Showing papers on "Stress corrosion cracking published in 2021"

A phase field formulation for dissolution-driven stress corrosion cracking

Abstract: We present a new theoretical and numerical framework for modelling mechanically-assisted corrosion in elastic–plastic solids. Both pitting and stress corrosion cracking (SCC) can be captured, as well as the pit-to-crack transition. Localised corrosion is assumed to be dissolution-driven and a formulation grounded upon the film rupture–dissolution–repassivation mechanism is presented to incorporate the influence of film passivation. The model incorporates, for the first time, the role of mechanical straining as the electrochemical driving force, accelerating corrosion kinetics. The computational complexities associated with tracking the evolving metal–electrolyte interface are resolved by making use of a phase field paradigm, enabling an accurate approximation of complex SCC morphologies. The coupled electro-chemo-mechanical formulation is numerically implemented using the finite element method and an implicit time integration scheme; displacements, phase field order parameter and concentration are the primary variables. Five case studies of particular interest are addressed to showcase the predictive capabilities of the model, revealing an excellent agreement with analytical solutions and experimental measurements. By modelling these paradigmatic 2D and 3D boundary value problems we show that our formulation can capture: (i) the transition from activation-controlled corrosion to diffusion-controlled corrosion, (ii) the sensitivity of interface kinetics to mechanical stresses and strains, (iii) the role of film passivation in reducing corrosion rates, and (iv) the dependence of the stability of the passive film to local strain rates. The influence of these factors in driving the shape change of SCC defects, including the pit-to-crack transition, is a natural outcome of the model, laying the foundations for a mechanistic assessment of engineering materials and structures.

Influence of grain refinement on the corrosion behavior of metallic materials: A review

Abstract: Grain refinement can strengthen the mechanical properties of materials according to the classical Hall-Petch relationship but does not always result in better corrosion resistance. During the past few decades, various techniques have been dedicated to refining grain, along with relevant studies on corrosion behavior, including general corrosion, pitting corrosion, and stress corrosion cracking. However, the fundamental consensus on how grain size influences corrosion behavior has not been reached. This paper reviews existing literature on the beneficial and detrimental effects of grain refinement on corrosion behavior. Moreover, the effects of microstructural changes (i.e., grain boundary, dislocation, texture, residual stress, impurities, and second phase) resulting from grain refinement on corrosion behavior are discussed. The grain refinement not only has an impact on the corrosion performance, but also results in microstructural changes that have a non-negligible effect on corrosion behavior or even outweigh that of grain refinement. Grain size is not the only factor affecting the corrosion behavior of metallic materials; thus, the overall influence of microstructures on corrosion behavior should be understood.

A coupled mechano-chemical peridynamic model for pit-to-crack transition in stress-corrosion cracking

Abstract: We introduce a coupled mechano-chemical peridynamic model to describe stress corrosion cracking. In this model, two mechanisms, stress-dependent anodic dissolution and diffuse corrosion layer-assisted fracture, are considered to influence pitting and crack propagation in stress corrosion cracking. Diffusion peridynamic bonds (acting as dissolution bonds at the solid/liquid interface) and mechanical peridynamic bonds are used to represent the interactions between material points. Mechanical bonds can be damaged by mechanical stretching or by anodic dissolution. The magnitude of the dissolution fluxes for diffusion peridynamic bonds depends on both mechanical deformation and the applied electrical potential. The coupling between anodic dissolution and mechanical damage leads to cracks that initiate in the corrosion damage layer and propagate into the bulk. A 2D three-point bending/corrosion test demonstrates the concept. We verify the model in 3D using an experimental test from the literature for the case of stress-corrosion cracking process in a steam turbine steel sample. The model's results capture the pit-to-crack transition time, the pit size and shape at fracture, as well as the morphology of cracks that spring from, and connect the pits.

Duplex Stainless Steels—Alloys for the 21st Century

Abstract: Duplex stainless steels were first manufactured early in the 20th century, but it was the introduction in the 1970s of the argon-oxygen decarburisation (AOD) steel making process and the addition of nitrogen to these steels, that made the alloys stronger, more weldable and more corrosion resistant. Today, duplex stainless steels can be categorised into four main groups, i.e., “lean”, “standard”, “super”, and “hyper” duplex types. These groups cover a range of compositions and properties, but they all have in common a microstructure consisting of roughly equal proportions of austenite and ferrite, high strength, good toughness and good corrosion resistance, especially to stress corrosion cracking (SCC) compared with similar austenitic stainless steels. Moreover, the development of a duplex stainless-steel microstructure requires lower levels of nickel in the composition than for a corresponding austenitic stainless steel with comparable pitting and crevice corrosion resistance, hence they cost less. This makes duplex stainless steels a very versatile and attractive group of alloys both commercially and technically. There are applications where duplex grades can be used as lower cost through-life options, in preference to coated carbon steels, a range of other stainless steels, and in some cases nickel alloys. This cost benefit is further emphasised if the design engineer can use the higher strength of duplex grades to construct vessels and pipework of lower wall thickness than would be the case if an austenitic grade or nickel alloy was being used. Hence, we find duplex stainless steels are widely used in many industries. In this paper their use in three industrial applications is reviewed, namely marine, heat exchangers, and the chemical and process industries. The corrosion resistance in the relevant fluids is discussed and some case histories highlight both successes and potential problems with duplex alloys in these industries. The paper shows how duplex stainless steels can provide cost-effective solutions in corrosive environments, and why they will be a standard corrosion resistant alloy (CRA) for many industries through the 21st century.

