Behavior Of Austenitic Stainless Steel Research Articles

Influence of Carbide Precipitation and Rolling Direction on Intergranular Stress Corrosion Cracking of Austenitic Stainless Steels in Hydrogenated High-Temperature Water

Abstract The intergranular stress corrosion cracking (IGSCC) growth behavior of austenitic stainless steels (SS) in hydrogenated high-temperature water were studied using compact tension specimens ...

The effect of test temperature on SCC behavior of austenitic stainless steels in boiling saturated magnesium chloride solution

The stress corrosion cracking (SCC) of the austenitic stainless steels of types 304, 310 and 316 was investigated as a function of test temperature in boiling saturated magnesium chloride solution (MgCl 2) using a constant load method. Both of types 304 and 316 exhibited similar corrosion elongation curves, while the corrosion elongation curve of type 310 was different from those of types 304 and 316, in terms of the three parameters such as time to failure ( t f), steady-state elongation rate ( l ss) and transition time to time to failure ratio ( t ss/ t f) obtained from the corrosion elongation curves for these stainless steels. The relationship between the time to failure and a reciprocal of test temperature fell in two straight lines on a semi-logarithmic scale as well as the relationship between the steady-state elongation rate and a reciprocal of test temperature. These regions were considered to correspond to a SCC-dominated region and a hydrogen embrittlement (HE)-dominated region from the value of ( t ss/ t f) and the fracture appearance. The relationship between the steady state elongation rates versus time to failure on a logarithmic scale became a straight line, whereas the slopes of the line for the stainless steels were different with the different fracture mechanism such as SCC and HE. It was found that the linearity of the relationship can be used to predict the time to failure for the stainless steels in the corrosive environment. In addition, type 310 did not suffer from HE, which means that type 310 showed only SCC. This would be explained by whether or not a formation of α′-martensite takes place.

Structure Evolution and Solidification Behavior of Austenitic Stainless Steel in Pulsed Magnetic Field

To understand the solidification behavior of austenitic stainless steel in pulsed magnetic field, the solidification process is investigated by means of the self-made high voltage pulse power source and the solidification tester. The results show that the solidification structure of austenitic stainless steel can be remarkably refined in pulsed magnetic field, yet the grains become coarse again when the magnetic intensity is exceedingly large, indicating that an optimal intensity range existed for structure refinement. The solidification temperature can be enhanced with an increase in the magnetic intensity. The solidification time is shortened obviously, but the shortening degree is reduced with the increase of the magnetic intensity.

Intergranular Stress Corrosion Cracking Behavior of Austenitic Stainless Steels in Hydrogenated High-Temperature Water

Abstract The influence of material factors on the intergranular stress corrosion cracking (IGSCC) susceptibility of austenitic stainless steels under hydrogenated high-temperature water were studie...

Effect of strain rate on stress-strain behavior of alloy 309 and 304L austenitic stainless steel

The effect of strain rate on stress-strain behavior of austenitic stainless steel 309 and 304L was investigated. Tensile tests were conducted at room temperature at strain rates ranging from 1.25×10−4s−1 to 400 s−1. The evolution of volume fraction martensite that formed during plastic deformation was measured with X-ray diffraction and characterized with light microscopy. Alloy 304L was found to transform readily with strain, with martensite nucleating on slip bands and at slip band intersections. Alloy 309 did not exhibit strain-induced transformation. Variations in ductility and strength with strain rate are explained in terms of the competition between hardening, from the martensitic transformation and a positive strain rate sensitivity, and softening due to deformational heating. Existing models used to predict the increase in volume fraction martensite with strain were examined and modified to fit the experimental data of this study as well as recent data for alloys 304 and 301LN obtained from the literature.

