Austenitic Stainless Steel AISI Research Articles

Effect of Hydrogen Charging on the Mechanical Properties of High-Strength Copper-Base Alloys, Austenitic Stainless Steel AISI 321, Inconel 625 and Ferritic Steel 1.4511

Hydrogen embrittlement (HE) poses the risk of premature failure for many metals, especially high-strength steels. Due to the utilization of hydrogen as an environmentally friendly energy source, efforts are made to improve the resistance to HE at elevated pressures and temperatures. In addition, applications in hydrogen environments might require specific material properties in terms of thermal and electrical conductivity, magnetic properties as well as corrosion resistance. In the present study, three high-strength Cu-base alloys (Alloy 25, PerforMet® and ToughMet® 3) as well as austenitic stainless AISI 321, Ni-base alloy IN 625 and ferritic steel 1.4511 are charged in pressurized hydrogen and subsequently tested by means of Slow Strain Rate Testing (SSRT). The results show that high-strength Cu-base alloys exhibit a great resistance to HE and could prove to be suitable for materials for a variety of hydrogen applications with rough conditions such as high pressure, elevated temperature and corrosive environments.

Artificial Neural Networks and Experimental Analysis of the Resistance Spot Welding Parameters Effect on the Welded Joint Quality of AISI 304.

The automobile industry relies primarily on spot welding operations, particularly resistance spot welding (RSW). The performance and durability of the resistance spot-welded joints are significantly impacted by the welding quality outputs, such as the shear force, nugget diameter, failure mode, and the hardness of the welded joints. In light of this, the present study sought to determine how the aforementioned welding quality outputs of 0.5 and 1 mm thick austenitic stainless steel AISI 304 were affected by RSW parameters, such as welding current, welding time, pressure, holding time, squeezing time, and pulse welding. In order to guarantee precise evaluation and experimental analysis, it is essential that they are supported by a numerical model using an intelligent model. The primary objective of this research is to develop and enhance an intelligent model employing artificial neural network (ANN) models. This model aims to provide deeper knowledge of how the RSW parameters affect the quality of optimum joint behavior. The proposed neural network (NN) models were executed using different ANN structures with various training and transfer functions based on the feedforward backpropagation approach to find the optimal model. The performance of the ANN models was evaluated in accordance with validation metrics, like the mean squared error (MSE) and correlation coefficient (R2). Assessing the experimental findings revealed the maximum shear force and nugget diameter emerged to be 8.6 kN and 5.4 mm for the case of 1-1 mm, 3.298 kN and 4.1 mm for the case of 0.5-0.5 mm, and 4.031 kN and 4.9 mm for the case of 0.5-1 mm. Based on the results of the Pareto charts generated by the Minitab program, the most important parameter for the 1-1 mm case was the welding current; for the 0.5-0.5 mm case, it was pulse welding; and for the 0.5-1 mm case, it was holding time. When looking at the hardness results, it is clear that the nugget zone is much higher than the heat-affected zone (HZ) and base metal (BM) in all three cases. The ANN models showed that the one-output shear force model gave the best prediction, relating to the highest R and the lowest MSE compared to the one-output nugget diameter model and two-output structure. However, the Levenberg-Marquardt backpropagation (Trainlm) training function with the log sigmoid transfer function recorded the best prediction results of both ANN structures.

Failure analysis of an AISI 310 stainless steel beam reinforcement fracture during service in a rolling beam furnace

This work investigated the premature failure of a beam reinforcement made of austenitic stainless steel AISI 310 used in the entrance of a rolling beam furnace working continuously at cycles from 650 to 850 °C. Fracture surface and microstructural investigations allowed to identify the fracture mechanism as fatigue failure. The fracture was probably initiated at the oxidized grain boundaries at an early stage of service life, when no microstructure degradation was present, while most of the fatigue crack propagation occurred after the precipitation of secondary phases. The microstructure investigation revealed severe microstructure degradation with the presence of intermetallic sigma (σ) phase (area fraction = 19 %) and M23C6 carbides (area fraction = 1 %), which were formed during the high-temperature exposure. Cracking of σ phases and decohesion at σ /austenite matrix interfaces were observed near the fracture and in the small punch test samples. Such discontinuities provide an easy path for crack propagation.

