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One of the most commonly used corrosion resistant construction materials are austenitic stainless steels, mainly AISI 304. Any deviation from the welding technology in the case of this steel may result in welding defects or even loss of corrosion resistance. The purpose of this work was explored the influence of remelting using the TIG method (141) on the properties and structure of welded joints of AISI 304. The scope of this paper included making test joints of 2 mm thick sheets and then remelting them. The further part of this work consisted in carrying out: mechanical, macroscopic and microscopic examinations, hardness and corrosion resistance tests, SEM/EDS analysis. As a result of tests it was found that remelting of a joint causes a significant increase in hardness, lower elongation and general corrosion resistance, but increases the resistance to intercrystalline corrosion. Flexural strength and tensile strength were not changed by remelting. [ABSTRACT FROM AUTHOR]

Austenitic stainless steels are commonly used in low temperature applications because of their mechanical properties specially preserving the ductility. The strain-induced martensitic transformation greatly affects the plastic behavior of the metastable austenitic stainless steels. This paper provides a simple constitutive model for considering the strain-induced martensitic transformation of the metastable austenitic stainless steels at low temperature. A modified kinetics model is represented to consider the effect of TRIP in martensite evolution explicitly. In addition, a modified power law hardening for the continuously reforming material is represented to describe the great hardening effect of the phase transformation. Developing an incremental integration algorithm, the constitutive model was implemented in the Abaqus/Standard via a user-defiened material subroutine (UMAT). The results showed that the rate of martensite evolution with plastic strain in the modified model is accelerated which significantly affects the plastic behavior. In addition, the hardening behavior could be well described with the modified power law. Numerical examples show the capability of the constituative model in simulating the strain-induced transformation at low temperatures. [ABSTRACT FROM AUTHOR]

The present study describes the process characteristics of the Cold-Metal-Transfer (CMT) Pin-Welding by welding structures on austenitic stainless steel (AISI 304) and characterizes the corresponding mechanical properties. Pin-Welding technology enables the possibility of welding small-scaled structures out of the welding wire. The mechanical properties and microstructures of the welded structures were investigated on different pin formations. Experimental samples extracted from the welded structure were subjected to tensile and hardness tests and microstructural examinations. Tensile test results were obtained lower than the welding wire owing to the process heat input, but both presented similar proportional results. The structures hardness formed out of wire diameter of 0.8 mm and 1.2 mm was obtained in an interval between 200-250 HV. Because the base metal has nearly similar hardness values, the whole structure exhibits a stable hardness distribution after the welding process. [ABSTRACT FROM AUTHOR]

Highlights • Elastic and plastic strains were out of phase for non-proportional loading. • With loading strain distribution in material differed significantly. • Substructural evolution under in phase loading resulted moslty in planar dislocations. Abstract Effect of in-phase and out of phase cyclic loading on fatigue behaviour was evaluated for 304LN stainless steel using tubular specimens. It was found that additional hardening observed for out of phase loading was a consequence of more grains participating in deformation process. Further, strains in matrix were higher and evenly distributed across grains for out of phase loadings as quantified through misorientation analysis. Disparities in misorientation studies were accounted by substructural development investigated through electron microscopy. Additionally, elastic and plastic strains were found to be out of phase with respect to total strains for out of phase loading. [ABSTRACT FROM AUTHOR]

In spite of its huge technical significance, there does not seem to be consensus about how to model the precipitation contribution to the creep strength. Most contributions in the literature are based on a constant internal stress (also called back stress or threshold stress) from the precipitation. It is well-known and it will also be demonstrated in the paper that this assumption is at variance with observations except for some ODS alloys. There is, however, one model developed by Eliasson et al. (Key Eng Mater 171-174:277-284, 2000) that seems to be able to represent experimental data without the use of any adjustable parameters. It has successfully been applied to describe the creep strength of austenitic stainless steels. Due to the fact that various mechanisms contribute to the creep strength in these steels, the model has not been fully verified. The purpose of this paper is to apply the model to published creep data for Cu-Co alloys, where the precipitation totally dominates the strength contribution to validate the model. In the paper, it is demonstrated that the model can indeed describe the influence of applied stress, alloy composition and heat treatment for the three analysed Cu-Co alloys. [ABSTRACT FROM AUTHOR]

Highlights • The 316LN austenitic stainless steel joints were PWHT at 760 °C for 1 h. • The PWHT has no detrimental effect on the tensile strength of the joints. • The fracture toughness of the weldments were investigated at cryogenic temperature. • The fracture mechanism of the joints were evaluated. Abstract In the present work, the correlation between microstructural evolution and fracture toughness in 316LN joints welded by Tungsten Inert Gas (TIG) was investigated. The effect of post-weld heat treatment (PWHT) on the microstructure and toughness was characterized. The welding process can significantly change the equiaxed grains of base metal to cells and dendrites, while the PWHT can increase the dendrite size, mitigate the texutre intensity, reduce the dislocation density, and slightly weaken the ultimate tensile strength of the joints. Fracture toughness tests reveal that the strain-induced martensitic transformation at cryogenic temperatures can remarkably deteriorate the fracture toughness. Due to the microstructural evolution during PWHT, the J-integral values at 77 K and 4.2 K decrese to 85% and 54% of those in the as-welded conditions, respectively. The fracture morphology of the as-welded joint shows a characterization of ductile fracture, while the PWHT joint features a mixture of ductile and brittle fracture. [ABSTRACT FROM AUTHOR]

