Small Precipitates Research Articles

Characterisation of Thunderstorms with Multiple Lightning Jumps

Several works have shown that lightning jumps are precursors of severe weather in deep-convective thunderstorms. Since 2017, the Meteorological Service of Catalonia has operationally run an algorithm that identifies lightning jumps (LJs) in real time. It has resulted in being an effective tool for nowcasting severe weather with a lead time between 15 min and 120 min in advance. This time can be of high value for managing emergencies caused by severe phenomena or heavy rains. The present research focused on the events’ analysis in which more than one lightning jump occurred, searching for those elements that differentiate single warning cases. Thunderstorms producing LJs were divided into two main categories, depending on the number of jumps triggered during the life cycle. Besides, both classes were split into two main sub-types, based on the level of the LJ that occurred. Multiple LJ thunderstorms produce more Level 2—related to severe weather—jumps than Level 1—small hail or intense precipitation—while in the case of a single LJ, the opposite behaviour occurs. In general, multiple LJ thunderstorms with at least one Level 2 jump are the more intense and have a higher vertical development. Finally, lineal and well-organised thunderstorms are the more common modes in those intenser cases.

Changes in Terrestrial Evaporation across Poland over the Past Four Decades Dominated by Increases in Summer Months

Given the importance of terrestrial evaporation (ET) for the water cycle, a fundamental understanding of the water quantity involved in this process is required. As recent observations reveal a widespread ET intensification across the world, it is important to evaluate regional ET variability. The specific objectives of this study are the following: (1) to assess annual and monthly ET trends across Poland, and (2) to reveal seasons and regions with significant ET changes. This study uses the ET estimates acquired from the Global Land Evaporation Amsterdam Model (GLEAM) dataset allowing for multi-year analysis (1980–2020). The Mann–Kendall test and the Sen’s slope were applied to estimate the significance and magnitude of the trends. The results show that a rising temperature, along with small precipitation increase, led to the accelerated ET of 1.36 mm/y. This was revealed by increased transpiration and interception loss not compensated by a decrease in bare soil evaporation and sublimation. The wide-spread higher water consumption especially occurred during the summer months of June, July, and August. Comparing the two subperiods of 1980–2020, it was found that in 2007–2020, the annual ET increased by 7% compared to the reference period of 1980–2006. These results can serve as an important reference for formulating a water resources management strategy in Poland.

Transient deformation and long-term tectonic activity in the Eastern Alps recorded by mylonitic pegmatites

Mylonitic pegmatites from the Austroalpine basement north of the Deferregen-Antholz-Vals shear zone (DAV) in the Eastern Alps record episodic deformation at greenschist facies conditions after the Eoalpine tectonometamorphic event and before uplift in the Oligocene. Fluorapatite-allanite-epidote coronae around monazite formed at about 60 Ma. They postdate a main mylonitic foliation and predate a second shear band foliation. Deformation of quartz is controlled by crystallographic orientation: Dislocation glide in favourable orientation forms elongate high-aspect-ratio grains. Localised recrystallisation takes place at sites of increased dislocation densities in less favourable oriented quartz and distributed microcracking in unfavourable orientation. Distributed microcracking of quartz occurred quasi-instantaneously coeval with cataclastic deformation of garnet and tourmaline, indicating transient high stresses. During subsequently decreasing stresses, small isometric quartz grains precipitate within the shear band boundaries from the pore fluid, probably derived from recrystallisation of fluid-rich quartz porphyroclasts. Cataclasites with mylonitic components record a coeval or subsequent stage of transient deformation, reflecting the main activity of the DAV with uplift from greenschist facies conditions. The mylonitic pegmatites record systematically changing deformation mechanisms during episodic deformation at greenschist facies conditions dominantly governed by changing stresses and strain-rates, as opposed to changing temperatures.

