Behavior Of Austenitic Stainless Steel Research Articles

Effect of Nitrogen on the Corrosion Behavior of Austenitic Stainless Steel in Chloride Solutions

The effect of partial replacement of nickel with nitrogen on the corrosion resistance of newly designed austenitic stainless steel samples without and with heat treated was investigated in 3.5wt% and 5wt% NaCl solution using open-circuit, potentiodynamic, cyclic anodic polarization and electrochemical impedance spectroscopy techniques. The results showed that, passivation in sample 1 where the highest addition of nickel and low addition of nitrogen is different from that for sample 4 where the nitrogen is greatest and the nickel is reduced almost to the third comparing sample 1. The difference in responses of heat treated samples to localized and general corrosion could be attributed to the difference in their phase compositions. The appearance of ferrite phase for samples (2, 4, 5 and 6) after heat treatment resulted in lowering the general and localized corrosion resistance than as forged samples in contrast with samples 1 and 3, where they still pure austenite. The obtained results are confirmed by surface examination.

The role of grain boundaries in the initial oxidation behavior of austenitic stainless steel containing alloyed Cu at 700 °C for advanced thermal power plant applications

The role of grain boundaries during the early stages of oxidation in austenitic stainless steels containing alloyed Cu was investigated using APT, TEM, EBSD, EPMA, and XRD. The oxidation experiments were performed at 700°C in air with 20% water vapor. Within 4μm from the grain boundaries, the oxide layer exhibits a dual-layer structure consisting of a thin Fe-rich spinel oxide on a protective Cr2O3 oxide. Away from the grain boundaries, non-protective spinel oxide layers are formed as the outer and inner oxide layers. A critical grain size that prevents the formation of fast-growing spinel oxides is discussed.

Evaluating the effects of hydroxyapatite coating on the corrosion behavior of severely deformed 316Ti SS for surgical implants.

The present work investigates the effects of severe plastic deformation by cold rolling on the microstructure, the mechanical properties and the corrosion behavior of austenitic stainless steel (SS) 316Ti. Hydroxyapatite coating (HA) was applied on the deformed material to improve their corrosion resistance. The martensitic transformation due to cold rolling was recorded by X-ray diffraction spectra. The effects of cold rolling on the corrosion behavior were studied using potentiodynamic polarization. The electrochemical tests were carried out in Ringer's solution at 37±1 °C. Cold rolling markedly enhanced the mechanical properties while the electrochemical tests referred to a lower corrosion resistance of the deformed material. The best combination of both high strength and good corrosion resistance was achieved after applying hydroxyapatite coating.

Inhibition effect of butan-1-ol on the corrosion behavior of austenitic stainless steel (Type 304) in dilute sulfuric acid

The electrochemical behavior of austenitic stainless steel (Type 304) in 3M sulfuric acid with 3.5% recrystallized sodium chloride at specific concentrations of butan-1-ol was investigated with the aid of potentiodynamic polarization, open circuit measurement and weight loss technique. Butan-1-ol effectively inhibited the steel corrosion with a maximum inhibition efficiency of 78.7% from weight-loss analysis and 80.9% from potentiodynamic polarization test at highest concentration studied. Adsorption of the compound obeyed the Freundlich isotherm. Thermodynamic calculations reveal physiochemical interactions and spontaneous adsorption mechanism. Surface characterizations showed the absence of corrosion products and topographic modifications of the steel. Statistical analysis depicts the overwhelming influence and statistical significance of inhibitor concentration on the inhibition performance.

Effect of Nitrogen on Stress Corrosion Behavior of Austenitic Stainless Steels Using Electrochemical Noise Technique

Stress corrosion cracking (SCC) studies were conducted on austenitic stainless steels with two different nitrogen contents (0.07 and 0.22 wt.% N) in boiling acidified sodium chloride medium using constant load technique. Progress of SCC was monitored using electrochemical noise (EN) technique to understand the effect of nitrogen addition on SCC initiation and propagation. With increase in nitrogen content, the characteristic frequency of corrosion events, fn increased, whereas the characteristic charge, q decreased simultaneously indicating the increased stability of passive film resulting in higher resistance to SCC.

Effect of Residual Stress on the Corrosion Behavior of Austenitic Stainless Steel

In this paper we demonstrate that the residual stress introduced by several different surface finishes affects the critical current density for passivation and the passive current density in the anodic polarization curve of austenitic stainless steel and that those critical current densities can be reduced by controlling the residual stress by applying a cavitating jet to the backs of specimens. The results show that the current density either increased or decreased depending on the surface finish, and that was decreased by introducing compressive residual stress for all surface finishes.

