Cracking Of Austenitic Stainless Steel Research Articles

A continuum damage model for the stress corrosion cracking of austenitic stainless steel

In the present work, the mechanical behavior of stress corrosion cracking phenomenon is described. Such phenomenon presents strong complexity due to metallurgic and electrochemical aspects. A methodology for modeling both SSR (Slow Strain Rate) and CL (Constant Load) tests based upon thermodynamics of continuum solids and elastoplastic damage is proposed. In this macroscopic approach, besides the classical variables (stress, total strain, plastic strain), an additional scalar variable related to the damage induced by stress corrosion is introduced. An evolution law depending on the corrosive environment parameters is proposed for this damage variable. The model accounts for the stress corrosion effect through a reduction of the mechanical resistance of the material induced by the damage variable. The model prediction is compared with the curves obtained experimentally in different acid solutions at room temperature showing a good agreement. The alloy/environment system studied here is an AISI 304 austenitic stainless steel in acid aqueous solution containing sodium chloride.

Effect of weld metal copper content on HAZ cracking in austenitic stainless steel welded with Al brass

Austenitic stainless steel has good weldability but is sensitive to hot cracking such as solidification and liquation cracking. In the present study, specimens of dissimilar metals made from austenitic stainless steel and Al brass were welded by the GTAW process using four different filler metals. Cracks were detected in the heat affected zone of the stainless steel when welded with CuAl, CuSn and NiCu filler metals, but no cracks were detected when a Ni filler metal was used. The cracks propagated along the grain boundary in the heat affected zone near the fusion line to the base metal of 316L stainless steel. The cracks were located inside the weld bead with very fine hairline cracking. All cracks initiated at the fusion line and moved forward in the base metal. From energy dispersion spectroscopy (EDS), the Cu peak was detected only in the crack-opening area.

Fissuration en relaxation des jonctions soudées en aciers inoxydables austénitiques

Cet article represente une synthese des etudes menees au CEA/SRMA, en collaboration avec l'ENSMP, sur la fissuration en relaxation (F.E.R.) des aciers inoxydables austenitiques. Initialement, l'etude a porte sur l'endommagement des Zones Affectees (Z.A.) des soudures en aciers stabilises au titane de type AISI 321. Une demarche de simulation experimentale de Z.A. par des traitements thermo-mecaniques a ete mise en place. Un essai de relaxation sur eprouvette CT a egalement ete mis au point afin de reproduire en laboratoire ce type de fissuration. Outre la validation de cette demarche, il a ete montre que l'ecrouissage joue un role preponderant sur la fragilisation intergranulaire et que le vieillissement attenue cette fragilisation contrairement a ce qui est couramment admis dans la litterature. Cette remise en cause du role premier de la precipitation des carbonitrures de titane permet d'elargir le champ d'investigation aux aciers non stabilises pour lesquels il existe un certain nombre de cas de fissuration similaires a ceux attribues a la F.E.R. En appliquant la demarche precedente a des aciers de type AISI 316 et AISI 304, on montre aussi que l'ecrouissage est un facteur de fragilisation intergranulaire. Parallelement, on etablit, par approche locale de la rupture, un modele d'endommagement intergranulaire utilisable pour l'evaluation du risque de fissuration sur des composants reels.

Linking Grain Boundary Structure and Composition to Intergranular Stress Corrosion Cracking of Austenitic Stainless Steels

AbstractGrain boundary structure and composition is assessed in austenitic stainless steels along with its influence on intergranular stress corrosion cracking (IGSCC) in high-temperature water. Brief examples are presented illustrating effects of grain boundary character and segregation on behavior in specific light-water-reactor environments. Although grain boundary engineering can produce an increased fraction of “special” boundaries in austenitic stainless alloys, practical benefits depend on the boundary orientation distribution. It is critical to recognize that only ∑3s appear to be more resistant to SCC and the behavior of other low ∑ boundaries is uncertain. Grain boundary composition can have a dominant effect on IGSCC under certain conditions, but altered interfacial chemistry is not required for cracking. In high-potential oxidizing environments, IGSCC susceptibility is a direct function of the boundary Cr concentration. Non- equilibrium thermal segregation of Cr and Mo is often present in mill-annealed stainless steels and may influence cracking susceptibility. This initial grain boundary composition alters subsequent radiation-induced segregation and delays irradiation-assisted SCC susceptibility to higher doses. Other alloying elements and impurities in 300-series stainless steels have been seen to enrich grain boundaries, but few have any significant impact on IGSCC susceptibility. One exception is Si that strongly segregates during irradiation. Recent results suggest that Si may accelerate crack propagation in both low- and high-potential water environments. Critical research is still needed to isolate individual grain boundary characteristics and quantitatively link them to IGSCC.