Nationwide Radar-Based Precipitation Nowcasting—A Localization Filtering Approach and its Application for Germany

One approach to improve advection methods is the short-term ensemble prediction system (STEPS). STEPS decomposes precipitation fields into different spatial scales and filters those having a short lifetime. The latter is achieved by using an auto-regressive (AR) model that considers a sequence of observations. However, such a model tends to smooth nowcasting fields especially in small but convective precipitation areas and at longer lead-times. With focus on the deterministic configuration of STEPS, i.e., the spectral prognosis model (SPROG), this article 1) extends the STEPS approach by estimating spatially localized parameters of the AR process, 2) conducts a sensitivity analysis of the SPROG model to the order of the AR process, the spatial decomposition levels, and post-processing, and 3) analyzes the forecast skill of the extended STEPS. For such purpose, the performance of the localized AR model was demonstrated and evaluated at several precipitation thresholds and window sizes using a varied set of precipitation events collected by the radar network of the German Weather Service. The statistical results exhibited an improved performance of the localized AR model over SPROG when both are evaluated at precipitation thresholds and window sizes larger than 0.1 mm h <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula> and 1 km, respectively, and for lead-times up to 2 h. The analysis suggested a first-order AR process, six cascade levels, and a mean adjustment post-processing procedure. Our results show a key role of the localization aspect when generating nationwide forecasts in scenarios that include large precipitation areas which are non-uniformly distributed having isolated convective features.

Effect of Tempering Treatment on Microstructural Evolution and Mechanical Behavior of Heavy-Wall Heat Induction Seamless Bend Pipe.

In this paper, the microstructure and mechanical properties of heavy-wall seamless bend pipe after quenching at different tempering temperatures, including 550 °C, 600 °C, 650 °C, and 700 °C, were studied. Microstructure and dislocations observations were characterized by means of an optical microscope, a scanning electron microscope, a transmission electron microscope, and X-ray diffraction. As the tempering temperature increases, the dislocation density in the test steel gradually decreases, and the precipitation behavior of (Nb, V)(C, N) increases. The sample tempered at 650 °C exhibits a granular bainite structure with a dislocation cell structure and a large number of smaller precipitates. The yield platforms of tempered samples at 650 °C and 700 °C are attributed to the pinning effect of the Cottrell atmosphere on dislocations. The sample tempered at 650 °C not only presents the highest strength, but also the highest uniform elongation, which is attributed to the higher strain-hardening rate and instantaneous work-hardening index. This is closely related to the multiplication of dislocations, the interaction between dislocations and dislocations, and the interaction between dislocations and precipitates during plastic deformation of the 650 °C-tempered samples with low dislocation density, which delays the occurrence of necking.

Functional responses of biological soil crusts to simulated small precipitation pulses in the Monte desert, Argentina

In arid areas, biological activity responds to precipitation pulses, with different activation thresholds for different organisms. Biocrusts, communities of cyanobacteria, green algae, lichens and mosses living in the soil surface, contribute to soil fertilization by fixing atmospheric nitrogen (N), carbon (C), and solubilizing phosphorus (P). In this study, we hypothesized that biocrusts respond to low simulated precipitation pulses, lower than 10 mm, increasing nutrient availability. We expected biocrust organisms to increase soil net CO2 exchange, N fixation, soil N and P availability in response to small water pulses.In order to evaluate these predictions, we artificially irrigated soils with different covers, including those dominated by bare soil, mosses, and lichens, simulating precipitation pulses of 1, 3, 5, and 10 mm. We measured variables that change at short time scales (hourly), such as net CO2 exchange, N fixation and soil nitrate and phosphate availability, and those that change at larger time scales (years), such as organic matter and total N. Organic matter, total N, and phosphate concentrations were higher in soils with moss dominated biocrusts than in bare soils, indicating their importance to soil fertility in the long term. Soil net CO2 exchange, phosphate, and nitrate availability responded to the simulated precipitation pulses in all soil covers. Net CO2 exchange increased in all soil covers, but phosphate availability decreased in response to precipitation in moss dominated biocrusts. Nitrate availability was lower in lichen dominated biocrusts, although it increased in all soil covers in response to precipitation. These results show that although all the soils analyzed respond to low simulated precipitation pulses, biocrust organisms may retain soil nutrients and decrease availability to other organisms.

Splitting of dissolving precipitates during plastic shear: A phase field study

Using a phase field model, we have investigated the role of plasticity on the morphological evolution of a precipitate during its diffusion-controlled dissolution, when submitted to shear loading. It is shown that the plastic strain pattern in the matrix strongly influences the local dissolution rate and consequently the final shape of the precipitate. Finally, it is demonstrated that for sufficiently fast and intense shear loadings, plasticity can induce splitting of the precipitate: this process could explain why small precipitates are observed in shear bands in Ti alloys forged parts.

