Austenitic SS Research Articles

Effect of Cyclic Load Frequency on the Fatigue Crack Nucleation and Growth of Annealed and Prestrained Austenitic SS 304

ABSTRACTThe austenitic stainless steels are widely used in several engineering fields due to their high ductility, corrosion and high temperature performance. Despite its noble properties, components manufactured in austenitic stainless steel are subject to fatigue failure. Studies indicate that loading frequency can impact the austenitic stainless steel fatigue performance. In this scenario, the present study aims to evaluate the effect of frequencies of 3 and 30 Hz on the fatigue behavior of SS 304 alloy under load control in order to identify in which fatigue stage the effect is outstanding. Therefore, fatigue and fracture mechanics tests were evaluated on the alloy annealed at 1000°C. Furthermore, fatigue tests were also applied to the alloy after previous tensile plastic strain of 0.5. The analyses denoted a significant reduction in fatigue strength with increasing frequency, especially for the strained alloy. Fatigue crack nucleation is encouraged with greater load frequency. This behavior may be attributed to strain‐induced martensite and other strain mechanisms such as twinning and slip bands that are encouraged by lower strain rates but are relieved by auto‐heating achieved in higher frequencies, as mentioned in the literature, which decrease the strength to fatigue nucleation.

FeNi as raw material for stainless steel 316 and its mechanical properties

The manufacture of cast stainless steel 316 (SS 316) requires one essential raw material element, pure nickel. The demand for pure nickel is quite high, its price is the highest among other raw materials and it is still being imported. This study aims to utilise local ferronickel (FeNi) as a raw material for stainless steel and determine the effect of the percentage of FeNi usage on the mechanical properties of austenitic SS 316, which is a metal biomaterial widely used as a bone implant. This material is a potential replacement for nickel for stainless steel production. In this study, local FeNi at percentages of 0%, 23%, 45%, or 70% was added to other casting raw materials. The foundry process was carried out, and the samples were subjected to composition, tensile, hardness, and toughness tests. Results showed that all the samples had a chemical composition that met the SS 316 standard, indicating that the FeNi raw material can be used as raw material for SS 316, although impurities were still found at each percentage addition of FeNi. The tensile strength and hardness were still below the SS 316 standard but ductility was higher than the SS 316 standard at all percentages of FeNi.

Synergistic effect of temperature, concentration and solution flow on corrosion and passive film of austenitic SS 304L and 316L in concentrated sulfuric acid

The synergistic effect of temperature, sulfuric acid concentration and solution flow on the corrosion behavior and passive film properties of austenitic SS 304L and 316L have been investigated in concentrated sulfuric acid. Design of experiment was used and electrochemical techniques were employed. It was found that investigated parameters synergistically affect the corrosion behavior and passive film properties. Surface films formed at high concentrations are less defective and increasing temperature and solution flow introduced more defects; however, the passive film repairs itself. Increasing the temperature and solution flow resulted in higher passive film coverage and cracking of the passive film, respectively.

Tribological behavior and biocompatibility of novel Nickel-Free stainless steel manufactured via laser powder bed fusion for biomedical applications

Due to the risk of releasing carcinogenic nickel ions from conventional 316L stainless steel under a corrosive human body environment, a new variant of steel termed nickel-free stainless steel (NiFSS) has been investigated. The present study investigates the tribological properties and biocompatibility of NiFSS manufactured via laser powder bed fusion (PBF-LB/M). The ferritic NiFSS exhibited significantly lower coefficient of friction (0.08 to 0.28) and wear rate (1.60 × 10-6 mm3/Nm to 6.60 × 10-6 mm3/Nm) compared to reported values for austenitic 316L SS, under both dry and simulated body fluid (SBF) conditions and various sliding geometries. This improvement is attributed to the superior hardness (3.394 ± 0.1340 GPa) and elastic modulus (238 ± 9.0797 GPa) of NiFSS. To assess the biocompatibility, the viability of mouse pre-osteoblastic MC3T3-E1 cells was evaluated with an Alamar Blue assay when the cells were cultured on top of PBF-LB/M built NiFSS and 316L SS samples. The results indicated that even though cell growth was most optimal on regular cell culture plastic, cell viability was better maintained on PBF-LB/M built NiFSS compared to 316L SS. Therefore, the results of the present study propose that PBF-LB/M fabricated NiFSS holds promise for application in biomedical devices for joint arthroplasty.