The tensile behaviour of austenitic stainless steel after cryorolling and subsequent annealing has been reported. The defect structures generated during cryorolling, lead to the formation of α’ and ε-martensite. Subsequent annealing leads to the formation of refined austenitic grains surrounded by martensitic islands. These martensitic islands consist of α’ phase only. The dislocation-martensite interaction leads to discontinuous yielding for high Ultimate Tensile Strength (UTS)/Yield Strength (YS) ratio. In case of annealing at 923 K (650 °C) for 10 min after 30% cryorolling leads to nearly 30% untransformed martensite whereas only 7% martensite remains after annealing for 1 h. The effect of remnant martensite on tensile behaviour leading to yield plateau has been discussed in this work. It can be noticed that sample with 20% cryo rolling and annealed at 650 °C for 1 h shows higher YS (721 MPa) with YS/UTS ratio of 0.79 and ~ 18% uniform elongation. Sample with 30% cryo rolling and annealed at 650 °C for 1 h shows YS of 305 MPa with YS/UTS ratio of 0.27 and uniform elongation of ~ 24%. Therefore, 20% cryo rolled and annealed at 650 °C for 1 h has the best combination of mechanical properties. [ABSTRACT FROM AUTHOR]

Friction stir lap welding-a precursor to the friction stir cladding- stainless steel on plain carbon steel was attempted. Refined microstructure with fully recrystallized austenitic grains with ∼3 μm grain size and intermixing with base steel sample resulted in defect free lap weld. The pin affected region of the base carbon steel resulted in grain refinement from initial grain size of 8 μm to 2 μm. The microhardness values across the joint line showed stable values of ∼250 HV on the stainless steel side and ∼200 HV on the carbon steel side. Lap shear tests showed consistent load bearing capacity of ∼7 kN for the stainless steel-carbon steel joint. The weld between stainless steel and carbon steel showed 100% joint efficiency with similar yield strength of ∼440 MPa as the base steel sample and with an increase in ultimate tensile strength to ∼600 MPa as compared to ∼500 MPa for the base steel sample. The failure of clad tensile samples occurred in the base steel plate. Corrosion characterization of the clad surface was conducted in 3.5 wt.% sodium chloride solution. The potentiodynamic polarization showed positive corrosion potentials with a large passive range of ∼500 mV for the clad surface and a decrease in corrosion rates by more than an order as compared to the base steel sample. The friction stir lap welded stainless showed similar electrochemical properties as of the base stainless steel sheet. [ABSTRACT FROM AUTHOR]

The recent progress in investigation techniques and the accumulation of relevant simulation results across the scales allow the development of a multiscale modeling framework for the rationalization, analysis and physical assessment of the flow stress of many industrial materials, with almost no fitting parameters. Although the construction of this framework is not yet complete, it has reached a maturity level enabling the investigation of some complex properties such as irradiation hardening. In this paper, modeling and experimental results are reviewed in order to derive the constitutive equations of the yield stress and of its fundamental components accounting for the microstructure features, such as dislocation network, precipitates, dislocation loops and voids. This approach is challenged in the case of reactor pressure vessel, high-Cr ferritic-martensitic and austenitic stainless steels. Predictions are discussed in connection with the well-known experimental trends reported in the literature. [ABSTRACT FROM AUTHOR]

A novel constitutive model has been developed for predicting flow responses of super-austenitic stainless steel over a wide range of strains (0.05-0.6), temperatures (1173-1423 K) and strain rates (0.001-1 s−1). Further, the predictability of this new model has been compared with the existing Johnson-Cook (JC) and modified Zerilli-Armstrong (M-ZA) model. The JC model is not befitted for flow prediction as it is found to be exhibiting very high (~ 36%) average absolute error (δ) and low (~ 0.92) correlation coefficient (R). On the contrary, the M-ZA model has demonstrated relatively lower δ (~ 13%) and higher R (~ 0.96) for flow prediction. The incorporation of couplings of processing parameters in M-ZA model has led to exhibit better prediction than JC model. However, the flow analyses of the studied alloy have revealed the additional synergistic influences of strain and strain rate as well as strain, temperature, and strain rate apart from those considered in M-ZA model. Hence, the new phenomenological model has been formulated incorporating all the individual and synergistic effects of processing parameters and a ‘strain-shifting’ parameter. The proposed model predicted the flow behavior of the alloy with much better correlation and generalization than M-ZA model as substantiated by its lower δ (~ 7.9%) and higher R (~ 0.99) of prediction. [ABSTRACT FROM AUTHOR]

