In the present study, investigation and comparison laser and tungsten inert gas (TIG) welding techniques for dissimilar butt joint of 304L and 316L stainless steel sheets was carried out. The effects ...of voltage and laser beam spot size during laser welding and effects of voltage, traveling speed and presence of backing gas during TIG welding on yield strength, elongation, hardness and weld width were investigated. Moreover, in order to examine the mechanical and metallurgical behavior of the weld, microstructure analysis was used. Results showed that welding depth of TIG welding was higher than laser method. It was observed that strength and toughness of samples decreased by increasing voltage in TIG and laser welding. Additionally, by increasing beam spot size in laser welding, strength, toughness and hardness increased. Also, the presence of backing gas during TIG welding resulted in the increase of strength, toughness and hardness of the samples.
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•Enhancement of the strength and toughness because of increase of beam spot size.•Change of temperature gradient resulted in layer microstructure in TIG samples.•TIG samples with backing gas had higher strength and finer isothermal layers.•Massive austenite in laser samples because of massive transformation.
Microbiologically influenced corrosion (MIC) of 2205 duplex stainless steel (DSS) in the presence of Pseudomonas aeruginosa was investigated through electrochemical and surface analyses. The ...electrochemical results showed that P. aeruginosa significantly reduced the corrosion resistance of 2205 DSS. Confocal laser scanning microscopy (CLSM) images showed that the depths of the largest pits on 2205 DSS with and without P. aeruginosa were 14.0 and 4.9μm, respectively, indicating that the pitting corrosion was accelerated by P. aeruginosa. X-ray photoelectron spectroscopy (XPS) results revealed that CrO3 and CrN formed on the 2205 DSS surface in the presence of P. aeruginosa.
•LPR and EIS showed that P. aeruginosa reduced the corrosion resistance of 2205 DSS.•The largest pit depth on 2205 DSS was 4.9μm after 14days incubation in sterile medium.•The largest pit depth on 2205 DSS was 14μm after 14days incubation with P. aeruginosa.•The accelerated pitting was due to the formation of CrO3 and CrN by P. aeruginosa.
•316L stainless steel samples with various grain sizes were successfully fabricated.•The fracture morphologies were systematically analyzed.•The dimple size increased with the increase of average ...grain size.•The grain size effects on dimple size and the strength/ductility were uncovered.
The aim of this work is to understand the relationship among average grain size, dimple size and tensile properties of 316L stainless steel via directly experimental results. We have successfully prepared samples with the average grain size from a few microns to tens of microns through cold rolling and annealing processes. Uniaxial tensile tests were performed to confirm the Hall-Petch relationship between the grain size and yield strength. In order to uncover the grain size dependence of ductility, the fracture morphologies in details were observed. It revealed that the dimple size is positively related to the value of D1/2 (D is the average diameter of grain size). A larger grain size was believed to result in a larger dimple so as to achieve a higher ductility (uniform elongation).
Microstructure and corrosion behavior of 316L stainless steel fabricated by selective laser melting (SLM) for bipolar plate were investigated and the subsequent heat treatment effect was also ...clarified. Results showed that sub-grains widely existed in the SLM 316L and the dislocations in the grain boundary migrated and disappeared after heat treatment. The as produced SLM 316L exhibited inferior corrosion resistance than the wrought in 0.5 M H2SO4 solution with 50 ppm Cl− and 2 ppm F− ions at 70 °C due to the SLM defects (molten pool boundaries, non-equilibrium phases etc.), and short, stress relief annealing did not homogenize the non-uniform structures. However, recrystallization heat treatment can improve the durability due to the more uniform structure and thicker passive film. Meanwhile, the proportion of the oxides in passive film formed on SLM 316L increased after heat treatment, especially for the chromic oxide, leading to a better anti-corrosive property.
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•316L stainless steel was prepared by selective laser melting (SLM) with optimized parameters.•As produced SLM 316L exhibited inferior corrosion resistance than the wrought in PEMFCs at 70 °C.•Recrystallization heat treatment could improve the durability due to the homogenized structure and thicker passive film.
•A comprehensive experimental programme including 34 cross-section tests has been carried out.•A range of cross-section sizes and stainless steel material grades has been investigated.•Fundamental ...data on the structural performance of stainless steel cross-sections under combined loading have been established.
Stainless steel has been gaining increasing use in a variety of engineering applications due to its unique combination of mechanical properties, durability and aesthetics. Significant progress in the development of structural design guidance has been made in recent years, underpinned by sound research. However, an area that has remained relatively unexplored is that of combined loading. Testing and analysis of stainless steel cross-sections under combined axial load and bending is therefore the subject of the present paper and the companion paper (Zhao et al., submitted for publication). The experimental programme covers both austenitic and duplex stainless steels, and five cross-section sizes including three square hollow sections (SHS) and two rectangular hollow sections (RHS). In total, five stub column tests, five four-point bending tests, 20 uniaxial bending plus compression tests and four biaxial bending plus compression tests were carried out to investigate the cross-sectional behaviour of stainless steel tubular sections under combined loading. The initial loading eccentricities for the combined loading tests were varied to provide a wide range of bending moment-to-axial load ratios. For each type of test, the test setup, experimental procedures, full experimental load–deformation histories and key test results are reported in detail. All the experimental results are then employed in the companion paper (Zhao et al., submitted for publication) for the validation of finite element (FE) models, by means of which a series of parametric results is generated, and for the assessment of the design provisions given in EN 1993-1-4 (2006) and SEI/ASCE-8 (2002). Improved design rules for stainless steel cross-sections under combined loading are also sought through extension of the deformation-based Continuous Strength Method (CSM).
