Abstract Austenitic Stainless Steel Research Articles

Oxidation Damage Evolution in Low-Cycle Fatigue Life of Niobium-Stabilized Austenitic Stainless Steel.

Austenitic stainless steel is a vital material in various industries, with excellent heat and corrosion resistance, and is widely used in high-temperature environments as a component for internal combustion engines of transportation vehicles or power plant piping. These components or structures are required to be durable against severe load conditions and oxidation damage in high-temperature environments during their service life. In this regard, in particular, oxidation damage and fatigue life are very important influencing factors, while existing studies have focused on materials and fracture behavior. In order to ensure the fatigue life of austenitic stainless steel, therefore, it is necessary to understand the characteristics of the fracture process with microstructural change including oxidation damage according to the temperature condition. In this work, low-cycle fatigue tests were performed at various temperatures to determine the oxidation damage together with the fatigue life of austenitic stainless steel containing niobium. The characteristics of oxidation damage were analyzed through microstructure observations including scanning electron microscope, energy-dispersive X-ray spectroscopy, and the X-ray diffraction patterns. In addition, a unified low-cycle fatigue life model coupled with the fracture mechanism-based lifetime and the Neu-Sehitoglu model for considering the influence of damage by oxidation was proposed. After the low-cycle fatigue tests at temperatures of 200–800 °C and strain amplitudes of 0.4% and 0.5%, the accuracy of the proposed model was verified by comparing the test results with the predicted fatigue life, and the validity by using the oxidation damage parameters for Mar-M247 was confirmed through sensitivity analysis of the parameters applied in the oxidation damage model. As a result, the average thickness of the oxide layer and the penetration length of the oxide intrusion were predicted with a mean error range of 14.7% and 13%, respectively, and the low-cycle fatigue life was predicted with a ±2 factor accuracy at the measurement temperatures under all experimental conditions.

The effect of cold rolling and high-temperature gas nitriding on austenite phase formation in AISI 430 SS

Austenitic stainless steel is the most commonly used material in the production of orthopedic prostheses. In this study, AISI 430 SS (0.12 wt. % C; 1 wt. % Si; 1 wt. % Mn; 18 wt. % Cr; 0.04 wt. % P and 0.03 wt. % S) will be modified by creating austenite and removing its ferromagnetic properties via the high-temperature gas nitriding process. Cold rolling with various percentage reduction (30, 50, and 70 %) was followed by gas nitriding at a temperature of 1200 °C with holding times of 5, 7, and 9 hours, then quenching in water was carried out on as-annealed AISI 430 SS. The formation of the austenite phase was examined by XRD (x-ray diffraction). The microstructure and element dispersion were observed using SEM-EDS (scanning electron microscope-energy dispersive spectrometry), whereas the mechanical properties after gas nitriding and water quenching were determined by Vickers microhardness testing. At all stages of the gas nitriding process, the FCC iron indicated the austenite phase was visible on the alloy's surface, although the ferrite phase is still present. The intensity of austenite formation is produced by cold rolling 70 % reduction with a 5-hour gas nitriding time. Furthermore, the nitrogen layer was formed with a maximum thickness layer of approximately 3.14 µm after a 50 % reduction in cold rolling and 9 hours of gas nitriding process followed by water quenching. The hardness reached 600 HVN in this condition. This is due to the distribution of carbon that is concentrated on the surface. As the percent reduction in the cold rolling process increases, the strength of AISI 430 SS after gas nitriding can increase, causing an increase in the number of dislocations. The highest tensile strength and hardness of AISI 430 SS of 669 MPa and 271.83 HVN were obtained with a reduction of 70 %.

The Construction of Superhydrophobic Structure on Stainless Steel by an Optimized Chemical Etching Technics

Abstract Austenitic stainless steel is a widely used engineering material in industry and daily life due to its excellent corrosion resistance. The construction of superhydrophobic structure on stainless steel can endow it with special wetting properties and open up new paths for its application. In this study, stainless steel plate was first etched in a hydrofluoric acid solution with a low concentration of 40 wt%, and a micro-nano structure was obtained in a short time of 2 h. The surface was then modified in myristic acid to achieve superhydrophobicity. The superhydrophobic structure on the steel showed a high contact angle (CA) of 166 deg, excellent self-cleaning performance, and greatly improved corrosion resistance compared with the original counterpart. Meanwhile, its wear durability was evaluated by sandpaper abrasion test and the superhydrophobic structure maintained its property after moving 125 cm on the 1000-grit sandpaper under a pressure of 3.2 kPa.