In the present investigation, the effect of multi-pass hot rolling in the temperature range of 700-1000 °C on the microstructure and mechanical properties of nitrogen alloyed austenitic stainless steel was studied with the aid of optical microscopy, tensile testing and x-ray diffraction measurements. The microstructural changes that occurred in the hot rolled specimens were elongation of grains in rolling direction, nucleation of new grains at the grain boundaries of elongated grains and growth of nucleated grains to form fully recrystallized grains. Elongated grains formed at lower rolling temperature (700-800 °C) due to inadequate strain/temperature for the initiation of dynamic recrystallization. At higher rolling temperature (900-1000 °C), fine grains formed due to dynamic recrystallization. Tensile properties showed strong dependency on the rolling temperature. Tensile strength increased with the decrease in the rolling temperature at the cost of ductility. Maximum strength was observed in samples hot rolled at 700 °C with yield strength of 917 MPa and ductility of 25%. This variation in the tensile properties with the rolling temperature is attributed to changes in the dislocation density and grain structure. The estimated yield strength from the dislocation density, solid solution and grain boundary strengthening closely matched with experimentally determined yield strength confirming the role of dislocation density and grain size in the strengthening. [ABSTRACT FROM AUTHOR]

A hydrogen-charged Type-316L austenitic stainless steel represents a slight loss of tensile ductility and cup-and-cone fracture accompanied by small-sized dimple. The reduction in the dimple size is interpreted to be attributed to void sheets caused by localized slip deformations by hydrogen. This paper aims to clarify the contribution of an internal pressure to the characteristic void growth of a hydrogen-charged Type-316L stainless steel during slow strain rate tensile (SSRT) test in air at room temperature. The internal pressure of pre-existing voids in the specimen charged by 100 MPa hydrogen gas at 270 °C for 200 h was simulated by diffusion-desorption analysis of hydrogen with the finite differential method (FDM). The subsequent impact of the internal pressure on the void growth was simulated by fracture-mechanics approach with the finite element method (FEM). The simulations performed under various void morphologies and fracture toughness suggested that the internal pressure in the voids was significantly low, hardly affecting the void growth. [ABSTRACT FROM AUTHOR]

The formation mechanism of an internal crack was clarified from the viewpoint of the crystallography and thermal expansion. An inverse pole figure map obtained by EBSD pattern showed that the crack propagated along the grain boundaries having high ∑ values within the columnar zone. After the crack initiation, these positions were considered to undergo cracking followed by propagation toward the equiaxed side. Near the termination position, the grains ahead of crack propagation had a Schmid factor higher than 0.45 consuming elastic strain energy. Thermal expansion measurements showed that the grain with (0 0 1) orientation had the largest expansion while that with (0 1 1) the smallest. The grain boundaries neighboring the combination of (0 0 1) and (0 1 1) grains had the largest thermal stress. Therefore, thermal stress contributed to the initiation of cracking. It was thus proposed to enlarge the equiaxed zone to prevent cracking by discontinuing the crack propagation. [ABSTRACT FROM AUTHOR]

The tribo-electrochemical behavior of AISI 316L has been investigated under tribocorrosion conditions in a 3% NaCl solution and the material damage evolution with time has been analyzed. A numerical contact model based on a Boundary Element Method (BEM) has been developed in order to determine the contact pressure distribution and to quantify the worn material as a function of time. The time dependence of the tribological behavior of the material has been described. At the initial state, the high contact pressures generate a material flow causing an increase in the worn area. After around 300 cycles, the Archard wear model linearly describes the wear evolution with time. The proposed model describes the evolution with time of the wear profiles of the tested material and takes into account the plastic behavior of the material during the first cycles. [ABSTRACT FROM AUTHOR]

Most of industrial hot deformation processes are performed in variable conditions where the strain rate and/or deformation temperature are not constant. In this work, hot compression tests in both constant and varying strain rate conditions were performed on 304L austenitic stainless steel using a Gleeble 3800 machine. The variations in microstructure and flow stress during and after the transient deformation stage are carefully analysed. It is clearly shown that, following the abrupt increase of strain rate, both the flow stress and substructural changes are subjected to a transient period over strains of ~0.2, before reaching states similar to those developed through constant strain rate conditions at the new strain rate. When the strain rate was rapidly decreased, the flow stress transient stage extended over a lower strain interval than the substructure transient period. It is shown that local misorientation distributions are good indicators of the deformation microstructure of low SFE materials as they capture small variations in deformation structures which cannot be analysed from stress-strain curves alone. [ABSTRACT FROM AUTHOR]

Microstructure evolution and mechanical properties of AISI 316 LN austenitic stainless steel (SS) after cryorolling with different strains were investigated by means of optical, scanning and transmission electron microscopy, X-ray diffractometer, microhardness tester, and tensile testing system. The deformation-induced martensite transition and the deformation microstructure occurred during cryorolling process were always composed of high-density dislocations, deformation twins, and deformation-induced martensites. Following the strain, the dislocation density in deformation microstructure approached saturation state and the volume fraction of deformation twins combined with deformation-induced martensites increased significantly. At the 70% strain, original austenite was transformed into martensite completely. Further increasing the strain to 90% would refine the martensitic lamellae to nanoscale. The deformation degree also led to remarkable increase of the strength and hardness of the cryorolled SS, and drastic reductions of the elongation. Due to the cryorolling, the tensile fracture morphology changed from typical ductile rupture to a mixture of quasi-cleavage and ductile fracture. [ABSTRACT FROM AUTHOR]