Long-term in vitro corrosion behavior of Zn-3Ag and Zn-3Ag-0.5Mg alloys considered for biodegradable implant applications

In this paper, Zn-3Ag and Zn-3Ag-0.5Mg alloys were studied in terms of applicability as biodegradable implant materials. The performed tensile, compression and bending tests indicate a high strengthening effect induced by the Ag and Mg additions, additionally resulting in grain size refinement. It was shown that sustaining plastic strain during deformation depends on the applied stress causing asymmetric mechanical behavior of the tested Zn-based materials. Electrochemical measurements and immersion tests in Hanks' solution lasting up to 180 days revealed that Ag and Mg contribute to the change of the Zn matrix's open circuit potential and the formation of micro-galvanic cells between the Zn grains and precipitates. The fine-grained microstructure and evenly distributed small precipitates led to uniform corrosion occurring via pit formation on the corroded surface due to intergranular and micro-galvanic corrosion mechanisms. The corrosion rate of the Zn-3Ag-0.5Mg alloy after 180 days was almost twice that of pure Zn and the Zn-3Ag alloy.

Parameter Optimization of Segmental Multicluster Fractured Horizontal Wells in Extremely Rich Gas Condensate Shale Reservoirs

For economic and efficient development of extremely high-condensate shale gas reservoirs, a numerical model of segmental multicluster fractured horizontal well was established considering the effect of condensate and desorption, and the optimization of fracturing segments, fracturing clusters, half-length of main fracture, fracture permeability, fracture mesh density, and fracture distribution patterns were studied. It is indicated that the horizontal well whose design length is 2,700 m performs best when it has 43 fracturing segments with three clusters in each segment and the fracture permeability is 300 mD. The production capacity of horizontal wells is positively linearly correlated with the half-length of fractures. Increasing fracture half-length would be an effective way to produce condensate oil near wellbore. An effective fractured area can be constructed to remarkably improve productivity when the half-length of the fracture is 50 m and the number of secondary fractures is four in each segment. On the basis of reasonable fracture parameters, the staggered type distribution pattern is beneficial to the efficient development of shale gas-condensate reservoirs because of its large reconstruction volume, far pressure wave, small fracture interference, and small precipitation range of condensate.

Small precipitation events enhance the Eurasian grassland carbon sink

Different sizes of precipitation are specifically essential in controlling plant physiological processes in ecosystems and extremely important for predicting the effects of precipitation on arid and semiarid region carbon cycle. However, the sizes of precipitation events and their role in carbon flux processes remain unclear. A consecutive three years (2014–2016) eddy covariance flux measurements were conducted to investigate the changes in carbon fluxes under different sizes of precipitation in Mongolia – typical steppe (TPL), meadow steppe (MDW) and shrubland (SHB). Most of the precipitation distributions were dominated by small size events over all sites of the study area. Gross primary productivity reached highest on days with 2 mm d−1 and 5 mm d−1 of precipitation in 2015 and 2014, respectively in TPL, whereas the highest gross primary productivity observed at 10–25 mm d−1 precipitation size in both MDW and SHB. The ecosystem respiration changed positively with different sizes of precipitation events, except for the 5 mm d−1 and 10 mm d−1 precipitation size in the study sites. There existed positive relationship between net ecosystem CO2 exchange (NEE) and small size precipitation event in both TPL and MDW. The slight association was detected between NEE and small size precipitation (<2 mm) events in SHB during the study years. By contrast, the strong relationship was observed between large precipitation sizes and NEE (p < 0.01) in SHB. Overall, this study highlights the different responses of carbon flux to changes in the event size distribution of precipitation in grassland ecosystems which may help to predict how grassland structure and characteristic will respond to climatic change.