Deformation behavior of Austenitic stainless steel at subzero temperature

Austenitic stainless steel is one of the second generation advanced high strength steel which finds application in automobile, aerospace and cryogenic components. The component made of austenitic steel might operate in subzero temperature condition because of its excellent formability even at subzero temperature. In the present work several tensile tests were performed on austenitic stainless-steel sheet of thickness 1.2 mm at 0°C, -40°C, -80°C, -120°C and at different strain rates of 0.01/sec,0.001/sec,0.0001/sec. The resultant mechanical properties, like yield strength, tensile strength, elongation percent and strain hardening exponent, along with phase fractions and microstructural properties were analyzed to understand the reasons for change in mechanical properties, on comparing with room temperature properties. It was noticed that tensile strength is 635 Mpa, & strain hardening exponent is 0.38 at room temperature (25 °C) and tensile strength is 1236 Mpa, & strain hardening exponent is O.49 at -120°C. Similarly, XRD characterization revealed that strain induced martensite increased from zero percent at 25°C (room temperature) to 57 percent at-120°C Similarly EBSD characterization revealed that grain average misorientation which also increased from room temperature to-120°C.

The role of the thickness on the tribological properties of FeAlCr intermetallic alloy thin films deposited on austenitic steel

Abstract

Boronizing of AISI 316L Stainless Steel Using Spark Plasma Sintering Technique

Austenitic stainless-steel has been widely used. Although it offers excellent corrosion resistance, processability, and nonmagnetic properties, it is inferior in terms of wear resistance and hardness. Therefore, the purpose of this study is to form iron boride on an austenitic stainless-steel surface using the spark plasma sintering (SPS) method and to evaluate its properties. The SPS method was utilized because the rapid heating involved in the process reduces the processing time. AISI 316L as a sample material was boronized for 3.6 ks at 1073 – 1273 K at applied pressures of 4 MPa and 8 MPa with a powder mixture of B4C and KBF4. The Vickers hardness profile results showed that the hardness of the untreated sample was ~ 200 HV whereas that of the boronized sample was ~ 2300 HV. The wear test profile showed that the wear resistance of the boronized sample was significantly improved. Moreover, according to elemental analyses, boron diffused from the sample surface to 200 μm and 60 μm when the applied pressure was 8 MPa and 4 MPa, respectively. This indicated that boron diffused to a greater depth when the applied pressure was increased.

Welding Investigation on GMAW−Cold Metal Transfer of AISI 201LN for Superior Weld Quality

Austenitic stainless steel of AISI 201LN grade has found applications in liquefied natural gas tanks and cryogenic components. They are fabricated using gas tungsten arc welding (GTAW), but weld speed is low due to manual operation. This work aims welding investigation on AISI 201LN Gr. steel with a new hybrid welding approach (i.e., gas metal arc welding [GMAW] combined cold metal transfer [CMT]) for obtaining superior weld quality. Weld experiments were carried out at different welding speed, for example, 300, 400, 600, and 900 mm/min, to study weld quality and its mechanical properties. The microstructural examination of test coupons at higher welding speed shows finer structure in heat-affected zone as well as on weld metal. It was observed that the weld coupon having low heat input (at high weld speed) has maximum tensile strength. Scanning electron microscope analysis shows finer dimples at higher welding speed confirming ductile mode of fracture.