The low-cycle fatigue, deformation and final fracture behaviour of an austenitic stainless steel

The low-cycle fatigue (LCF) behaviour of SUS304-HP austenitic stainless steel was investigated systematically using tension-compression cycling under fully reversed total strain amplitude control conditions at room temperature in laboratory air. In addition to tests at constant strain amplitudes, incremental step tests (IST) were also carried out. Cyclic stress response, during companion specimen tests (CST), revealed combinations of a variable cyclic hardening, stable behaviour and softening, depending on the applied cyclic strain amplitude, while during incremental step tests it exhibited cyclic hardening character at all strain levels. Microstructure observations using optical and transmission electron microscopy (TEM) revealed that with increasing total strain amplitudes the slip band density increased and the dislocation structure changed from a planar array to a more cellular-like structure. Cyclic deformation-induced austenite/martensite transformation was observed at higher cyclic strain amplitudes. The change in microstructures during cycling is responsible for the fatigue hardening/softening behaviour of the material. The SEM micrographs revealed that at low-strain amplitudes the inclusion-type nucleation occurred near the surface, while at the higher strain amplitudes crack initiation characterized by cleavage cracking occurred not only near the surface but also in the interior of the specimen. Linear or single-slope behaviour was seen both in cyclic stress–strain and Coffin-Mason plots. Masing cyclic stress–strain behaviour was presented only in the IST method but not in the CST method.

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 mechanism of localized corrosion resistance and repassivation for nitrogen-bearing stainless steel was investigated using anodic potentiodynamic polarization technique. The solutions used for this study contained 0.0, 0.05 and 0.33 M Fe3+ for solutions I, II and III, respectively, in a total Cl− ion concentration 1 M. The pitting attack was found to be retarded by nitrogen addition and the samples were able to passivate as the nitrogen increase. Addition of nitrogen allows the decrease in the wt.% of Ni, but to a certain limit. Nitrogen is adsorbed on the interface of the metal oxide and results in the repulsion of Cl− ions. Moreover, it reacts with H+ ions in the solution leading to higher pH, which explains the retardation effect of nitrogen to corrosion.

Effect of ion irradiation and implantation of H and He on the corrosion behavior of austenitic stainless steel

It is important to evaluate the effect of irradiation on the corrosion behavior of materials to be used in spallation neutron sources. Solution annealed high purity Fe–18Cr–12Ni specimens were used in this study. Ni 3+ and H + or He 2+ ions were injected at 473–773 K. After corrosion test, the specimens were examined with atomic force microscope (AFM) to evaluate the corrosion behavior. It was shown that the corrosion rate of the irradiated area increased with increasing dose and temperature. H implantation accelerated corrosion. On the other hand, He implantation seemed to suppress corrosion. Mechanisms for these effects of the different irradiation conditions on the corrosion behavior are discussed.

Correlation between PIII nitriding parameters and corrosion behaviour of austenitic stainless steels

In this work, nitrogen plasma immersion ion implantation (PIII) treatment of austenitic stainless steels 1.4301 and 1.4571 was performed to investigate the influence of the process conditions on the corrosion properties. Short treatment, high voltage and high temperature result in a decreased corrosion potential while no correlation to layer thickness, nitrogen concentration or lattice expansion was found. Except for the possibility of small CrN agglomerates at high temperatures, no direct explanation for the results can be provided and it is argued that intrinsic stress accumulation and relaxation may be responsible.

Effects of S Content and Surface Finish on Pitting Corrosion of Austenitic Stainless Steels Containing Mo in Chloride and Bromide Solutions

Pitting corrosion behavior of austenitic stainless steels with Mo was investigated in chloride and bromide solutions. The steels with higher S content as 0.009 mass% showed higher pitting potential in 1 kmol/m3 bromide solution than 1 kmol/m3 chloride solution. On the other hand, the steels with lower S content as 0.0003 mass% showed opposite results. The higher pitting potential was observed in chloride solution. This tendency became profound with passivation treatment by nitric acid. From the experimental results above, it is highly believed that chloride ions are more detrimental to sulfide inclusions induced pitting than bromide ions, whereas pitting due to breakdown of passive film other than sulfide inclusion is more easily caused in solutions containing bromide ions than chloride ions.

Friction and Wear Behavior of Austenitic Stainless Steel: Influence of Atmospheric Humidity, Load Range, and Grain Size

Research conducted on steels is motivated by a technological need to further improve their properties. Among the different steel types, austenitic stainless steels possess good corrosion resistance and formability. However, they also have a relatively low yield strength. One way of increasing the yield strength is by grain refining. This work presents a study on the effect of relative humidity and applied load range on the friction and wear of AISI 304 austenitic stainless steel characterized by two different grain sizes: 2.5 and 40 μm. Using a precision microtribometer, with applied loads in the μN regime, it was found that capillarity plays a dominant role. At the same loads, in high humidity environments, both the fine and coarse grain steels exhibit high friction relative to measurements performed under dry conditions. At loads greater than 2 mN a reversal in microfrictional behavior occurs in that microfriction was greater under dry conditions than under moist conditions. At loads of 2 N, using a standard ball-on-disk tribometer, severe wear was evident at low humidities while relatively lower wear was observed at high humidities indicating a lubricating effect of water.

