Stainless Steel In Air Research Articles

A physics‐informed neural network for creep life prediction of austenitic stainless steels in air and liquid sodium

AbstractCreep life prediction of component materials exposed to air and liquid sodium environments is critical to ensure the safe operation and structural integrity of a sodium‐cooled fast reactor. In this paper, a method for predicting the creep life of a wide range of austenitic stainless steels in air and liquid sodium was proposed based on a physics‐informed neural network. Based on the established datasets for sodium corrosion rates and creep life in air and liquid sodium, the predictive performance of physical equations, conventional machine learning models, and the proposed model were assessed. Subsequently, a data‐driven creep life assessment framework was established, providing insight into the engineering application of machine learning methods in high‐temperature structure assessment. The results show that the creep fracture of austenitic stainless steel is accelerated by liquid sodium corrosion. The proposed physics‐informed neural network exhibits enhanced suitability and accuracy for predicting the sodium corrosion rate and creep life than physical equations and conventional machine learning methods.

High-temperature Corrosion of ~ 30 Pct Porous FeCr Stainless Steels in Air: Long-Term Evaluation Up to Breakaway

In this work, a long-term (up to 6000 hours) corrosion evaluation of three porous (~ 30 pct of initial porosity) ferritic iron-chromium alloys with different Cr contents (20, 22, and 27 wt pct of Cr) was carried out at 600 °C, 700 °C, 800 °C, and 900 °C in air. Mass gain measurements and SEM analyses revealed that at temperatures above 600 °C, all alloys exhibit breakaway corrosion, whereas at 600 °C, none of the alloys were heavily oxidized even after 6000 hours. Based on the results, the diffusion character of the corrosion of porous chromia-forming alloys was identified. The microstructure changes at high temperatures in porous alloys containing 22 wt pct of Cr were determined in detail by transmission electron microscopy. The proposed prediction model indicated that the lifetimes of the Fe20Cr and Fe22Cr alloys were determined as 1250 hours (± 535 hours) and 1460 hours (± 640 hours), respectively. It is in agreement with the long-term oxidation experiment. For the Fe27Cr alloy, the deviation between predicted and observed lifetimes occurs. The proposed model allows for qualitative estimation of the porous alloys’ lifetime with experimentally validated accuracy.

Laser-induced in-plane curving of ripples on biomedical stainless steel and their relationship to biological functions

ABSTRACT Laser-induced periodic surface structures (LIPSS) on biomedical stainless steel in air and water were systematically studied. The LIPSS exhibit in-plane curves near the ripple centres in the individual tracks of laser scan and the curving was opposite to the laser scan direction. The collective in-plane curving of LIPSS, a hitherto unknown feature for single train pulsed laser processing, is attributed to the accumulative effect of laser ablation and redeposition, which modifies the interference between the surface scattered wave and the incident laser beam. Combinations of media, scan-speed, and laser fluence, showed that the roughness can be increased by slowing the scan-speed. Ripples fabricated in the flowing water with slow scan-speed and high laser power are helpful for the hydrophilicity of biomaterials. A contact angle as low as 47.00 ± 9.35° is obtained towards high surface hydrophilicity. The results provide new insights on LIPSS about their formation and biomedical applications.

Micro-asperity tribocorrosion of CoCrMo, Ti6Al4V, and 316 stainless steel in air and physiological solution: Small scale reciprocal sliding of a single diamond tip

Fretting and corrosion of metallic medical devices are significant degradation mechanisms that impact performance. Multi-asperity contact surfaces undergo a progressive engagement-damage-redistribution process distributed over the nominal contact surface, implying that relatively short-lived fretting contact engagements of individual asperities are a central element to fretting corrosion processes in modular taper junctions of total hip replacements. In this work, the contact mechanics of single asperity hard-metal surfaces under small scale reciprocal sliding (SSRS) between two contacting surfaces in air and solution (i.e., tribocorrosion), typically less than 100 μm cyclic motion are presented and discussed for Ti–6Al–4V, CoCrMo, and 316L SS alloys. Characteristic scaling factors, based on asperity radius, hardness, and modulus, for characteristic stress and a dimensionless asperity radius are presented based on the interaction between elastic and plastic contact mechanics. The contact and tribological interactions of a 17 μm radius spherical diamond asperity was used to explore damage effects on these alloys in both air and phosphate buffered saline. The volume abraded, depth of penetration, extent of plastic deformation and oxide debris formation were captured as functions of cycles, load, and solution presence/absence. Damage was analyzed and quantified using digital optical microscopy, atomic force microscopy and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). The results were analyzed with ANOVA statistics (α < 0.05). The extent of damage follows CoCrMo < Ti–6Al–4V < 316L SS. The wear characteristics varied significantly between alloys with more plastic deformation associated with CoCr and more shearing particle and ribbon formation present for Ti–6Al–4V and 316L SS. Solution immersion did not significantly increase volume loss for any alloy but did increase the amount of released and embedded oxide debris for 316L SS. Titanium also exhibited oxide debris generation and embedding. Importantly, significant (<5 μm) penetration depths were obtained after 100 cycles, indicating that single asperities, continuously engaged with metal under very low loads, rapidly generate extensive debris and plastic deformation.

