Type 304L Research Articles

Microstructural Characterization of 316L-Type Stainless Steel Exposed to SiFX Species in Argon Atmosphere

ABSTRACTNowadays, Si3N4 coatings are used to increase the hardness of 316L-type stainless steel for a wide variety of applications. These coatings are normally prepared by chemical vapor deposition (CVD) or variant techniques such as the hybrid solid-gas precursor system chemical vapor deposition (HYSYCVD), where Na2SiF6 is used as a solid precursor. Within the reaction chamber the Si-F gas species interact with nitrogen precursors to form Si3N4; however, during silicon nitride formation there is always certain amount of residual Si-F gas species which may affect the integrity of the steel surface. Therefore, in this work the effect of the Si-F species on the surface of 316L type stainless steel under argon atmosphere has been investigated. Stainless steel samples were prepared under two surface conditions (abraded and mirror polished), and were exposed to Si-F species considering various parameters such as: argon gas flow rate equal to 10 cm3/min, different temperatures (300, 500, 700, 900°C), and three exposure times (30, 60, 90 minutes). After exposure, the substrates were characterized by X-ray diffraction (XRD) and by scanning electron microscopy (SEM). The results show that the FeF2 phase is formed at low temperatures while the formation of different oxides is directly related to the processing temperature. What is more, these oxides are also strongly influenced by processing time; however temperature is the parameter that most significantly influences the oxides formation.

Irradiation behavior of Ti-stabilized 316L type steel

Type 316L austenitic steels are widely used for the in-vessel internal structures of fission reactors (core, core support, etc.) and for experimental irradiation facilities. The modifications of 316L Type steel (316L, 316L(N), US 316, J 316, JPCA, etc.) have been considered as structural material for International Thermonuclear Experimental Reactor (ITER). The results of investigation the irradiation behaviour of Ti-stabilized 316 L type steel (0.04 C–15 Cr–11 Ni–2.5 Mo–0.5 Ti) are presented in this work. The specimens cut out from 316L-Ti steel forging were irradiated in the SM-2 reactor up to a dose ∼4 and 10 dpa at 265 ± 15 °C. The tensile properties, fracture toughness and changes in resistance to intergranular stress corrosion cracking (IGSCC) have been investigated after irradiation. The results for Ti-stabilized 316L steel were compared with those for 316L(N)-IG steel irradiated at the same condition.

Corrosion assessment of nitric acid grade austenitic stainless steels

The corrosion resistance of three indigenous nitric acid grade (NAG) type 304L stainless steel (SS), designated as 304L1, 304L2 and 304L3 and two commercial NAG SS designated as Uranus-16 similar to 304L composition and Uranus-65 similar to type 310L SS were carried out in nitric acid media. Electrochemical measurements and surface film analysis were performed to evaluate the corrosion resistance and passive film property in 6 N and 11.5 N HNO 3 media. The results in 6 N HNO 3 show that the indigenous NAG 304L SS and Uranus-65 alloy exhibited similar and higher corrosion resistance with lower passive current density compared to Uranus-16 alloy. In higher concentration of 11.5 N HNO 3, transpassive potential of all the NAG SS shows a similar range, except for Uranus-16 alloy. Optical micrographs of all the NAG SS revealed changes in microstructure after polarization in 6 N and 11.5 N HNO 3 with corrosion attacks at the grain boundaries. Frequency response of the AC impedance of all the NAG SS showed a single semicircle arc. Higher polarization resistance ( R P) and lower capacitance value (CPE-T) revealing higher film stability for indigenous NAG type 304L SS and Uranus-65 alloy. Uranus-16 alloy exhibited the lowest R P value in both the nitric acid concentration. Auger electron spectroscopy (AES) study in 6 N and 11.5 N HNO 3 revealed that the passive films were mainly composed of Cr 2O 3 and Fe 2O 3 for all the alloys. The corrosion resistance of different NAG SS to HNO 3 corrosion and its relation to compositional variations of the NAG alloys are discussed in this paper.