The material studied is a commercially available 316LVM stainless steel with an initial grain size of 30 μm. To refine the microstructure down to the nanoscale, hot (at 1000 °C) and room temperature hydrostatic extrusion were applied with a total true strain of 1.4. An annealed sample with coarse grains of 35 μm in diameter was used as a reference sample. The results indicate that after hot hydrostatic extrusion, the microstructure consisted mainly of cells with tangled dislocation walls, while after room temperature hydrostatic extrusion, twins of various width and shear bands could be distinguished. Hydrostatic extrusion is also an efficient way to tailor the corrosion resistance and mechanical properties of 316LVM stainless steel. Performed at room temperature, hydrostatic extrusion resulted in an ultra-high-strength material with limited but sufficient ductility. Performed at high temperature, hydrostatic extrusion resulted in a material with a very good combination of strength (approximately 900 MPa) and ductility (elongation to failure higher than 20%). Both hydrostatically extruded steels maintained good passivation behavior in 0.1 M H 2 SO 4 . In the presence of chloride ions, susceptibility to localized attack increased for the steel extruded at room temperature, but did not change for the hot-extruded steel. [ABSTRACT FROM AUTHOR]

In the present work, specimens of the metastable austenitic stainless steel AISI 347 with different surface morphologies were investigated in stress-controlled fatigue tests in the high cycle fatigue (HCF) regime at ambient temperature. Specific surface morphologies were generated by cryogenic turning with CO2 snow cooling. As a result of the metastable austenite microstructure, phase changes from paramagnetic austenite to ferromagnetic martensite take place in the near-surface regime during cryogenic turning as well as in the whole specimen volume during monotonic and/or cyclic elastic-plastic deformation. The metastability of AISI 347 was characterized according to the MS-temperature determined from the chemical composition and by X-ray diffraction measurements with in situ cooling. Microhardness and strength of both phases were measured. Near-surface microstructure was analyzed by optical and scanning electron microscopy after focused ion beam preparation. Besides a partially martensitic surface layer, a thin nanocrystalline layer, both induced by cryogenic turning, was observed. In case of cyclic loading, the martensitic surface layer leads to a reduction of plastic strain amplitude as well as a retardation of crack initiation and consequently to an increase in fatigue life. [ABSTRACT FROM AUTHOR]

Deformation induced martensitic transformation (DIMT) usually occurs in metastable austenitic stainless steels. Recent studies have shown that DIMT may occur in the austenite phase of low alloyed duplex stainless steels. The present study demonstrates that DIMT can also take place in a high alloyed Fe-23Cr-8.5Ni duplex stainless steel, which exhibits an unexpectedly rapid transformation from γ-austenite into α′-martensite. However, an inhibited martensitic transformation has been observed by varying the initial microstructure from a coarse alternating austenite and ferrite band structure to a fine equiaxed microduplex structure. [ABSTRACT FROM AUTHOR]

This article presents a finite element investigation into the web crippling strength of cold-formed stainless-steel lipped channels with circular web perforations under end-two-flange loading. The cases of web openings located both centred and offset to the load bearing plates are considered. In order to take into account the influence of the circular web openings, a parametric study involving 2190 finite element analyses was performed, covering duplex EN 1.4462, austenitic EN 1.4404 and ferritic EN 1.4003 stainless-steel grades; from the results of the parametric study, strength reduction factor equations are determined. The strength reduction factor equations are first compared to equations recently proposed for cold-formed carbon-steel lipped channels. It is demonstrated that the strength reduction factor equations proposed for cold-formed carbon steel are conservative for the stainless-steel grades by up to 10%. New coefficients for web crippling strength reduction factor equations are then proposed that can be applied to all three stainless-steel grades. [ABSTRACT FROM AUTHOR]

The paper presents the results of the basic mechanical properties determined in the static tensile test, impact un-notched Charpy test and hardness of austenitic stainless steel type 316L produced by two techniques: classical pressing and sintering in a vacuum with rapid cooling and selective laser melting (SLM). In this work fracture surface of Charpy test, samples were studied. The results indicate that application of selective laser melting (SLM) makes it possible to double increase the strength properties of components manufactured from austenitic stainless steel type 316L compared to sintering in a vacuum. Resulted in mechanical properties strongly depend on porosity characteristic and the presence of superficial oxides in the case of sintered steel and the character of observed microstructural defects deriving from non-fully melted powder particles and the formation of voids between subsequently melted pool tracks during the SLM. [ABSTRACT FROM AUTHOR]

Alloy 709 (UNS S31025) has shown enhanced performance, particularly in creep strength, over current generation high temperature structural materials, specifically Type 316 stainless steel and Grade 91. Accurate knowledge of the thermal properties of the material is important to design efficient systems and to allow calculation of thermally induced stresses and stress gradients. Thermal diffusivity, thermal conductivity, specific heat capacity, and coefficients of thermal expansion have been determined for Alloy 709 as a function of temperature in the range of 20–850 °C. The results do not vary significantly for the three heats of Alloy 709 tested, and compare well with those reported for other high Cr, high Ni austenitic stainless steels. Deviations from monotonic behavior have been observed for the specific heat capacity and to a lesser degree for the thermal conductivity, while the thermal expansion and thermal diffusivity increase nearly linearly with increasing temperature. [ABSTRACT FROM AUTHOR]

