Cracking Of Stainless Steel Research Articles

Leak-tight crack repair for 304L stainless steel using friction surfacing

Friction surfacing (FS) was investigated as a method for sealing 50 μm wide thru-cracks in 3-mm-thick 304L stainless steel (304L) plate. Friction surfacing was performed using two sizes of 304L consumable rod, with diameters of 9.52 mm and 12.7 mm, on two substrate conditions (clean and oxidized). Friction surfacing was able to deposit a 600 μm thick coating and repair cracks to a depth of 100 μm - 200 μm below the original surface, when using the 12.7-mm-diameter consumable rod for both substrate conditions. Helium leak rates of 10−10 atm-cc/s were achieved on crack repairs, designating them as leak-tight by the ANSI N14.5 standard. Optical and scanning electron microscopy were used to investigate the coating microstructure and bond interfaces. In this study, the 12.7-mm-diameter rod performed better with disruption of the oxide layer on the oxidized substrate and providing a more homogenous coating. Mechanical properties of the coated samples were evaluated by performing micro-indentation, tensile, bending, and adhesion testing. Higher hardness in the coatings was observed due to the fine equiaxed grains resulting from dynamic recrystallization. Complete consolidation of plastically deformed material on the substrate and a strong diffusion bond across the interface was observed. This was reflected in tensile and bending properties of the FS coatings being comparable to those of uncoated specimen. No delamination of the FS coating was observed during adhesion testing. The results demonstrate that friction surfacing is a viable option to seal cracks in stainless steels.

Hydrogen Induced Cracks in Stainless Steel 304 in Hydrogen Pressure and Stress Corrosive Atmosphere

The phenomena of hydrogen induced cracking (HIC) in 304 stainless steels was considered in a hydrogen pressure and stress corrosive atmosphere. Microstructures with chloride pits and stress corrosion cracks around the HIC were analyzed by SEM/EDS. Abnormal phase transformations induced by the hydrogen were analyzed using TEM and diffraction. In the hydrogen pressure atmosphere, pits and pores were observed on the surface of the 304 stainless steels. In addition, it was determined that Cl, an etchant component, was concentrated at a high concentration in the pits. SCC (stress corrosion cracking) was induced in the Cl atmosphere by stress caused by the abrasive embedded in the pits. It was assumed that the SCC mechanism is similar to HIC in that it occurs in the surface tensile stress and Cl atmosphere and is accompanied by grain boundary cracks similar to IGSCC (inter-granular SCC). The deformation induced phase transformation accompanied by planar slip should be related to the main cause of HIC in the hydrogen pressured atmosphere. Abnormal forbidden spots between the main diffraction spots were induced by the HIC in the hydrogen attacked area, where the microstructure was hardened. Understanding the HIC mechanism related to chloride corrosion can be used to assess the fitness of austenitic stainless steels for uses where there is a possibility of various susceptible cracking in hydrogen and chloride atmospheres.

Development of mechanisms of hydrogen cracking of metal systems and methods to protect steel products from corrosion-mechanical destruction

The brittle destruction of high-strength metals and alloys used in the chemical and oil refining industry, caused by the influence of aggressive hydrogen-containing media, is a serious scientific issue, the relevance of which has increased dramatically in recent decades due to the discovery of the anomalous hydrogen effects on the complex properties of metals and alloys (abnormal plastic auto-deformation of iron, structural-phase transformations, synergistic effects of microplasticity, effect of reversible shape loss in amorphous metal alloys, and many others). A significant number of hydrogen sources (corrosion in aqueous solutions, hydrogen absorption in the production of welding operations and application of technological protective coatings or cathodic protection of underground pipelines) causes significant difficulties in describing the processes of hydrogen degradation of metal materials. Degradation is manifested in various ways, such as: hydrogen cracking of high-strength steels; hydrogen participation in the process of stress corrosion cracking of stainless steels; cracking of nuclear reactor tubes made of zirconium alloys and embrittlement of titanium alloys by hydride formation, GaAs degradation of monolithic microwave integrated circuits on satellites, etc. The harmful effect of hydrogen on mechanical properties was first noted by Johnson in 1875. Since then, scientists have made many advances in the development of metals with optimal parameters of strength and plasticity. Despite many years of research, the problem of interaction of metal-hydrogen systems remains open due to the variety of approaches and techniques to the assessment of embrittlement effects of hydrogen and hydrogen-containing media. So far it has not been possible to establish a single mechanism of interaction of hydrogen with metal materials, which would explain the whole set of phenomena, related to hydrogen destruction. Therefore, to analyze the mechanisms of hydrogen cracking of metal systems and to develop methods of steel products protection from corrosion-mechanical destruction are relevant areas of scientific and practical activities.

