Susceptibility Of Austenitic Stainless Steels Research Articles

A novel method for evaluating solidification cracking susceptibility of austenitic stainless steel using trapezoidal hot cracking test during laser welding

A novel evaluation method was developed for evaluating solidification cracking susceptibility of austenitic stainless steel using trapezoidal hot cracking test laser welding. By changing different chemical compositions and welding speeds, the critical restraint width was named and regarded as a new index to evaluate cracking susceptibility. First of all, the average critical restraint width of SUS310S, 316 and 302 was measured as 22.97 mm, 18.17 mm and 17.38 mm during laser welding at a speed of 1.0 m/min, respectability. Single phase austenite under mode A appeared in 310S while the other could form austenite and a small amount of ferrite based on mode FA, therefore, the solidification cracking susceptibility was 310S > 316 > 302. Then, the critical restraint widths of SUS310S and 304 had a tendency of decrease with increasing welding speed from 0.5 m/min to 1.0 m/min during laser welding. The lower heat input could decrease primary and secondary dendrite arm spacings, causing a reduction in the segregation degree. In addition, the fine dendrite along grain boundary of weld center could contribute to form zigzag interface which would be beneficial to interrupt the continuous residual liquid film. Thus, the solidification cracking susceptibility tended to decrease with an increase in laser welding speed from 0.5 m/min to 1.0 m/min. Above all, the developed evaluation method could improve the applicability, feasibility and progressiveness of hot cracking test.

Corrosion by Polythionic Acid in the Oil and Gas Sector: A Brief Overview.

Polythionic acid (PTA) corrosion is a significant challenge in the refinery industry, leading to equipment degradation, safety risks, and costly maintenance. This paper comprehensively investigates the origin, progression, mechanism, and impact of PTA corrosion on various components within refinery operations. Special attention is afforded to the susceptibility of austenitic stainless steels and nickel-based alloys to PTA corrosion and the key factors influencing its occurrence. Practical strategies and methods for mitigating and preventing PTA corrosion are also explored. This paper underscores the importance of understanding PTA corrosion and implementing proactive measures to safeguard the integrity and efficiency of refinery infrastructure.

Correlation between machining-induced surface alterations and stress corrosion cracking susceptibility of au stenitic stainless steels

Correlation between machined surface alterations and stress corrosion cracking (SCC) susceptibility of austenitic stainless steels is investigated. The machining-induced residual stress, roughness, micro-hardness and dislocation density were characterized and the surface/subsurface cracks were examined after SCC tests in boiling magnesium chloride solution. The results showed SCC crack initiation and early propagation were highly related to the machining-induced alterations. By establishing a quantitative relationship between the surface characteristics and surface crack density, the comprehensive impact of the residual stress, surface roughness as well as the dislocation density on SCC susceptibility is revealed. The predicted crack density is in good agreement with the measured data. As a result, the SCC susceptibility of the machined surface is described by the surface integrity properties.

Evaluating Localized Corrosion Susceptibility of Austenitic Stainless Steels Exposed to Varying Nitrate to Chloride Ratio Droplets

Austenitic stainless steels (SS), utilized extensively in coastal environments due to their enhanced corrosion resistance, are susceptible to localized corrosion and stress corrosion cracking (SCC) when exposed to chloride environments. One potential scenario under which SCC may pose a concern is the interim storage and the eventual transport of spent nuclear fuels (SNF) in SS canisters. The SS canisters may be subjected to marine sea-salts and elevated temperatures; however, assessing the current damage state on the surface of these canisters is difficult due to high radiation levels dictating confinement within a limited-access overpack. Hence, accelerated tests are needed in order to help predict potential materials degradation on the surface of these canisters. Another important factor related to SNF storage is the fact that the canisters are located in a variety of climates across the United States. Salt compositions and daily fluctuations of relative humidity (RH) and temperature differ widely by location. Of particular interest, inland sites have a higher nitrate concentration in comparison to coastal locations. One governing brine property for corrosion is the amount of nitrate present in the brine as this can serve to passivate a corroding alloy. Herein, we evaluate the influence of nitrate to chloride ratios on the pitting susceptibility of SS304L under full immersion and cyclic RH conditions. The results of this study are discussed in terms of potential canister degradation. Acknowledgements SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. This document is SAND2022-3796 C.