A comparative study on characterisation of ASS 316L at room and sub-zero temperatures

ABSTRACT Austenitic Stainless Steel 316 L grade has wide applications in industries like pharmaceutical, chemical, petrochemical, medical equipment, and many specific subzero temperature products. These subzero applications are increasing in modern-day products to solve many issues like Natural gas storage and transport and many more. It is an ideal material for these applications due to its superior properties at these operating temperatures. In the present investigation tensile tests for ASS316 L material is conducted by considering the various parameters like different temperatures (room temperature(RT), 0°C, −25°C, −50°C) along with different orientation (0°,45°,90°), and crosshead speeds (3, 5 and 7 mm/min). The temperature variation was achieved by regulating the liquid CO2 cylinder connected using a pipe system to the closed furnace of the Universal Testing Machine setup is electronic controlled system. The output data were used to analyse the Mechanical Characteristics of the material. Then the fractured specimens at the room temperature and sub-zero temperatures were studied and analysed the failure modes in the material for the above changing variables. It was observed that the failure mode is changing from a ductile fracture to brittle when decreasing the temperature below zero degrees centigrade as predicted.

Evaluation of mechanical performance of friction welded AISI304L grade stainless steel joints

Austenitic stainless steel (ASS) rods of AISI304L Grade when welded have the significant issue of hot breaking and loss of erosion resistance. To reduce these problems the solid state friction welding is the best way to weld the AISI304L alloy and required testing is needed for the further process. In this research work, friction welded AISI304L rods of 10 mm diameter have been used for conducting the experimental testing of tensile strength (TS), fatigue strength (FS), hardness strength and temperature transformation during the friction welding. The results obtained show that the maximum tensile strength of the friction welded joint is 532 MPa, which is equivalent to 94.16% of the base metals tensile strength. The fatigue strength of the notched specimens is lower than un-notched specimens due to the high crack propagation in notched specimens.

A load-holding time prediction method based on creep strain relaxation for the cold-stretching process of S30408 cryogenic pressure vessels

Austenitic stainless steel (ASS) has been widely used for cryogenic pressure vessels. Its high strain hardening characteristic allows cold-stretching. In the cold-stretching process, the load-holding time is a critical operating parameter which affects the final deformation of the material. In this paper, a load-holding time prediction method for the cold-stretching process of S30408 cryogenic pressure vessels is proposed, based on room-temperature creep strain relaxation. The proposed correlation has only one variable, the maximum circumferential stress applied to the cylindrical shell, which can be easily obtained by finite element analysis. Consequently, the strain rate measurement during the cold-stretching process is significantly simplified. The prediction method and the strain rate measurement were verified by experimental measurements conducted on two vessels manufactured via the cold-stretching process. The measured strain relaxation times accurately matched the calculated values and the load-holding time for the process was well predicted.

Thermo-mechanical modeling of metallic alloys for nuclear engineering applications

Abstract Austenitic stainless steel 304 (SS304) alloy has been used exclusively in nuclear power systems due to its excellent mechanical properties at elevated temperature environments. Despite its wide popularity, the effect of various factors such as temperature, applied strain, and strain rate on the mechanical strength of the alloy needs to be investigated. In light of this, this research article focuses on development of a finite element based analytical modeling approach for modeling the mechanical strength of SS304 with respect to considered input factors. The proposed analytical approach combines the interface of finite element modeling and the heuristic optimization algorithm of genetic programming. The developed analytical model shows good conformance of the mechanical strength with the experimental observations. Sensitivity and parametric analysis of the derived model was also able to accurately predict the elastic and plastic regime of the alloy and shows that temperature remains the major factor in influencing the mechanical strength of the alloy. The proposed approach is anticipated to be useful for nuclear engineers for optimizing the design criteria for nuclear pressure vessels which can lead to increased material savings and hence lead to more sustainable design of nuclear power generation facilities.

EBSD Characterization of Pilgered Alloy 800H After Heat Treatment

Austenitic stainless steel alloy 800H pipes were received in an as-pilgered condition. The pilgering process produces high levels of cold work through complex deformation processes. The pipes are subsequently solution annealed. To assess the influence of heat-treatment parameters on 800H, samples of the as-pilgered material were heat treated in the temperature range 600°C–1200°C for varying lengths of time. Using electron backscatter diffraction (EBSD), the recrystallization dynamics and grain size of all samples was measured. Additionally, the kernel average misorientation and grain orientation spread methods were employed to qualitatively analyze fine details in the strain levels in the matrix of both deformed and recrystallized grains. For 1-h anneal times, it was found that recrystallization of 800H initiates above heat-treatment temperatures of 800°C, and complete recrystallization of deformed material occurs above heat-treatment temperatures of 950°C. No significant increases in average grain size were observed until temperatures reached in excess of 1000°C. Increasing the heat-treatment time to more than 1 h had a negligible effect on the grain size for every heat-treatment temperature that was assessed. In high-temperature applications, pipes typically fail because of diffusion-based creep mechanisms. Therefore, accurate control of the grain size and microstructure during heat treatments is obligatory. This work provides a framework for controlling manufacturing processes to produce favorable microstructures in 800H for creep-based applications.