Quantitative analysis of prediction models for hot cracking in industrial stainless steels using standardized requirements

In this paper, a systematic analysis of different methods of δ-ferrite estimation is carried out based on the well-known relationship between δ-ferrite content and hot cracking in stainless steels. Additionally, the influence of certain chemical requirements on δ-ferrite stabilization and their relationship to hot cracking is evaluated by the application of a deterministic algorithm based on stringency levels. The results obtained from the application of the stringency level method and prediction diagrams permit the selection of the best option among materials according to their standardized specifications. In addition, the advantage of this integrated method is that we can evaluate particular elemental influences and assign relative weightings to create a database for materials selection.

Internal oxidation and probabilistic fracture model of irradiation assisted stress corrosion cracking in stainless steels

A probabilistic fracture model is applied to irradiation assisted stress corrosion cracking effect, assuming that the oxidized part of stainless steel sample plays an essential role in the crack initiation, propagation and the sample failure. The Weibull statistical distribution of time-to-failures, estimated through the correlation with the statistical distribution of oxide strengths, including both the surface oxide layer and oxidized grain boundaries, fully describe the experimental scatter obtained in the constant load time-to-failure tests. Large failure uncertainties in these type of tests originate from an intrinsic stochastic behavior of the oxide cracking due to subcritical crack propagation process.

Analysis of the intergranular corrosion susceptibility in stainless steel by means of potentiostatic reactivation tests

Abstract: Intergranular corrosion cracking in stainless steels is a selective corrosion attack due to a local (grain boundary) Cr depletion. An undesired Cr carbides (Cr 23 C 6 ) precipitation after heat treatment in the sensitization temperature range (usually between 550 and 850°C, depending on the steel chemical composition) is obtained with a kinetics that is mainly influenced by the C content. In this work, the sensitization susceptibility of four sensitized stainless steels was investigated by means of potentiostatic reactivations tests. In addition, chronoamperometric tests and scanning electron microscope (SEM) observations of the specimens surfaces were performed in order to analyze the evolution of the corrosion morphologies.

Inspection of stress corrosion cracking in welded stainless steel pipe using point-focusing electromagnetic-acoustic transducer

Point-focusing electromagnetic-acoustic transducers (PF-EMATs) for shear-vertical (SV) waves were developed for crack inspection of stainless-steel pipes. The transducer has improved defect detectability by accumulating SV waves generated by concentric line sources at a focal point in phase. An optimum frequency for defect detection was found to be 2MHz, with which a crack of 0.5mm depth near a weld was clearly detected. The EMAT exhibited defect detectability comparable to that of a conventional phased-array piezoelectric transducer, indicating that this new EMAT is highly practical for the non-contacting evaluation of stress-corrosion cracking in stainless steels.

Probabilistic fracture mechanics of irradiation assisted stress corrosion cracking in stainless steels

A probabilistic fracture mechanics model is applied to irradiation assisted stress corrosion cracking effect, assuming that the oxidized part of stainless steel sample plays an essential role in the crack propagation and sample failure. The Weibull statistical distribution of time-to-failures, estimated through the correlation with the statistical distribution of oxide strengths, fully accounts for the experimental results/scatter obtained in the constant load time-to-failure tests. Large failure uncertainties in these type of tests originate from intrinsic stochastic behavior of the oxide cracking due to subcritical crack propagation process.

Growth Retardation of Fatigue Crack by Cold Expanded with Ring Indented Method for AISI 304 Stainless Steel

Drilled, cold expanded with ring indented method was employed for crack-tip on the both sides and front side of the specimens, thus build up the residual compressive stresses, strain hardening and plasticity induced closure, and lead toward crack growth retardation. The compact tension specimens of AISI 304 stainless steel were used drilled, cold expanded with ring indented in the fatigue test. The experimental methods were drilled (Φ=2mm ) and cold expanded (Φ=2.074mm) and both sides at 2mm and 1mm position of the crack-tip in the specimen, then apply 0kN, 6KN, and 9kN test loads, respectively. The experimental results showed that, for the same test position, the number of delay cycles result from cold expanded than that of drilled and the number of delay cycles are 220798. For the same position, the stronger test load is, the greater crack growth retardation effect is. And, This study proposed some useful information on utilizing cold expanded with ring indented method for AISI 304 Stainless Steel crack growth retardation.