Technical note Corrosion and cracking under insulation of type 304 stainless steel at ambient temperature

Corrosion pitting was found under insulation on type 304 austenitic stainless steel pipes used in an ethylene plant since 1980 to transport hydrocarbon products at – 170 ° C. Preliminary investigations established that the corrosion was confined to areas adjacent to the circumferential weld seams. Chlorides were present on the external surface of the pipes owing to ingress through defective insulation. Detailed examination of specimens from the affected pipes revealed that stress corrosion cracks had initiated in the corroded areas near the welds where defects and high residual stresses can be encountered. The cracks had initiated intergranularly before changing to a transgranular mode of crack propagation, typical of stress corrosion cracking of austenitic stainless steels in chloride environments. The evidence suggests that the cracks developed while the plant was not operating when the pipework would have been at ambient temperature.

In situ TEM study of stress corrosion cracking of austenitic stainless steel

A constant deflection device designed for use within a transmission electron microscope (TEM) was used to investigate the change in dislocation configuration ahead of a crack tip during stress corrosion cracking (SCC) of type 310 austenitic stainless steel in a boiling MgCl 2 solution, and the initiation of stress corrosion microcracking. Results showed that crack tip corrosion processes during SCC-enhanced dislocation emission, multiplication and motion. SCC microcracks initiated when the corrosion-enhanced dislocation emission and motion had fully develop. A passive film formed during corrosion of austenitic stainless steel in the boiling MgCl 2 solution generated a tensile stress. During SCC, the additive tensile stress generated at the metal/passive film interface assists the applied stress to enhance dislocation emission and motion.

Isolating the effect of radiation-induced segregation in irradiation-assisted stress corrosion cracking of austenitic stainless steels

Post-irradiation annealing was used to help identify the role of radiation-induced segregation (RIS) in irradiation-assisted stress corrosion cracking (IASCC) by preferentially removing dislocation loop damage from proton-irradiated austenitic stainless steels while leaving the RIS of major and minor alloying elements largely unchanged. The goal of this study is to better understand the underlying mechanisms of IASCC. Simulations of post-irradiation annealing of RIS and dislocation loop microstructure predicted that dislocation loops would be removed preferentially over RIS due to both thermodynamic and kinetic considerations. To verify the simulation predictions, a series of post-irradiation annealing experiments were performed. Both a high purity 304L (HP-304L) and a commercial purity 304 (CP-304) stainless steel alloy were irradiated with 3.2 MeV protons at 360 °C to doses of 1.0 and 2.5 dpa. Following irradiation, post-irradiation anneals were performed at temperatures ranging from 400 to 650 °C for times between 45 and 90 min. Grain boundary composition was measured using scanning transmission electron microscopy with energy-dispersive spectrometry in both as-irradiated and annealed samples. The dislocation loop population and radiation-induced hardness were also measured in as-irradiated and annealed specimens. At all annealing temperatures above 500 °C, the hardness and dislocation densities decreased with increasing annealing time or temperature much faster than RIS. Annealing at 600 °C for 90 min removed virtually all dislocation loops while leaving RIS virtually unchanged. Cracking susceptibility in the CP-304 alloy was mitigated rapidly during post-irradiation annealing, faster than RIS, dislocation loop density or hardening. That the cracking susceptibility changed while the grain boundary chromium composition remained essentially unchanged indicates that Cr depletion is not the primary determinator for IASCC susceptibility. For the same reason, the visible dislocation microstructure and radiation-induced hardening are also not sufficient to cause IASCC alone.

高温濃厚臭化リチウム水溶液中におけるステンレス鋼用の腐食抑制剤

The new inhibitor for stainles steel (mainly high purity ferritic stainless steel) in the high temperature concentrated aqueous solution of lithium bromide was investigated. According to the results of the electrochemical measurements, and the immersion tests using autoclaves, the mixture of three chemicals, LiOH+Na2SO3+SbCl3, is effective as an inhibitor for stainles steel to prevent hydrogen generation, pitting corrosion and macro-cell corrosion with copper.The reasons of this result are assumed that the sodium sulfite in this inhibitor remains the free-corrosion potential of stainless steel lower, and antimony in this inhibitor prevents hydrogen generation. This inhibitor also prevents stress corrosion cracking of austenitic stainless steel in the high temperature concentrated aqueous solution of lithium bromide.

