Behavior Of Austenitic Stainless Steel Research Articles

Corrosion behavior of austenitic stainless steel and nickel-based welded joints in underwater wet welding

Marine structures such as ports, bridges, pipelines, vessels, and platforms are an essential part of modern infrastructure, where the use of higher-strength steel provides savings in logistics and construction. However, the repair of higher-strength steels can be challenging, especially underwater. Wet shielded metal arc welding is the most widely used and least expensive method for underwater welding repairs, but is very susceptible to hydrogen-induced cracking. Thus, researchers and welding engineers aim to reduce the amount of hydrogen in the weld material. Recent success has been achieved through the use of austenitic welding consumables, such as austenitic stainless steel and nickel-based electrodes. The use of these consumables drastically reduces the amount of diffusible hydrogen in the weld metal. However, these austenitic materials usually have different corrosion potential as compared to the structural steel the weld beads are applied to. This creates the risk of severe galvanic corrosion. In the presented study, the corrosion behavior of welds created with austenitic stainless steel and nickel-based electrodes were studied. Samples were aged for 1.5 years in the Baltic Sea. Simultaneously, the effectiveness of corrosion protection systems such as coating and Impressed Current Cathodic Protection (ICCP) were evaluated. Localized corrosion occurred in the heat-affected zone when austenitic electrodes were used in the corrosive environment. The localized corrosion depth after 1.5 years in the Baltic Sea and in the salt spray layer was approximately 250 µm and 390 µm, respectively. The ICCP system and the use of a coating were effective in preventing localized corrosion. The low pitting corrosion density of 2.5 × 103 m−2 corresponds to grade A1 according to the standard and was found to be negligible as compared to the localized corrosion in the heat-affect zone.

Comparison of conventional and severe shot peening effects on the microstructure, texture, roughness, hardness, and electrochemical behavior of austenitic stainless steel

In the present research, microstructure, texture, roughness, hardness, and electrochemical behavior of AISI 316L austenitic stainless steel before and after shot peening were studied to elucidate the effect of conventional and severe shot peening (CSP and SSP) processes. After the shot peening, the fraction of strain-induced martensite (SIM) and mechanical twins (MTs) in the sub-surface layer was increased. The fraction of SIM and MTs in the SSP sample was higher than in the CSP sample. The XRD patterns indicated that the SSP sample had a higher peak broadening compared to the CSP sample. In the CSP and SSP samples, a gradient microstructure was formed along the depth direction. The microstructure of the topmost layer of the CSP and SSP samples exhibited numerous ultrafine grains. The grain refining during severe shot peening was faster because of the accumulation of more strain. The CSP and SSP samples revealed a gradient distribution of elements. After the SSP, the intensity of ⟨110⟩‖ED fiber texture decreased from 12.7 to 11.6 × R and the average intensity of ⟨100⟩‖ED fiber texture increased from 1.7 to 2.0 × R, respectively, compared to the CSP sample. The surface roughness of the SSP sample (Rq = 73.6 nm and Ra = 45.2 nm) was lower than that of the CSP sample which represented the roughness decreased with surface coverage increasing from 100 % to 1500 %. Also, the wettability increased after the conventional and severe shot peening processes. In addition, the microhardness of the CSP and SSP samples showed a gradient distribution. The CSP sample had the lowest corrosion current density (0.13 μA/cm2) whereas the NP (non-peened) sample exhibited the highest current density (0.65 μA/cm2). The presence of ⟨100⟩-oriented grains in both CSP and SSP samples led to the higher corrosion resistance of shot-peened steels compared to the NP sample. The presence of favorable texture with higher intensity in the CSP sample was responsible for the higher corrosion resistance of the CSP sample compared to the SSP sample. Finally, the gradient distribution of elements along the depth direction in the CSP and SSP steels improved the corrosion resistance of the surface.

High-temperature corrosion and carburization behaviour of austenitic stainless steels in impurity-added CO2 environments

The corrosion and carburization behaviour of four austenitic stainless steels were evaluated in CO2 and CO2+impurities (CH4, CO and O2) at 600 °C. Exposure to CO2, CO2+CH4, and CO2+CO environments showed poor corrosion resistance, especially in 316 grades with the spallation of Cr2O3 layer and breakaway corrosion. Conversely, materials showed improved corrosion resistance in CO2+O2 environment with thin Cr2O3 layer. TEM analysis of 316LN revealed carbon-accumulated layer at the Cr2O3–matrix interface for highly corrosive environments. The degradation of Cr2O3 adherency is correlated with the carbon-accumulated layer, resulting from the high carbon activity in CO2, CO2+CH4, and CO2+CO environments.