Comparison of Stress Relaxation Cracking Susceptibility of Austenitic Stainless Steels

Coal-fired power plants often have welded joints made up of 347H stainless steel. However, this alloy is known to fail because of stress relaxation cracking. Thus, quantitative evaluation methods are needed as screening measures. In this study, a Gleeble® thermomechanical simulator was implemented in 347H and Super 304H alloy heat-affected zone (HAZ) simulation and stress relaxation testing. In the case of 347H, carbide dissolution in the HAZ reduced the hardness value and promoted grain growth. Alternatively, the respective extent of precipitate dissolution and hardness reduction in the nitrogen-containing Super 304H was relatively small. The stress relaxation tests were performed at a temperature of 700°C (1292°F), which was maintained for up to 70 h. Consequently, all 347H specimens fractured within 32 h. Furthermore, the time to rupture substantially decreased as the strain was increased from 5 to 10% and then to 15%. Additionally, the hardness near the fractured surface increased, and the plastic deformation primarily occurred near the grain boundaries. Conversely, the Super 304H specimens did not fracture during the 70-h testing period, at which time their hardness distribution was observed to still be relatively uniform. These results demonstrate that the susceptibility of stress relaxation cracking can be quantitatively determined according to the material and strain.

Hot‐cracking susceptibility of fully austenitic stainless steel using pulsed‐current gas tungsten arc‐welding process

AbstractThe pulsed‐current gas tungsten arc‐welding process (PCGTAW) has recently been recommended as an approach to eliminate the high susceptibility of austenitic stainless steel to hot cracking. Within a wide range of variables, in the present study, the effects of pulse frequency, time ratio, and pulse current on the cracking susceptibility of austenitic stainless‐steel thin sheets are investigated. A fan‐shaped cracking test specimen is adopted, and suitable final dimensions are obtained by conducting some preliminary experiments. A good correlation is found between the maximum crack length, which is taken as a cracking susceptibility index, and the pulse form variables. The results are found to be significantly improved when compared with those of the continuous‐current process, which indicates that the PCGTAW process has an effective role in reducing the hot‐cracking susceptibility. The optimal conditions of the pulse form variables based on the hot‐cracking susceptibility are determined. The optimal values of the time ratio are found to be less than 50%, together with a pulse frequency of less than 1 Hz. Some new microstructure measures, such as columnar structure ratio, grain orientation angle, puddle diversion angle, and overlapping ratio, which are originally defined in this work, in addition to grain size and puddle form factor (aspect ratio), are used to interpret the hot‐cracking behavior. All are found to have a direct impact on the hot‐cracking susceptibility. The results obtained from microstructure examinations showed that the cracks formed are either intergranular or transgranular cracks.

Role of residual ferrites on crevice SCC of austenitic stainless steels in PWR water with high-dissolved oxygen

The crevice stress corrosion cracking (SCC) susceptibility of austenitic stainless steels was evaluated in simulated pressurized water reactor (PWR) environments. To simulate the abnormal condition in temporary clamping devices on leaking small bore pipes, crevice bent beam (CBB) tests were performed in the oxygenated as well as hydrogenated conditions. No SCC cracks were found for SS316 in both conditions. SS304 also showed good resistance in the hydrogenated condition. However, all SS304 specimens showed SCC cracks in the oxygenated condition, indicating poor crevice SCC resistance. It was found that residual ferrites were selectively dissolved because of the galvanic corrosion coupled with the neighbouring austenite phase, resulting in SCC initiation in SS304. Crack morphologies were mostly transgranular assisted by the damaged δ-ferrite and deformation-induced slip bands.

Effect of MC carbide formation on weld solidification cracking susceptibility of austenitic stainless steel

The effect of secondary phase formation such as MC carbide during welding on solidification cracking susceptibility of fully austenitic stainless steels with various amounts of alloying elements and carbon was investigated. The solidification cracking susceptibility of Fe-24mass%Cr-26mass%Ni stainless steels with various amounts of niobium, titanium, zirconium, and carbon was evaluated by the Trans-Varestraint test.The addition of alloying elements such as niobium, titanium, and zirconium increased the brittle temperature range (BTR). The BTRs depend on the type and combination of the alloying elements and carbon content. Titanium was the most influential element on the increase in BTR compared to the other elements. The increase in carbon content tended to decrease the BTR, especially for the specimen containing titanium. The alloying elements formed phases such as the film-like MC-type carbide (MC) phase and granular Laves phase in the specimens containing 0.05% C, and a lot of the acicular MC phases in the specimens containing 0.20% C. The start temperature of the secondary phase formation differed depending on the type of the alloying element, and the temperature tended to increase with increasing carbon content. When the additions of niobium and titanium were compared, the amount of titanium segregation during solidification was smaller due to the formation of MC phases. Solidification simulation revealed that a higher amount and faster formation of the MC phase during solidification in 2Ti–20C contributed to reducing the BTR by increasing the carbon content. Thus, it is considered that the weld solidification cracking susceptibility depended on the type and amount of formation morphology, as well as start temperature during solidification corresponding to the composition of alloying elements and carbon.

