Behavior Of Austenitic Stainless Steel Research Articles

Morphologies and characteristics of deformation induced martensite during low cycle fatigue behaviour of austenitic stainless steel

Abstract Quantification, formation and nucleation micro-mechanisms of deformation induced martensite during low cycle fatigue behaviour of austenitic stainless steel have been investigated at various strain amplitudes tested at ambient temperature. The evolutionary deformation induced martensite has been quantified through magnetic measurement technique. It has been found that as strain amplitude increases, the volume fraction of deformation induced martensite increases. Extensive analytical transmission electron microscopy studies showed more than one nucleation site for martensitic transformation and the transformation micro-mechanisms have been observed to be: γ (fcc) → ɛ (hcp), γ (fcc) → α′ (bcc), γ (fcc) → deformation twins → α′ (bcc) and γ (fcc) → ɛ (hcp) → α′ (bcc).

Review of Several Studies on High Temperature Oxidation Behaviour and Mechanism of Austenitic Stainless Steels

Three studies on the oxidation behaviour of austenitic stainless steels were described in the present paper. (1) High temperature oxidation behaviour and its mechanism in austenitic stainless steels with high silicon: Sulfur contained as impurity in steel showed a harmful influence to the oxidation resistance of 19Cr-13Ni-3.5Si stainless steels. It was found that the abnormal oxidation was caused from the surroundings of MnS inclusions. (2) Effect of a small addition of yttrium on high temperature oxidation resistance of Si-containing austenitic stain less steels: The oxidation resistance of 19Cr-10Ni-1.5Si steels was improved remarkably even with only 0.01%Y addition, which is the same concentration as added for de-oxygenation. Y was enriched at the grain boundary of oxide scale and metal-oxide interface. It was suggested that Y-containing steels shoed good oxidation resistance, because the enriched Y at the grain boundary and metal-oxide interface prevented the diffusion of iron and oxygen ions through the oxide scale. (3) Effect of grain size on the oxidation behaviour of austenitic stainless steels: Type 304, 316 and 310 steels with finer grain size showed better oxidation resistance than those with coarser grain size at 850°C. The oxide scale of steels with coarser grain size easily spalled during the cooling process.

Strain Rate Effect on the Mechanical Behavior of Austenitic Stainless Steel during Machining

Machining is characterized by a large amount of localized plastic strain on material due to chip formation; hence, there is a commitment among the strain process, strain hardening, and heat softening, generating shear bands. Understanding these shear zones is important because it contains information that can be applied to the improvement of machining techniques related to process optimization, and to materials and tools innovation. In this sense, the aim is to analyze the strain and the strain hardening with the strain rate variation as from the chip formed during the austenitic stainless steel AISI 304 turning. The results showed that the cut type, orthogonal or semi-orthogonal machining, affects the way the material strains, and that the strain rate has no significant effect on the strain and strain hardening of the austenitic stainless steel AISI 304 for the range investigated.

Effect of very high cutting speeds on shearing, cutting forces and roughness in dry turning of austenitic stainless steels

Behavior of austenitic stainless steels has been studied at very high cutting speeds. Turning tests were carried out using the AISI 303 austenitic stainless steel. In particular, the influence of cutting speed on tool wear, surface quality, cutting forces and chip geom- etry has been investigated. These parameters have been compared when performing machining at traditional cutting speeds (lower than 350 m/min) versus high cutting speeds. The analysis of results shows that the material undergoes a significant change in its behavior when machining at cutting speeds above 450 m/min, that favors the machining operation. The main compo- nent of cutting forces reaches a minimum value at this cutting speed. The SEM micrographs of the machined surfaces show how at the traditional cutting speeds the machined surfaces contain cavities, metal debris and feed marks with smeared material particles. Surfaces machined at high cutting speeds show evidence of ma-

Effects of concentration of sodium chloride solution on the pitting corrosion behavior of AISI 304L austenitic stainless steel

The pitting corrosion behavior of the austenitic stainless steel in aqueous chloride solution was investigated using electrochemical technique. Corrosion potential (Ecorr) measurement, potentiodynamic experiments, potential-hold experiments in the passive range, and microscopic examination were used for the evaluation of corrosion characteristics. The experimental parameters were chloride ion concentration, immersion time and anodic-hold potential. Ecorr measurements along with microscopic examinations suggest that in or above 3.5 % NaCl at pH 2 pitting took place on the surface in absence of applied potential after 6 hour immersion. The potentiodynamic experiment reveals that Ecorr and pitting potential (Epit) decreased and current density in the passive region increased with the increase of chloride ion concentrations. A linear relationship between Epit and chloride ion concentrations was found in this investigation. The analysis of the results suggests that six chloride ions are involved for the dissolution of iron ion in the pitting corrosion process of austenitic stainless steel.