The compression and tensile consecutive deformation behavior and microstructure evolution of Mn18Cr18N steel were investigated by cyclic loading tests at room temperature and strain amplitude from 0.005 to 0.15. The results indicated that the cyclic loading stress-strain curves of the steel show plastic deformation characterized by almost the same working hardening rates without yield plateaus at various strain amplitudes. At the lower strain amplitudes from 0.005 to 0.01, the stress amplitudes and subsequent yield surface radius decreased with cycles, which suggest that stress softening occurs during cyclic loading. At the strain amplitudes from 0.02 to 0.15, the stress amplitudes and subsequent yield surface radius increased with cycles, which imply that stress hardening occurs during cyclic loading. With the increasing of strain amplitudes, the cyclic hardening coefficients monotonically increased, while the cyclic softening coefficients rapidly decreased. The maximum flow stress increased up to 1549.6 MPa after three cycles at the strain amplitude of 0.15, which increased by 395.4 MPa compared to the maximum uniaxial tensile flow stress. It was also demonstrated that the cyclic loading stress-strain behaviors (cyclic softening and hardening) depend on internal stress component rather than effective stress component. TEM observation shows that planar slip with parallel substructures along one direction at high number cycles evolved from various dislocation configurations at low number cycles occurs at the lower strain amplitude of 0.005; double planar slip with grid substructures along two directions at high number cycles evolved from parallel substructures along one direction at low number cycles occurs at the higher strain amplitude of 0.04. Internal stress could be released by dislocation rearrangement and activation of cross slips during cyclic loading process, which induce stress softening at lower strain amplitudes; while slipping and twining alone two intersectional directions caused stress hardening at higher strain amplitudes. [ABSTRACT FROM AUTHOR]

Austenitic stainless steels are the mostly used stainless steels in sheet metal forming and are subject of a large variety of applications including plate heat exchangers. During cold plastic deformation of heat exchanger plates, the martensitic transformation can take place. Martensite formation can be considered as a function of temperature, stress or strain. This paper is focused on the influence of martensite transformation on the corrosion resistance of AISI 316 austenitic stainless steel. Corrosion analysis showed that martensitic transformation which occurs due to cold forming process and under cyclic loading conditions had a substantially influence on the corrosion resistance of plate heat exchangers made by AISI 316 austenitic stainless steel. The role of molybdenum in the passive film formation has been considered and it was attributed to the ability of Mo to form insoluble chloride complexes at the base of pits. However, the protective film formed as a result of passivation or repassivation process was continuously broken due to continuously martensitic transformation as a result of cyclic working conditions of plate heat exchanger. The martensite volume expansion continuously broke the passive film and consequently new unprotected surfaces were exposed to chlorine-treated water, which was used as thermal agent for the plate heat exchanger. During working period, the heat exchanger plates are subjected to fluctuating stresses and strains that may result in cracks or fracture after a sufficient number of fluctuations. Fatigue fractures are caused by simultaneous action of cyclic stress, tensile stress and plastic strain. The martensite transformation as a result of applied cold plastic deformation process, changes not only the steel structure, but also its physical and chemical properties. The magnetic properties of stainless steel are very dependent on the elements added into the alloy. Having different corrosion potentials, it is easy for them to become the anode and the cathode, respectively, of a corrosion battery. [ABSTRACT FROM AUTHOR]

Austenite stability against the deformation induced α′-martensite (DIM) formation and the cyclic deformation behavior of grain-refined structures with the grain size between 13 and 0.6 µm under fatigue loading were investigated in a 301LN Cr-Ni austenitic stainless steel. The DIM transformation in the course of cycling at constant total strain amplitudes of 0.4% and 0.6% was recorded by magnetic measurements and microstructures examined by electron backscatter diffraction and X-ray diffraction. The cyclic deformation behavior was followed by the evolution of the stress amplitude. The results evidenced that the austenite stability increases with the decreasing average grain size down to about one micrometer, obtained in annealing at 900 °C for 1 s. On the contrary, the stability decreases drastically in the submicron, non-homogeneous grain structures created at the lower temperatures of 800–700 °C. In these structures, submicron grains seem to be stable, and the precipitation of CrN is considered to contribute to the reduced stability of grains with a few-micron-size present among submicron grains. Under cyclic loading, the level of initial stress amplitude varied considerably in dependence on the refined austenite grain size. At the 0.6% strain amplitude, the initial softening was followed by cyclic hardening. The level of the final stress amplitude was related to the fraction of DIM formed during cycling straining. [ABSTRACT FROM AUTHOR]

Bare and Al 2 O 3 -coated austenitic steel samples are exposed to lead-fast-reactor relevant corrosive conditions. Selective leaching of Ni, Mn and Cr is observed in bare samples exposed to high temperature stagnant lead (550 °C, 10 −8 wt.% oxygen, 1000 and 4000 h). By contrast, corrosion is not observed in either pristine (4000 h) or irradiated (1000 h) coated samples. Further characterization and testing methods include SEM, TEM, STEM, EDS, cyclic nanoimpact, microindentation, scratch, and thermal cycling. Overall, the results show that the coatings retain structural integrity under the conditions investigated, which is a crucial prerogative for corrosion protection with ceramic coatings. [ABSTRACT FROM AUTHOR]