Effect of Tritium and Decay Helium on the Fracture Toughness Properties of Stainless Steel Weldments

J-Integral fracture toughness tests were conducted on tritium-exposed-and-aged Types 304L and 21-6-9 stainless steel weldments in order to measure the combined effects of tritium and its decay product, helium-3 on the fracture toughness properties. Initially, weldments have fracture toughness values about three times higher than base-metal values. Delta-ferrite phase in the weld microstructure improved toughness provided no tritium was present in the microstructure. After a tritium-exposure-and-aging treatment that resulted in ~1400 atomic parts per million (appm) dissolved tritium, both weldments and base metals had their fracture toughness values reduced to about the same level. The tritium effect was greater in weldments (67 % reduction vs. 37% reduction) largely because the ductile discontinuous delta-ferrite phase was embrittled by tritium and decay helium. For both base metals and weldments, fracture toughness values decreased with increasing decay helium content in the range tested (50-800 appm).

Correlation of meso- and micro-scale hardness measurements with the pitting of plastically-deformed Type 304L stainless steel

Short lengths of circular section Type 304L stainless steel were cut from a pipe and compressed into an oval shape using controlled conditions. Heterogeneous strain hardening in the range 0–25% was thus introduced into the material. The mechanical deformation process was modelled using ABAQUS finite element modelling software to calculate the distributions of strain hardening and residual stress throughout a typical specimen. Samples were then exposed to an environment intended to induce pitting over the surfaces. Correlation between the computer model and the observed pitting was obtained. Finally, micro- and meso-scale hardness measurements were made on similarly deformed specimens and found to correlate well with the FE results. It was concluded that pitting was associated with regions of greatest equivalent plastic strain and showed little relation to the regions of high tensile residual stress. An empirical relationship between the Vickers Hardness number and the equivalent plastic strain is determined.

Corrosion mechanisms of austenitic stainless steels in nitric media used in reprocessing plants

Austenitic stainless steels type 304L, 316L and 310Nb are largely used as structural materials for equipments handling nitric acid media in reprocessing plants. In almost all nitric media, these materials, protected by a chromium(III) oxide rich layer, remain in their passive state. However, in some particular nitric media, their corrosion potential may be shifted towards their transpassive domain. In this domain, they can suffer intergranular corrosion, even though they are not sensitized owing to their very low carbon content. The corrosion potential of the steel depends greatly on the cathodic reaction involved in the oxido-reduction process between the elements Fe, Cr, Ni of the steel and the oxidizing species of the medium. Three cases of an increase in the corrosion potential can be found in reprocessing media: pure nitric acid–water solutions, in which the cathodic reaction is the reduction reaction of HNO 3; nitric acid media containing oxidizing species, in which the cathodic reaction is the reaction of reduction of the oxidizing species into the reduced one; nitric media containing metallic elements electrochemically more noble than the steels, causing galvanic coupling. In each case, the mechanism and the relevant situations we experimentally studied are described.

An improved method for calculation of creep damage during creep–fatigue cycling

Thermal mechanical cycling can result in creep–fatigue cycles in which the creep dwell has a wide variety of positions within the cycle. The effects of creep dwell position have been investigated using tests on three austenitic stainless steels: Type 316H, cast Type 304L and Type 347 weld metal. The analysis of these tests has resulted in the proposal of a new method to calculate creep damage. This method has been shown to give better predictions for the creep damage at failure than both the standard ductility exhaustion approach and the time fraction approach. In particular, the new method gives improved predictions of creep damage at failure for cycles with intermediate dwells and for cycles with low strain ranges. The present paper summarises the validation of this new method, the effects of multiaxial states of stress and the effects of compressive dwells.

Photocurrent and capacitance investigations into the nature of the passive films on austenitic stainless steels

Photocurrent and capacitance measurements of semiconductor passive films formed on metals and alloys can be used to study the electronic properties and reveal indirect information about structure and composition. The current work used these techniques to investigate the electronic properties of the passive films formed on three austenitic stainless steels, types 304L, 316L and 254SMO, in borate. Evidence was found for the existence of a large number of localised mid bandgap states, consistent with amorphous oxides. However, the flat-band potentials of the austenitic stainless steel passive films were found to be independent of both composition and measuring frequency. The most credible explanation for the bandgap values determined from photocurrent measurements is that the passive films are formed as dual layers, iron oxide outer layer and chromium oxide inner layer. This model does not need to evoke the potential dependent bandgaps used by previous authors.