Failure Analysis of Stress Corrosion Crack of 1Cr18Ni9 Stainless Steel Cylinder Body

As a kind of corrosion resistant material, stainless steel is widely used in petroleum, chemical, pharmaceutical. Stress corrosion cracking is a main reason that why the stainless steel became disabled. Therefore, it is very necessary to research and study the stress corrosion cracking of stainless steel .The failure analysis to the sample is conducted aiming at the stress corrosion of the stainless steel piston cylinder in a factory. The analysis includes macro analysis, metallographic observation, scanning electron microscopy analysis and XRD analysis. The results of the study show that it is nonmetallic inclusion on the grain boundary, the chloridion in the industrial circulating water and the rough columnar austenitic grains in the organization of the samples that lead to the stress corrosion cracking of the piston cylinder.

Nanoscale characterisation of grain boundary oxidation in cold-worked stainless steels

Atom-probe tomography was employed to characterise specimens containing the oxidised part of a grain boundary from a 304 stainless steel coupon specimen exposed to simulated PWR primary water. A TEM foil containing part of the same oxidised grain boundary was also extracted and characterised for comparison. Surface and grain boundary oxide compositions were identified and Ni enrichment was observed around the oxides. The data provides novel information on the role of the minor impurities and the formation of early-stage oxides. These studies were conducted as part of a broader investigation of the mechanisms underlying stress corrosion cracking in stainless steels.

Insights into Stress Corrosion Cracking Mechanisms from High-Resolution Measurements of Crack-tip Structures and Compositions

AbstractResults are presented employing cross-sectional analytical transmission electron microscopy (ATEM) to examine intergranular stress corrosion cracking (IGSCC) of austenitic stainless alloys in high-temperature water environments. Microstructural, chemical and crystallographic characterization of buried interfaces at near-atomic resolutions is used to investigate corrosion/oxidation reactions, composition changes and deformation events at crack tips. Information obtained by a wide variety of high-resolution imaging and analysis methods indicates the processes occurring during crack advance and provides insights into the mechanisms controlling SCC. Examples of crack tips produced in oxidizing and hydrogenated water are presented for both Fe-base stainless steels (SSs) and Ni-base stainless alloys. Cracks in SSs show similar characteristics in both environments, with oriented oxide films at crack walls and cracks ending in few-nm-wide tips. Many of these same features are seen for alloy 182 in oxidizing water suggesting a common mechanism, generally consistent with a slip oxidation process. A distinct difference is seen at alloy 600 and alloy 182 tips produced in hydrogenated water. Penetrative attack along grain boundaries without evidence for significant plastic deformation is believed to indicate a major role of active-path corrosion/oxidation in the SCC process.

Relationship between the structure-selective corrosion and corrosion cracking of stainless steels

It is shown that the structure-selective corrosion observed in sulfuric media, in cyclohexane-oxidation media, and in the process of carbamide production may serve as a source of initiation of corrosion cracking. In this case, fracture occurs under relatively low loads. We analyze possible scenarios of the development of this process depending on the rate of structure-selective corrosion. It is shown that corrosion cracking is especially dangerous for the devices made of bimetallic materials and operating at elevated temperatures. This can be explained by additional loading caused by the strong difference between the coefficients of linear thermal expansion of the base metal and the cladding layer.

Cracking of stainless steel through bulkhead initiators (TBI): A metallurgical investigation

Through Bulkhead Initiators (TBI), fabricated from AISI 302 extruded and cold worked rod, is a shock-based system employing high explosive and pyrotechnic charges. The explosive is press loaded to required densification. TBI is initiated by explosive stimulus generated by mild detonating cord (MDC). This causes detonation of the donor charge explosive, transfers the resulting shock across the bulkhead and gets attenuated. During one of the above tests, the tested unit gave the required pressure output as expected. However the housing developed cracks on the body. Detailed metallurgical analysis indicated that the material yielded and failed in dimple mode of failure during shock transfer. Further, the material had heavy sulfide inclusions, which helped in void formation by de-bonding from the matrix.