Thermal fatigue behavior of 441 ferritic stainless steel in air and synthetic automotive exhaust gas

Thermal fatigue behavior of 441 ferritic stainless steel in air and synthetic automotive exhaust gas

Effect of Cathodic Polarisation Switch-Off on the Passivity and Stability to Crevice Corrosion of AISI 304L Stainless Steel.

The effects of cathodic polarisation switch-off on the passivation of AISI 304L stainless steel in air and its crevice corrosion susceptibility in 3.5 wt.% NaCl aqueous electrolyte were investigated. Scanning Kelvin probe (SKP) data showed that the oxide film is significantly destabilised and the rate of steel passivation in air is slowed down. Thermal desorption analysis (TDA) highlighted that hydrogen absorption is proportional to the applied cathodic current density. A special crevice corrosion set-up was designed to realise simultaneous reproducible monitoring of potential and galvanic current to study the impact of prior cathodic polarisation on crevice corrosion onset.

High temperature corrosion evaluation and lifetime prediction of porous Fe22Cr stainless steel in air in temperature range 700–900 °C

This work describes a high temperature corrosion kinetics study of ∼30 % porous Fe22Cr alloys. The surface area of the alloy (∼0.02 m2 g−1) has been determined by tomographic microscopy. The weight gain of the alloys was studied by isothermal thermogravimetry in the air for 100 h at 700–900 °C. Breakaway oxidation was observed after oxidation at 850 °C (∼100 h) and 900 °C (∼30 h). The lifetime prediction shows the investigated porous alloy can be used for >3000 h at temperatures <700 °C. At temperatures ≥700 °C, the lifetime of the porous alloy is limited by the available chromium reservoir.

Electrochemical corrosion resistance of thermal oxide formed on anodized stainless steel

PurposeThe purpose of this paper is to investigate and explain thermal oxide effect on electrochemical corrosion resistance anodized stainless steel (SS).Design/methodology/approachElectrochemical corrosion resistance of thermal oxides produced on anodized 304 SS in air at 350°C, 550°C, 750°C and 950°C in 3.5 wt.% NaCl solution have been investigated by dynamic potential polarization, EIS and double-loop dynamic polarization. Anodized 304 SS were obtained by anodization at the constant density of 1.4 mA.cm-2 in the solution containing 28.0 g.L-1H3PO4, 20.0 g.L-1C6H8O7, 200.0 g.L-1H2O2 at 70°C for 50 min. SEM and EDS had been also used to characterize the thermal oxides and passive oxide.FindingsInterestingly, anodized 304SS with thermal oxide produced at 350°C displayed more electrochemical corrosion and pitting resistance than anodized 304 SS only with passive oxide, as related to the formation of oxide film with higher chromium to iron ratio. Whereas, anodized 304SS with thermal oxide formed at 950°C shows the worse electrochemical corrosion and pitting resistance among those formed at the high temperatures due to thermal oxide with least compact.Originality/valueWhen thermally oxidized in the range of 350°C–950°C, electrochemical corrosion and pitting corrosion resistance of anodized 304 SS decrease with the increase of temperature due to less compactness, more defects of thermal oxide.

Role of mean stress on fatigue behavior of a 316L austenitic stainless steel in LWR and air environments

Mean stress effects on fatigue life of a stainless steel in air and boiling water reactor (BWR) environments were evaluated by load-controlled tests. In stress-life, non-zero mean stresses increase life in low cycle fatigue regime in both environments and in high cycle regime in air. In high cycle fatigue regime in BWR environment, higher fatigue life was observed with negative mean stress while a decrease of the fatigue limit was found for positive one. In strain-life, the mean stress effects are insignificant. All data are well correlated with a Smith-Watson-Topper parameter showing no interaction between mean stress and BWR environment.

High-Temperature Oxidation Behavior of a Cu-Bearing 17Cr Ferritic Stainless Steel.

The isothermal oxidation behavior of 17Cr-0.85Si-0.5Nb-1.2Cu ferritic stainless steel in air was studied from 850°C to 1050°C by analyzing its weight gain after oxidation. The kinetic curves were plotted using the oxidation weight-gain data, and the structure, surface morphology, and element distribution of the oxide films were analyzed by XRD, SEM, and EDS. The results showed that the oxidation kinetics curves at 850°C and 950°C followed a parabolic law, and a continuous and dense oxide film composed of Cr2O3 and MnCr2O4, FeCr2O4, and Cu-Cr rich spinel was formed, which reveals that the steel displayed good oxidation resistance. When the temperature was increased to 1050°C, the oxidation kinetics curves gradually changed from parabolic to linear after 40 h exposure, which indicated that the oxidation resistance significantly worsened. A lower oxidation resistance was observed at 1050°C due to the formation of a large amount of Fe2O3 on the surface and the volatilization of the inner Cr2O3 layer.