Cavitation wear behaviour of austenitic stainless steels with different grain sizes

The cavitation erosion behaviour of two different austenitic stainless steels in water with different pH values and room temperature have been studied by means of a 20-kHz ultrasonic vibrator operating at a peak-to-peak amplitude of 40 μm. The austenitic stainless steels used were AISI 304 (18Cr–10Ni) steel and a high nitrogen (HN) containing steel. Each of the steels were fabricated to yield three different grain sizes: 2.5 μm, 20 μm and 45 μm. The grain size in both steels was adjusted by inducing an austenite–martensite–austenite phase transformation. Grain refining results in an improvement of the mechanical properties: hardness, yield strength, tensile strength, fatigue strength as well as an enhancement in the corrosion resistance. The grain size of the steels has an important effect on the nature of damage produced on the surface of the samples. The resistance to cavitation erosion increases continuously with decreasing grain size. It was also found that cavitation erosion resistance of the two steels is sensitive to variations in the pH: a decrease of this value produces an increase in surface damage. This work shows that the HN steel exhibits better cavitation erosion resistance than AISI 304 steel. Also, hardness, tensile strength, yield strength and grain size of both steels can be correlated with the cavitation resistance R e.

Effect of some thiophene derivatives on the electrochemical behavior of AISI 316 austenitic stainless steel in acidic solutions containing chloride ions: I. Molecular structure and inhibition efficiency relationship

The electrochemical behavior of austenitic stainless steel (AISI 316) was studied in an acid medium that contains chloride ions in absence and presence of some thiophene derivatives. The corrosion rate as well as pit growth of the steel was inhibited variably with each of the sulfur-containing compound present in the corroding medium. The thiophene derivatives studied were 2-acetyl thiophene (AcT), 2-thiophene carboxylic acid (TCA), 3-thiophene carboxyaldehyde (TCAL) and 2-thiophene carboxylic hydrazide (TCH). Electrochemical techniques such as potentiodynamic polarization, Tafel experiments, polarization resistance and electrochemical impedance spectroscopy were used to investigate the electrochemical behavior of the steel. The results showed distinct effects for the different thiophene derivatives used that depended on the molecular structure and the electron density of the sulfur atom of the thiophene ring. The order of inhibition efficiency was TCH > TCA > TCAL > AcT. It was also concluded that the inhibitors studied were of the mixed type. This conclusion was realized by comparing the change in the values of the anodic and cathodic Tafel slopes. Inhibition efficiencies of ca. 97% were achieved using these inhibitors in 0.5 M H 2SO 4.

Strategy for the design of thermomechanical processes for AISI type 304L stainless steel using dynamic materials model (DMM) stability criteria and model for the evolution of microstructure