On the ability of some cyclic plasticity models to predict the evolution of stored energy in a type 304L stainless steel submitted to high cycle fatigue

Fatigue analyses of materials are generally based on a so-called stabilized cycle, on which plastic strain amplitude, plastic energy, maximum shear stress and so on are determined. The part of plastic energy which is dissipated in heat cannot be used to accumulate damage and it should be worthwhile extracting only the part of plastic energy which is stored in material microstructure in order to build a consistent damage model. In this paper, some cyclic plasticity models including a polycrystalline model are reformulated in the thermodynamic framework in order to test their capacity to predict both the stress-strain behaviour and the partition of plastic energy for a high cycle fatigue test on a type 304L stainless steel. For an equivalent description of stress-strain loops, the number of kinematic hardening variables chosen in a model may qualitatively alter the prediction of plastic energy partition due to the modification of the isotropic hardening variable. Measurements of the specimen temperature increase due to plastic dissipation is therefore proposed as a convenient complementary experimental data to identify the constitutive equation of the isotropic hardening variable of a cyclic plasticity model.

Effect of heat treatment and chemical composition on the corrosion behavior of FeAl intermetallics in molten (Li + K)carbonate

The corrosion performance of various Fe–Al alloys in 62 mol. %Li 2CO 3-38 mol.%K 2CO 3 at 650 °C has been studied using the weight loss technique. Alloys included FeAl with additions of 1, 3 and 5 at.% of either Ni or Li with or without a heat treatment at 400 °C during 144 h. For comparison, 316L type stainless steel was also studied. The tests were complemented by X-ray diffraction (XRD), scanning electronic microscopy and microchemical studies. Results showed that FeAl base alloy without heat treatment had the highest corrosion rate but by either heat treating it or by adding either Ni or Li the mass gain was decreased. When the FeAl base alloy was heat treated and alloyed with either 5Ni or 1Li the degradation rate reached as low values as those found for 316L stainless steel which had the lowest degradation rate. Both Ni and Li improved the adhesion of external protective layer either by avoiding the formation of voids or by lowering the number of precipitates and making them more homogenously distributed.

Defects characterization of welded specimens by transmission electron microscopy

Austenitic Type 304L stainless steel (SS) and martensitic Alloy EP-823 have been identified as candidate structural materials to contain spallation target for transmutation of nuclear waste. Welded specimens consisting of either or both materials have been evaluated by transmission electron microscopy (TEM) to determine the dislocation density near the heat-affected-zone (HAZ) and the base material. The results indicate that the average dislocation density determined from the TEM micrographs taken at different locations was much higher near HAZ compared to that of the base material. Further, the estimated dislocation density was higher on the Alloy EP-823 side of the weld than that of the Type 304L SS side possibly due to the faster rate of solidification of the martensitic alloy. Higher dislocation density is an indication of enhanced residual stress resulting from the welding operation.

Effect of macroalloying with Cu on the corrosion resistance of rapidly solidified NiAl intermetallic in 0.5 M H 2SO 4

The effect of Cu contents on the corrosion resistance of NiAl intermetallic rapidly solidified in 0.5 M H 2SO 4 at room temperature has been evaluated using electrochemical techniques. Cupper contents included 15, 20 and 25 wt.% and techniques included potentiodynamic polarization curves, linear polarization resistance and potentiostatic tests. For comparison, the same tests were performed on a 316L type stainless steels. The results showed that all the intermetallics exhibited a better corrosion resistance than the 316L type stainless steel for at least ten times but there was not a big difference between the different NiAl alloys with and without Cu for times longer than 4 h. For times shorter than 5 h, the corrosion current density of the NiAl alloys increased as the Cu contents decreased up to 20% but it increased when the Cu contents increased further up to 25%. A similar behavior occurred with the passive current density. These results were discussed in terms of the incorporation of cuprus oxide particles in to the external passive layer modifying its electrochemical properties. The pitting potential values decreased with additions of Cu respect to the unalloyed NiAl material. Corrosion morphologies showed a preferential dissolution of a phase respect to another due to the formation of micro galvanic cells due to the addition of Cu.