A new method for predicting susceptibility of austenitic stainless steels to intergranular stress corrosion cracking

Microstructures of type 304 austenitic stainless steel, produced through thermo-mechanical processing, were analysed with large area EBSD and optical image analysis assessments of the attacked grain boundary cluster after DL-EPR testing. The thermo-mechanically processed microstructures were exposed to acidified potassium tetrathionate (K2S4O6) solution under tensile stress and the lengths and distributions of the initiated intergranular crack nuclei were assessed. The crack populations were quantified by fitting a Gumbel extreme value statistics distribution to evaluate their characteristic crack length. A factor (susceptibility parameter) is introduced to rank the degree of susceptibility to intergranular stress corrosion cracking of thermo-mechanically processed microstructures. This accounts for the network connectivity of the sensitised grain boundaries, the grain size and the degree of sensitisation. Similar rankings are obtained for this susceptibility parameter and characteristic crack lengths of the assessed microstructures, in which the thermo-mechanical treatments increased the population of grain boundaries with resistance to stress corrosion cracking.

Corrosion Susceptibility of Austenitic Stainless Steels in Direct Carbon Fuel Cell

The direct carbon fuel cell (DCFC) is a future energy technology which is an efficient process for electrical energy generation from carbon-based sources. This technology has an extremely high theoretical efficiency due to favourable thermodynamics of the electro-oxidation reactions in the process. However, several technical challenges exist which must be addressed before the technology can be commercialized. One of the challenges is the corrosion of metal parts in the cell which limits the service life of the unit. In recent year, research on the development of new alloys and surface engineering have been done to address the corrosion issues in molten carbonate fuel cells. However, the literature on the corrosion behaviour of metals in a slurry system (coal + carbonate) is limited. Austenitic stainless steels are known for their high temperature corrosion resistance and excellent mechanical properties. In this work, the corrosion susceptibility of two types of austenitic stainless steels, i.e. 316L (16 wt.% Cr and 10wt. % Ni) and 235 MA (21 wt.% Cr and 11 wt.% Ni) were compared for fuel cell tank body application. The corrosion behaviour of the two stainless steels were evaluated in a slurry, which contained 20 wt% coal and 80 wt% ternary-eutectic (Li2CO3: 43.5 mol%, Na2CO3: 31.5 mol%, and K2CO3: 25.0 mol%), with nitrogen as a sweep gas at 800⁰C was examined for a 30-day period. The results indicate that the weight gain (due to corrosion product build-up) for both the stainless steels was marginal after 7 day exposure, i.e., 0.4% and 0.5% for 316L and 253 MA, respectively. However, after 30 days exposure, the weight gain increased to 0.98% for 316L, whereas for 253MA the weight gain remained at ~ 0.5%. Thus, the study suggest that 235 MA stainless steel is superior to 316L stainless steel in the coal-carbonate slurry environment. The corrosion mechanisms of the stainless steels will be discussed in the presentation.

Relationship between Alloy Element and Weld Solidification Cracking Susceptibility of Austenitic Stainless Steel

Relationship between Alloy Element and Weld Solidification Cracking Susceptibility of Austenitic Stainless Steel

Prediction of steel resistance to stress corrosion cracking in seawater based on accelerated tests and structural studies

The paper presents the tests results of resistance of various structural steel classes to SCC in chloride solutions. The experiments were performed using cantilever bending tests developed by NRC “Kurchatov Institute” – CRISM “Prometey” with stepwise increasing load of Charpy-type precracking specimens. The criterion estimation of resistance to SCC when β = σSCC/σC > 0.85 was confirmed by the laboratory test results compared with the case studies of corrosion-mechanical fracture of shipbuilding structures in real life service conditions. A new approach of SCC susceptibility of austenitic stainless steels in marine conditions is proposed. It is based on estimation of the critical temperature of SCC when testing for SSRT in a concentrated solution of calcium chloride at temperatures from 20°C to 100°C. Specific features of the structural-phase composition of steels that detrimentally affect the resistance to SCC were discovered during the complex testing.