Anomalous oxidation rate-temperature dependence of alumina-forming austenitic stainless steels exposed to 500–600 °C supercritical water

The oxidation behavior of austenitic stainless steels with 0 and 2.5 wt% Al exposed to 500–600 °C supercritical water was studied. The oxidation rate-temperature dependence of base steel (0 wt% Al) followed the conventional Arrhenius law, while the alumina-forming austenitic stainless steel (AFA steel, 2.5 wt% Al) exhibited an anomalous oxidation rate-temperature dependence, which is attributed to the special phase transition and oxidation behavior of B2-NiAl precipitates in the AFA steel.

The effect of long-term exposure in mixed sulfuric acid and copper sulfate solution on corrosion behavior of austenitic stainless steels

Corrosion resistance of austenitic stainless steels in sulfuric acid solutions depends mainly on concentration and temperature of the sulfuric acid, the presence of contaminants and velocity flow. Current studies aim mostly at evaluation of electrochemical parameters in sulfuric acid solutions. Research focused on long-term exposure is lacking. This article deals with the corrosion behavior of AISI 304 and AISI 316L stainless steels in mixed 10 wt. % sulfuric acid and 10 wt. % copper sulfate solution. Sensitized (650 °C/40 hours) and solution annealed (1050 °C/15 min) specimens together with the untreated (as received) ones are evaluated by long-term (22-month) exposure immersion test at the temperature of 22 ± 3 °C on the bases of optical microscopy, SEM and mass losses. Both tested stainless steels in as received and solution annealed state proved high corrosion resistance in the given corrosive environment. The cross-sections edges of sensitized specimens revealed a close relationship between local corrosion sites and weakened grain boundaries, which indicates incipient intergranular corrosion.

A critical review on deformation-induced transformation kinetics of austenitic stainless steels

Deformation-induced austenite to martensite transformation is an important phenomenon during the deformation of metastable fully austenitic transformation induced plasticity (TRIP) steels. The kinetics of austenite to martensite transformation influence the deformation behaviour of austenitic stainless steels but is often neglected by the materials community. In this paper, after an initial discussion on thermodynamics and mechanism, the importance of deformation-induced transformation kinetics is briefly outlined and the influence of various parameters like grain size, deformation temperature, strain rate, stress state and prior austenite deformation on the transformation kinetics is critically assessed. Variation of transformation kinetics with various parameters has been identified and justified. These variations could act as a ready reference for designing austenitic stainless steels with the desired set of mechanical properties and deformation behaviour. Further in this paper, selected models that can predict the transformation kinetics are reviewed and compared. In the end, research fronts related to transformation kinetics that can be further explored have been identified.

Test on seismic behaviors of stainless steel bolted extended end-plate beam-column joints

This study conducted tests on the seismic behavior of austenitic stainless steel bolted extended end-plate beam-column joints, which have been few reported. Considering the influence of material type, end-plate thickness, bolt diameter, panel zone thickness, and loading scheme, 11 stainless steel joints and two carbon steel joints were designed and tested. Material properties, joint failure modes, moment-rotation curves, bolt load distributions, and joint component yield sequences were reported in detail. Experimental research showed that the beam-column joints in austenitic stainless steel experienced four failure modes, i.e. plastic hinge at the beam end, fracture failure of weld between the beam flange and end-plate, bolt rupture failure, and composite failure. All the tested joints had good seismic behavior, with rotation capacity greater than 0.03 rad. The influence of joint configurations on the seismic behavior were analyzed. The results indicated that the end-plate thickness, end-plate stiffener, and bolt diameter had a substantial impact on the joint seismic behavior, while the thickness of column web in panel zone, material properties, and loading scheme had a comparatively small effect. The initial rotational stiffness and moment resistance(yield moment) of joint obtained from the experiment were compared with the predictions of the EN1993-1-8, Design Guide 16, and JGJ 82-2011. Comparisons indicated that the EN1993-1-8 overestimated the initial rotational stiffness; Both the EN1993-1-8 and JGJ 82-2011 underestimated the moment resistance, while the predictions from the Design Guide 16 were significantly higher than the moment resistance and closer to the ultimate moment.

