surface roughness and corrosion resistance. Nano-sized grains, multi-directional mechanical twins and strain-induced martensite were formed on the surfaces, and the volume fraction of strain-induced martensite in the ultrasonically peened specimen was higher than that of the shot-peened specimen. The ultrasonically peened specimen which had smoother surface and contained more strain-induced martensite showed superior general and localized corrosion resistance to the as-received and shot-peened specimens.     

The relation between microstructure and corrosion behavior of AZ80 Mg alloy following different extrusion temperatures

Cast AZ80 alloy was subjected to conventional extrusion pressing at 250 °C, 300 °C, and 350 °C. In order to characterize the changes in their microstructure a thorough study was done through various microscopy analyses including Optical Microscope, SEM, and TEM.Corrosion performance of each condition was investigated in 3.5% NaCl solution saturated with Mg(OH)₂ (pH ≈ 10.5) using immersion and AC and DC polarization tests. The local potential difference on the surface resulting from different compositions of second phase particles to the matrix was investigated using scanning Kelvin probe force microscopy (SKPFM) technique.The results show grain refinement by a factor of about 15-20 and obvious evidence of dynamic recrystallization were identified leading to the formation of nano-sized grains after the extrusion process.The corrosion resistance of cast AZ80 alloy drastically decreases after the thermo-mechanical processes and the main factor is high dependence on different phase rearrangements before and after the extrusion process, especially β phase. For the extrusion conditions, different corrosion resistances are attributable especially to dislocation rearrangement results by grain growth after dynamic recrystallization.     

Effect of tensile strain on the rate of marine corrosion of steel plates

It has been observed in the shipping industry that the rate of corrosion of steel plate may increase with longer duration of exposure, typically over many years. This effect has been attributed to the flexure of ships plates causing the loss of protective rust layers. The present paper describes the results of laboratory experiments in which plates with pre-existing rusts were subject to high levels of tensile strain, with and without subsequent exposure and corrosion. All rusts were obtained by exposing the steel to a natural marine environment, including the atmospheric and tidal zones. Careful observation of the rusts under tensile strain conditions showed that only strains near and beyond the elastic limit of the steel have the capacity to cause significant damage to the rust layers. Subsequent short-term exposure tests on pre-corroded and pre-strained steel coupons showed that there can be a moderate (10–15%) increase in the short-term corrosion rate.     

Influence of stress on passive behaviour of steel bars in concrete pore solution

The influence of stress on passive behaviour of steel bars in concrete pore solution was studied with electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The passive ability of steel decreased as the applied load increased and higher load had much greater influence on passivation than repeated loading of small magnitude. A micro-crack model was presented to explain the damage of passive layer by loads. Lower load caused micro-cracks in the passive film which might be completely recovered after unloading. Under higher load more micro-cracks were produced in the passive film and some may penetrate the film, leading to irreversible damages.     

Corrosion behaviour of low-carbon bainitic steel under a constant elastic load

The corrosion behaviour of low-carbon bainitic weathering steel in an environment containing chlorine ions (Cl⁻) was studied by applying different constant elastic loads. The results showed that the applied elastic load reduces the resistance of the rust layer to Cl⁻ diffusion because of the porous structure as well as the enhanced anion selectivity in the rust: this leads to more severe corrosion of the steel compared with load-free conditions. The corrosion rate increased with increasing loads. Corrosion enhancement can be attributed to mechanical-chemical interactions at the steel surface.     

Effect of AC on stress corrosion cracking behavior and mechanism of X80 pipeline steel in carbonate/bicarbonate solution

The influence of various AC current densities on stress corrosion cracking behavior and mechanism of X80 pipeline steel was investigated in carbonate/bicarbonate solution by polarization curves and slow strain rate tensile tests. With the increasing AC current density, the SCC susceptibility of the steel increases, especially at high AC current density. A significant difference in the SCC behavior and mechanism is found for the steels with or without AC application. In the absence of AC, the fracture mode is intergranular and the mechanism is attributed to anodic dissolution. Under AC application, the cracks propagation is transgranular, and the mechanism is mixed controlled by both anodic dissolution and hydrogen embrittlement.     