Effect of Additions of Ru and Pd on the Electrochemical Behaviour of Austenitic Stainless Steel in Organic Acids

Effect of Additions of Ru and Pd on the Electrochemical Behaviour of Austenitic Stainless Steel in Organic Acids

Experimental insight into the cyclic softening/hardening behavior of austenitic stainless steel using ultrasonic higher harmonics

The correlation of cyclic hardening/softening behavior of 304 stainless steel (SS) was investigated using nonlinear ultrasonic wave technique. Results reveal that primary hardening leads to the increase of acoustic nonlinearity, while secondary hardening causes the reverse tendency. This distinct phenomenon is governed by two competitive mechanisms: in the primary-hardening stage, the ascended acoustic nonlinearity is related to the increase of planar dislocation structures. While in the second-hardening stage, the decrease of acoustic nonlinearity is partly caused by the development of cell structures. In addition, the deformation-induced martensitic transformation also contributes to the increase of acoustic nonlinearity under higher stress amplitudes.

Oxidation behavior of austenitic stainless steels as fuel cladding candidate materials for SCWR in superheated steam

Oxidation behavior of austenitic stainless steels as fuel cladding candidate materials for supercritical-water-cooled reactor (SCWR), including three types of 15Cr–20Ni stainless steels (1520 SSs), in the temperature range of 700–780°C superheated steam have been investigated. Effect of temperature, dissolved oxygen (DO), degree of cold work (CW), and machined layer by cold drawing process on the oxidation kinetics assuming power-law kinetics are discussed. Characteristics of oxide layers and its relation to oxidation behaviors are also discussed. The effect of DO on the weight gain behavior in superheated steam at 700°C was minor for all specimens at least up to 200ppb DO. The tube-shaped specimens of 1520 SSs showed very good oxidation resistance at 700–780°C. There was no clear difference in the oxidation kinetics among the three investigated types of 1520 SSs. The machined layer formed at the tube surface has a significant role to mitigate oxidation in superheated steam. A fine-grained microstructure near the surface due to recrystallization by cold drawing process is effective to form the protective Cr2O3 layer. It has been suggested that since Cr diffusion in the outside surface of tubes is accelerated as a result of an increased dislocation density and/or grain refinement by cold drawing, tube specimens show very slow oxidation kinetics. Breakdown of the protective Cr2O3 layer and nodule oxide formation were partly observed on the tube-shaped specimens of 15Cr–20Ni SSs. The reliability of Cr2O3 layer has to be carefully examined to predict the oxidation kinetics after long-term exposure.

The effect of temperature on the SSRT behavior of austenitic stainless steels in SCW

The effects of temperature on the tensile properties and stress corrosion cracking (SCC) susceptibility of austenitic stainless steels AL-6XN, HR3C, and 316Ti in deaerated supercritical water were studied by performing slow-strain-rate tensile (SSRT) tests. The SSRT tests were carried out in deaerated supercritical water at temperatures of 550, 600, and 650°C, a pressure of 25MPa, and a strain rate of 9.26×10−7s−1. The results show that AL-6XN exhibits the highest ultimate tensile strength and yield strength at each temperature, followed by HR3C and then 316Ti. Temperature has a large effect on the tensile properties of each material. The SCC susceptibility of AL-6XN increases with increasing temperature, whereas 316Ti exhibits the opposite trend. The fracture surfaces of all HR3C specimens and the 316Ti specimen tested at 550°C are dominated by an intergranular fracture morphology, showing the high susceptibility of these specimens to SCC. Transgranular fracture was observed for specimens of AL-6XN strained at 600 and 650°C.

Tensile behavior of an austenitic stainless steel subjected to multidirectional forging

The mechanical behavior of a chromium-nickel austenitic stainless steel with submicrocrystalline structures produced by multidirectional forging (MDF) to a total strain of ~ 4 at temperatures of 700 and 600°C was studied. This processing resulted in the formation of uniform ultrafine grained structure with an average crystallite size of 360 and 300 nm, respectively, and high dislocation density. The tensile tests were carried out in a wide temperature range 20-650°C. At ambient temperature, the yield stress (YS) comprised 900 MPa and 730 MPa in the samples subjected to MDF at 600 and 700°C, respectively. It should be noted that this strength was achieved along with elongations of 16% and 22% in the samples subjected to MDF at 600 and 700°C. The YS decreased and elongation-to-failure tends to increase with increasing test temperature and approaching 235 MPa and 51%, respectively, at 650°C. Effect of temperature on mechanical behavior of stainless steel with submicrocrystalline structure is discussed.