Mechanical behavior of austenitic stainless steels produced by wire arc additive manufacturing

Wire arc additive manufacturing (WAAM) is an innovative technology with the potential to drive the transformation and upgrading of metallic manufacturing industry and construction sector. The advantages of WAAM technology in rapid manufacturing, design freedom, and energy saving have attracted attentions in the construction field. This research study focuses on investigating the microstructural and mechanical behavior of austenitic stainless steels produced by wire arc additive manufacturing through test programs. The stainless steel plates were first additively manufactured using cold metal transfer technology with three types of feedstock wires (ER304, ER308L, ER316L). Tensile coupon specimens and microstructural observation samples were extracted from the WAAM plates. The electron backscatter diffraction (EBSD) experiments were conducted to identify and analyze the microstructures of the WAAM austenitic stainless steels. Five test orientations, namely θ = 0˚, 30˚, 45˚, 60˚, 90˚ relative to the printing layer direction, were designed to investigate the mechanical properties anisotropy. Two types of specimen surface condition (milled type and as-built type) were considered to assess the impact of geometric undulation. The geometric features of the as-built specimens were obtained using 3D laser scanning. A total of 60 tensile tests with the aid of digital image correlation (DIC) system were conducted to obtain the stress–strain responses of the WAAM austenitic stainless steels. The mechanical properties anisotropy of the WAAM austenitic stainless steels was analyzed in detail.

Block shear failure of austenitic stainless steel bolted connections

Austenitic stainless steel possesses very high ductility and ultimate-to-yield strength ratio, which could possibly affect the block shear failure mechanism and the corresponding ultimate capacity of bolted connections made of this material. In response to this concern, a comprehensive experimental and numerical study on the block shear behaviour of austenitic stainless steel bolted connections (ASSBCs) is conducted and reported in this paper. Based on the results of 15 experimental tests, it is found that the governing block shear mechanism of ASSBCs (for 14 out of the 15 tests) at the ultimate load corresponds to cracking of the shear sections prior to fracture of the tensile sections. This differs significantly from the conventionally accepted block shear mechanism of mild steel bolted connections, which is net section fracture of the tension area and yielding of the shear area. This observation was further confirmed by a numerical study based on validated finite element models, where three block shear mechanisms were identified for ASSBCs. A thorough parametric study was then carried out to clarify the effects of key design parameters on the block shear behaviour of ASSBCs. Finally, the experimental and numerical results are used to evaluate the applicability of existing design equations to predicting the block shear capacity of ASSBCs. An improved block shear equation is subsequently proposed based on the available data.

Experimental investigation on mechanical behaviour of austenitic stainless steel fabricated through wire arc additive manufacturing

Fabrication of intricate and customized components using wire arc additive manufacturing (WAAM) is a promising technique with wide-ranging applications in sectors including but not limited to automotive, aerospace, and marine. This article focuses on the mechanical behaviour of austenitic stainless steel (SS316LSi) -fabricated WAAM components. Tensile and hardness tests were used to examine the mechanical behaviour of the WAAM-fabricated structure in the top, bottom, and center zones. The results show that the mechanical behaviour of WAAM fabricated structure falls in the range of wrought SS316L. The average tensile strength parameter values of ultimate tensile strength, yield strength and elongation percentage estimated in the deposited structure are 538.06 MPa, 236.33 MPa, and 43.3%, respectively. Microhardness values at the bottom, top, and middle regions, are 182.52 HV, 179.36 HV and 174.75 HV respectively. Results reveal no disbonding between layers, reasonable ductility and stable fusion in the fabricated structure. Reduced manufacturing times and expenses are anticipated by manufacturing parts via the WAAM route, which will aid the industrial applicability of this process towards global technical competence.

Grain size effect on near-threshold fatigue crack propagation in CrMnFeCoNi high-entropy alloy fabricated by spark plasma sintering

High-entropy alloys (HEAs), which comprise five or more elements and have an equiatomic composition, are known to exhibit superior static strength and ductility. The present study evaluated the effect of grain size on fatigue crack propagation in a CrMnFeCoNi alloy comprising a single-phase solid solution with a face-centered-cubic structure and fabricated by spark plasma sintering. Stress intensity factor-K decreasing tests were conducted with force ratios from 0.1 to 0.8, and no noticeable differences in fatigue threshold were observed between specimens having fine-grained and coarse-grained structures at relatively low force ratios. This result was attributed to fatigue crack reflection inside coarse grains. The magnitude of crack closure was high even in the fine-grained specimens and exceeded that of austenitic stainless steel having the same fine grains. Thus, the effect of grain size on the threshold stress intensity factor range was not significant in the present CrMnFeCoNi alloy, in contrast to the behavior of austenitic stainless steels.