Effect of surface nanocrystallization on the corrosion behaviour of AISI 409 stainless steel

The influence of surface mechanical attrition treatment (SMAT) on the corrosion behaviour of AISI 409 grade stainless steel in 0.6 M NaCl was studied. SMAT using 2 mm ∅ 316L stainless steel (SS) balls for 15, 30 and 45 min and 5 mm ∅ balls for 15 min offers a better corrosion protective ability. In contrast, treatment using 5 mm ∅ balls for 30 and 45 min and by using 8 mm ∅ balls for 15, 30 and 45 min, induces microstrain and defect density that results in a decrease in corrosion resistance.     

Localized corrosion behaviour of reinforcement steel in simulated concrete pore solution

The correlation of localized corrosion behavior and microstructure of reinforcement steel in simulated concrete pore solutions was investigated. The SEM/EDS analysis showed that most of ferrite, minor amount of pearlite and some MnS inclusions existed on the steel surface. The SKPFM results indicated a higher corrosion tendency at the ferrite grain boundaries, pearlite grains and MnS inclusions. The EIS and electrochemical polarization measurements demonstrated the influence of pH and chloride concentration on the corrosion behavior. In situ optical observations and AFM images revealed a detail of the localized corrosion behavior, which was in good agreement with the results from the other measurements.     

Electrochemical corrosion of X65 pipe steel in oil/water emulsion

The electrochemical corrosion behavior of X65 pipeline steel in the simulated oil/water emulsion was investigated under controlled hydrodynamic and electrochemical conditions by rotating disk electrode technique. Results demonstrated that mass-transfer of oxygen plays a significant role in the cathodic process of steel in both oil-free and oil-containing solutions. Electrode rotation accelerates the oxygen diffusion and thus the cathodic reduction. The higher limiting diffusive current density measured in oil-containing solution is due to the elevated solubility of oxygen in oil/water emulsion. The anodic current density decreases with the increase of electrode rotating speed, which is attributed to the accelerated oxygen diffusion and reduction, enhancing the steel oxidation. Addition of oil decreases the anodic dissolution of steel due to the formation of a layer of oily phase on steel surface, increasing the reaction activation energy. The steel electrode becomes more active at the elevated temperature, indicating that the enhanced formation of oxide scale is not sufficiently enough to offset the effect resulting from the enhanced anodic dissolution reaction kinetics. The corrosion reaction mechanism is changed upon oil addition, and the interfacial reaction is activation-controlled, rather than mass-transfer controlled. When sand particles are added in oil/water emulsion, there is a significant increase of corrosion of the steel. The presence of sands in the flowing slurry would impact and damage the oxide film and oily film formed on the steel surface, exposing the bare steel to the corrosive solution.     

Descaling ability of low-alloy steel wires depending on composition and rolling process

Low-alloy steels made by industrial processes are covered with an iron oxide layer. Descaling is necessary before any shaping operations by wire drawing can be done to transform wires. In order to ease the descaling stage, this oxide layer must have low adhesion. This paper presents a study of the descaling ability of different steels. The results presented in this paper show that it is possible to qualitatively predict the adhesion capacity of the scale depending on the alloy’s composition and on the mechanical and oxidation conditions during the hot rolling stage.     

Effect of alternating voltage on corrosion of X80 and X100 steels in a chloride containing solution – Investigated by AC voltammetry technique

AC corrosion of the X80 and X100 steels in 0.1 M NaCl solution were studied by the AC voltammetry technique. Corrosion electrochemical kinetics and solid/solution interface structure changes under the influence of AC voltage were characterized. Results illustrate that corrosion potential of the two steels shift negatively with the increase of AC amplitude and decrease of AC frequency. The anodic processes are under charge-transfer control and the anodic Tafel slopes increase with the increase of AC magnitude. The cathodic processes are under diffusion control at low AC amplitudes, while they become increasingly under charge-transfer control with higher AC amplitudes.     