ICONE15-10399 Present State Of Crack Growth And Crack Initiation Studies Performed In The Halden Reactor

To evaluate factors affecting irradiation assisted stress corrosion cracking (IASCC) behavior, the OECD Halden Reactor Project (HRP) is performing in-core crack growth and crack initiation studies in the Halden boiling water reactor (HBWR). In the crack growth studies, compact tension (CT) specimens are prepared from irradiated stainless steels (SSs), types 316NG, 347, 304L and 304 with neutron fluences in the range of 9.0x10^<20> - 1.2x10^<22> n/cm^2 (E > 1 MeV). The crack growth measurements are conducted in simulated boiling water reactor (BWR) and pressurized water reactor (PWR) environments. In a crack initiation study, miniature tensile specimens are machined from a type 304L SS irradiated to 8.0x10^<21> n/cm^2 (E > 1 MeV). Two specimens are installed in each test unit which has pressurized bellows for loading and a linear variable differential transformer (LVDT) for failure detection. Constant load is applied to the specimens in the 15 test units which are exposed to a simulated BWR environment. 5 signal changes indicating specimen failure have been detected since May 2002, when the test began.

Effect of large strains on grain boundary character distribution in AISI 304L austenitic stainless steel

Austenitic stainless steel of 304L type was thermo-mechanically processed to enhance special low CSL boundaries. Rolling reductions of above 60% of thickness was employed prior to annealing. It was observed that during recovery and recrystallization, twinning induced CSL boundary of Σ3 type. However, 80% of thickness reduction during grain growth regime, retarded Σ3 type grain boundary formation.

Corrosion of Austenitic Alloys in Supercritical Water

Abstract The purpose of this study was to determine the mechanism by which austenitic iron- and nickel-based alloys oxidize in pure supercritical water. Austenitic stainless steel alloys Type 304 (UNS S30400) and Type 316L (UNS S31603) and nickel-based Alloy 625 (UNS N06625) and Alloy 690 (UNS N06690) were exposed in deaerated supercritical water over the temperature range from 400°C to 550°C. Exposure experiments resulted in the formation of a two-layer oxide on Type 304 and Type 316L in which the outer layer is porous magnetite (Fe3O4) and the inner layer is a denser iron-chromium spinel. In Alloy 690 the outer layer is iron-rich and the inner layer is composed of chromia (Cr2O3), nickel oxide (NiO), and Ni(Cr,Fe)2O4. The oxide on Alloy 625 was too thin to measure. Inner and outer oxides have the same grain orientation as the matrix on the stainless alloys, and on Alloy 690, the inner oxide has a common orientation with the matrix but the outer layer consists of randomly oriented oxides. The inner/outer...

Electrochemical study of Type 304 and 316L stainless steels in simulated body fluids and cell cultures

The electrochemical corrosion behaviour of Type 304 and 316L stainless steels was studied in Hanks’ solution, Eagle’s minimum essential medium (MEM), serum containing medium (MEM with 10% of fetal bovine serum) without cells, and serum containing medium with cells over a 1-week period. Polarization resistance measurements indicated that the stainless steels were resistant to Hanks’ and MEM solutions. Type 304 was more susceptible to pitting corrosion than Type 316L in Hanks’ and MEM solutions. The uniform corrosion resistance of stainless steels, determined by R p, was lower in culturing medium than in Hanks’ and MEM. The low corrosion resistance was due to surface passive film with less protective to reveal high anodic dissolution rate. When cells were present, the initial corrosion resistance was low, but gradually increased after 3 days, consistent with the trend of cell coverage. The presence of cells was found to suppress the cathodic reaction, that is, oxygen reduction, and increase the uniform corrosion resistance as a consequence. On the other hand, both Type 304 and 316L stainless steels became more susceptible to pitting corrosion when they were covered with cells.