The dynamic materials model (DMM) [1] is a proven technique for studying constitutive behavior of materials. In this model, the efficiency of power dissipation through microstructural changes, given by η = 2m/(m + 1), where m is the strain rate sensitivity, is plotted as a function of temperature and strain rate to obtain a DMM processing map. The different domains exhibited by the map are correlated with specific microstructural processes occurring during hot working. Prasad [1] has shown that flow instability will occur during hot deformation if ξ (e) = {∂ ln[m/(m + 1)]/ ∂ ln e} + m < 0, where e, is the strain rate. The variation of the instability parameter, ξ (e) with temperature and strain rate, constitutes an instability map, which may be superimposed on the processing map for delineating the regimes of flow instability. The optimal domains predicted by the DMM processing maps are quite wide. In practice, in a wide domain it is very difficult to control the microstructure of the product. Hence, some refining procedure needs to be established for the precise control of the microstructure during working. Malas and Seetharaman [2] proposed stability criteria based on DMM. According to them the optimal processing windows for safe working are: 0 < m ≤ 1, ṁ < 0, s ≥ 1, and ṡ < 0, where ṁ = ∂m/∂ ln e, s = ∂ log σ/∂(1/T ), ṡ = ∂s/∂ log e and T = temperature in K . The apparent activation energy Q = sRT/m, where R = gas constant. In this methodology the reasonable “safe” processing range corresponds to the processing condition where a desirable and fairly constant value of Q is operative. These criteria can be used to refine the safe processing window to achieve better microstructural control during processing. In order to control the development of microstructure during hot working, a new strategy for systematically calculating near-optimal control parameters for hot deformation process has been proposed [3]. This approach involves developing state-space models from available material behavior and hot deformation process models. The control system design consists of two basic stages, and analysis and optimization are critical in both stages. In the first stage, the kinetics of certain dynamic microstructural behavior and intrinsic hot workability of the material are used, along with an approximately chosen optimality criterion, to calculate the optimum strain (e(t)), strain-rate (e(t)), and temperature (T (t)) trajectories for processing. A suitable process simulation model is then used in the second stage to calculate process control parameters, such as ram velocity, die profiles, and billet temperature, which approximately achieve the strain, strain-rate, and temperature trajectories calculated in the first stage. This process design approach treats the deforming material as a dynamic system and involves developing statespace models from available material behavior and hot deformation process models. The design approach requires three basic components for defining and setting up the optimization problem: (1) a dynamic system model, (2) physical constraints, and (3) an optimality criterion. The system models of interest are material behavior and deformation process models. Constraints include the hot workability of the workpiece and the limitations of the forming equipment. Optimality criteria could be related to achieving a particular final microstructure (grain size), regulating temperature, and/or maximising deformation speeds. Fig. 1 describes the steps involved in the proposed new approach [3]. The microstructure development optimization determines optimal trajectories of strain, strain rate, and temperature. From these optimal trajectories, the process optimization stage determines optimal process control parameters, namely the die shape, the ram velocity profile and billet temperature. Goals of the first stage are to achieve enhanced workability and prescribed microstructural parameters. In the second stage, a primary goal is to achieve the thermo-mechanical conditions obtained from stage one for predetermined regions of the deforming workpiece. In the first stage, models of material behavior that describe the kinetics of primary metallurgical mechanisms such as dynamic recovery, dynamic recrystallization, and grain growth during hot working are required for analysis and optimization of material system dynamics. The objective is to define the acceptable ranges of temperature and strain rate over which the material exhibits a “safe” processing window. The complete details of this approach are available elsewhere [3]. The aim of the present investigation is to evaluate the constitutive flow behavior of austenitic stainless steel

Effect of cold work on low-temperature sensitization behaviour of austenitic stainless steels

The effects of cold work and low-temperature sensitization heat treatment of non-sensitized austenitic stainless steels have been investigated and related to the cracking in nuclear power reactors. Types 304, 304L and 304LN developed martensite after 15% cold working. Heat treatment of these cold worked steels at 500 °C led to sensitization of grain boundaries and the matrix and a desensitization effect was seen in 11 days due to fast diffusion rate of chromium in martensite. Types 316L and 316LN did not develop martensite upon cold rolling due to its chemical composition suppressing the martensite transformation (due to deformation) temperature, hence these were not sensitized at 500 °C. The sensitization of the martensite phase was always accompanied by a hump in the reactivation current peak in the double loop electrochemical potentiokinetic reactivation test, thus providing a test to detect such sensitization. It was shown that bending does not produce martensite and therefore, is a better method to simulate weld heat affected zone. Bending and heating at 500 °C for 11 days led to fresh precipitation due to increased retained strain and desensitization of 304LN due to faster diffusion rate of chromium along dislocations. The as received or solution annealed 304 and 304LN with 0.15% nitrogen showed increased sensitization after heat treatment at 500 °C, indicating the presence of carbides/nitrides.

Electrochemical behaviour of Mo‐containing austenitic stainless steels in buffer solution

AbstractThe effect of pH on the electrochemical behavior of austenitic stainless steels in naturally aerated and nitrogen‐deaerated buffer solutions has been studied.Potentiodynamic and ac impedance techniques were used. The results indicate that corrosion current (Icorr) decreases with pH. By examining the impedance data for the seven tested steels under various conditions, it seems that the total resistance (RT) value is a suitable indication parameter for explaining the role of molybdenum and the other supplementary alloying additions (Ni, N, Cu and Mn) on the passive film behaviors as a function of pH of the forming solutions. As a general trend, the RT values for all steels tended to be lower in the basic buffer than in the acidic solutions.

