Behavior Of 316L Stainless Steel Research Articles

Indigenous Production of Porous 316L through Powder Metallurgy and Investigation of their Mechanical Properties

Nowadays, 316L stainless steel implant materials exhibit a promising position in the field of biomaterials application, especially in medical due to their higher strength compared to other ceramic base materials. Therefore, in this work, the production of 316L implant materials and examination of the mechanical characteristics were carried out. Powder Metallurgy process has been chosen to produce the implant materials due to its high advantages in demonstrating the high mechanical properties of the green sample. 316L stainless steel with zinc streate powder of three different compositions, i.e., the first of 99% 316L stainless steel and 1% zinc stearate, the second of 97% 316L stainless steel and 3% zinc streate, and the third of 95% 316L stainless steel and 5% zinc streate, were cold pressed individually at 600 MPa pressure using UTM and sintered the green samples at 1120 °C for 1 hour and 30 minutes. Sintering temperature and time were the same for all the specimens. We investigated the mechanical behaviour of 316L stainless steel implant materials of different compositions at the same temperature for the same duration of time. After that, the mechanical properties and densification of this material were investigated.

Effect of laser‐scan strategy on microstructure and fatigue properties of 316L additively manufactured stainless steel

AbstractThe particular roles of grain morphology and defects, controlled using laser‐scan strategies, on the mechanical properties and the fatigue behavior of 316L stainless steel are investigated. Microstructural characterization and X‐ray tomography analysis was performed to understand the genesis of polycrystalline microstructure and defects. Tensile and fatigue tests were performed to analyze the effect of defect population and microstructural properties on plasticity and damage mechanisms during monotonic and cyclic loading. The effect of the grain‐size and shape and type of defect was carefully investigated to evaluate the mechanisms driving the mechanical behavior under quasi‐static and fatigue loading. It is shown that the laser‐scan strategy determines the anisotropy in the plane perpendicular to the building direction. Moreover, contrary to the existing literature, for 316L obtained by AM, the grain size and shape does not affect the mechanical properties, and LoF defects drive the fatigue life, independent of the defect/grain size ratio.

Improvement on surface quality of 316L stainless steel fabricated by laser powder bed fusion via electrochemical polishing in NaNO3 solution

Poor surface quality necessitates polishing of the parts manufactured by laser powder bed fusion (LPBF) to meet the requirements of use and service. Electrochemical polishing is one of the effective post-treatment methods to reduce the surface roughness. In this manuscript, polishing behavior of 316L stainless steel fabricated by LPBF in the eco-friendly NaNO3 solution was investigated. Different electrochemical tests including current efficiency, open circuit potential, and polarization behavior were carried out in this solution to investigate the influence of section orientation on the electrochemical polishing behavior. Test results indicated that electrochemical dissolution of the transverse section is more difficult than the longitudinal section because of the near-equiaxed dendrites and smaller grains diameter. The electrochemical polishing experiments showed that the polished surface presents hollowed-out retiform structure which is not conducive for the reduction of surface roughness value at low current density and the roughness value significantly decreases with the increase of total quantity of electricity at high current density. The weight loss of the transverse section is smaller than that of the longitudinal section at all current densities and electric charges, but the difference decreased with increasing current density. The electrochemical polishing at the current density of 40 A·cm−2 resulted in maximum reduction of the surface roughness with minimum weight loss. Finally, interior surfaces with longitudinal section and transverse section were polished successfully. The roughness values decreased from 17.3 and 18.3 μm to 2.4 and 2.6 μm, respectively.

Accelerated deterioration mechanism of 316L stainless steel in NaCl solution under the intermittent tribocorrosion process

In this research, the tribocorrosion behavior of 316L stainless steel in simulated seawater was investigated under continuous and intermittent sliding at open circuit potential. The tribocorrosion mechanism was discussed in terms of wear morphologies, mechanical property as well as chemical composition. Meanwhile, microstructure evolution inside the wear track and open circuit potential recorded after sliding were analyzed to quantify the repassivation kinetics and evaluate the impact of the regenerated passive film on wear. The results showed that the wear rate increased under intermittent sliding when the pause time is long enough to repassivate after sliding. Repeated sliding promoted the refinement of the grain inside the sliding area, which was beneficial to the generation of the thicker and more compact passive film inside the wear track. The ruptured passive film often acted as abrasives during subsequent sliding. Therefore, the accelerated material loss under intermittent sliding was attributed to the periodic mechanical removal of the thickened passive film and the enhanced abrasive wear inside the wear track.