True stress measurement of nuclear fuel rod cladding material subjected to DSA regime

Austenitic stainless steel (ASS) grade 304 is being extensively used in various high-temperature applications, which makes it important to study their properties at elevated temperatures, especially the flow stress behavior. The literature reveals flow stress of the material depends on influence of various input parameters, the important ones being the strain, strain rate and temperature. It is often noticed that these process parameters are determined by trial-and-error approach, which results in increased material failure and power losses. Constitutive models have also been developed to find the relationships between them, but these models have computational limitations and cannot capture the true stress behavior at elevated temperatures. Therefore, there is a need for formulation of a generalized explicit model/expression that can predict accurately the behavior ASS 304 at elevated temperatures. Therefore, this work proposed a new variant of genetic programming, gene expression programming (GEP), to formulate a model for true stress of ASS 304. True stress model formulated based on M-MGGP methodology has outperformed the GEP approach. Further investigation is carried out by sensitivity and parametric analyses to determine the relationships between process parameters, and it was found that the temperature has highest impact on the true stress of ASS 304 steel.

Fatigue Failure of Hydroformed AISI 316L Stainless Steel Bellows

Austenitic stainless steel AISI 316L is used for components of cryogenic engine in satellite launch vehicles due to its better mechanical properties at low temperatures. In one such application, AISI 316L stainless steel bellows are used in electro-pneumatic command valve of a cryogenic engine. This valve employs a hydro-formed bellow of 0.14mm thickness as an actuator element. When one of the electro-pneumatic command valve was vibrated without pressure, crack was noticed at the inner diameter of the bellow. Detailed metallurgical analysis indicated that the cracking to be due to fatigue.

Investigation of the electro-chemical corrosion of laser-melted layers of stainless steel in artificial saliva

Austenitic stainless steel is one of the materials commonly used for manufacturing of orthodontic appliances and brackets. In this study, samples of AISI 321 (EN X6CrNiTi 18-10) steel in initial condition and after laser surface melting were investigated in artificial saliva with pH 5.6. Two tests were conducted: measurement of open circuit potentials (free potentials) Ef until reaching steady state potentials Ess and potentiodynamic anodic polarisation. The samples’ surface was characterised by SEM, and EDX analysis was also done. Small amount of pits were observed on the surface of all samples – untreated and laser-melted layers as well. The steady state potential of the base metal was about +238 mV, while that of the laser-melted layers was approximately 50 mV lower. The pitting potentials Epit of the laser-treated samples were lower than those of the untreated stainless steel (+802 mV). It was established that the laser-melted surface layers of stainless steel are more susceptible to pitting corrosion in artificial saliva with higher acidity than those of the base metal.

Resistance Spot Welds of 304I Austenitic Stainless Steel, Part 1:Fundamental, Simulation, Weld Growth, Tensile Strength And Failure Mode Analysis

Austenitic stainless steel(ASS) is very common material that used in many industries today. Suitable joining method should be of low cost; reliable and long life. In such situation, the industries may prefer to use the resistance spot welding (RSW) for such ASS sheet. The weld quality of RSW joint is usually considered by nugget size which relies on the welding parameters. This paper analyzes the weld nuggets' characteristic of 304L austenitic stainless steel with relevant to its basic welding parameters (current, weld time and force). The entire experiment is carried out by varying the welding current and welding time at first attempt and the welding current and electrode force at second attempt. The increment of current and weld time has resulted proportional increment of nugget diameters; whereas the force increment has resulted reduction of nugget diameters. These results have been relatively compared with simulation results for the proper weld region identification. Eventually the welded joints were characterised by tensile shear test, macro graph and elongation measurement to relate the changes that happened due to the variations of welding parameters.