Microstructure and corrosion behavior of austenitic stainless steel treated with laser

Surface modification of AISI316 stainless steel by laser melting was investigated experimentally using 2 and 4 kW laser power emitted from a continuous wave CO 2 laser at different specimen scanning speeds ranged from 300 to 1500 mm/min. Also, an investigation is reported of the introduction of carbon into the same material by means of laser surface alloying, which involves pre-coating the specimen surfaces with graphite powder followed by laser melting. The aim of these treatments is to enhance corrosion resistance by the rapid solidification associated with laser melting and also to increase surface hardness without affecting the bulk properties by increasing the carbon concentration near the surface. Different metallurgical techniques such as optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize the microstructure of the treated zone. The microstructures of the laser melted zones exhibited a dendritic morphology with a very fine scale with a slight increase in hardness from 200 to 230 Hv. However, the laser alloyed samples with carbon showed microstructure consisting of γ dendrite surrounded by a network of eutectic structures (γ+carbide). A significant increase in hardness from 200 to 500 Hv is obtained. Corrosion resistance was improved after laser melting, especially in the samples processed at high laser power (4 kW). There was shift in I corr and E corr toward more noble values and a lower passive current density than that of the untreated materials. These improvements in corrosion resistance were attributed to the fine and homogeneous dendritic structure, which was found throughout the melted zones. The corrosion resistance of the carburized sample was lower than the laser melted sample.

An overview on constitutive modelling to predict elevated temperature flow behaviour of fast reactor structural materials

This overview emphasized the aspects of formulation and application of various constitutive models developed by us in recent past viz. Johnson- Cook (JC), modified Zerilli-Armstrong (MZA), strain compensated Arrhenius type model and artificial neural network (ANN) model to predict elevated temperature flow behaviour of fast reactor structural materials. It has been shown that the JC model is not able to represent the high temperature flow behaviour of both alloy D9 and the modified 9Cr-1Mo as it does not incorporate the coupled effect of strain and temperature, and of strain rate and temperature. The new materials model based on Zerilli-Armstrong (ZA) equation considers the coupled effects of temperature and strain and of strain rate and temperature on the flow stress and hence has the capability to predict flow stress over a wider domain temperature and strain rate in comparison with JC model. The formulation and application of strain compensated Arrhenius type constitutive model to predict high temperature flow behaviour of alloy D9 and modified 9Cr-1Mo has been discussed. Development and application of a generic ANN based constitutive model to predict high temperature deformation behaviour of austenitic stainless steels has been highlighted. Finally, a comparative analysis of the merits and shortcomings of these models has been made.

Analysis and mathematical modelling of elevated temperature flow behaviour of austenitic stainless steels

High temperature flow behaviour of various grades of austenitic stainless steels viz. 304L, 304, 304 (as-cast), 316L and 15Cr–15Ni–Ti modified austenitic stainless steels (alloy D9) were analyzed by performing isothermal hot compression tests in a wide range of temperatures (1073 K to 1473 K for 304L, 304, 304 (as-cast), 316L and 1123 K to 1523 K for alloy D9) and strain rates (0.001–1 s −1). It has been observed that all these materials show strain hardening, strain rate hardening, thermal softening, coupled effect of temperature and strain, and temperature and strain rate on flow stress in the hot working domain. The modified Zerilli–Armstrong (MZA) model which considers the above significant effects on flow stress has been applied to predict the flow behaviour of these materials. The material constants of the MZA model for each material have been evaluated and subsequently applied to predict the flow stress. It has been demonstrated that the MZA model could adequately represent the elevated temperature flow behaviour of these materials over the entire ranges of strain, strain rate and temperature.

ChemInform Abstract: The Effect of Copper on the Anodic Dissolution Behavior of Austenitic Stainless Steel in Acidic Chloride Solution.

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The effect of weld geometry and post-weld heat treatment on the corrosion behaviour of austenitic stainless steel immersed in 1.0 M NaCl solution

The variation of welding parameters such as weld geometry and post-weld heat treatment on the corrosion behaviour of austenitic stainless steel in a saline environment of 1.0 M NaCl was investigated in this work. Rods of austenitic stainless steel of known chemical composition were prepared and welded using electric arc welding technique varying the aforementioned parameters. Thereafter, samples for the corrosion behaviour investigation were then cut out of the welded rods. The analysis of the experimental data revealed that the best weld geometry was chamfered and a post-weld heat treatment carried out at temperatures in excess of 700 °C followed by air cooling improves the quality of a weld.