Creep deformation and constitutive modelling of 316LN SS with varying nitrogen content

In this investigation, two different constitutive models were employed to examine the creep deformation and damage behaviour of nuclear grade austenitic 316LN SS with four different nitrogen contents (0.07–0.22 wt%) at 923 K. Creep deformation resistance of the alloys investigated by “internal-stress based kinetic creep law” for primary and secondary creep stages revealed an increase in internal stress and decrease in obstacle spacing accompanied with lower dynamic recovery with increasing nitrogen. The aforementioned outcomes substantiated the experimentally observed beneficial role of nitrogen on lowering of creep strain rate with increasing nitrogen level. In contrast to the above observations, the analysis of coupled creep deformation and damage using the Kachanov-Rabotnov model and the subsequent development of iso-damage contours indicated evolution of higher creep damage at lower strains with increasing nitrogen content. With increasing % nitrogen, damage rate dominated over the strain rate thus justifying the observed significant intergranular damage at and above 0.14% N. Based on the above results and in-house studies on low cycle fatigue and creep–fatigue interaction, optimum nitrogen content is suggested between 0.07 and 0.14% N in 316LN SS that combines the benefits of low nitrogen content and strengthening effects of high nitrogen content.

Formability investigation of perforated austenitic SS 304L sheets using SPIF

Incremental sheet forming (ISF) is a progressive and highly flexible method of producing sheet metallic components in batches of limited quantities. It is also used for making prototypes at a low cost. Advantages of ISF are: higher sheet formability; elimination of molds and dies or use of simple molds and dies; formed parts with a good surface finish; use of commonly available vertical CNC milling machine and the possibility of quick changes in design. The low accuracy of formed parts and slow speed of the process are the disadvantages of ISF. Perforated metallic sheets have many applications in different industries because of their attractive display exposable to the atmospheric air and lighter weight than nonperforated metallic sheets. Its formability varies with the hole dimensions, ligament width, material chemistry, and forming parameters. In this paper, the effects of hole size, and other input parameters on the formability of the sheet are investigated. One millimeter thick SS 304L perforated sheets with 2 mm and 3 mm diameter holes are used for the present work. FLD and FLSD were drawn after performing the straight groove and wall angle tests. The highest formability was observed in the sheet with 2 mm diameter holes. XRD line profile analysis was done and correlated the formability with the crystallite size and dislocation density. SEM micrographs of fracture surfaces were taken and the fractographic parameters were correlated with formability. FE simulation was done using the optimized process parameters and the simulation results were compared with the experimental results. Contour and spiral tool path comparison was done numerically and experimentally.

Dissimilar welding of austenitic SS and ferritic SS in last decades

Materials are very crucial and important factor in different industrial processes. Austenitic treated steel utilized overall in different significant businesses like synthetic, petrochemical, thermal energy station and vehicle dependent principally upon their corrosion opposition yet additionally for their formability, their solidarity, and their properties at outrageous temperatures. In any case, the expense of such steel is a significant worry to the ventures as the expense of austenitic treated steel is expanding step by step, because of the deficiency of its constituent Ni (Nickel). Thus, to keep away from this issue, the businesses could utilize a blend weld of two Steel having lower level of Ni. which would require right decision of filler material, welding method for an imperfection free sound weld. This paper endeavors an introductory survey of the most common way of joining significant contrasts among austenitic and ferritic Tempered Steel, its microstructure and corrosion opposition properties and mechanical properties in different Cycles and blends.

Study on narrow gap welding of martensitic grade P92 and austenitic grade AISI 304L SS steel for ultra-supercritical power plant application

Study on narrow gap welding of martensitic grade P92 and austenitic grade AISI 304L SS steel for ultra-supercritical power plant application

Damage Evolution Simulations via a Coupled Crystal Plasticity and Cohesive Zone Model for Additively Manufactured Austenitic SS 316L DED Components