Oxidation and corrosion protection of ZG12Cr9Mo1Co1NiVNbNB (CB2) ferritic stainless steel by inorganic composite coatings at 650 °C

Inorganic silicate composite coatings were developed to inhibit the oxidation and corrosion of ZG12Cr9Mo1Co1NiVNbNB (CB2) stainless steel in air and water vapor containing environment at 650 °C. The results indicated that water vapor accelerates greatly the oxidation and corrosion of CB2 steel by transforming the protective Cr2O3 scales into non-protective multilayered scales. The excellent inhibition action of the coatings was attributed to barrier effect accompanying with the consumption of O2 and water by NiCrAlY powders. The Cr-rich oxide layer grew at the interface of the coatings and substrate steel retards the outwards diffusion of Fe and Cr.

Corrosion fatigue model of austenitic stainless steels used in pressurized water reactor nuclear power plants

Low cycle fatigue behavior of 316LN stainless steel (SS), 304 SS and 308L weld metal was investigated in air and high-temperature pressurized water environment. The effects of mechanical factors and environmental factors on fatigue lives were considered. The fatigue mean curve and design curve for nuclear-grade austenitic SSs in air are obtained by fitting fatigue data. The corrosion fatigue model for nuclear-grade austenitic SSs in high-temperature pressurized water environment is proposed based on environmental fatigue correction factor method, which mainly considers the effects of strain rate, temperature and dissolved oxygen concentration.

High-performance thermal emitters based on laser-engineered metal surfaces

Effective thermal management is of paramount importance for all high-temperature systems operating under vacuum. Cooling of such systems relies mainly on radiative heat transfer requiring high spectral emissivity of surfaces, which is strongly affected by the surface condition. Pulsed laser structuring of stainless steel in air resulted in the spectral hemispherical emissivity values exceeding 0.95 in the 2.5–15 µm spectral region. The effects of surface oxidation and topography on spectral emissivity as well as high temperature stability of the surface structures were examined. High performance stability of the laser textured surfaces was confirmed after thermal aging studies at 320°C for 96 hours.

Structural, tribological and corrosion properties of plasma nitrided-chromized-316L stainless steel in air and artificial seawater

To improve the protective performance of 316L stainless steel surface in seawater, a series of modified layers on the 316L stainless steel were fabricated by plasma nitriding, vacuum solid powder chromizing and duplex surface treatment of nitriding-chromizing, respectively. The microstructure, mechanical properties, tribological properties and corrosion resistance of different modified layers were contrastively investigated. The results of x-ray diffraction (XRD) and transmission electron microscope (TEM) showed that the nitrided layer was mainly CrN and Fe4N phases, and the chromized layer was mainly Fe-Cr and Cr23C6 phases. The surface hardness of 316L stainless steel was improved to varying degrees by nitriding and chromizing due to the formation of hard phases such as CrN and Cr23C6 on the surface of 316L. The friction coefficient and wear rate can be obviously reduced by nitriding treatment. However, the nitriding treatment can cause the precipitation of Cr from the solid solution of 316L to form CrN, resulting in the decrease of corrosion resistance in seawater. In contrast, chromizing treatment can significantly improve the corrosion resistance of 316L by increasing the chromium content of stainless steel surface. The duplex surface treatment of nitriding and chromizing made the 316L stainless steel had the highest surface hardness and plastic deformation resistance and showed the excellent tribological properties in both atmosphere and seawater.

A comparison of the dry sliding wear behavior of NiCoCr medium entropy alloy with 316 stainless steel

The aim of this work was to determine the wear behavior of the f.c.c. medium entropy alloy NiCoCr, which has been shown by others to possess both a very good strength-ductility balance and an especially high fracture toughness. Pins of NiCoCr were tested in dry sliding wear against disks of yttria-stabilized zirconia at a sliding velocity of 0.1 m/s both in air and in argon. Identical wear tests on 316 stainless steel were performed for comparison. It was found that the wear rates of the NiCoCr pins were lower than those of the 316 stainless steel in air, but that the wear rates of the two materials were almost identical in dry argon. Scanning electron microscopy analysis of both the worn pins' surfaces and cross sections indicated that the worn surface of NiCoCr pins were flatter and showed less fracture due to the better toughness compared to the 316 stainless steel pins. Wear tests in air resulted in the formation of oxides. X-ray photoelectron spectroscopy of the NiCoCr pin showed that the oxides in the debris were Cr2O3 and Co2O3. The oxides play an important role in the development of a mechanically mixed layer, which formed on the NiCoCr pin's tip to protect the contacting material during wear tests in air.