Chloride Stress Corrosion Cracking of Austenitic Stainless Steels in Salt Producing Plant

Chloride Stress Corrosion Cracking of Austenitic Stainless Steels in Salt Producing Plant

Stress corrosion cracking of Type 304 stainless steel with mixed Mode I/III loading

The role of hydrogen and crack tip strain rate on the stress corrosion cracking of austenitic stainless steels continues to be an unresolved issue for a number of conditions. Previous studies using Mode I and III loaded samples have been used to suggest that the preference of cracking in Mode I loaded samples supports a hydrogen induced cracking mechanism. However, the lack of crack opening and environmental ingress to the crack tip in Mode III loading leaves some doubt about these conclusions. Stress corrosion cracking tests using a new test sample where the mode mixity between Mode I and III can be varied have been conducted and are reported for sensitized Type 304 SS tested in 0.21 M H 3 BO 3 +0.01 M (580 ppm) NaCl. Tests were conducted with samples with cracks at angles of 0, 30 and 45° to the principal loading stress. The results from these tests clearly demonstrated the crack velocity does not decrease with increasing amounts of Mode III loading in contrast to expectations from a hydrogen induced cracking mechanism. The crack velocity showed a slight maximum for samples with crack angles of 30° relative to 0 and 45°. The reason for this maximum is not known but could be the result of increasing crack tip strain rates with increasing Mode III loading.

Strain Oxidation Cracking of Austenitic Stainless Steels at 610°C

Abstract Strain oxidation cracking of both forged and welded austenitic stainless steels (SS) was studied. Creep and slow strain rate tests (SSRT) were performed in vacuum, air, and a gas furnace environment (air + carbon dioxide [CO2] + water [H2O]). Results showed cracking was environmentally dependent. Almost no cracking was observed in vacuum, whereas intergranular cracking was observed with increasing severity in passing from an air to a gas furnace environment. The most severe cracking was associated with formation of a less protective film formed in the gas furnace environment (air: haematite-like M2O3 oxide; gas furnace environment: spinel M3O4 oxide). Cracking depended strongly on the carbon content and the sensitization susceptibility of the material: the higher the carbon content, the more susceptible the alloy. This cracking was believed to be similar to other oxidation-induced cracking phenomena.

Effects of Potential and Stress on Stress Corrosion Cracking of Austenitic Stainless Steels in Concentrated Chloride Solutions

The chemical-mechanical correlation model for stress corrosion cracking (SCC) was used to analyze the effect of electrode potential (E) on SCC of austenitic stainless steels (SS) in concentrated chloride solutions. The analysis produced a value of the mechanical constant (Qc/m = 20.6 kJ/mol) which was the same as that obtained at open-circuit potentials (OCP). Analysis also revealed that the effect of E on SCC mainly affected the environmental factor (β) of the model. A theory developed about the physical meaning of β was able to predict the dependence of β on E in concentrated chloride solutions, based upon repassivation properties.

Effects of Stress and Temperature on Stress Corrosion Cracking of Austenitic Stainless Steels in Concentrated Magnesium Chloride Solutions

Experimental data from published literature on stress corrosion cracking (SCC) of austenitic stainless steels (SS) as influenced by temperature and stress in concentrated chloride solutions were analyzed using the chemical-mechanical correlation model. Effects of stress and temperature on SCC were analyzed using 63 sets of data for times to failure (tf) from 17 references. The data followed a systematic pattern which was described by the chemical-mechanical correlation model. An equation of tf as a function of stress and temperature was developed using an environmental parameter β that depends upon temperature, molybdenum concentration, and yield strength of the SS.

Empirical Learning Investigations of the Stress Corrosion Cracking of Austenitic Stainless Steels in High-Temperature Aqueous Environments

Abstract A collection of data documenting the stress corrosion cracking (SCC) behavior of austenitic stainless steels (SS) in high-temperature aqueous environments was investigated using empirical ...

Irradiation-assisted stress corrosion cracking of austenitic stainless steels: recent progress and new approaches

Irradiation-assisted stress corrosion cracking (IASCC) of several types of BWR field components fabricated from solution-annealed austenitic stainless steels (SSs), including a core internal weld, were investigated by means of slow-strain-rate test (SSRT), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), and field-emission-gun advanced analytical electron microscopy (FEG-AAEM). Based on the results of the tests and analyses, separate effects of neutron fluence, tensile properties, alloying elements and major impurities identified in the American Society for Testing and Materials (ASTM) specifications, minor impurities, water chemistry, and fabrication-related variables were determined. The results indicate strongly that minor impurities not specified by the ASTM-specifications play important roles, probably through a complex synergism with grain-boundary Cr depletion. These impurities, typically associated with steelmaking and component fabrication processes, are very low or negligible in solubility in steels and are the same impurities that have been known to promote intergranular SCC significantly when they are present in water as ions or soluble compounds. It seems obvious that IASCC is a complex integral problem which involves many variables that are influenced strongly by not only irradiation conditions, water chemistry, and stress but also iron and steelmaking processes, fabrication of the component, and joining and welding. Therefore, for high-stress components in particular, it would be difficult to mitigate IASCC problems at high fluence based on the consideration of water chemistry alone, and other considerations based on material composition and fabrication procedure would be necessary as well.