Influence of cutting edge microgeometry on the cutting forces when machining difficult-to-cut materials

The paper presents research investigating the influence of cutting tools microgeometry on the cutting forces when milling difficult-to-cut materials. Austenitic stainless steel AISI 316L and nickel alloy Inconel 718 were machined with cemented carbide tools with various cutting edge rounding size while measuring the cutting forces during the process. From the standpoint of milling difficult-to-cut materials lowering the cutting forces load on the tool can be difficult to achieve without significant reduction of cutting parameters. Previous research into the cutting edge microgeometry suggests that modification of the cutting edge of milling tools can substantially extend the effective tool life, reduce cutting forces in the process and ensure higher quality of the machined surface. Results of long term wear tests of tools with cutting edge rounding sizes of 15, 30 and 45 µm are compared to the results of a sharp unprepared cutting tool, and the results of each machined material are also compared. Possible influence of cutting edge radius on the process for both materials was tested for cutting conditions constituting finishing operation. The most effective cutting edge radius size differed between the materials, with 15 µm rounding performing the best for AISI 316L and the sharp unprepared tool performing the best for the Inconel 718 alloy.

Analyzing microstructural, residual stress, and mechanical characteristics in dissimilar welds of Inconel 59 and AISI 904L through double-pulsed gas metal arc welding

In this research, dissimilar welding of the nickel-based superalloy Inconel 59 and austenitic stainless steel AISI 904L steel was successfully done with double-pulsed gas metal arc welding (DP-GMAW) using the filler ERNiCrMo-13. Macroscopic analysis showed a defect-free weld with an aspect ratio of 2.4, attributed to the efficient heat delivery (0.642 kJ/mm) in DP-GMAW. The microstructure of the weld joint was examined through both optical microscopy and scanning electron microscopy. Examination of the microstructure of the weld interface exposed grain coarsening near the heat-affected zone on the AISI 904L side. In contrast, the weld fusion zone contained fine equiaxed dendrites. Microsegregation and alloying element migration across the entire weld area were assessed through energy dispersive X-ray spectroscopy point analysis and line mapping, revealing controlled microsegregation across the region. X-ray diffraction (XRD) analysis was used to ascertain the average grain size (38.41 nm) and secondary phase composition. The XRD-cosα method was used to assess the residual stress of the weld joint, revealing tensile residual stress in the weld zone and compressive residual stress in other regions. Tensile, Charpy impact, and Vickers hardness tests were conducted in the study to evaluate the strength, toughness, and hardness of a dissimilar weld. The impact of two cryogenic treatments, namely shallow and deep, on tensile and toughness characteristics was investigated in this study. The cryogenic treatments significantly enhanced the mechanical properties of weld samples compared to their as-welded condition, leading to an 11.5% increase in tensile strength and a 10% improvement in toughness.

Numerical analysis of maximum force in deep drawing processes of prismatic parts

The high competitiveness of the industrial sector and the short time for developing new products drives the use of process analysis tools that enable speeding up the design phase. In sheet metal stamping projects, numerical simulation has become indispensable. As a replacement for traditional trial-and-error methods, the finite element method (FEM) enables the optimization of process-related variables. Consequently, it is possible to mitigate some of its main problems, such as the emergence of fracture, wrinkling, and springback. A second alternative for analyzing the process, even faster and cheaper, is based on the use of analytical calculations. These can predict, among other parameters, the forces involved in stamping. This study aims to evaluate the degree of accuracy of equations predicted in the literature to estimate the maximum stamping force of non-axisymmetric parts. For this purpose, analytical results of the stamping force of 1 mm thick austenitic stainless steel AISI 304 sheets were compared to results obtained via numerical simulation.

Mechanical Properties of Indentation in Plasma Nitrided and Nitrocarburized Austenitic Stainless Steel AISI 321