Formation mechanism of MnS inclusion during heat treatments and its influence on the pitting behavior of 316L stainless steel fabricated by laser powder bed fusion

The formation mechanism of MnS inclusions during heat treatment and its effect on the pitting behavior of laser powder bed fusion (L-PBF)-fabricated 316L stainless steel (SS) were investigated. MnS inclusions precipitated at the grain boundaries of the samples, and the spherical oxide particles can become nucleation sites. The quantity and size of the MnS inclusions increased with prolonged heating. Compared with the as-received sample, the pitting of heat-treated L-PBF-fabricated 316L SS samples was mainly induced by the newly generated MnS inclusions rather than the fabricated gas pores and extended along the grain boundaries; this caused the dramatic pitting resistance deterioration.

The Influence of Intralayer Porosity and Phase Transition on Corrosion Fatigue of Additively Manufactured 316L Stainless Steel Obtained by Direct Energy Deposition Process.

A direct energy deposition (DED) process using wires is considered an additive manufacturing technology that can produce large components at an affordable cost. However, the high deposition rate of the DED process is usually accompanied by poor surface quality and inherent printing defects. These imperfections can have a detrimental effect on fatigue endurance and corrosion fatigue resistance. The aim of this study was to evaluate the critical effect of phase transition and printing defects on the corrosion fatigue behavior of 316L stainless steel produced by a wire laser additive manufacturing (WLAM) process. For comparison, a standard AISI 316L stainless steel with a regular austenitic microstructure was studied as a counterpart alloy. The structural assessment of printing defects was performed using a three-dimensional non-destructive method in the form of X-ray microtomography (CT) analysis. The microstructure was evaluated by optical and scanning electron microscopy, while general electrochemical characteristics and corrosion performance were assessed by cyclic potentiodynamic polarization (CCP) analysis and immersion tests. The fatigue endurance in air and in a simulated corrosive environment was examined using a rotating fatigue setup. The obtained results clearly demonstrate the inferior corrosion fatigue endurance of the 316L alloy produced by the WLAM process compared to its AISI counterpart alloy. This was mainly related to the drawbacks of WLAM alloys in terms of having a duplex microstructure (austenitic matrix and secondary delta-ferrite phase), reduced passivity, and a significantly increased amount of intralayer porosity that acts as a stress intensifier of fatigue cracking.

Strain-Controlled Fatigue Behavior and Microevolution of 316L Stainless Steel under Cyclic Shear Path.

Based on the twin bridge shear specimen, the cyclic shear experiments were performed on 1.2 mm thin plates of 316L metastable austenitic stainless steel with different strain amplitudes from 1 to 5% at ambient temperature. The fatigue behavior of 316L stainless steel under the cyclic shear path was studied, and the microscopic evolution of the material was analyzed. The results show that the cyclic stress response of 316L stainless steel exhibited cyclic hardening, saturation and cyclic softening, and the fatigue life is negatively correlated with the strain amplitude. The microstructure was analyzed by using electron back-scattered diffraction (EBSD). It was found that grain refinement and martensitic transformation during the deformation process led to rapid crack expansion and reduced the fatigue life of 316L.

The corrosion behavior of 316L stainless steel in an Fe(II)EDTA-based liquid-phase denitrification system

The corrosion behavior of 316L stainless steel in an Fe(II)EDTA-based liquid-phase denitrification system

Investigation of the Crevice Corrosion Behavior of 316L Stainless Steel in Sulfate-Reducing Bacteria-Inoculated Artificial Seawater Using the Wire Beam Electrode

Investigation of the Crevice Corrosion Behavior of 316L Stainless Steel in Sulfate-Reducing Bacteria-Inoculated Artificial Seawater Using the Wire Beam Electrode

Tailored deformation behavior of 304L stainless steel through control of the crystallographic texture with laser-powder bed fusion

Laser-powder bed fusion (L-PBF) has gained significant research interest, not only for its profound advantage of producing near-net shape complex geometries of metallic parts, but also for the possibility of producing tailored microstructures. Here we exploit the capability of manipulating the crystallographic texture by L-PBF to tailor the deformation behavior of austenitic stainless steels. In specific, by adjusting the laser power and the laser scanning speed, tailored crystallographic textures can be obtained, along the uniaxial loading direction in 304L stainless steel samples produced by L-PBF. In situ neutron diffraction and uniaxial tension and compression tests are undertaken to investigate the extent of the transformation induced plasticity effect and to correlate it with the tailored macrostructures. The influence of the initial and the evolving crystallographic texture on the deformation behavior is demonstrated and elaborated accordingly. The observed asymmetry in the deformation behavior between tension and compression is also discussed in detail.