This study presents a microstructural model applicable to additively manufactured (AM) austenitic SS 316L components fabricated via a direct energy deposition (DED) process. The model is primarily intended to give an understanding of the effect of microscale and mesoscale features, such as grains and melt pool sizes, on the mechanical properties of manufactured components. Based on experimental observations, initial assumptions for the numerical model regarding grain size and melt pool dimensions were considered. Experimental observations based on miniature-sized 316L stainless steel DED-fabricated samples were carried out to shed light on the deformation mechanism of FCC materials at the grain scale. Furthermore, the dependency of latent strain hardening parameters based on the Bassani–Wu hardening model for a single crystal scale is investigated, where the Voronoi tessellation method and probability theory are utilized for the definition of the grain distribution. A hierarchical polycrystalline modeling methodology based on a representative volume element (RVE) with the realistic impact of grain boundaries was adopted for fracture assessment of the AM parts. To qualify the validity of process–structure–property relationships, cohesive zone damage surfaces were used between melt pool boundaries as the predefined initial cracks and the performance of the model is validated based on the experimental observations.

Effect of Stress and Temperature on Rupture Life of Dissimilar Weld Joint of Austenitic 316LN SS and Ferritic-Martensitic P91 Steel

Effect of Stress and Temperature on Rupture Life of Dissimilar Weld Joint of Austenitic 316LN SS and Ferritic-Martensitic P91 Steel

Parametric analysis and simulation of surface roughness and tool flank wear in machining of low carbon alloy steel

Austenitic SS influences in most frequently applied corrosion resistance or in higher surface loading were it is required. The present investigation represents the quality attributes namely surface roughness and tool wear rate in turning of AISI 316L steel using DoE. Taguchi method has been employed with L9 (34) orthogonal array of the three significant factors, i.e., speed, feed and depth of cut, to achieve the minimum surface roughness and tool wear rate. The Analysis of variance was performed to identify the influencing factors which affect the responses. The outcomes from the research reveal that the minimum surface roughness was achieved at cutting speed 170 m/min, feed rate 0.10 mm/rev, depth of cut 0.15 mm and the minimum too wear rate was attained at 170 m/min cutting speed, 0.07 mm/rev feed rate and 0.15 mm depth of cut was determined using the experimental study and compared with the prediction model from design of experiments. The results shows that both the values were good in agreement with experimental as well as prediction results.

Helium-hydrogen synergistic effects on swelling in in-situ multiple-ion beams irradiated steels* *Project supported by the National Natural Science Foundation of China (Grant No. 11935004).

The development of reliable fusion energy is one of the most important challenges in this century. The accelerated degradation of structural materials in fusion reactors caused by neutron irradiation would cause severe problems. Due to the lack of suitable fusion neutron testing facilities, we have to rely on ion irradiation experiments to test candidate materials in fusion reactors. Moreover, fusion neutron irradiation effects are accompanied by the simultaneous transmutation production of helium and hydrogen. One important method to study the He–H synergistic effects in materials is multiple simultaneous ion beams (MSIB) irradiation that has been studied for decades. To date, there is no convincing conclusion on these He–H synergistic effects among these experiments. Recently, a multiple ion beam in-situ transmission electron microscopy (TEM) analysis facility was developed in Xiamen University (XIAMEN facility), which is the first triple beam system and the only in-running in-situ irradiation facility with TEM in China. In this work, we conducted the first high-temperature triple simultaneous ion beams irradiation experiment with TEM observation using the XIAMEN facility. The responses to in-situ triple-ion beams irradiation in austenitic steel 304L SS and ferritic/martensitic steel CLF-1 were studied and compared with the results in dual- and single-ion beam(s) irradiated steels. Synergistic effects were observed in MSIB irradiated steels. Helium was found to be critical for cavity formation, while hydrogen has strong synergistic effect on increasing swelling.

Machinability, weldability and surface treatment studies of SDSS 2507 material-A review

Super duplex stainless steel 2507, is a difficult to machine material due to high chromium content. Knowledge on machinability, weldability and surface treatment of 2507 super duplex stainless steel material is necessary due to the increase in demand of this material in variety of application in engineering and medical fields. In this review, machinability studies on turning and milling of SDSS 2507 is discussed. Weldability of SDSS 2507 material is also reviewed in this paper. Effect of heat and chemical treatments on strength, ductility, resistance to corrosion, wear, crack propagation and pitting characteristics of this material are included. Machining with wet, minimal quantity lubrication and dry conditions are analyzed. From the review, it was found that machinability can be improved by machining at high cutting speed and low feed rate along with proper selection of tool. Welding of SDSS 2507 material with similar and dissimilar materials is also discussed. Literatures on the studies on machining of SDSS 2507 material, especially on milling of SDSS material is very less compared to turning operation. Review revealed that SDSS 2507 material possess better strength, ductility and corrosion resistance properties compared to Austenitic SS and Ferritic SS. The present paper recommends the usage of tougher insert grades for machining. From this review, it is clear that SDSS 2507 material can be used in corrosion prone environments due to its high resistance to corrosion and pitting characteristics. SDSS 2507 material can also replace duplex stainless steel in storage and transportation of petroleum products, piping, etc. due to its exceptional characteristics.