Work Hardening and Tensile Behaviour of an Austenitic Stainless Steel at High Temperature

The work hardening and tensile behaviour of AISI 316L austenitic stainless steel deformed at temperatures between 600 and 1000°C has been investigated. The alloy has been heat-treated according two different roots: the first solutioning treatment was imposed at 1100°C and the second was designed at 875°C to reduce the dynamic ageing that occurs at temperatures up to 650°C in AISI 316L. In the solutionised material the work hardening data presented two linear regions: at high stresses the linearity has been described as the conventional Stage III of work hardening, whilst at low stresses the linearity has not been rationalised in any conventional stage of work hardening. In the second heat treatment alloy the work hardening data showed a single linear region at high stresses, whilst no linear stage occurred at low stresses. Therefore, the work hardening and tensile behaviour of AISI 316L has resulted to be significantly affected by the two different heat treatments and dynamic aging has been proved to influence work hardening behaviour well beyond the range of temperatures in which serrated yielding occurs.

Influence of glyoxal on localized corrosion of austenitic stainless steel in spring water

AbstractThis paper presents the research regarding the influence of glyoxal on electrochemical and corrosion behaviour of austenitic stainless steel in water. For this purpose, model solutions containing glyoxal in water in concentrations ranging from 0.1 to 1 % were prepared. Spring water was used as control electrolyte. From the potentiostatic polarisation data (using the standard three‐electrode system), the corrosion current (icorr), corrosion potential (Ecorr) and polarisation resistance (Rp) were calculated. The research included also the conductivity, total dissolved soils, salinity, resistivity and pH, absolute potential, and relative potential of model solutions. The presence of glyoxal at the highest concentration of 1 % in the water solution has accelerating effect on corrosion.

Effect of Low-Temperature Sensitization on Intergranular Stress Corrosion Cracking Behavior of Austenitic Stainless Steels in Simulated Boiling Water Reactor Environment

Abstract Intergranular stress corrosion cracking (IGSCC) is a generic form of cracking observed for austenitic stainless steels in boiling water reactors (BWR). Sensitization has been a basic reason for IGSCC and it occurs as a result of the formation of chromium carbides (Cr23C6) at grain boundaries near weld-ments. Low-carbon stainless steels are used to prevent sensitization and reduce susceptibility to IGSCC. Type 304L (UNS S30403) stainless steel does not sensitize during welding, but prolonged exposure to BWR conditions are found to promote low-temperature sensitization (LTS). Addition of N to Type 304L stainless steel is known to enhance not only the alloy strength, but also its sensitization resistance. Molybdenum-containing Type 316LN (UNS S31653) stainless steel has been demonstrated to be resistant to sensitization, LTS, and IGSCC and is currently used in BWR. Type 304LN stainless steel has not been used for such applications so far. The effect of nitrogen addition to Type 304L stainless steel ...

The Effects of Pre-Oxidation and Alloy Chemistry of Austenitic Stainless Steels on Glass/Metal Sealing

An oxidation treatment is often performed on austenitic stainless steel prior to joining to alkali barium silicate glass to produce hermetic seals. The thin oxide formed during this pre-oxidation step acts as a transitional layer and a source of Cr and other elements that diffuse into the glass during the subsequent bonding process. Pre-oxidation is performed in a low pO2 atmosphere to avoid iron oxide formation; the final oxide is composed of Cr2O3, MnCr2O4 spinel, and SiO2. Significant heat-to-heat variations in the oxidation behavior of austenitic stainless steel were observed in this work, resulting in inconsistent glass/metal seal behavior. Twenty-five (25) stainless steel heats were examined including 304L, 316L, and experimental high sulfur alloys similar to 303SS. The objectives were to characterize the oxidation kinetics, the oxide morphologies, and compositions that affect glass/metal adhesion. It was found that poor glass sealing is associated with a more continuous layer of SiO2 at the metal/oxide interface. The effects of alloy chemistry, in particular Mn and Si concentrations, on glass/metal sealing behavior were empirically determined. A criterion based on the Mn/Si ratio was developed for use in selecting heats with good glass/metal bonding characteristics. To test this criterion, four other austenitic stainless steels were evaluated: 21-6-9 (also known by original Armco Steel Co. trade name Nitronic® 40), 22-13-5 (Nitronic® 50), Nitronic® 60, and Gall-Tough® (Carpenter Technology Corp.). These alloys have compositions significantly different from 300-series alloys, but they were still found to comply with the compositional guidelines developed for predicting glass/metal adhesion.

Effects of Plasma Nitriding (10% N2–90% H2) on Microstructure, Thermal Stability and Corrosion Behaviour of Austenitic Stainless Steel

Effects of Plasma Nitriding (10% N₂–90% H₂) on Microstructure, Thermal Stability and Corrosion Behaviour of Austenitic Stainless Steel

Localized Corrosion Behavior of Austenitic Stainless Steels under Stress Loading Environment

Three elements (the material, the environment, and the stress) relate closely to the occurrence of the stress corrosion cracking (SCC). SCC can occur in austenitic stainless steels during operation under tensional stress in chloride environment. And it is important to evaluate the passivation behavior of the stainless steels that has high corrosion resistance by a passive film under the stress loading environment, because it is assumed that the stress have a effect in the passivation, breakdown of the passive film and repassivation. In this present work, the corrosion behavior of type 304 and 316 stainless steels in sodium chloride solutions using a constant strain is measured by the electrochemical measurement. On the basis of the results that the polarization curve measurement and the potentiostatic polarization curve measurement obtained, the localized corrosion sensitivity was increased in stress loading environment.