The effect of delta-ferrite content on the stress corrosion cracking of austenitic stainless steels in a sulphate solution

The susceptibility to stress corrosion cracking of a CF3 cast austenitic stainless steel, heat treated to generate a range of delta-ferrite contents, and weld metal that contained either 0 or 6% delta-ferrite has been assessed in a buffered, sulphate environment at 250°C using slow strain rate and constant displacement tests under open circuit conditions and at various applied electrode potentials. The susceptibility to cracking of the CF3 material decreased with increasing delta-ferrite content in the range 2–7% and the 0% delta-ferrite weldment was more susceptible to cracking than the 6% weldment. Sensitization increased the susceptibility of the 0% deltaferrite weldment but had little effect on the 6% weldment. Bolt-loaded WOL data for the weldments indicated that the plateau crack growth rates were higher and the K Iscc values lower for the 0% than the 6% delta-ferrite material. Plateau crack growth rates were ~ 10 −7 mm/s for the 6% delta ferrite weldment and ~ 10 −5 mm/s for the 0% delta ferrite weldment. For the test conditions investigated, the CF3 steel was less susceptible to stress corrosion cracking than either of the weldments.

The role of hydrogen in stress-corrosion cracking of austenitic stainless steel in hot MgCl2 solution

The role of hydrogen in stress-corrosion cracking (SCC) of austenitic stainless steel was investigated in boiling chloride solution. The tests in the mixed melted salt verified that hydrogen-induced cracking (HIC) could occur at 160 °C if sufficient hydrogen could be supplied continuously. It was found that the threshold SCC intensity factors of both 321 and 310 steels were lower than those of HIC during dynamic charging at high fugacity at 40 °C and 160 °C. In addition, anodic polarization decreased hydrogen concentration and promoted SCC in hot LiCl solution, while cathodic polarization increased hydrogen concentration and restrained SCC. Hydrogen could be introduced into the specimen and be concentrated at the crack tip during SCC. It could promote anodic dissolution and SCC remarkably, although it was not enough to produce cracking.

The effect of pre-creep on stress corrosion cracking of austenitic stainless steel and brass

The effect of pre-creep on the stress corrosion cracking (SCC) of austenitic stainless steel in a 42% MgCl 2 solution and brass in an ammonia solution was investigated using constant load and constant deflection samples. For both austenitic stainless steel and brass, pre-creep had no influence on the failure time and the threshold stress intensity of SCC if the constant load sample was used. Since for constant deflection samples, pre-creep could greatly increase the threshold stress intensity of SCC for both austenitic stainless steel and brass, constant deflection specimens are not suitable for investigating the effect of pre-creep on SCC. Pre-cathodic protection at a non-cracking potential for long times could inhibit the SCC of brass during subsequent exposure in cracking potential range. This is, however, attributed to the change of composition and pH value of the solution rather than the effect of pre-creep.

Hydrogen-facilitated corrosion and stress corrosion cracking of austenitic stainless steel of type 310

The effects of hydrogen precharge and stress on anodic dissolution for Type 310 austenitic stainless steel (ASS) have been investigated. An experiment determining the effect of hydrogen on stress corrosion cracking (SCC) was carried out in a boiling 42 pct MgCl2 solution and in a 2.5 mo/L H2SO4 + 1 mol/L HC1 solution. The results showed that both hydrogen and stress would increase the dissolution rate, and the effects of hydrogen and stress on the dissolution rate were synergistic rather than simply additive. Hydrogen lowered the threshold stress and the shortened fracture time of SCC in a boiling MgCl2 solution by a factor of 1/5 and 10, respectively.

The stress corrosion cracking of austenitic stainless steels in H 3BO 3 + NaCl solutions between 100°C and 200°C

The stress corrosion cracking of 316L austenitic stainless steel in H 3BO 3 + NaCl aqueous media between 100 and 200°C has been studied. The results obtained from slow strain rate and constant load tests, the polarization curves, the rapid tensile straining tests and the fractographic investigation of the fracture surface by scanning electron microscopy, permit the examination of the nature of mechanisms at work. The experimental crack propagation velocities and those calculated from Faraday's law have been compared. The analysis of the electrochemical behaviour in the absence of stress has revealed the potential ranges of maximum stress corrosion cracking susceptibility. Etch-pitting and stereographic observations are employed in order to determine the cracking crystallography. The transgranular fracture surfaces show crystallographic morphology and though the cracking is cleavage-like and is discontinuous in some cases, the cracks propagate mainly under the control of localized anodic dissolution. This process seems to be the limiting factor of the phenomenon whatever the proposed mechanisms may be. In fact, the crack propagation velocity seems to be clearly consistent with a film rupture-dissolution-repassivation process, although it proves insufficient to quantify the phenomenon. The influence of the various environment parameters (temperature, concentration of chemical species, oxygen) which have been studied, has confirmed the importance of the localized anodic dissolution on the cracks propagation.