Modelling of hydrogen diffusion and hydrogen induced cracking in supermartensitic and duplex stainless steels

This is a review based on classic and recent published literature regarding hydrogen diffusion and hydrogen assisted cracking in stainless steels. The majority of the reviewed literature is related to supermartensitic, duplex and super duplex stainless steels. Recent models for hydrogen diffusion and hydrogen assisted fracture in the presence of sharp notches are presented and discussed. New approaches in cohesive FE modelling of hydrogen assisted cracking are presented and reviewed as a possible method for building a bridge between the modelling of micro mechanisms in the fracture process zone and the global fracture response.

Investigation of the Influence of Shot Peening on Stress Corrosion Cracking of Stainless Steel Welded Joints

High residual tensile stress is an important factor contributing to stress corrosion cracking (SCC). Shot peening can impose compressive stresses on the surface of welded joints that negate the tensile stresses to enhance the SCC resistance of welded joints. In the present work, the distribution of residual stress caused by welding is measured by X-ray diffraction method. The maximum stress in the weld is close to the yield strength of AISI 304 stainless steel, and the stresses are negative at both ends of the weld and far from the weld. The X-ray method is also used to measure stress caused by shot-peening. The results show that the higher the peening coverage, the higher the residual compressive stresses in the surface of weldments. While under the same condition, the residual compressive stresses induced by glass beads shot-peening are larger than those by cast steel shots. Temperature and stress fields of welding are simulated by using ABAQUS codes. The 3-D solid elements are used in FEM. Temperature depending on material properties as well as the convection and radiation as boundary conditions are considered. The 3-D linear reduced-integration elements are used to simulate the shot peening process. The results of simulation have a good agreement with experimental data. All unpeened and peened weldments are immersed in boiling 42% magnesium chloride solution during SCC test. Unpeened specimens crack after immersion for 6 hours. The steel-peened specimens with 50% coverage crack after 310 hours, while the steel-peened specimens with 100% coverage crack for 3500 hours. However, steel-peened specimens with 200% coverage and glass-peened specimens with 50%, 100% and 200% coverage are tested for a total of 3500 hours without visible stress corrosion cracks in the peened surfaces. The experiment results indicate that shot peening is an effective method for protecting weldments against SCC and weldments peened by glass beads resist SCC better than those peened by steel shots.

Quantitative Evaluation of Cracks under Water by Microwaves

Quantitative evaluation of small cracks in stainless steel under water, which simulated the environment of unclear reactor, by using microwave, was demonstrated. The crack depth was evaluated by means of the microwave dual frequency technique, and the crack closure stress was estimated based on the compliance technique.

High-resolution imaging of complex crack chemistry in reactor steels by NanoSIMS

High-resolution analysis using a Cameca NanoSIMS 50 has been used to map the oxide chemistry in intergranular cracks in stainless steels. The technique has proven ideal for this type of sample, as it is able to discern between the different oxide layers and clarify the role of minor segregants such as boron and sulphur. Results are compared with analysis of the same sample by scanning auger microscopy and its interpretation discussed. The short time required to prepare and examine multiple regions present the NanoSIMS as an optimum tool for corrosion characterization.

Stress corrosion cracking of stainless steels

Stress corrosion cracking of stainless steels

Effects of Hydrogen Peroxide on Corrosion of Stainless Steel, (IV)

Corrosive conditions in BWRs are determined mainly by hydrogen peroxide (H2O2). Then, a high temperature, high-pressure H2O2 water loop was fabricated to identify the effects of H2O2 on corrosion and stress corrosion cracking of stainless steel. By changing concentrations of H2O2 and O2, in situ measurements of electrochemical corrosion potential (ECP) and frequency dependent complex impedance of test specimens were carried out and then characteristics of oxide film on the specimens were determined by multilateral surface analyses, i.e., laser Raman spectroscopy and secondary ion mass spectroscopy. The following points were experimentally confirmed. 1. The hematite ratio in the oxide films of the specimens exposed to H2O2 was expressed as a logarithmic function of [H2O2]. The hematite ratio was measurable for 8 ppm O2, but negligibly small for 200 ppb O2. 2. H2O2 exposure led to thicker oxide layers than O2 exposure and Cr depletion did. 3. The oxide film thickness first increased as [H2O2] decreased from 100 to 10 ppb and then it decreased. This meant that a large dissolution rate caused a thin oxide film in spite of the large growth rate of oxide film, while a low growth rate caused a thinner oxide film at low [H2O2].