Theoretical approach to influence of nitrogen on solidification cracking susceptibility of austenitic stainless steels: computer simulation of hot cracking by solidification/segregation models

ABSTRACTThe effect of nitrogen on the solidification cracking susceptibility of austenitic stainless steels (SUS316L and SUS310S) was quantitatively evaluated by transverse-Varestraint test. The amount of nitrogen in Ar shielding gas during GTA melt-run welding was varied in order to vary the nitrogen content in the weld metals. The solidification brittle temperature range of SUS316L was enlarged with an increase in the nitrogen content in the weld metal, while that of SUS310S was very slightly increased with an increase in the nitrogen content. Numerical analysis of solidification segregation during welding revealed that the solid–liquid coexistence temperature range of SUS316L was enlarged with an increase in the nitrogen content in the weld metal, whereas that of SUS310S was almost constant regardless of the nitrogen content. A nitrogen itself essentially had a negligible effect on the solidification cracking susceptibility of fully austenitic stainless steels because a nitrogen neither solidification-segregated in the weld metal nor reduced the solidified temperature during welding. However, the nitrogen increased the solidification cracking susceptibility of austenitic stainless steels with two-phase solidification because the solidification segregation of P and S was promoted by reducing the amount of δ-ferrite in the weld metal.

Numerical analysis on solidification cracking susceptibility of type 316 stainless steel considering solidification mode and morphology computer simulation of hot cracking by solidification/segregation models

ABSTRACTThe two-phase solidification model was constructed considering the solidification mode and morphology. The effects of the solidification mode and morphology as well as δ-ferrite on the solidification cracking susceptibility of austenitic stainless steels (SUS316L) were clarified by a numerical analysis. The solid–liquid coexistence temperature range (SLCTR), correlating the solidification brittle temperature range (solidification cracking susceptibility), was calculated based on the computer simulation of supercooling and solidification segregation behaviours. In the peritectic–eutectic solidification model, the solidification mode greatly influenced the solidification segregation as well as the SLCTR, although the solidification segregation and the SLCTR would be discontinuously changed at the solidification mode transition. The SLCTR calculated by peritectic–eutectic solidification model was larger than that by divorced eutectic solidification model at the ferritic–austenitic mode solidification, while an opposite tendency was observed at the austenitic–ferritic mode solidification. The amounts of δ-ferrite calculated by each solidification model were comparable in any solidification modes. The SLCTR was approximately decreased with an increase in the amount of δ-ferrite in any solidification models. It followed that solidification cracking susceptibility would be dominantly influenced by δ-ferrite and additionally by the solidification mode and morphology.

Effects of Applied Strain and Sensitization on SCC Behavior of 304 Stainless Steel in Atmospheric Corrosion Environments

Austenitic stainless steels have relatively good corrosion resistance due to the formation of a Cr-rich passive film. However, in atmospheric corrosion environments near seashore, austenitic stainless steels can suffer from localized attacks such as pitting corrosion and crevice corrosion. This is due to the formation of thin water layers containing high concentration of chloride ions on the stainless steels. In addition, when the steels are subjected to tensile stress or deformation, stress corrosion cracking (SCC) can occur from pits. Since it is well-know that sensitization can enhance SCC susceptibility of austenitic stainless steels, it is needed to clarify the effect of deformation and sensitization on the SCC of the steels in atmospheric corrosion environments. In this study, crack initiation and propagation behavior of sensitized 304 stainless steels was investigated under a MgCl2 solution droplet. The experimental results demonstrated that cracks were initiated from pits by applying plastic deformation. It was confirmed that hydrogen evolution was observed during propagation of the cracks. In the presentation, SCC mechanism of sensitized 304 stainless steels in atmospheric corrosion environments will be discussed.