Pitting corrosion of cold rolled solution treated 17-4 PH stainless steel

In the present paper the effects the of cold rolling on pitting corrosion of 17-4 precipitation hardening stainless steel in 3.5 wt% NaCl solution was investigated. In order to clarify the effect of cold rolling the metastable pitting has been examined in more details. The results presented show that cold rolling increases the dissolution rate of metastable pitting in a manner which facilitates the transition from metastable to stable pitting. On the other hand, the frequency of occurrence of metastable pits decreases with cold working. In overall, cold rolling has no significant effect on pitting potential.     

Microstructure and corrosion behaviour of pulsed plasma-nitrided AISI H13 tool steel

The effect of pulsed plasma nitriding temperature and time on the pitting corrosion behaviour of AISI H13 tool steel in 0.9% NaCl solutions was investigated by cyclic polarization. The pitting potential (E_pit) was found to be dependent on the composition, microstructure and morphology of the surface layers, whose properties were determined by X-ray diffraction and scanning electron microscopy techniques. The best corrosion protection was observed for samples nitrided at 480 °C and 520 °C. Under such experimental conditions the E_pit-values shifted up to 1.25 V in the positive direction.     

Micro-electrochemical characterization of corrosion of welded X70 pipeline steel in near-neutral pH solution

The local corrosion behavior of welded X70 pipeline steel in near-neutral pH solution was studied by micro-electrochemical measurements, including scanning vibrating electrode and local electrochemical impedance spectroscopy. The microstructure of the welded steel was observed by optical microscopy and scanning electron microscopy. It is demonstrated that the microstructure of weld metal consists of acicular ferrite and grain boundary ferrite, while that of heat-affected zone is a mixture of acicular ferrite, bainitic ferrite and a few martensite/austenite microconstituents. The microstructure of base steel is typically ferrite and pearlite. Electrochemical corrosion mechanism of welded X70 steel does not experience change upon hydrogen-charging, or stressing, or both. Hydrogen-charging is capable of enhancing the local anodic dissolution of the steel. The resistance of corrosion product layer decreases with hydrogen-charging, and heat-affected zone has the largest dissolution current upon hydrogen-charging. The increase of applied stress enhanced the anodic dissolution of welded X70 steel, especially the heat-affected zone, in near-neutral pH solution. Maximum current is observed in heat-affected zone, and increases with the increase of applied stresses. The total synergistic effect of hydrogen-charging (10 mA/cm²) and applied stress (550 MPa) on anodic dissolution of welded X70 steel in near-neutral pH solution is determined to be within the range of 5.7 and 6.5, with a maximum value encountering in heat-affected zone.     

Stress corrosion cracking behavior of X70 pipe steel in an acidic soil environment

Stress corrosion cracking (SCC) behavior of X70 pipe steel was investigated in an extracted acidic soil solution by slow strain rate test (SSRT), potentiodynamic polarization curve measurements and surface analysis technique. The SCC process and mechanism of X70 steel in the acidic soil solution is mixed-controlled by both anodic dissolution and the hydrogen involvement. With the different applied potentials, the dominance of SCC process changes. At a relatively less negative potential, the steel SCC is based primarily on the anodic dissolution mechanism. When the applied potential is shifted negatively, hydrogen is involved in the cracking process, resulting in a transgranular cracking mode. With the further negative shift of applied potential, the SCC of the steel follows completely a hydrogen-based mechanism, with a river-bed shaped brittle feature of the fracture surface. Heat treatment alters the microstructure of the steel, resulting in a change of SCC susceptibility. In particular, the quenched steel with a bainite microstructure has a high susceptibility to SCC in the acidic soil, while the as-received steel with a ferrite matrix have a low SCC susceptibility.     

Effects of cold working path on strain concentration, grain boundary microstructure and stress corrosion cracking in Alloy 600

Grain boundary microstructure, strain distribution and stress corrosion cracking (SCC) in one dimensional (1D), two dimensional (2D) and three dimensional (3D) cold worked Alloy 600 were investigated. The cold working decreased the annealing twins and increased low angle boundaries. 2D cold working caused lower strain concentration at grain boundaries than 1D and 3D cold working. The intergranular SCC (IGSCC) susceptibility was the highest in 1D cold worked alloy while lowest in 2D cold worked alloy. The IGSCC susceptibility displayed a strong correlation with the grain boundary strain concentration and the grain boundary microstructure.     