Temperature controls diel oscillation of the CO2 concentration in a desert soil

The diel dynamic of the CO2 concentration in soils in relation to temperature is not yet fully understood. Air temperature might control the soil CO2 concentration due to thermal convective venting at sites experiencing large temperature differences between the atmosphere and the soil. Therefore, the objective of this study was to determine the soil CO2 concentration and its temporal dynamic in a deep desert soil in relationship to soil and air temperature based on high frequency measurements. For this purpose, CO2 concentration and temperature were measured in six soil depths (ranging from 15 to 185 cm) in a coarse-textured desert soil in the North of Chile every 60 min together with precipitation and air temperature for one year. The mean CO2 concentration calculated across the whole measuring period increased linearly with soil depth from 463 ppm in 15 cm to 1542 ppm in 185 cm depth. We observed a strong diel oscillation of the CO2 concentration that decreased with soil depth and a hysteretic relationship between the topsoil CO2 concentration and both air and soil temperature. The Rayleigh-Darcy number calculated for different times indicates that thermal convective venting of the soil occurred during the night and in the early morning. A small precipitation event (4 mm) increased the CO2 concentrations in 15, 30, and 50 cm depths for several days but did not alter the amplitude of the diel oscillation of the CO2 concentration. The diel oscillation of the CO2 concentration and the hysteretic relationship between soil CO2 concentration and air temperature were likely caused by thermal convection, leading to transport of CO2-rich air from the soil to the atmosphere at night. In conclusion, our results indicate that the soil CO2 concentration can be largely controlled by convection caused by temperature differences, and not only by diffusion. The results have important implications as they provide further evidence that thermal convective venting contributes to gas exchange at sites experiencing large temperature differences between the atmosphere and the soil, which is relevant for soil chemical reactions.

Increasing the Robustness of Biopharmaceutical Precipitation Assays – Part I: Derivative UV Spectrophotometric Method Development for in-line Measurements

In vitro precipitation assays are often applied to support drug and formulation development. Current methods applied to quantify the amount of dissolved drug, in particular (U)HPLC, require time-consuming sample preparation. Furthermore, small precipitates formed during the nucleation phase may not be removed quantitatively by filtration or centrifugation of the sample. Given the drawbacks of standard (U)HPLC analyses during the application in transfer experiments, it was the aim of this work to develop a robust and simple to implement in-line UV spectrophotometric method which accurately reflects the precipitation profile obtained from in vitro transfer assays. Based on the three model compounds cinnarizine, dipyridamole, and ketoconazole, the manuscript describes the development of a design of experiments (DoE) based approach to develop derivative UV spectrophotometric methods accounting for the change in media composition over time due to the dilution of simulated intestinal with simulated gastric fluid. An R script was developed which automatically identifies suitable wavelengths for in-line measurements. As an outcome of this study, a fast, robust, accurate, and specific derivative UV spectrophotometric methodology for measuring the concentration of dissolved drugs in in vitro transfer experiments was successfully developed. This method can flexibly be applied to multi-compartmental precipitation assays.

Microstructure and mechanical properties of a 2 wt% Nb bearing low carbon steel

Design of advanced alloys with simple compositions is a new strategy to improve the recyclability of the alloys. In this study, a 2 wt% Nb bearing low carbon steel (2Nb steel) without addition of Ni, Cr and W was designed and processed by hot forging. The as-hot-forged steel shows a fine grain size microstructure with NbC precipitates formed. Microstructure and tensile properties were characterized at ambient and elevated temperatures. The yield stress and ultimate tensile stress of the as-forged 2Nb steel are 339 MPa and 498 MPa at room temperature, 297 MPa and 430 MPa at 600 °C, respectively. The good high temperature strength was related to the pinning effect of large NbC precipitates present at the grain boundaries and small precipitates formed in the grain interior that hinder the movement of grain boundaries and dislocations, respectively.

Microstructure and mechanical properties of a novel high-density steel having high tungsten content

A novel high strength and high-density steel was obtained by the addition of tungsten element. Compared with traditional steel, the novel steel exhibits a higher density (＞9 g/cm3), while maintaining high strength, and good ductility. Small precipitates of the μ phase dispersed in the matrix.

Daily Power Generation Forecasting Method for a Group of Small Hydropower Stations Considering the Spatial and Temporal Distribution of Precipitation—South China Case Study

This paper proposes a multimodal deep learning method for forecasting the daily power generation of small hydropower stations that considers the temporal and spatial distribution of precipitation, which compensates for the shortcomings of traditional forecasting methods that do not consider differences in the spatial distribution of precipitation. First, the actual precipitation values measured by ground weather stations and the spatial distribution of precipitation observed by meteorological satellite remote sensing are used to complete the missing precipitation data through linear interpolation, and the gridded precipitation data covering a group of small hydropower stations are constructed. Then, considering the time lag between changes in the daily power generation of the group of small hydropower stations and precipitation, the partial mutual information method is used to estimate the “time difference” between the two, and combined with the precipitation grid data, a data set of the temporal and spatial distribution of precipitation is generated. Finally, using only the temporal and spatial distribution of precipitation and historical power generation data, a multimodal deep learning network based on a convolutional neural network (CNN) and multilayer perceptron (MLP) is constructed, and a highly accurate prediction model for the daily power generation of small hydropower stations is obtained. Taking the real power generation data of a group of small hydropower stations in southern China as an example, after considering the temporal and spatial distribution of precipitation, the prediction accuracy of the proposed method is as high as 93%, which is approximately 5.8% higher than before considering the temporal and spatial distribution of precipitation. In addition, compared with mainstream methods such as support vector regression (SVR) and the long–short-term memory network (LSTM) (the average accuracy is about 87%), and the average accuracy improvement of the proposed method is approximately 6%.