オーステナイト系ステンレス鋼の凝固割れ感受性に及ぼす窒素の効果に関する理論的検討

The effect of nitrogen on the solidification cracking susceptibility of austenitic stainless steels (SUS316L and SUS310S) was quantitatively evaluated by transverse-Varestraint test. The amount of nitrogen in Ar shielding gas during GTA melt-run welding was varied in order to vary the nitrogen content in the weld metals. The solidification brittle temperature range (BTR) of SUS316L was enlarged with an increase in the nitrogen content in the weld metal, while that of SUS310S was very slightly increased with an increase in the nitrogen content. Numerical analysis of solidification segregation during welding revealed that the solid-liquid coexistence temperature range of SUS316L was enlarged with an increase in the nitrogen content in the weld metal, whereas that of SUS310S was almost constant regardless of the nitrogen content. A nitrogen itself essentially had a negligible effect on the solidification cracking susceptibility of fully-austenitic stainless steels, because a nitrogen neither solidification-segregated in the weld metal nor reduced the solidified temperature during welding. However, a nitrogen increased the solidification cracking susceptibility of austenitic stainless steels with two-phase solidification, because the solidification segregation of P and S was promoted by reducing the amount of δ-ferrite in the weld metal.

Microstructural properties controlling hydrogen environment embrittlement of cold worked 316 type austenitic stainless steels

Austenitic stainless steels with three different nickel contents were cold worked to various forming degrees at various temperatures to obtain a wide variety of cold worked microstructures. Dislocation density analyses using the Williamson–Hall method provide first indications that strain hardening using technically relevant cold forming parameters increases the susceptibility of austenitic stainless steels to hydrogen environment embrittlement mainly by creating a microstructure with a “critical” amount of dislocations. Although an effect of prior-existing martensite may not be totally excluded, this effect seems to be minor compared to the effect of dislocation substructure. Macroscopic residual stresses have no significant influence on the susceptibility of cold worked austenitic stainless steels to hydrogen environment embrittlement in tensile tests.

Slow strain rate tensile tests on irradiated austenitic stainless steels in simulated light water reactor environments

Irradiation stress corrosion cracking (IASCC) is a critical degradation mechanism for reactor internal components that contributes to the safe and economic operation of reactors. As nuclear power plants age and irradiation dose increases, IASCC becomes an increasingly important issue because of its potential impact on the integrity of reactor internal components. In this study, slow strain rate tensile tests were conducted on irradiated tensile specimens at strain rates between 3 and 7×10−7s−1 to evaluate cracking susceptibility of austenitic stainless steels in simulated light water reactor (LWR) environments. Significant increases in yield strength were observed for all irradiated specimens and a dose dependence of irradiation hardening was obtained at temperatures relevant to LWRs. Ductility and strain hardening capability were also found decrease rapidly with the increase of dose. After the tests, the specimens were examined using a scanning electron microscopy to characterize fracture morphology. The area fractions of non-ductility fracture were used to evaluate the IASCC susceptibility along with the tensile properties. IASCC susceptibility was also compared for several stainless steels irradiated in the Halden and BOR-60 reactors. A possible neutron spectrum effect was discussed.

Corrosion resistance of austenitic stainless steel in sulphuric acid

The resistance and susceptibility of austenitic stainless steel, Type 304, exposed to strong tetraoxosulphate (VI) acids (2 and 5 M concentrations) contaminated with sodium chloride at ambient temperatures was investigated by gravimetric and metallographic/scanning electron microscopy surface characterization methods. Scanning electron microscope (SEM) was used to examine and characterize the test specimen’s surface morphology after immersion in the corrosive media. Surface corrosion deposit composition was analyzed with the SEM paired with energy dispersive spectrometer (EDS). This paper reports the observed severe general and pitting corrosion and the resistance of the steel to corrosion at different concentrations of the acid chloride media. The results obtained showed the weak corrosion resistance/appreciable corrosion susceptibility of the stainless steel alloy to the test environments.

Role of residual stresses induced by industrial fabrication on stress corrosion cracking susceptibility of austenitic stainless steel

Effect of residual stress generated during tube fabrication, roll expansion and machining of stainless steel on the stress corrosion cracking (SCC) susceptibility was studied by testing fabricated tubes, tube–tube sheet joint and heavily machined plate of austenitic stainless steel (SS) in boiling MgCl 2. U bend samples of machined plate were exposed to acidified SO 4 + Cl − environment at room temperature to study its ambient temperature SCC behavior. The results correlate the SCC behavior of the SS tubes and roll expanded joints to the nature and magnitude of residual stresses present. The study also highlights the distinct difference in ambient temperature SCC behavior of machined vs. nonmachined surfaces.