A previously published dislocation density based flow stress model has been refined and made more consistent with underlying physical assumptions. The previous model included many temperature dependent parameters that are taken as constant in the current work. The model has also been simplified with respect to dynamic strain aging. Additional contributions to flow stress from the Hall-Petch effect and solute hardening have now been explicitly included in the model. Furthermore, the dynamic recovery part of the model has been improved. [ABSTRACT FROM AUTHOR]

A combination of scanning Kelvin probe force microscopy (SKPFM) and electron backscatter diffraction (EBSD) has been applied to investigate the hydrogen release from thermally hydrogen-precharged type 304 austenitic stainless steel (γ-SS). The evolution of contact potential difference (CPD) well exhibits the evolution of hydrogen concentration in the near surface area. It is found for the first time that the hydrogen diffusivity in γ-SS depends on the crystallographic orientation. The hydrogen diffusion out from (001) and (101) grains is faster than from (111) grains while no obvious difference is found between (001) and (101) grains. [ABSTRACT FROM AUTHOR]

The tensile behavior of hydrogen-charged 304-type austenitic stainless steel, with and without prestrain, is investigated. The specimens are thermally charged with hydrogen in 15 MPa hydrogen gas at 300 °C for 72 h. Tensile behavior of the specimen is compared with the specimen aged in vacuum at 300 °C. The effect of the charging condition on the stability of microstructure is determined by characterizing prestrained specimens before and after charging. The hydrogen content in the specimens is determined using thermal desorption spectroscopy (TDS). Analysis of X-ray diffraction (XRD) data and electron backscattered diffraction (EBSD) shows that the fraction of martensite increases after charging in hydrogen by 5-10%. The fracture surfaces of the uncharged and charged specimens are examined for characteristic features. Flow stress and ductility of the charged and prestrained and charged specimens are discussed in terms of the martensite fraction and hydrogen content. [ABSTRACT FROM AUTHOR]

The possibilities are studied for using an electromagnetic eddy-current technique of monitoring the phase composition and hardness of austenitic chromium-nickel steel that has been subjected to hardening frictional treatment in different technological regimes. It is shown that an eddy-current structuroscope and a Vektor eddy-current defectoscope make it possible to control the amount of straininduced martensite and the microhardness of the surface of metastable austenitic steel after nanostructuring frictional treatment with different numbers of gliding indenter scans (passes). The Vektor eddycurrent defectoscope allows one to monitor the phase composition of austenitic steel that has been subjected to nanostructuring frictional treatment in a temperature range from −196 to +250°C. [ABSTRACT FROM AUTHOR]

Variation of Crack Tip Opening Displacement (CTOD) test values can have a significant effect on the Engineering Critical Assessment of a structure. This paper examines the development of CTOD with increasing load in an austenitic stainless steel. The silicone replication method giving variation of CTOD across the specimen thickness, and Digital Image Correlation (DIC) are compared to each other, and in turn to clip gauge measurements from tests. Results from Finite Element models are also presented. Estimations of CTOD from BS 7448-1, ISO 12135 and ASTM E1820, and a proposed modification from JWES are compared to the experimental data from the crack cast in silicone compound - assumed to be the actual CTOD. The DIC measurement showed consistency with crack replicas, and a formula is given to estimate CTOD using DIC. For high strain hardening austenitic stainless steel, both the JWES and ASTM E1820 estimations provide adequate accuracy for CTOD. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the effect of strain rate on volume fraction of martensite (VFM) in 304L austenitic stainless steel through dome test. Findings of this study show that martensitic transformation affects the deformation mode and formability of this material. Three strain rates are applied by controlling forming punch speed to conduct the stretching experiments and VFM is measured using magnetic saturation method. Results of the present study reveal that maximum VFM of 56% forms at the pole at low strain rates, whereas VFM of 47% is seen at high strain rates, and transforms in the region close to the flange. It is noted that blanks show good formability under low strain rate and poor formability at high strain rates. The relationship between VFM and strain rate, strain, percentage of shell reduction, equivalent of stress, and triaxiality are discussed. The experimental procedure is simulated and predicted findings show good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Austenitic steels 304 L and 316 L are used extensively as nuclear structural materials. The objective of this study is to determine if their corrosion behavior can be improved by developing an Al-containing surface layer by a complex surface treatment, including substrate modification by growth of oxide layers using anodic oxidation, cyclic voltammetry and autoclaving in water, as well as a micro-arc oxidation (MAO) treatment in 0.1 M NaAlO2 aqueous solution. The processes and structures obtained by MAO under various experimental conditions were characterized by X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectrometry analysis. The corrosion behavior, studied by Tafel potentiodynamic polarization, was correlated to the microstructure and the chemical composition of the surface layers which are strongly dependent on the treatment parameters. An overall description of the electrochemical processes involved in the growth of aluminum coating, the surface properties improvement, together with some consideration about the new materials development for energy technologies are presented. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Though strain rates are hardly fixed during the actual transients in nuclear power plants (NPP), most of the existing environmental fatigue ε – N data were obtained under simple loading histories with constant strain rates. In an effort to incorporate the actual loading conditions, strain rate was changed during the low cycle fatigue (LCF) test. The LCF tests were performed in a strain control mode in both simulated pressurized water reactor (PWR) environment and 310 °C air to evaluate the effects of mixed strain rates on fatigue life. The test results indicated that the modified strain rate approach and average strain rate method could be applied to the fatigue evaluation considering environmental effects. The cyclic stress response showed that the trend of hardening with mixed strain rate was consistent with a negative strain rate sensitivity, which was observed in the constant strain rate test. In addition, the increase in striation spacing on the fracture surface is in good agreement with the increase of bulk dislocation density and reduction of fatigue life. [ABSTRACT FROM AUTHOR]