Fracture characteristics and heat treatment of laser powder bed fusion additively manufactured GRCop-84 copper

Laser Powder Bed Fusion (LPBF) of Glenn Research Copper 84 (GRCop-84), a Cr2Nb (8 at. % Cr, 4 at. % Nb) precipitation hardened alloy, produces a fully dense high conductivity alloy with a yield strength of 500 MPa and ultimate tensile strength (UTS) of 740 MPa, superior to other competing copper alloys, and 20% elongation at fracture for material stressed perpendicular to the build direction. The high thermal stability of the Cr2Nb precipitate in the copper matrix reduces coarsening and maintains a 300 MPa yield, 520 MPa UTS and 26% elongation after a 900 °C, 5-h heat treatment, while a 3 h 450 °C heat treatment increases yield to 810 MPa, UTS to 970 MPa with 9% elongation at fracture, for samples stressed perpendicular to the build direction. Tensile strength anisotropy based on print direction was attributed to internal stress and columnar grain formation. Void nucleation during tensile fracture was initiated by brittle fracture of precipitate particles within the copper matrix. Fracture cusps contain matching precipitate fragment geometry on opposing sides located near the cusp center in at least 80% of fracture cusps. An optimal precipitate size of 100 nm is predicted for maximum tensile strength from precipitates on fracture surfaces, while tensile testing with varying heat treatments shows maximum strength with 100 nm and smaller precipitates. Cr2Nb precipitates are shown to transition between polycrystalline and monocrystalline structures at high temperature.

Porosity‐Permeability Evolution During Simultaneous Mineral Dissolution and Precipitation

AbstractPermeability in reactive porous media evolves in complex ways that are hard to predict. Macroscopic empirical equations are often used to estimate permeability evolution but fail to reflect the impact of pore scale reactions on permeability. This work aims to understand the evolution of permeability in systems where mineral dissolution and precipitation occur simultaneously. Pore network models are used for permeability simulation of a Paluxy sandstone using pore and pore‐throat size distributions from the analysis of X‐ray CT images. Pore and pore‐throat radii are increased and decreased to reflect the effects of dissolution and precipitation reactions. Varying spatial distributions of reactions are simulated and the resulting porosity and permeability values compared with commonly used macroscopic equations. It is observed that when dissolution occurs at the inlet and precipitation at the outlet, porosity increases while permeability decreases. Similar results are also observed in the respective opposite scenario where precipitation occurs at the inlet and dissolution at the outlet. When dissolution and precipitation reactions are randomly distributed throughout the network, porosity increases with little change in permeability that is not captured by the empirical equations. When reactions are controlled by pore and pore‐throat sizes, such as dissolution occurring in pores and pore‐throats of small size and precipitation in pores and pore‐throats of larger size, porosity and permeability decrease. When precipitation occurs in pores and pore‐throats of smaller size and dissolution in pores and pore‐throats of larger size, porosity and permeability increase and is described relatively well by the Verma‐Pruess porosity‐permeability equation.

Formation Mechanism of Laves Phase with Two Morphologies in a Novel 9Cr-3W-3Co-1CuVNbB Steel During Creep Process