Tribological behavior investigation of 316L stainless steel samples processed by selective laser melting

Selective Laser Melting (SLM) is a widely used process-based on melting powder material through a high laser beam. Process parameters significantly influence the microstructure, surface texture, and mechanical properties of materials in SLM. In this experimental investigation, we have used SLM core parameters, including scan speed, layer thickness, hatch spacing, and laser power, to observe their influence on the tribological behavior of 316L Stainless Steel (SS) samples. Samples were fabricated using SLM, and the wear test was performed according to the ASTM G-99 test standard on a dry sliding wear testing machine, keeping the process parameters (load, speed, wear track diameter, and time) constant for all samples. The Scanning Electron Microscopic (SEM) analysis showed columnar and cellular microstructure of the samples before the wear. In contrast, shallow plowing grooves, delamination marks, and cracks were observed in worn-out samples caused due to formation of abrasive and adhesive wear. Taguchi's statistical design of experiment was used to optimize the selected parameters for response variables like density and specific wear rate. From the Taguchi analysis the high density and minimum specific wear rate values were achieved at a scan speed of 900 mm/s, a laser power of 300 W, and a hatch spacing of 90 µm.The validation of obtained parameters has been done through Analysis of variance (ANOVA) to develop a linear correlation between the chosen parameters.

Pitting behavior of 316L stainless steel in direct culture with mesenchymal stem cells

Corrosion is one of the dominating reasons for failure of metallic implants. The corrosion behavior of the 316 L stainless steels (316 L SS) in direct culture with bone marrow derived mesenchymal stem cells (BMSCs) was studied via electrochemical measurements. The adhesion, proliferation and apoptosis of BMSCs could be detected by electrochemical impedance spectroscopy (EIS). The presence of BMSCs could decline the stability of the passive films and lower the pitting potential of the 316 L SS. The pitting corrosion preferentially initiated at the peripheries of the BMSCs, which was driven by surface overpotential potential generated from the negative transmembrane potential.

The influence of heat treatment on the microstructure and corrosion behavior of selective laser melted 316L stainless steel in Ringer’s solution

The aim of this study is to investigate the effect of heat treatment on the microstructure and corrosion behavior of 316L stainless steel (SS) in Ringer’s solution. The corrosion performance of the as-received, heat-treated at 450 °C (HT1), and 1050 °C (HT2) SS alloys manufactured by selective laser melting was evaluated. The heat treatment at 450 °C and 1050 °C relieved about 38% and 62% of the compressive residual stress derived from the selective laser melting (SLM) process, respectively. The charge transfer resistance of the as-received, HT1, and HT2 was 102, 140, and 12 kΩ cm2 in the Ringer’s solution, respectively. This severe reduction in corrosion resistance for the HT2 sample can be attributed to the high possibility of harmful phases such as MnS forming during heat treatment and possibly depletion of chromium content in the inclusions compared to the alloy matrix.

The Corrosion Susceptibility of 304L Stainless Steel Exposed to Crevice Environments.

The present study focuses on the corrosion behavior of 304L stainless steel in crevice corrosion environments. The specimen with a salt deposit of 0.1 g/m2 was assembled with a crevice former made of Poly-tetra fluoroethylene (PTFE) to make a test device. The assembled test devices were kept at the ambient temperature of 45 °C in combination with a relative humidity of 45%, 55%, and 70%. After testing for 5000 h, the corroded area of the specimen exposed to 70% humidity was three times larger than that subjected to 45% humidity. For the specimen sustaining a tensile force, the crack growth rate was approximately 1.4 mm/year at the stress level of 300 MPa in a crevice corrosion environment with 0.1 g/m2 of sea salt deposited on the surface. The small portion of intergranular cracking occurred at the surface due to the existed strain on the surface. As cracks propagate in a grain, the grain undergoes a greater localized deformation, and some secondary cracks would develop inside the grain; transgranular cracking was vigorous due to the path corrosion that nucleated at the slip steps.

Desulfurization behavior of Si-killed 316L stainless steel melt by CaO-SiO2-CaF2-Al2O3-MgO slag

The desulfurization behavior of 316L stainless steel (STS316L) melt with the CaO-SiO2-CaF2-Al2O3-MgO slag was investigated with different CaO/SiO2 (=C/S) ratio and CaF2 content at 1873 K. As the C/S ratio increased, the sulfide capacity increased, whereas the sulfide capacity of the high C/S (=1.7) slag was not affected by CaF2 content. The overall mass transfer coefficient (kO) increased with C/S ratio, but was constant above a critical C/S value, and it was also constant across varied CaF2 content at relatively high C/S (=1.7) condition. Since the metal condition of the present study was constant, the change in kO was caused by slag phase mass transfer coefficient (ks) and sulfur distribution ratio (LS), which were affected by the physicochemical properties of the slag. Since desulfurization reaction requires consideration of both kinetic and thermodynamic factors, the ‘logCS2−−logη’ (where CS2− is sulfide capacity and η is viscosity), was proposed as a meaningful physicochemical parameter. If the slag basicity is relatively high, at which the kO is equivalent regardless of slag compositions, the desulfurization reaction is controlled by metal phase mass transfer. However, if the slag basicity becomes lower, at which the kO significantly decreases, the desulfurization reaction is assumed to be controlled by slag phase mass transfer and/or mixed controlled process.