Analysis of tensile deformation and failure in austenitic stainless steels: Part II – Irradiation dose dependence

Irradiation effects on the stable and unstable deformation and fracture behavior of austenitic stainless steels (SSs) have been studied in detail based on the equivalent true stress versus true strain curves. An iterative finite element simulation technique was used to obtain the equivalent true stress–true strain data from experimental tensile curves. The simulation result showed that the austenitic stainless steels retained high strain hardening rate during unstable deformation even after significant irradiation. The strain hardening rate was independent of irradiation dose up to the initiation of a localized necking. Similarly, the equivalent fracture stress was nearly independent of dose before the damage (embrittlement) mechanism changed. The fracture strain and tensile fracture energy decreased with dose mostly in the low dose range <∼2 dpa and reached nearly saturation values at higher doses. It was also found that the fracture properties for EC316LN SS were less sensitive to irradiation than those for 316 SS, although their uniform tensile properties showed almost the same dose dependencies. It was confirmed that the dose dependence of tensile fracture properties evaluated by the linear approximation model for nominal stress was accurate enough for practical use without elaborate calculations.

A new constitutive model of austenitic stainless steel for cryogenic applications

Abstract A series of uniaxial tensile test under cryogenic temperature was carried out for AISI 304 and 316 austenitic stainless steels (ASS) in this study. Typical non-linear hardening phenomena under the cryogenic environment, such as transformation induced strain hardening and threshold strain for the 2nd hardening, has been observed in a quantitative manner. The important factors affecting the non linear material behavior of austenitic stainless steel including phase transformation, discontinuous yielding and micro-damage are modeled using constitutive equations system based on strain decomposition at the small strain formulation. A strong nonlinearity of strain hardening is described using the coupling of modified Bodner’s plasticity model and phase transformation induced strain model. The strain (threshold strain for onset of 2nd hardening) dependent plasticity model was proposed in the hardening function of Bodner’s model. In order to explicitly express the phase transformation induced strain, TI model (Tomita and Iwamoto model [Y. Tomita, T. Iwamoto, Constitutive modeling of TRIP steel and its application to the improvement of mechanical properties, International Journal of Mechanical Sciences 37 (1995) 1295–1305.]), which is a function of accumulated plastic strain and volume fraction factor of martensite, is selected in this study. Also the unified damage model, which can be connected with elasto-plastic constitutive equation developed in this study, is suggested, and the utility of proposed model was validated by the comparison between experiments and numerical evaluations.

Effect of low-frequency rotary electromagnetic-field on solidification structure of continuous casting austenitic stainless steel

To understand the solidification behavior of austenitic stainless steel in rotary electromagnetic-field, the influence of low-frequency rotary electromagnetic-field on solidification structure of austenitic stainless steel in horizontal continuous casting was investigated based on industrial experiments. The results show that the solidification structure of austenitic stainless steel can be remarkably refined, the central porosity and shrinkage cavity can be remarkably decreased, and the equiaxed grains zone are enlarged by means of application of appropriate low-frequency electromagnetic-field parameters. The industrial trials verify that the stirring intensity of austenitic stainless steel should be higher compared with that of plain carbon steel. Electromagnetic stirring affects the macrostructure even if the average magnetic flux density of the electromagnetic stirring reaches 90 mT (amplitude reaches 141 mT) with the frequency of 3-4 Hz. Due to a higher viscosity, rotating speed of molten stainless steel is 20%-30% lower than that of molten carbon steel in the same magnetic flux density.

Very high cycle fatigue behaviour of austenitic stainless steel and the effect of strain-induced martensite

Metastable austenitic stainless steels are known to undergo a partial transformation of austenite into martensite as a consequence of plastic deformation. This transformation process depends on the chemical composition, the accumulative strain as well as the strain rate, the temperature and the microstructure. As most manufacturing processes of metallic components lead to plastic deformation in the material, the utilization of this transformation effect to adjust the monotonic and cyclic strength behaviour for the highly stressed areas of a component is evident. It is shown that monotonic and cyclic strength properties can be systematically changed by controlling the deformation-induced martensite content. The austenitic stainless steel studied was found to show a constant fatigue limit from 10 6 to 10 9 cycles that is primarily attributed to the strengthening effect of martensitic transformation. Load-increase tests were used to estimate an optimum martensite content in predeformed specimens to reach a maximum fatigue limit.