Coarse Laves precipitates can strongly deteriorate the creep rupture strength of tempered martensite ferritic heat-resistant steels. In this study, we demonstrated two independent paths, i.e., isolated at the interface and neighboring phase-assisted, of Laves phase precipitation during the creep process in G115 steel. In particular, blocky-like Laves phase particles adjacent to the M23C6 and Cu-rich precipitate (CRP) are firstly captured. Most of the Laves phases are found to precipitate at the high-angle grain boundaries (HAGBs) whereas only a small amount precipitate at the low-angle grain boundaries (LAGBs). Among them, the M 23 C 6 are more preferential nucleation sites for the Laves phase. Crystallographic analysis indicates that the Laves phase obeys a specific orientation relationship (OR) with the M23C6, i.e., (110)M23C6// (10‾13)Laves and [1‾13] M23C6 // [ 03‾31 ]Laves. Solute segregation at grain boundaries and interphase boundaries (M23C6/ferrite and CRP/ferrite) is expected to be the main cause for the heterogeneous precipitation of Laves phase. The growth of the isolated Laves phase is dominated by the grain boundary diffusion mechanism, while that of Laves phase next to theM23C6 and CRP is controlled by the trans-interface diffusion controlled (TIDC) mechanism, which results in two morphologies of Laves phase. The work may improve the understanding of roles of M23C6 and CRP in precipitation mechanism of Laves phase, and provide a more accurate guide for the development of heat-resistant steels with superior creep strength.

How tree species, tree size, and topographical location influenced tree transpiration in northern boreal forests during the historic 2018 drought.

Trees in northern latitude ecosystems are projected to experience increasing drought stress as a result of rising air temperatures and changes in precipitation patterns in northern latitude ecosystems. However, most drought-related studies on high-latitude boreal forests (>50°N) have been conducted in North America, with few studies quantifying the response in European and Eurasian boreal forests. Here, we tested how daily whole-tree transpiration (Q, Litersday-1 ) and Q normalized for mean daytime vapor pressure deficit (QDZ , Liters day-1 kPa-1 ) were affected by the historic 2018 drought in Europe. More specifically, we examined how tree species, size, and topographic position affected drought response in high-latitude mature boreal forest trees. We monitored 30 Pinus sylvestris (pine) and 30 Picea abies (spruce) trees distributed across a topographic gradient in northern Sweden. In general, pine showed a greater QDZ control compared to spruce during periods of severe drought (standardized precipitation-evapotranspiration index: SPEI<-1.5), suggesting that the latter are more sensitive to drought. Overall, QDZ reductions (using non-drought QDZ as reference) were less pronounced in larger trees during severe drought, but there was a species-specific pattern: QDZ reductions were greater in pine trees at high elevations and greater in spruce trees at lower elevations. Despite lower QDZ during severe drought, drought spells were interspersed with small precipitation events and overcast conditions, and QDZ returned to pre-drought conditions relatively quickly. This study highlights unique species-specific responses to drought, which are additionally driven by a codependent interaction among tree size, relative topographic position, and unique regional climate conditions.

Oxidation and carburization behaviour of two type 316H stainless steel casts in simulated AGR gas environment at 550 and 600 °C

• Duplex oxide and carburized layers form on steels exposed to AGR reactor coolant • Cracking in the oxide layer increases the oxidation and carburization rates • Carbon locates in the austenite lattice and predominately M 23 C 6 carbides • Diffusion of substitutional solutes is the rate-limiting mechanism of carburization • Small precipitates lead to a reduced carburization rate at 550ºC The time-dependent oxidation and carburization behaviour of two type 316H austenitic stainless steels with varying Mn content and differing average austenite grain size of 142 µm in ‘Low Mn’ (0.98 wt.% Mn) and 81 µm in ‘High Mn’ (1.52 wt.% Mn), were assessed at 550 °C and 600 °C in the presence of simulated reactor primary gas coolant containing 500 vppm H 2 O, 100 vppm H 2 , 300 vppm CH 4 and 1 vol.% CO, balanced with CO 2 . Rupture and spallation of the initial protective chromia layer occurs in the ‘High Mn’ steel after 2000 h at 550 °C, and leads to the formation of a magnetite/spinel oxide layer that reaches 75% surface coverage only after 8000 h. In contrast, ‘Low Mn’ steel reaches ~ 85% coverage after only 1000 h at the same temperature. The development of an inner carburized layer occurs gradually in both steels once the duplex oxide layer is forming. The differences in steel behaviour are reduced at 600 °C, where both oxidation and carburization are significantly accelerated. Only 0.02 wt.% carbon remains in solid solution in the austenite lattice in the carburized layer, the excess carbon atoms precipitating out in the form of Cr-rich M 23 C 6 particles, present both inter- and intragranularly. The experimental values of the activation energy for carburization suggest that diffusion of substitutional solutes as the rate-limiting mechanism of the process. Previously observed carburization depths of ≥ 200 µm in ex-service austenitic stainless steels, may be achieved by pre-conditioning 316H steel in simulated reactor gas coolant for ≥ 6000 h at 600 °C.