Destructive techniques to monitor nuclear reactor component health may not always be available during service, as they are time-consuming and often require pre-installed inspection coupons. ...Non-destructive evaluation (NDE) techniques can bridge this gap by rapidly identifying the state of mission-critical reactor components, via inference between NDE-measurable material properties and those of ultimate interest, such as ductility and toughness. Here, we demonstrate one such inference about the health of thermally aged cast austenitic stainless steels. Observations of surface acoustic wave peak (SAW) splitting correlate with spinodal decomposition-induced embrittlement as destructively measured by Charpy impact energy. Elastodynamic calculations and molecular dynamics simulations of the effects of spinodal decomposition on elastic moduli support that the new acoustic modes present are due to stiffening in the δ-ferrite domains. Finally, this discovery enables one to probe structure-property relationships in materials in a greatly accelerated manner, suggesting that similar inference methods can be used to determine material fitness-for-service, or to quickly uncover new structure-property relationships.
•AM 316 L microstructure consists of cells network with elemental enrichment at borders.•Cells border is highly corrosion resistant; limiting penetration of attack into metal.•Cells present on LMD ...specimens were about 10 times larger than those in SLM samples.•LMD, SLM and wrought 316 L had similar corrosion potential and passive current density.•Potential passivity range was found to be in the order: SLM > LMD > wrought material.
This work compares the microstructure and corrosion resistance of 316 L stainless steel samples prepared using two different additive manufacturing methods: selective laser melting (SLM), and laser metal deposition (LMD). A wrought material was used as reference. The specimens showed marked differences in their microstructure, as a result of the specific manufacturing conditions. All samples displayed similar corrosion potential and passive current density values. However, variations were seen in their potential passive range (SLM > LMD > Wrought). The wider passivity of the SLM specimen can be associated with its finer microstructure, which leads to a more stable native oxide.
The Small Punch (SP) test with constant deflection rate is a miniature technique that can provide estimates on the material tensile properties. Linear correlations are usually used for relating the ...maximum force and displacement at maximum force, recorded during the SP test, to the ultimate tensile strength. Fitting coefficients used in the correlations are calibrated on data from flat SP specimens. SP test requires only a small amount of testing material which represents a clear benefit when irradiated samples have to be tested. Therefore, there is a considerable interest in using SP for testing fuel cladding material properties. In this study we show that the same correlation equations, albeit with adjusted fitting coefficients, can be used to estimate the ultimate tensile strength from tube SP specimens made out of P91 ferritic/martensitic and 15-15Ti austenitic stainless steel. The calculated fitting coefficients lead to reasonable estimates of the ultimate tensile strength at temperatures of up to 650 °C although the coefficients themselves have been computed at room temperature. The coefficients are more suited for assessing ductile materials as the models used for computing the coefficients do not take into account damage (degradation of the material stiffness) or crack initiation and propagation, observed during the SP tests of brittle material. Finally, using the calculated ratios of maximum forces and displacements at maximum forces, one can map the two values of a given curved SP test to the equivalent flat SP values.
•Small punch test applied to nuclear fuel cladding type specimens.•Correlation equations applied to curved small punch specimens.•Correlation coefficients for curved small punch specimens developed.•Mapping of Fm and vm values from the flat to the curved small punch specimens.
The effect of tensile elastic stress on passivation behavior and surface chemistry of 2205 duplex stainless steel is investigated. Elastic stress increases the potential drop at the film/solution ...interface, donor density and defects diffusion coefficient, resulting in the increase of passive current density. High elastic stress (≥60%σs) leads to the generation of soluble CrO3, the increase of oxidized Cr and Fe(Ⅱ) content and the decrease of film thickness, resulting in the quasi-steady-state current density no longer independent of potential. Passive film become denser from spontaneous passivation to primary passivation and Fe(III) compounds dominate the passive film under secondary passivation.
•Passivation of 2205 DSS under elastic stress is studied.•Elastic stress results in the increase of Iss by decreasing d and increasing φf/s, ND, and D0.•High elastic stress (≥60% σs) leads to further increase of Iss, which is no longer independent of potential.•Elastic stress facilitates the increase of oxidized Cr and Fe(Ⅱ) content.•Potential makes passive film become denser until transpassivation occurs.
Microbiologically influenced corrosion (MIC) of S32654 (654SMO) super austenitic stainless steel (SASS) by acid producing bacterium (APB), Acidithiobacillus caldus SM-1, a strain of sulfur-oxidizing ...bacteria (SOB) used in biohydrometallurgy field, was investigated using electrochemical measurements and surface characterizations during a 14-day immersion test. The results indicated that S32654 SASS was susceptible to MIC by APB, and A. caldus SM-1 was capable of producing an aggressive acidic environment underneath the biofilm, resulting in the dissolution of the passive film and severe pitting attacks against S32654 SASS, which is commonly regarded as a corrosion resistant material.
•The MIC behavior of S32654 SASS in the presence of Acidithiobacillus caldus SM-1 was investigated.•The sulfuric acid produced by A. caldus SM-1 led to a severe MIC attack against S32654 SASS.•The biogenic H2S may result in the formation of MoS2 under the biocatalysis.
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