Effects of inclusions on the precipitation of chi phases and intergranular corrosion resistance of hyper duplex stainless steel

During the initial stage of aging heat treatment at 850 °C, inclusions such as (Cr, Mn, Al) oxides and (Cr, Mn, Al, Fe) oxides of a hyper duplex stainless steel act as preferential precipitation sites for the chi phase like ferrite/austenite phase boundaries and ferrite/ferrite grain boundaries. The chi phase is precipitated around the inclusions due to the blocking and piling up the alloying elements such as Mo and W around the inclusions. The precipitation of Mo and W enriched chi phase around the inclusions decreases the intergranular corrosion resistance due to the formation of Mo and W depleted zones.     

Characterization of inclusions of X80 pipeline steel and its correlation with hydrogen-induced cracking

In this work, the microstructures of an X80 pipeline steel were characterized, and their susceptibilities to hydrogen-induced cracking (HIC) were investigated by hydrogen-charging, electrochemical hydrogen permeation and surface characterization. It is found that the microstructure of X80 pipeline steel consists of a polygonal ferrite and bainitic ferrite matrix, with martensite/austenite (M/A) constituents distributing along grain boundaries. The inclusions existing in the steel include those enriched with Si, Al oxide, Si–ferric carbide and Al–Mg–Ca–O mixture, respectively. The majority of inclusions are Si-enriched. Upon hydrogen-charging, cracks could be initiated in the steel in the absence of external stress. The cracks are primarily associated with the Si- and Al oxide-enriched inclusions. The diffusivity of hydrogen in X80 steel at room temperature is 2.0 × 10⁻¹¹ m²/s, and the estimated hydrogen trapping density in the steel is as high as 3.33 × 10²⁷ m⁻³.     

Characterization of corrosion of X65 pipeline steel under disbonded coating by scanning Kelvin probe

Corrosion of X65 pipeline steel under a disbonded coating was studied by scanning Kelvin probe measurements. Three types of specimen were designed and prepared to investigate the effects of immersion time, oxygen concentration and wet-dry cycle on Kelvin potential profile and thus corrosion behavior of the steel. Kelvin potential measured on “intact” area is shifted negatively with time, indicating an increasing water uptake under the “intact” coating. With the increase of the amount of solution, it is expected that the electrolyte concentration and electrochemical reaction rate change, resulting in a significant decrease of interfacial potential. Moreover, there is a more negative Kelvin potential on disbonded area than that on “intact” area. The negative shift of Kelvin potential is attributed to corrosion reaction of steel occurring under the disbonded coating. Due to the narrow geometry of coating disbondment, an oxygen concentration difference exists along the depth of the disbondment. The corrosion behavior under disbonded coating strongly depends on the oxygen partial pressure and local geometry. With continuous purging of nitrogen and removing of oxygen, Kelvin potential tends to be identical throughout the disbonded area. During wet-dry cycle, the thickness of solution layer trapped under disbonded coating decreases due to evaporation of water. With the decrease of solution layer thickness, the measured Kelvin potential decreases, indicating that the effect associated with the reduction of oxygen solubility in the concentrated solution during drying of electrolyte is favored over that related to the enhanced oxygen diffusion and reduction. There exists a critical thickness of solution layer, below which the oxygen solubility is sufficiently low to support the electrochemical corrosion reaction of steel.     

Synergistic effect of sulfate-reducing bacteria and elastic stress on corrosion of X80 steel in soil solution

In this paper, the individual and simultaneous effects of stress and sulfate-reducing bacteria on corrosion of X80 steel were conducted by electrochemical impedance spectroscopy, scanning electron microscope and X-ray photoelectron spectroscopy. Both elastic stress and activity of SRB enhance corrosion of the steel and, furthermore, they have synergistic effects on corrosion behavior of the steel. The activities of SRB give rise to the initiation of pits, and the applied elastic stress keeps and promotes the growth of pits. The activities of SRB and the applied elastic stress induce tiny secondary corrosion pitting at the bottom of the primary pitting.