Microstructure and stress corrosion behaviour of CMT welded AA6061 T-6 aluminium alloy joints

Abstract: Superior properties of AA6061 grade aluminium alloys are finding greater use in automotive, marine and aircraft applications due to its strength, weldability and high corrosion resistance. But it is highly susceptible to stress corrosion cracking owing to alter the phase composition and microstructure during welding process. In the present work, an experimental study of stress corrosion cracking is conducted on Cold Metal Transfer welded aluminium alloy joints using various heat input under constant stress intensity to understand the susceptibility of various zones to Stress Corrosion Cracking and the performance has been analysed using Tafel electrochemical technique. The result shows that the mechanism of cracking is established to be anodic mode with transgranular nature of crack propagation. In addition, a linear relationship is also inferred to predict the time to failure by extrapolating the rate of steady state elongation. The integrity of the dissimilar joints are analysed with the help of Optical Microscopy, SEM, EDAX and XRD sophisticated analytical techniques.

A comprehensive review on residual stresses in turning

Abstract: Residual stresses induced during turning processes can affect the quality and performance of machined products, depending on its direction and magnitude. Residual stresses can be highly detrimental as they can lead to creeping, fatigue, and stress corrosion cracking. The final state of residual stresses in a workpiece depends on its material as well as the cutting-tool configuration such as tool geometry/coating, cooling and wear conditions, and process parameters including the cutting speed, depth-of-cut and feed-rate. However, there have been disagreements in some literatures regarding influences of the above-mentioned factors on residual stresses due to different cutting conditions, tool parameters and workpiece materials used in the specific investigations. This review paper categorizes different methods in experimental, numerical and analytical approaches employed for determining induced residual stresses and their relationships with cutting conditions in a turning process. Discussion is presented for the effects of different cutting conditions and parameters on the final residual stresses state.

Effect of microstructure on corrosion behavior of high strength martensite steel—A literature review

Abstract: The high strength martensite steels are widely used in aerospace, ocean engineering, etc., due to their high strength, good ductility and acceptable corrosion resistance. This paper provides a review for the influence of microstructure on corrosion behavior of high strength martensite steels. Pitting is the most common corrosion type of high strength stainless steels, which always occurs at weak area of passive film such as inclusions, carbide/intermetallic interfaces. Meanwhile, the chromium carbide precipitations in the martensitic lath/prior austenite boundaries always result in intergranular corrosion. The precipitation, dislocation and grain/lath boundary are also used as crack nucleation and hydrogen traps, leading to hydrogen embrittlement and stress corrosion cracking for high strength martensite steels. Yet, the retained/reversed austenite has beneficial effects on the corrosion resistance and could reduce the sensitivity of stress corrosion cracking for high strength martensite steels. Finally, the corrosion mechanisms of additive manufacturing high strength steels and the ideas for designing new high strength martensite steel are explored.

Influence of aging on microstructure, mechanical properties and stress corrosion cracking of 7136 aluminum alloy

Abstract: The microstructure, mechanical properties and stress corrosion cracking (SCC) of 7136 aluminum alloy under T6, T79 and T74 aging treatments were studied and the effects of microstructure on the mechanical properties and SCC were discussed. The results show that the ultimate tensile strength and yield strength of the aging 7136 alloys follow this sequence from high to low: T6>T79>pre-aging>T74. For 7136 Al alloy after T6 aging, the average diameter of the precipitates was (5.7±1.7) nm, and the diameter of 60.7% (number fraction) precipitates was 2–6 nm, leading to a good precipitation strengthening. The KIC of T74-aging alloy is 38.2 MPa·m1/2, which is 26.1% more than that of T6-aging alloy and 17.5% more than that of T79-aging alloy. The improved fracture toughness in T74-aging alloy is mainly due to the reduction of the strength difference between intragranular and grain boundary. The SCC resistance of the aging 7136 alloys follows this sequence from high to low: T79 > T74 > T6. After T79 aging, the discontinuous grain boundary precipitates and narrow precipitate free zones were obtained in 7136 alloy, which was beneficial to SCC resistance.

Additive Manufactured 316L Stainless-Steel Samples: Microstructure, Residual Stress and Corrosion Characteristics after Post-Processing

Abstract: Additive manufacturing (AM) is a relatively new manufacturing method that can produce complex geometries and optimized shapes with less process steps. In addition to distinct microstructural features, residual stresses and their formation are also inherent to AM components. AM components require several post-processing steps before they are ready for use. To change the traditional manufacturing method to AM, comprehensive characterization is needed to verify the suitability of AM components. On very demanding corrosion atmospheres, the question is does AM lower or eliminate the risk of stress corrosion cracking (SCC) compared to welded 316L components? This work concentrates on post-processing and its influence on the microstructure and surface and subsurface residual stresses. The shot peening (SP) post-processing levelled out the residual stress differences, producing compressive residual stresses of more than −400 MPa in the AM samples and the effect exceeded an over 100 µm layer below the surface. Post-processing caused grain refinement and low-angle boundary formation on the sample surface layer and silicon carbide (SiC) residue adhesion, which should be taken into account when using the components. Immersion tests with four-point-bending in the heated 80 °C magnesium chloride solution for SCC showed no difference between AM and reference samples even after a 674 h immersion.