Creep surge effect under cyclic irradiation of structural materials for fusion reactors

Experimental investigations were performed on the radiation-creep behavior of austenitic stainless steels, α-Fe and Fe–Cr alloys. The effect of an abrupt increase of creep rate early after either switching on and switching off irradiation (radiation-induced creep surge) was revealed. The effect of electron irradiation on the thermal-activation parameters of creep was examined. The radiation creep surge effect is discussed in terms of a dynamic preference of dislocations under nonstationary conditions typical of the formation of new radiation-equilibrium flows of radiation induced point defects.

The electrochemical behavior of austenitic stainless steel with different degrees of sensitization in the transpassive potential region in 1 M H 2SO 4 containing chloride

This paper investigates electrochemical methods to estimate the degree of sensitization (DOS) for as-rolled and solution-treated austenitic stainless steels (AISI 304). The change in DOS was introduced by heat treatment of various time periods at 700 °C, and the electrochemical experiments were conducted at 27 °C in 1 M H 2SO 4 + 0.2 wt.% NaCl. The results show that there is no obvious difference in the anodic polarization curves of the specimens with the differences in DOS. However, the DOS of specimens can be clearly differentiated with AC impedance response in a particular transpassive potential region. In the transpassive potential region of the anodic polarization curve, as overpotential is increased beyond the breakdown potential, three types of anodic dissolution, passive dissolution, grain-boundary attack, and pitting can be characterized. The DOS can only be correctly evaluated with AC impedance response in the middle of the transpassive potential region, where anodic dissolution is of grain-boundary attack type, from 1.05 to 1.1 V. The chromium-depleted zone was preferentially attacked and an intergranular corrosion was found for the serious sensitized specimen after AC impedance test. The healing effect was observed in as-rolled specimens as the specimens were heated more than 72 h, but the effect was not found in the solution-treated specimens sensitized for up to 480 h at 700 °C.

Ratchetting process in the stainless steel AISI 316L at 300 K: an experimental investigation

The cyclic creep behaviour of austenitic stainless steel (316L) was studied at room temperature. Particular attention has been paid to the effect of peak stress (Σ max) and mean stress (Σ m) on the ratchet strain rate. Threshold stress (230 MPa) for the transition from retardation to acceleration in the cyclic creep has been observed and interpreted as a transition between planar slip to wavy slip. The effect of stacking fault energy on this threshold stress is also studied. The cyclic creep rate increases as a function of Σ max. The influence of maximum stress has been considered as an effect of tensile plastic strain history. This has been previously characterised in terms of back stress and effective stress. In particular, three domains have been identified—R 0, R I and R II—where the cyclic mechanisms are different. The slip mode and long-range internal stress state is at the origin of the three cyclic creep domains. Moreover, the evolution of internal stress states during cyclic creep test has been studied.

Surface engineering of austenitic stainless steel

The inherent poor tribological behaviour of austenitic stainless steels has been a barrier to their wider application under corrosion wear conditions. Therefore, researchers have long dreamt of developing new technologies to enhance the wear resistance of stainless steel surfaces without loss of their attractive ‘stainless’ characteristics. For example, the discovery of low temperature plasma nitriding in the mid 1980s allowed a new phase with a high hardness and good corrosion resistance to be produced on austenitic stainless steel surfaces. Since then much research and development has aimed to combine improvements in wear, corrosion and fatigue properties. This has been demonstrated by various low temperature surface alloying processes (including plasma, ion beam, gaseous and salt bath methods) and increasing numbers of academic publications, reflecting rapidly expanding niche markets in the food, chemical, nuclear and medical sectors. In this paper, the historical evolution and development of low temperature thermochemical surface alloying processes are overviewed. The research and development of low temperature surface alloying of austenitic stainless steels in an attempt to combine improvements in wear, corrosion and fatigue properties are also assessed. Finally, new directions and key areas for future development are identified and discussed.