Effect of Stacking Fault Energy on Cryo Deformation Behavior of Austenitic Stainless Steels

Effect of Stacking Fault Energy on Cryo Deformation Behavior of Austenitic Stainless Steels

Comparison of Metastable Pitting Behavior of Austenitic and Duplex Stainless Steels under U‐Bending Deformation

The metastable pitting behavior of austenitic stainless steel (304 SS) and duplex stainless steel (2205 DSS) under U‐bending deformation is comparatively investigated. This study highlights the effects of differences in inclusions and matrix between 304 SS and 2205 DSS with regard to the metastable pitting behavior under tensile and compressive deformation. The results show that the pit initiation frequency of 304 SS increases in the order: tensile < as‐received < compressive; in contrast, the initiation frequency of 2205 DSS increases in the order: as‐received < tensile < compressive. In addition, tensile and compressive deformation change the preferential initiation sites of metastable pitting in 2205 DSS. It is proposed that the types of transient signals can be comprehensively and objectively distinguished by the two parameters (t g/t rep) and [(I p/Q g):(I p/Q rep)]. The correlation relationship between transient signals and pitting morphologies is clarified by cluster analysis. Both tensile and compressive deformations promote the growth of a few metastable pits, thus increasing the transition probability from metastability to stability. Overall, both tensile and compressive deformations are detrimental to the pitting corrosion resistance of the experimental steels.

Very High Cycle Fatigue Behavior of Austenitic Stainless Steel in Annealed and Predeformed Condition

Abstract Engineering components in service nowadays are designed for a large number of loading cycles (∼109), which makes fatigue behavior in this cycle range (designated as very high cycle fatigue [VHCF]) a topic of significant interest. The present study aims to investigate the high cycle fatigue (HCF) and VHCF behavior in type 304 stainless steel in two different conditions (annealed and with a martensite volume fraction of ∼45 %) through low cycle fatigue predeformation at a subzero temperature. A fatigue diagram in the form of an S–N curve extending up to the VHCF range is generated, which shows different HCF and VHCF behaviors for the annealed and predeformed conditions. Further tests are carried out at different R ratios to generate constant-life Haigh diagrams for both conditions. Although no failure is observed in the VHCF range under the annealed condition, an internal crack initiation mode is observed under the predeformed condition (Type II behavior), which is attributed to the enhanced notch sensitivity under VHCF cycling induced by a significant extent of strain-induced martensite formed during predeformation. To address the influence of varying load history under service, specimens were prefatigued in HCF, followed by VHCF cycling. The HCF–VHCF boundary is found to be significantly impacted by the prior HCF damage, with lowering of the fatigue limit under VHCF.

Review of Creep-Thermomechanical Fatigue Behavior of Austenitic Stainless Steel

Research on the creep-thermomechanical fatigue (CTMF) behaviors of austenitic stainless steel for nuclear power plant pipelines is reviewed in the present paper. The stress response behavior, the main damage mechanisms, including thermomechanical fatigue, creep, oxidation, and dynamic strain aging (DSA), as well as the effects of strain dwell type, dwell time, and temperature-strain phase angle on fatigue life behavior of austenitic stainless steel under CTMF loading conditions are systematically discussed, and the coupled effects of various damage mechanisms are revealed. It is emphasized that CTMF is closer to the actual service condition of nuclear power plant pipes. It is pointed out that the traditional method of life design based on the isothermal fatigue test data is not conservative. Finally, the research on CTMF behaviors of austenitic stainless steel for nuclear power plant is summarized and prospected.

Effect of TiN inclusions on oxidation behavior of austenitic stainless steels

The effects of TiN inclusions on the oxidation behavior of modified stainless steels have been investigated systematically in this study. It was found that the oxidation rate of steel with TiN stringers is almost seven times faster than the clean one during the homogenized treatment. In the oxidation layers, the TiN stringers induce the spall fracture and facilitate the air permeation. At the oxidation interface, the TiN inclusions act as the nucleation sites for the oxides and promote the internal oxidation. The air permeation and internal oxidation causes the severe oxidation of modified austenitic stainless steels.

Experimental Analysis and Constitutive Modeling of Cyclic Behavior of 304 L Stainless Steel: Introduction of Isotropic Hardening Fading Effect

Abstract In this study, the mechanical behavior of austenitic stainless steel 304 L under low cycle fatigue was investigated under different uni-axial strain-controlled loadings of 0.5%, 0.8%, 1.0%, 1.2%, and 1.5%. The analysis of the experimentally determined strain versus stress hysteresis curves was carried out to achieve stress quantities such as amplitude stress, peak effective stress, and peak back stress. It was observed that in the early stage of cyclic loading, material underwent initial hardening, followed by softening phenomena which were more considerable in the lower strain range. Before the failure, the secondary hardening was observed at the final stage. In addition to accumulated plastic strain, it was shown that the peak back stress and peak effective stress which is associated with isotropic hardening and kinematic hardening behavior, respectively, are influenced by the strain range effect. Therefore, the coefficient of recall term that appeared in the Armstrong–Frederick nonlinear kinematic hardening model was considered to be dependent on the radius of the memory surface. Furthermore, to increase the ability of the plasticity constitutive model to show a smooth transition between various hardening stages, the radius of the yield surface which is associated with the isotropic hardening rule was equipped with the fading effect. Finally, by the comparison of numerical and experimental results, the capability of the rate-dependent constitutive model over classical rate-independent plasticity in the prediction of mechanical behavior of steel 304 L under strain-controlled cyclic loading was revealed.