Effect of load on the fretting behavior of SAF 2507 super duplex stainless steel in air and sea water

PurposeThis paper aims to study the influence of load and environment medium on the fretting behavior of SAF 2507 SDSS.Design/methodology/approachIn this study, the effect of load on the fretting behavior of SAF 2507 SDSS in air and sea water were studied. The fretting wear tests under different loads were conducted with a ball-on-flat contact configuration. The friction coefficient, wear volume, surface morphology and oxidation component were determined.FindingsWith the increase of applied load, the friction coefficient decreases both in air and sea water. The fretting mechanism is gradually transformed from partial slip regime to slip regime in air while the fretting counterparts are all in the state of gross slip in sea water. In sea water, the friction coefficient is lower while the wear loss is higher compared with that in air.Research limitations/implicationsThis research suggests that the fretting behavior of SAF 2507 SDSS is related to load and environment medium.Practical implicationsThe results may help us to choose the appropriate load under different environments.Originality/valueThe main originality of the research is to reveal the fretting behavior of SAF 2507 SDSS under different loads in air and sea water, which would help us to realize fretting behavior of SAF 2507 SDSS is controlled by the combination of applied load and lubricating environment.Peer reviewThe peer review history for this article is available at: http://dx.doi.org/10.1108/ILT-08-2019-0335.

Effect of Niobium Addition on the High-Temperature Oxidation Behavior of 22Cr25NiWCoCu Stainless Steel in Air

The oxidation behavior of 22Cr25NiWCoCu stainless steel with 0–0.86 wt.% Nb addition was investigated at 900 °C in air. With an increase in Nb addition, the volume fraction and average particle size of Nb (C, N) increased, but the grain size decreased. The results of grazing incidence X-ray diffraction indicated that the steels with Nb additions promoted Cr2O3 formation. After 10–100 h of oxidation, Cr depletion occurred at the region with Nb (C, N) precipitates because of its high Cr consumption rate, leading to Fe oxide generation. Finally, after 100 h of oxidation, the outer layer of Fe2O3 and the inner layer of (Cr, Fe, Mn)3O4 were formed.

Evaluation of fatigue life and fatigue limit of circumferentially-notched Type 304 stainless steel in air and hydrogen gas based on crack-growth property and cyclic stress-strain response

Fatigue tests were performed using circumferentially-notched, round bar specimens with a stress concentration factor, Kt, of 6.6 for Type 304, metastable, austenitic stainless steel. The tests were carried out in ambient air and in 0.7 MPa hydrogen gas at room temperature. In a relatively higher stress amplitude regime (i.e., the amplitude resulting in Nf < 105), the hydrogen gas environment caused a marked degradation in fatigue life. In contrast, in a relatively lower stress amplitude regime (i.e., the amplitude resulting in Nf > 105), it appeared that fatigue life did not differ between air and hydrogen gas. It was also confirmed that the fatigue limit appeared not have been degraded in the hydrogen environment though there was a slight difference between the data obtained in two environments. The fatigue life curve and fatigue limit were predicted by assuming that the notch was equivalent to a circumferential crack. Consequently, there was a significant disparity between the prediction and the experimental results. As a result of microscopic observations of the fracture process in combination with elastic-plastic finite element analyses, these discrepancies were attributed to (i) complex cyclic plastic deformation behavior under large- and small-scale yielding conditions within the vicinity of the notch root, (ii) the retardation of crack initiation in the finite life regime, and (iii) the absence of non-propagating cracks at the fatigue limit, all of which are typical characteristics of metastable austenitic stainless steel.

Low Temperature Corrosion: Oxidation of Carbon Steel and Stainless Steel in Air

Low Temperature Corrosion: Oxidation of Carbon Steel and Stainless Steel in Air

Development of Fatigue Crack Growth Thresholds for Austenitic Stainless Steels Exposed to Air Environment for ASME Code Section XI

Fatigue crack growth thresholds ΔKth define stress intensity factor range below which cracks will not grow. The thresholds ΔKth are useful in industries to determine durability lifetime. Although massive fatigue crack growth experiments for stainless steels in air environment had been reported, the thresholds ΔKth are not codified at the American Society of Mechanical Engineers (ASME) Code Section XI, as well as other fitness-for-service (FFS) codes and standards. Based on the investigation of a few FFS codes and review of literature survey of experimental data, the thresholds ΔKth exposed to air environment have been developed for the ASME Code Section XI. A guidance of the thresholds ΔKth for austenitic stainless steels in air at room and high temperatures can be developed as a function of stress ratio R.