High temperature deformation behavior of Indian PHWR Calandria material SS 304L

Calandria, a horizontal stepped cylindrical vessel, houses the fuel channels (reactor core) of Indian Pressurized Heavy Water Reactors (IPHWRs). The Calandria and its support assembly is made from austenitic stainless steel SS 304L grade. Post Fukushima nuclear accident (2011), the realistic assessment of time line of structural degradation of Calandria during the progression of a postulated severe accident has become an important requirement. This calls for a detailed finite element analysis of Calandria assembly where material deformation behavior owing to both creep and plasticity up to very high temperatures arising during accident progression has to be modeled.Although stainless steel SS 304L finds wide application in nuclear industry, the material properties up to very high temperatures as required for present case, are not available in the open literature. Hence, in the present work, the tensile and creep-stress rupture properties of SS 304L have been generated for temperatures up to 1100 °C. Engineering stress-strain curves, yield strength, ultimate tensile strength, uniform elongation as well as Ramberg-Osgood fitting parameters are evaluated from the tensile test data. Creep test data is processed to evaluate creep curves, minimum creep rate, Norton-Bailey creep law parameters as well as Larson Miller Parameter based correlation for prediction of stress rupture life. The generated properties would be useful as material inputs to carry out realistic structural integrity assessment of Calandria assembly for loads arising under accident conditions.

Microstructure and Tensile Properties of Diffusion Bonded Austenitic Fe-Base Alloys—Before and After Exposure to High Temperature Supercritical-CO2

Austenitic Fe-base alloys, SS 316H and Alloy 800HT, were diffusion bonded for use in compact-type heat exchangers in supercritical-carbon dioxide (S-CO2) Brayton cycles. For diffusion bonded 316H, grain boundary migration across the bond-line was observed despite the formation of some Cr-rich carbide, and its tensile properties were similar to those of as-received 316H. However, diffusion bonded Alloy 800HT exhibited severely degraded elongation compared to as-received 800HT due to the formation of continuous Ti-rich carbides along the bond-line. Post-bond heat treatment (PBHT) was found to improve elongation at fracture for diffusion bonded alloys. However, a subsequent corrosion test in S-CO2 at 600 °C (20 MPa) for 1000 h resulted in a loss of elongation. This was much more severe for PBHT-ed 800HT due to the formation of Cr-rich carbides at the bond-line. Meanwhile, it was found that the effect of ageing on loss of elongation during high temperature exposure was greater than that of S-CO2 environment.

Long-term exposure of MgAl2O4 and Y2O3 thermal barrier coatings in molten sodium

Thermal barrier coatings (TBCs) of magnesium aluminate spinel (MgAl2O4) and yttria (Y2O3) were investigated for long term compatibility with molten sodium for applications in sacrificial core catcher of Future Fast Reactors (FFRs). Thermal barrier ceramic coatings were deposited over austenitic grade stainless steel SS 316LN (flat and cylindrical samples), with an intermediate NiCrAlY bondcoat, using Atmospheric Plasma Spray (APS) technique. The coated samples were exposed to high purity molten sodium at 400 °C under an inert argon atmosphere for 500 h and 1000 h. Sodium exposed samples were subjected to post-cleaning by vacuum distillation followed by chemical cleaning for effective removal of sodium from the specimens. Visual examinations revealed discoloration in the Na exposed samples. Microstructural characterization of Na exposed samples revealed densification in the ceramic topcoats. X-ray diffraction analysis on the topcoats did not reveal any phase change or formation of any corrosion product upon interaction with sodium. Tensile adhesion test on cylindrical samples, as per ASTM C633, revealed ~62% and ~33% drop in the bonding strength after 1000 h of sodium exposure for spinel and yttria coatings, respectively. The mechanical properties were correlated to the microstructural characteristics of the TBC system before and after Na exposure.