Very High Cycle Fatigue Behavior of Austenitic Stainless Steels with Different Surface Morphologies

The fatigue behavior of the two austenitic stainless steels AISI 904L and AISI 347 with different surface morphologies, (i) conventionally turned and finally polished, (ii) cryogenic turned using CO2 snow, as well as (iii) cryogenic turned and finally polished, was investigated using an ultrasonic fatigue testing system up to the very high cycle fatigue regime using an ultrasonic fatigue testing system. The AISI 904L is stable against deformation-induced phase formation while the AISI 347 is in the metastable state and shows martensite formation induced by cryogenic turning as well as mechanical loading. For the detailed characterization of the surface morphology, confocal microscopy, scanning electron microscopy, and X-ray diffraction methods were used. The specimens from stable austenite failed in the high cycle fatigue and very high cycle fatigue regime. Opposed to this, the metastable austenite achieved true fatigue limits up to load cycle N = 1 × 109 and failed only in the high cycle fatigue regime. Furthermore, due to surface modification, an increase of fatigue strength of metastable AISI 347 was observed.

Influence of 40% Cold Working and Annealing on Precipitation in AISI 316L Austenitic Stainless Steel.

Intergranular corrosion is one of the most important processes affecting the behaviour of austenitic stainless steels. Factors such as steel chemical composition, the degree of prior deformation and the exposure temperature affect the degree of sensitisation. AISI 316L (0% CW) steel was annealed at 650 °C for 5, 10, 30, 100, 300 and 1000 h to analyse the influence of isothermal annealing on the precipitation of secondary phases. AISI 316L steel after 40% cold working and subsequent annealing at 650 °C for 1, 1.5, 2, 5 and 10 h was investigated. Time–temperature sensitisation (TTS) diagrams were created based on corrosion test (ASTM A 262, practice A) results. In the case of AISI 316L (0% CW), M23C6, chi and sigma phases precipitated at grain boundaries, and the Laves phase was mainly inside of the grains. In the case of AISI 316L (40% CW), sigma, chi, Laves and M23C6 were identified and precipitated mainly along the grain boundaries as well as on the shear bands within different annealing times. It was confirmed that the increase in the annealing time caused an increase in the amounts of secondary phases. Secondary phases in the equilibrium state were calculated using Thermo-Calc software.

High-temperature corrosion behavior of austenitic stainless steel in quaternary nitrate molten salt nanofluids for concentrated solar power

Molten salt nanofluids have become a hot research topic due to its excellent thermal properties and heat transfer performance. However, there is a few research on the effect of nanofluids on the corrosion of metal materials. In order to know the influence of molten salt nanofluids on the corrosion of stainless steel, a low melting point quaternary nitrate was used as the base salt to analyze the corrosion law of nanofluids. By means of weight loss method, two different stainless steels (304, 316L) were put into the molten salt nanofluids with SiO 2 nanoparticles content of 1 wt% to test the corrosion behavior of stainless steel. The results of 500 h corrosion test revealed that the corrosion rate of mixed molten salt on 304 and 316L stainless steel is reduced by the addition of SiO 2 nanoparticles. The corrosion rates of molten salt nanofluids on 304 and 316L stainless steel were 0.0433 mm/y and 0.0233 mm/y, respectively. The surface morphology analysis by SEM, EDS, XRD and XPS test showed that the reticular silica nanostructures corrosion layer was formed on the surface of stainless steel, such structure can inhibit the corrosion of stainless steel. Therefore, molten salt nanofluids have the good compatibility with metal materials, and adding nanoparticles in molten salt can reduce the corrosion on stainless steel. • Investigating the corrosion behavior of stainless steels (304,316L) in the mixed molten salt and its nanofluids. • Confirming the corrosion reduction of stainless steel in the mixed molten salt nanofluids. • Discovering the nanostructure of reticulated SiO 2 in the corrosion layer of stainless steel. • Revealing the corrosion mechanism of stainless steel in the mixed molten salt containing SiO 2 nanoparticles.