In this work, we examined the influence of different types of selective laser melting (SLM) devices on the microstructure and the associated material properties of austenitic 316L stainless steel. ...Specimens were built using powder from the same powder batch on four different SLM machines. For the specimen build-up, optimized parameter sets were used, as provided by the manufacturers for each individual SLM machine. The resulting microstructure was investigated by means of scanning electron microscopy, which revealed that the different samples possess similar microstructures. Differences between the microstructures were found in terms of porosity, which significantly influences the material properties. Additionally, the build-up direction of the specimens was found to have a strong influence on the mechanical properties. Thus, the defect density defines the material’s properties so that the ascertained characteristic values were used to determine a Weibull modulus for the corresponding values in dependence on the build-up direction. Based on these findings, characteristic averages of the mechanical properties were determined for the SLM-manufactured samples, which can subsequently be used as reference parameters for designing industrially manufactured components.
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.
•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).
•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).
•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 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.
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 total of 196 new concrete-filled ferritic stainless steel tubular (CFFSST) joint results are reported.•CIDECT provisions exhibit remarkable scatter predictions for the CFFSST joints.•Existing ...design rules are generally not accurate for the CFFSST joints.•Improved design rules are proposed to predict the capacities of CFFSST X-and T-joints.
The behaviour and resistances of concrete-filled ferritic stainless steel tubular (CFFSST) joints were studied and presented in this paper based upon experimental and numerical investigations. A test program was firstly undertaken on a series of X- and T-joints with square and rectangular hollow section (SHS and RHS) chords. The stainless steel SHS/RHS tubes were cold-rolled from EN 1.4003 ferritic grade sheets, and the specimens were in-filled with either normal or high strength concrete. The experimental study including the detailed material properties, joint test setups, test procedures and results is reported. Numerical models were also developed and verified against the CFFSST joint test results, and followed by a parametric study generating further numerical results over a wider range of key joint parameters. The obtained experimental and numerical CFFSST joint capacities were compared with existing design recommendations as per the CIDECT Design Guide and design rules proposed by previous researchers. The comparison results indicate that the existing provisions are not capable of predicting the capacities of the investigated composite tubular joints in an accurate and reliable manner. Hence, modified design rules are put forward in this paper for the design of CFFSST joints.
This work studied the influence of cold deformation on the microstructure evolution and corrosion behavior of selective laser melted (SLMed) 316L stainless steel in a simulated cathode environment ...for proton exchange membrane fuel cells (PEMFCs). Results indicated that at < 50% deformation levels, the corrosion resistance was improved with an increase in deformation level, which was attributed to the deformation twins, refining sub-grains, and the formation of stable passive films. At 70% deformation level, martensite nucleation decreased the stability of the passive film and consequently reduced the corrosion resistance.
•Cold deformation showed negative and positive effects on the corrosion resistance of SLMed 316L SS.•The relationship between the microstructure and corrosion behavior were established.•Semiconductor types of the passive film were independent of cold deformation.
In this work, strengthening of 316L stainless steel was achieved through addition of 1 and 3 wt% TiC nanoparticles. The TiC nanoparticles and 316L powders were mixed using low energy ball milling and ...then processed by selective laser melting. The grains are significantly refined from 16.8 μm to 6.9 μm with the addition of 3 wt% TiC nanoparticles. Addition of 1 and 3 wt% TiC nanoparticles remarkably increased yield strength (694 MPa and 773 MPa) and ultimate tensile strength (888 MPa and 988 MPa). Meanwhile, the tensile elongation was kept at a high level (47% and 32%). The strength enhancement primarily results from Orowan strengthening by the nanoparticles, and the reduction of ductility is related to the suppression of twinning induced plasticity.
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