Most cohesive zone models were used to reproduce fatigue crack growth under small scale yielding and failed to predict elastic–plastic fatigue crack growth. In the present work a new cohesive zone model is introduced to give a uniform description of both fatigue crack growth and elastoplastic rupture. Damage accumulation of the cohesive model contains both monotonic damage as well as cyclic damage and validated by corresponding mixed-mode fracture and fatigue experiments of an austenitic stainless steel. Computations confirm that the present cohesive zone model may provide a uniform description for the whole fatigue crack growth regimes. [ABSTRACT FROM AUTHOR]

The present study elaborately explains the effect of welding parameters on the microstructure, texture, and mechanical properties of gas metal arc welded AISI 304 austenitic stainless steel sheet (as received) of 4 mm thickness. The welded joints were prepared by varying welding speed (WS) and current simultaneously at a fixed heat input level using a 1.2-mm-diameter austenitic filler metal (AISI 316L). The overall purpose of this study is to investigate the effect of the variation of welding conditions on: (i) Microstructural constituents using optical microscope and transmission electron microscope; (ii) Micro-texture evolution, misorientation distributions, and grain boundaries at welded regions by measuring the orientation data from electron back scattered diffraction; and (iii) Mechanical properties such as hardness and tensile strength, and their correlation with the microstructure and texture. It has been observed that the higher WS along with the higher welding current (weld metal W1) can enhance weld metal mechanical properties through alternation in microstructure and texture of the weld metal. Higher δ-ferrite formation and high-angle boundaries along with the 〈101〉 + 〈001〉 grain growth direction of the weld metal W1 were responsible for dislocation pile-ups, SFs, deformation twinning, and the induced martensite with consequent strain hardening during tensile deformation. Also, fusion boundary being the weakest link in the welded structure, failure took place mainly at this region. [ABSTRACT FROM AUTHOR]

Fatigue bending tests have been performed on welded pipes made from an austenitic stainless steel. Four types of loading were used: 1) constant amplitude, 2) a load expected at pressure vessel environment, 3) a Gaussian load, and 4) a specially constructed two-level block load. The twenty-eight test results are evaluated using three different models: 1) the classical Basquin equation neglecting the fatigue limit, 2) the ASME model with a fatigue limit, and 3) a model with continuously decreasing fatigue limit. No significant differences between the three models were found. Predictions based on constant amplitude results appear to be non-conservative. [ABSTRACT FROM AUTHOR]

To study the effect of chemical composition on microstructural features and mechanical properties of dissimilar joints between super duplex and austenitic stainless steels, welding was attempted by gas tungsten arc welding process with a super duplex (ER2594) and an austenitic (ER309LMo) stainless steel filler metal. While the austenitic weld metal had vermicular delta ferrite within austenitic matrix, super duplex stainless steel was mainly comprised of allotriomorphic grain boundary and Widmanstätten side plate austenite morphologies in the ferrite matrix. Also the heat-affected zone of austenitic base metal comprised of large austenite grains with little amounts of ferrite, whereas a coarse-grained ferritic region was observed in the heat-affected zone of super duplex base metal. Although both welded joints showed acceptable mechanical properties, the hardness and impact strength of the weld metal produced using super duplex filler metal were found to be better than that obtained by austenitic filler metal. [ABSTRACT FROM AUTHOR]

The effect of treatment time on the microstructure of AISI 304 austenitic stainless steel during liquid nitrocarburizing (LNC) at 703 K (430 °C) was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Experimental results revealed that the modified layer was covered with the alloy surface and the modified layer depth increased extensively from 2 to 33.4 μm with increasing treatment time. SEM and XRD showed that when the 304 stainless steel sample was subjected to LNC at 703 K (430 °C) for less than 4 hours, the main phase of the modified layer was expanded austenite. When the treatment time was prolonged to 8 hours, the abundant expanded austenite was formed and it partially transformed into CrN and ferrite subsequently. With the increased treatment time, more and more CrN precipitate transformed in the overwhelming majority zone in the form of a typical dendritic structure in the nearby outer part treated for 40 hours. Still there was a single-phase layer of the expanded austenite between the CrN part and the inner substrate. TEM showed the expanded austenite decomposition into the CrN and ferrite after longtime treatment even at low temperature. [ABSTRACT FROM AUTHOR]

Abstract: A Fe18Cr9Ni1Mn austenitic stainless steel is shown to be sensitive to liquid metal embrittlement in liquid sodium. Good wetting by sodium is achieved during long-term pre-exposure before tensile testing in liquid sodium with additions of Na2O. Pre-exposure does not affect the normal ductile fracture mode of the steel in reference tests in the temperature range investigated ([473–673K]). Intergranular cracking is found to play a key role in the fracture process in liquid sodium. [Copyright &y& Elsevier]