Electrochemical Impedance Analysis on Cryogenically Treated Dissimilar Metal Welding of 316L Stainless Steel and Monel 400 Alloy Using GTAW

An attempt was made to study the corrosion behavior of austenitic stainless-steel SS 316L/Monel 400 alloy dissimilar metal welded joints using gas tungsten arc welding. This combination of welded joints is used in re-heaters and heat exchangers in gas processing and oil refining industries. The welded specimens were subjected to post-weld treatments, such as annealing and deep cryogenic treatment. The welded specimens were sectioned into five different parts: SS 316L base, SS 316L HAZ, weld, Monel HAZ, and Monel base. The polarization method and electrochemical impedance analysis were used to analyze the corrosion resistance in a NaCl solution. A polarization graph, Nyquist plot, and Bode plot were constructed for all regions, separately, for the heat-treated and cryo-treated specimens, to analyze the variation in corrosion resistance in different regions, and then the results were compared. To validate the results of electrochemical impedance analysis, scanning electron microscope (SEM) and energy dispersive spectroscope (EDS) analyses were also performed. The results indicated that the cryo-treated specimens have better corrosion resistance when compared to the annealed ones. Weld region on both specimens exhibited better corrosion resistance when compared to other zones.

Structural relationships of metallurgical and mechanical properties influenced by Ni-based fillers on Gas Tungsten Arc Welded Ferritic /Austenitic SS dissimilar joints

Structural relationships of metallurgical and mechanical properties influenced by Ni-based fillers on Gas Tungsten Arc Welded Ferritic /Austenitic SS dissimilar joints

Research on the Application of Fen for Environmentally Assisted Fatigue Evaluation of the Austenitic SS Pipe Under Combined Transient Loads

Accumulative test data indicate that the effects of the light water reactor (LWR) environment could cause the fatigue resistance of primary pressure boundary components materials to be significantly reduced. Environmentally assisted fatigue (EAF) is the abbreviation of the environmentally assisted fatigue. In 2007, Nuclear Regulatory Commission (NRC) issued RG. 1.207. It was updated in 2014. And, it requires that the effects of LWR environment on the fatigue life reduction of metal components should be considered for new design plants. And it suggests to use environmental correction factor, Fen, to account for EAF. NRC regulation (NUREG), NUREG/CR-6909 (NRC, 2013, “Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials,” U.S. Nuclear Regulatory Commission, Argonne, IL, Standard no. NUREG/CR-6909), presents the detail Fen calculation formula. Fen is a function of temperature, strain rate, dissolved oxygen level in water, and sulfur content of the steel. Accordingly, Fen calculation will present a comparatively conservative result. Depending on the experience of the primary pressure boundary piping transient operation, Fen varies during each transient. More uncertainty and confusion are raised during the application of the Fen method. The research work in this paper includes: first, the typical character of piping thermal transient is derived based on the existing experience. Second, small specimen EAF tests are conducted depending on the above derived combined loading characters. Then effort is taken to improve the application of the Fen method for the combined multitransient loading conditions. And the results are compared with those of the lowest instantaneous Fen method and equalization of the weighted Fen method. Finally, a designed test plan is presented.

Investigations on joining of stainless steel tailored blanks by µ-PTA process

ABSTRACTPresent work is focused on the autogenous joining of tailored blanks, that is, sheets of different thickness but of the same material (austenitic stainless steel grade SS 316L). A thin sheet (1mm) and a thick sheet (3 mm) were joined autogenously using Indigenously developed micro-plasma transferred arc (µ-PTA) process. Effects of current, torch travel speed and stand of distance (SOD) were investigated to determine their optimum levels of joint tensile strength. The produced joint was characterized using different methods such as optical microscopy, scanning electron microscopy, uniaxial tensile tests, Vicker’s microhardness, and energy dispersive X-ray analysis. It was found that (19.4 A, 63 mm/min, 1.3 mm), (19.6 A,80 mm/min, 1.3 mm) and (19.8 A, 100 mm/min, 1.3 mm) with values of plasma flow rate at 0.4 Nl/min and shielding gas flow rate at 5 Nl/min, yielded sound weld Joint. Absence of heat affected zone was confirmed by very small variation in Vickers microhardness values across the fusion zone. This study establishes the capability of microplasma transferred arc process for joining stainless sheets of different thickness without any filler material and producing very good quality joint using much less power as compared to conventional fusion joining processes.