Corrosion Behavior of Austenitic Stainless Steel in High Sulphate Content

Austenitic stainless steels especially 316L has been used extensively in many sectors including construction, medical and household appliances due to their highly resistance to corrosion attack, reasonable cost and excel in mechanical properties. However, in corrosive media, 316L are susceptible to localised corrosion attack especially in seawater and high temperature. The corrosiveness of media increased as the anions contents increased. This paper presents the corrosion mechanism of 316L exposed to high concentration of sulphate in the salinity of seawater. The solution (media) was prepared according to the same composition as seawater including pH, salinity and dissolved oxygen. The corrosion mechanism were characterized to breakdown potential (Eb) of 316L which are the potential once reaches a sufficiently positive value and also known as pitting potential. This is the most point where localized corrosion susceptibility to evaluate and considered a potential, which could be an appropriate point according to any given combination of material/ambient/testing methods. The Eb value were identified at 4°C, 20°C, 50°C and 80°C and compared with Eb value of 316L in seawater. The Eb value of 316L in high sulphate are higher compared to seawater in every temperature which elucidate that some anions accelerate corrosion attack whereas some anions such as sulphate behaves as inhibiting effect to 316L.

Corrosion behavior of cold-worked austenitic stainless steels in liquid lead–bismuth eutectic

The effect of cold working on the corrosion behavior of austenitic stainless steels in liquid lead–bismuth eutectic (LBE) was studied to develop accelerator-driven systems for the transmutation of long-lived radioactive wastes and lead–bismuth cooled fast reactors. Corrosion tests on solution-treated, 20% cold-worked and 50% cold-worked 316SS and JPCA (15Cr–15Ni–Ti) were conducted in oxygen-controlled LBE. Slight ferritization caused by Ni dissolution and Pb–Bi penetration were observed for all specimens in the corrosion test conducted at 500°C for 1000h in liquid LBE with an intermediate oxygen concentration (1.4×10−7wt.%). In the corrosion test performed at 550°C for 1000h in liquid LBE with a low oxygen concentration (4.2×10−9wt.%), the depth of the ferritization of 316SS and JPCA increased with the extent of cold working. Only oxidation was observed in the corrosion test that was performed at 550°C for 1000h in liquid LBE with a high oxygen concentration (approximately 10−5wt.%). Cold working accelerated the formation of the double layer oxide and increased the thickness of the oxide layer slightly. In contrast, the ferritization accompanied by Pb–Bi penetration was widely observed with oxidation for all specimens corrosion tested at 550°C for 3000h under the high-oxygen condition. Cold working increased the depth of the ferritization of 316SS and JPCA. It is considered that cold working accelerated the ferritization and Pb–Bi penetration through the enhanced dissolution of Ni into LBE due to an increase in the dislocation density under conditions in which the protective oxide layer was not formed in liquid LBE.

Corrosion behaviour of austenitic stainless steel as a function of methanol concentration for direct methanol fuel cell bipolar plate

The corrosion behaviour of an AISI 304 stainless steel (304 SS) is investigated in aqueous acid methanol solutions (0.5 M H2SO4 + 2 ppm HF + x M CH3OH, x = 0, 1, 5, 10 and 20) at 50 °C to simulate the varied anodic operating conditions of direct methanol fuel cells. Electrochemical measurements including potentiodynamic polarisation, potentiostatic polarisation and electrochemical impedance spectroscopy tests, are employed to analyse the corrosion behaviour. The results reveal that the corrosion resistance of 304 SS is enhanced in solutions with higher methanol content. Scanning electron microscopy and inductively coupled plasma atomic emission spectrometry data indicate that the surface corrosion on 304 SS is alleviated when the methanol concentration is increased. According to the X-ray photoelectron spectroscopy and Mott–Schottky analyses, the passive films formed on the 304 SS after potentiostatic tests in all the test solutions are composed of a duplex electronic structure with an external n-type semiconductor layer and an internal p-type semiconductor layer. Further analyses of the surface conductivity conducted by measuring the interfacial contact resistance between the 304 SS and carbon paper reveal that the passive film formed in the solution with higher methanol content exhibits lower conductivity.