Behavior of 316L Stainless Steel Under Static and Dynamic Loading Conditions

In the present study, 316L stainless steel was characterized for microstructure and mechanical behavior under static and dynamic loading conditions. It showed a high ratio of tensile strength to yield strength with good ductility. Experiments on strain controlled tests, performed at 0.25 Hz frequency, resulted in reduction of fatigue life with increasing total strain amplitude. At higher strain amplitudes, secondary cyclic hardening was noticed. In contrast, cyclic hardening was observed for initial few cycles followed by softening up to failure at lower strain amplitudes.

Numerical simulation of thermal stress and life assessment of a thin double-layer metal hydride bed under combined thermal and mechanical loads

In this work, the finite element model of the hydrogen absorption process in the thin double-layered metal hydride bed (MHB) has been established. The Johnson–Cook constitutive model, considering the temperature softening and strain rate hardening effect, was used to simulate the mechanical behavior of 316L stainless steel during the hydrogen absorption and desorption processes. The simulation results agree well with the experimental results, which verifies the effectiveness of the numerical model. The equivalent stress distribution of the stainless steel bed in the process of hydrogen absorption and desorption has been calculated by the aforementioned model. The influence of the defect depth and opening angle on tank safety has been calculated and analyzed considering the possible defects in the welding process and service life. Finally, according to the American Society of Mechanical Engineers boiler and pressure vessel code criterion, the fatigue–creep interaction condition of the MHB was predicted and analyzed. This work can provide an effective reference for the design of a hydrogen storage bed.

Correlation between microstructure and cyclic behavior of 316L stainless steel obtained by Laser Powder Bed Fusion

AbstractIn this work, stainless steel 316L obtained by Laser Powder Bed Fusion (L‐PBF) has been produced and characterized. The experimental campaign focuses on the samples in the as‐built state under cyclic tension‐compression loadings. Low cycle fatigue (LCF) and high cycle fatigue (HCF) tests are carried out. Microstructure observations are performed before and after the loadings. As‐built L‐PBF 316L has a good LCF performance despite the presence of surface defects but a low fatigue limit in the HCF regime. Removing the surface roughness has a beneficial effect but does not improve the fatigue strength to that of machined wrought 316L. Observations on the microstructure of fatigue samples indicate that LCF is dominated by the local plastic deformation, which is mostly achieved by the slip in the studied material and is not sensitive to the defect. The lack‐of‐fusion defect impairs the fatigue resistance in the HCF regime.

Effect of Laser Speed and Hatch Spacing on the Corrosion Behavior of 316L Stainless Steel Produced by Selective Laser Melting.

In this work, the corrosion properties of 316L stainless steel (SS) obtained by selective laser melting (SLM) are analyzed. The electrochemical results of samples manufactured with an energy density between 40 and 140 J/mm3 are compared using different hatch distances and laser speeds. The analysis correlates the impact of the microstructure and processing defects of SLM 316L stainless steel on its behavior against corrosion. The optimal manufacturing conditions were selected considering the electrochemical results. Although the samples obtained with an energy density close to 90 J/mm3 show a high resistance to corrosion, their performance depends on the combination of selected parameters, obtaining the best results for an intermediate laser speed and a low hatch distance. These manufacturing conditions produce a higher breakdown potential, a faster repassivation of the steel and reduce the current density on electrochemical test.

Influence of H2S on the Cyclic Polarization Behavior of 316L Stainless Steel in Oilfield Brines

Cyclic polarization measurements were conducted for 316L stainless steel (SS) in a simulated oilfield brine under conditions close to the pass/fail boundary for pitting and stress corrosion cracking of the material but at different partial pressures of H2S, balanced with CO2 to a consistent total pressure. The potential was scanned until a defined anodic current density was achieved, and then reversed to yield insight with respect to the repassivation behavior. The forward scans in many cases showed unexpected additional waves that could not be explained based on complementary studies of H2S oxidation. The electrochemical measurements at varying H2S partial pressure were inconsistent with corrosion coupon testing. These results demonstrate that the use of electrochemical measurements to rank the aggressivity of different sour environments for the purposes of materials selection should be treated with caution.