Abstract: Advanced techniques were used to study the deformation mechanisms induced by fatigue tests in a metastable austenitic stainless steel AISI 301LN. Observations by Atomic Force Microscopy were carried out to study the evolution of a pre-existing martensite platelet at increasing number of cycles. The sub-superficial deformation mechanisms of the austenitic grains were studied considering the cross-section microstructure obtained by Focused Ion Beam and analysed by Scanning Electron Microscopy and Transmission Electron Microscopy. The results revealed no deformation surrounding the pre-existing martensitic platelet during fatigue tests, only the growth on height was observed. Martensite formation was associated with shear bands on austenite, mainly in the {111} plane, and with the activation of the other intersecting austenite {111}〈110〉 slip system. Furthermore, transmission electron microscopy results showed that the nucleation of ε-martensite follows a two stages phase transformation (γ fcc →ε hcp →α' bcc ). [Copyright &y& Elsevier]

In the present study, an experimental setup was designed and fabricated in order to accomplish friction welded joints between austenitic stainless steel and low-alloy steel. Thereafter, the effect of axial pressures on the mechanical properties of friction welded AISI 304 with AISI 1021 steels, produced by mechanical joining, have been investigated. Samples were welded under different axial pressures ranging from 75 to 135 MPa, at constant speed of 1250 rpm. The tensile strength, impact strength, and micro-hardness values of the weldments were determined and evaluated. Simultaneously, the fractrography of the tensile-tested specimens were carried out, so as to understand the failure analysis. [ABSTRACT FROM AUTHOR]

In order to establish more reliable formulae for calculating stacking fault energies (SFE) from the chemical compositions of austenitic stainless steels, SFE values were measured for 54 laboratory-melted heats and 2 commercial heats. The results were checked against those of a first-principle, atomistic calculation approach. More than ~20,000 data points for the width and angle of the Burgers vectors were determined from dark-field images of isolated extended dislocations in 56 heats of austenitic stainless steel using weak electron beams with g-3g diffraction conditions. Based on these numerous observations and on fundamental thermodynamic analyses, it is concluded that the SFE values for austenitic stainless steels are changed not only by chemical composition but also by heat treatment. In this paper, new formulae for calculating SFE values from the chemical compositions in three different heat treatment conditions have been proposed for austenitic stainless steels within given limited chemical composition ranges. In these formulae, the SFE values are calculated from the nickel, chromium, molybdenum, silicon, manganese, nitrogen, and carbon contents for the each heat treatment condition. The three heat treatment conditions studied were water cooling after solution heat treating (SHTWC), furnace cooling after solution heat treating, and aging after SHTWC. [ABSTRACT FROM AUTHOR]

Nanostructured metals and alloys possess very high strength but exhibit limited plasticity. Enhancement of the strength/ductility balance is of prime importance to achieve wide industrial applications. However, post-deformation heat treatment, which is usually used to improve plasticity, can lead to a decrease in other properties. In the case of austenitic stainless steels, heat treatment in the range from 480 to 815 °C can increase their susceptibility to intergranular corrosion. The aim of the work reported in this paper was to determine if nanostructured austenitic stainless steel is susceptible to intergranular corrosion if heat treated for 1 h at 700 °C. Samples of 316LVM austenitic stainless steel were hydrostatically extruded, in a multi-step process with the total true strain of 1.84 to produce a uniform microstructure consisting of nanotwins. These nanotwins averaged 21 nm in width and 197 nm in length. Subsequent annealing at 700 °C produced a recrystallised structure of 68-nm-diameter nanograins. The heat treatment improved the ductility from 7.8 to 9.2 % while maintaining the ultimate tensile strength at the high level of 1485 MPa. Corrosion tests were performed in an aqueous solution consisting of 450 ml concentrated HNO and 9 g NaF/dm (according to ASTM A262-77a). The evaluation of the corrosion resistance was based on transmission and scanning electron microscopic observation of the microstructure and chemical analyses. The results revealed that both the as-received and HE-processed samples are slightly susceptible to the intergranular corrosion after annealing at 700 °C for 1 h. [ABSTRACT FROM AUTHOR]

In oil and gas production environments, HS and Cl can coordinate to cause pitting or stress corrosion cracking (SCC) of stainless steels. There has been limited work conducted on corrosion and SCC of autenitic stainless steels in high H2S-CO2-Cl- environments. In this paper, by four-point bending test method and scanning electron microscopy analysis, SCC of 316L steel was investigated under high H2S-CO2 pressures with 150,000 ppm Cl at 60 °C. The effect of high H2S-CO2 pressure was discussed. The results indicated that the higher H2S-CO2 pressure can accelerate anodic dissolution process, deteriorate passive films, and aggravate SCC sensitivity. Using cyclic potentiodynamic polarization measurements, the corrosion behavior of 316L steel was studied in high H2S-CO2-Cl- environments. The effect of pH on pitting corrosion was discussed. Lower pH can promote both cathodic and anodic actions on 316L steel and facilitate passive film breakdown. [ABSTRACT FROM AUTHOR]