Metallurgical Studies of Austenitic Stainless Steel 304 under Warm Deep Drawing

Austenitic stainless steel 304 was deep drawn with different blank diameters under warm conditions using 20 t hydraulic press. A number of deep drawing experiments both at room temperature and at 150 °C were conducted to study the metallography. Also, tensile test experiments were conducted on a universal testing machine up to 700 °C and the broken specimens were used to study the fractography of the material using scanning electron microscopy in various regions. The microstructure changes were observed at limiting draw ratio (LDR) when the cup is drawn at different temperatures. In austenitic stainless steel, martensite formation takes place that is not only affected by temperature, but also influenced by the rate at which the material is deformed. In austenitic stainless steel 304, dynamic strain regime appears above 300 °C and it decreases the formability of material due to brittle fracture as studied in its fractography. From the metallographic studies, the maximum LDR of the material is observed at 150 °C before dynamic strain regime. It is also observed that at 150 °C, grains are coarse in the drawn cups at LDR.

Ultrasonic Beam Simulation of Austenitic Stainless Steel Pipeline Welding Cladding

Austenitic stainless steel shows clear acoustic anisotropy. How to detect and evaluate the material becomes research difficulty and popular problem in acoustic detection field. In the paper, Civa software is applied for simulating ultrasonic wave propagation in austenitic stainless steel cladding layer. The influence of included angle between acoustic wave propagation direction and crystal axis on acoustic wave propagation is studied. The study results show that: the focusing property is good when the included angle is 30°-45°, which is beneficial for ultrasonic testing of cladding layer. When the included angle is greater than 70° or so, actual propagation path of acoustic wave and propagation direction of acoustic wave have certain deviation angle with poor acoustic wave focusing property and rapid acoustic attenuation speed, which is not conducive to acoustic detection of cladding layer.

Strain Rate Effects on Strain-Induced Martensitic Transformation and Electrical Resistivity of Deforming Stainless Steel

Austenitic stainless steel was compressed at a strain rates of 103 s-1 using a Hopkinson pressure bar apparatus at temperatures of 77 K and 293 K. The electrical resistivity was measured to determine the volume fraction of martensite of a deforming specimen. A compressive specimen of the dumbbell type was suitable for attaching the lead-in wires of four-point probes to the specimen. The volume fraction of martensite formed at a strain rate of 103 s-1 was lower than that formed at a low strain rate regardless of the temperature, and the effect of the strain rate on the electrical resistivity was slight. However, since the volume fraction of martensite is expressed as a linear function of the electrical resistivity ratio as well as in the results obtained by the tensile test, the electrical resistivity was available as an index for estimating the volume fraction of martensite induced by dynamic deformation. The duration of the input wave was approximately 150 μs, and the appearance of the peak value of transient resistivity was approximately 1ms after the arrival of the input wave at the specimen. These results showed that the structure change evaluated using electrical resistivity was not completed in the time required for the stress wave to pass through the specimen, although the electrical resistivity immediately after dynamic deformation closely approached that obtained by the static test.

Low Cycle Fatigue Behavior and Mechanism of Newly Developed Advanced Heat Resistant Austenitic Stainless Steels at High Temperature

Austenitic stainless steel grade UNS S31035 (Sandvik Sanicro® 25) has been developed for the next generation of 700°C A-USC power plant. This paper will mainly focus on the study of low cycle fatigue behavior and damage mechanisms of the material at room temperature, 600C to 700C by using electron back scatter diffraction and electron channeling contrast image techniques. At room temperature, the material shows a hardening and softening behavior as usual. At high temperature, however, it shows only a cyclic hardening behavior. Dynamic strain ageing can be one of the mechanisms. The damage and fatigue crack initiation mechanisms due to cyclic loading at different temperatures and loading conditions have been identified. The interactions between dislocations or slip bands with grain boundary or twin boundary are the main damage mechanism at low temperature or at high temperature with large strain amplitudes. Strain localization due to dislocation slipping is the main mechanism for the damage in grain.