Nitriding Kinetics of Inconel 600

Ni-based alloys are preferred as structural materials over austenitic stainless steels in nitrogen containing atmospheres like in neutron detectors due to severe problem of nitriding of stainless steels and subsequent loss of nitrogen. Extensive work has been carried out in literature on the nitriding behavior of austenitic stainless steels whereas similar information on Ni-based alloys is very few. Hence, to assess the nitriding kinetics of a Ni-based alloy (Inconel 600) nitriding experiments were carried out. Inconel 600 was plasma nitrided at temperatures in the range of 450–600°C for time durations of 1 to 24h. Evolution of the microstructure and kinetics of nitrided layer formation and its growth were investigated using various experimental techniques like electron probe micro-analysis and electron microscopy. Nitriding at a temperature of 600°C for 24h resulted in the formation of a nitrided zone of ~14μm thickness. Inconel 600 was found to get internally nitrided resulting in the formation of nano-meter sized fcc CrN precipitates in Cr depleted Ni–Fe based matrix phase. Diffusion coefficient and activation energy values for the diffusion of nitrogen in fcc Ni-based matrix were evaluated using the studies on kinetics of growth of nitrided layer. These values were compared with the available information in literature on other Ni–Cr–Fe alloys.

Effect of nano/ultrafine grain with orientation obtained by reversion transformation on tensile behaviour of austenitic stainless steel

The nano/ultrafine grains with different orientations were obtained by reversion transformation for austenitic stainless steel, and their tensile properties were investigated at room temperature. Comparing with the transverse direction sample, the much slower transformation induced plasticity was responsible for excellent elongation of rolled direction sample and the much higher strength originated from the presence of a considerable number of nanotwin bundles and the finer dislocations inside twins. The lower strength and plasticity in transverse direction sample could be attributed to the forming of shear bands and lack of deformation nanotwins.

Prediction of Deformation Behavior of Austenitic Stainless Steel 304 in Dynamic Strain Aging Regime

Prediction of Deformation Behavior of Austenitic Stainless Steel 304 in Dynamic Strain Aging Regime

Hot deformation behavior of austenitic stainless steel for a wide range of initial grain size

The hot deformation behavior of AISI 304L stainless steel with a wide range of initial grain size was studied using hot compression tests corresponding to the temperature range of 900–1100°C under strain rates ranging from 0.001 to 1s−1. All flow curves showed typical single peak dynamic recrystallization (DRX) behavior. By increasing the initial grain size, the range of flow stress became tighter and the characteristic DRX peak tended to vanish. The application of constitutive equations to determine the hot working constants of this material was critically discussed and the values of 0.010 and 392kJ/mol were determined for stress multiplier and deformation activation energy, respectively. It was also found that the conventional value of 0.012 for stress multiplier and the calculated activation energy based on the chemical composition (398kJ/mol in this case) are applicable in hot deformation studies of AISI 304 stainless steel. The normalized critical stress and strain for initiation of DRX were found to be 0.92 and 0.53, respectively. These values were within the reported ranges for steels.

Effect of Laves Phase Precipitation on Fatigue Behavior of Austenitic Stainless Steel Type 347 in Laboratory Air and in 3%NaCl Solution

The effect of Laves phase precipitation on the fatigue behavior of a niobium-containing austenitic stainless steel, type 347, was investigated. When this material is exposed to the temperature range of 700-900°C, the precipitation of the Laves phase (Fe2Nb) occurs, resulting in the embrittlement of the material which is known as the Laves phase embrittlement. Rotary bending fatigue tests have been conducted in laboratory air and in 3%NaCl solution using a type 347 aged at 700, 800 or 900°C. In laboratory air, the fatigue strengths were improved by the aging at 700°C due to the fine Laves phase precipitation in γ-phase. Whereas the aging at 900°C decreased fatigue strengths, which could be attributed to the coarsening of precipitated Laves phases. In 3%NaCl solution, the fatigue strengths of 700°C aged specimens were lower than those in laboratory air. It is considered that the sensitization took place during the heat treatment, where chromium-depleted zones were formed along grain boundaries.

Effect of Cold Stretching on Fatigue Behavior of Austenitic Stainless Steel at Elevated Temperature

Cold stretching technique is an effective way to enable thinner wall thickness of the austenitic stainless pressure vessel and thus can achieve lightweight design.In order to investigate the risk increment of the cold stretched vessel,the fatigue behaviors of solution annealed(SA) and cold stretched(CS) S31603 austenitic stainless steel is systematic studied under stress controlling mode at 550 ℃.The results show that:Sustained cyclic hardening response is displayed for both SA and CS material,only the cyclic strain amplitude and mean strain response of CS material is lower than SA one.Abrupt jump of mean strain is found at 550 ℃ which could be attributed to the dynamic strain aging effects.The times of abrupt jump under different cyclic stress for both SA and CS materials are nearly the same.By comparing with the SA material,no more than 10% deformation of the CS material makes the yield strength enhance and the cyclic strain amplitude decrease,which contribute to improve the fatigue life of the material and provide guarantee for reliable operation of the cold stretched austenitic stainless pressure vessel at elevated temperature.