Determination of susceptibility to intergranular corrosion and electrochemical reactivation behaviour of AISI 316L type stainless steel

In this study, double loop electrochemical potentiokinetic reactivation (DLEPR) test was applied to determine the degree of sensitization in 316L type stainless steel, where obtained results were correlated with revealed microstructures after oxalic acid test and weight loss measurements of Streicher and Huey acid tests. Best agreement was provided with test parameters which are 1 M H 2SO 4 and 0.005 M KSCN at 0.833 mV/s scan rate at 30 °C. Specimens were classified structurally as absence of chromium carbides – step, no single grain completely surrounded by carbides – dual and one or more grain completely surrounded by carbides – ditch, in the as-etched structure, if the I r: I a (×100) ratios were obtained to be between 0 and 0.2, 0.2 and 5.0 and 5.0 and higher, respectively. It was also found that at high KSCN concentrations, reactivation current profile skewed to higher potentials where this was attributed the formation of metastable pits, during the anodic scan of the test procedure.

Influence of Phosphorus, Sulpher, and Oxygen on 65% Nitric Acid Corrosion Resistance of Super High-clean 316L Stainless Steel

For the purpose to verify the effect of decreasing phosphorus on corrosion properties of stainless steels, corrosion resistant tests in 65% nitric acid solutions were carried out for super-low phosphorus content 316L type stainless steels which were manufactured by the cold crucible type levitation melting method using Ca–CaF2 flux for aiming at the dephosphorization. By decreasing phosphorus content in these steels from 0.026 to 0.0002 mass%, the corrosion rate in 65% nitric acid solutions decreased remarkably. Especially even under 0.001% phosphorus content, the improvement of corrosion resistance against nitric acid solution could be observed.As for the non-metallic tramp elements, there were linear relations between corrosion rate and the very small amount of sulfur and oxygen contents in the super-low phosphorus stainless steels containing under 0.0002 mass% phosphorus. So the super high purification of these elements is also very effective for the improvement of corrosion resistance against nitric acid solutions.It is known that the corrosion of austenitic stainless steels containing over 0.003 mass% phosphorus in nitric acid solutions is intergranular corrosion. In the present work, it was confirmed that the corrosion of super-low phosphorus content 316L type stainless steels even at 0.0002 mass% was not uniform corrosion but intergranular corrosion.

Performance of a Clad Tungsten Rod Spallation Neutron Source Target

Tungsten rods, slip-clad with Type 304L stainless steel, performed successfully as a spallation neutron source target operating to a peak fluence of ~4 × 1021 p/cm2. The target was used as a neutron source during the Accelerator Production of Tritium (APT) materials irradiation program at the Los Alamos Neutron Science Center. Tungsten rods of 2.642-mm diameter were slip-fit in Type 304L stainless steel tubes that had an inner diameter of 2.667 mm. The radial gap was filled with helium at atmospheric pressure and room temperature. Los Alamos High Energy Transport (LAHET) calculations suggest a time-averaged peak power deposition in the W of 2.25 kW/cm3. Thermal-hydraulic calculations indicate that the peak centerline W temperature reached 271°C. The LAHET calculations were also used to predict neutron and proton fluxes and spectra for the complex geometry used in the irradiation program. Activation foil sets distributed throughout the experiment were used to determine target neutronics performance as a comparison to the LAHET calculations. Examination of the irradiated target assemblies revealed no significant surface degradation or corrosion on either the Type 304L or the W surfaces. However, it was clear that the irradiation changed material properties because post-proton-irradiation measurements on Type 304L test samples from the APT program demonstrated increases in the yield strength and decreases in the ductility and fracture toughness with increasing dose, and the wrought W rod samples became brittle. Fortunately, the slip-clad target design subjects the materials to very low stress.

45 MPa高圧水素ガス雰囲気下での金属材料の機械的特性評価

Mechanical properties of candidate materials for hydrogen container were studied in high pressure of gaseous hydrogen by using newly designed and installed facilities. Tensile properties, slow strain rate tensile properties, fatigue properties and fatigue crack growth properties of aluminum alloy AA6061-T6 and austenitic stainless steel of type 316L in 45 MPa gaseous hydrogen were similar to those properties tested in air. These data can give guideline not only to the reference standard and technical standard dealing with 35 MPa-class compressed hydrogen container but to future material development of various apparatuses for hydrogen.