Austenitic stainless steels are widely used due to their resistance to corrosion and to the possibility of using them at temperatures above 600 °C. Plasma nitriding and nitrocarburizing consist of a thermochemical process that introduces nitrogen and nitrogen/carbon, in atomic form, allowing the formation of second phases of these elements with the substrate. These thermochemical treatments of plasma nitriding and nitrocarburizing were performed on austenitic stainless steel AISI 312 at temperatures of 400 °C and 500 °C, obtaining thicknesses of around 12 μm and 24 μm, respectively. Mechanical properties of indentation were obtained using a Hit 300 nanoindenter (Anton Paar), in a load-unload cycle and with a depth of up to 10% of the layer, with Berkovich indenter. The elastic moduli obtained for the nitrided layers were 281 ± 21 GPa (400 °C) and 163 ± 32 GPa (500 °C) and for the nitrocarburized were 214 ± 12 GPa (400 °C) and 169 ± 25 GPa (500 °C). The indentation nanohardness obtained for the nitrided layers were 14.1 ± 1.0 GPa (400 °C) and 3.5 ± 1.2 GPa (500 °C) and for the nitrocarburized layers were 10.8 ± 0.8 GPa (400 °C) and 4.3 ± 1.2 GPa (500 °C). Therefore, these results indicate slightly higher values for the two mechanical properties indentation (elastic modulus and nanohardness) at 400 °C than at 500 °C caused by nitriding compared to nitrocarburizing treatment; however, when considering the percentages of standard deviations, the treatments at 500 °C present much higher values for these properties, as compared to the treatments at 400 °C, a behavior associated with the presence of chromium and iron nitrides.

Fatigue life evaluation of metastable austenitic stainless steel AISI 347 based on nondestructive testing methods for different environmental conditions

Due to aging nuclear power plants there is an increasing need for methods to evaluate the integrity of components and structures of nuclear engineering. During power plant operation, nuclear materials are exposed to the effects of temperature, corrosion and cyclic loading. These lead to microstructural changes resulting in material degradation, which can be detected by suitable nondestructive testing (NDT) methods. Fatigue testing setups for ambient temperature, distilled water and 300 °C were designed to represent relevant environmental conditions and instrumented with in-situ measurements of temperature, electric, micromagnetic and electrochemical NDT parameters. Constant amplitude and strain increase tests with specimens of metastable austenitic stainless steel AISI 347 (X6CrNiNb18-10, 1.4550) typically used for pipe components were conducted in total strain control. Data obtained were employed in short-time evaluation procedure StrainLife to generate fatigue life data. To establish an understanding between microstructure evolution and NDT data, scanning electron microscopic methods such as electron backscatter diffraction and energy dispersive X-ray spectroscopy were used. Electrochemical data yields fatigue life results as good as conventionally used parameters like stress and strain. These findings could enable usage of presented parameters for mobile or even online testing systems, since accessibility depending on application case can be much improved.

Kinetics of Nickel Diffusion into Austenitic Stainless Steels AISI 304 and 316L and Calculation of Diffusion Coefficients.

Diffusion bonding has many advantages, but it also has its specifics. When creating heterogeneous joints, problems arise with the creation of intermetallic phases. For this reason, an interlayer is needed to prevent the creation of these unfavorable phases. It is important to ensure that the interlayer is of sufficient thickness to prevent the elements from diffusing through the entire interlayer and the intermetallic phases from being formed again. Conversely, too thick an interlayer causes an increase in the heterogeneity of the bond properties. The creation of the initial diffusion bonds in a heterogeneous diffusion joint of AISI 304 and AISI 316L steel with a 0.2 mm thick nickel interlayer was made in a Gleeble 3500. The experiments to determine the diffusion kinetics were carried out in a vacuum furnace, with subsequent evaluation by EDX (Energy Dispersive X-ray Spectroscopy) analysis. Subsequently, the diffusion coefficients of nickel into both steels were determined, and generalized equations were formulated to calculate the diffusion coefficients for temperatures in the range of 950 to 1150 °C and holding times in the range of 3600 to 18,000 s. Equations are also given to determine the width of the diffused zone between each steel and the Ni interlayer.

Fine Blanking of Austenitic Stainless Steel Gears Using Carbon-Supersaturated High-Speed Steel Tools

Austenitic stainless steel gears were fabricated via the fine blanking process that can be used for mass production. A carbon-supersaturated (CS)-matrix high-speed steel punch was prepared to minimize the adhesive and abrasive wear damage. Its edge profile was tailored and finished to control the local metal flow around the punch edges and edge corners. This CS punch was utilized in fine blanking the AISI304 austenitic stainless steel gears. Ball-on-disc (BOD) testing was first employed to describe the frictional behavior of the CS tool steel disc against the AISI304 stainless steel balls. SEM-EDX analysis on the wear track revealed that a free-carbon tribofilm was formed in situ in the wear track to prevent adhesive wear via galling on the tool steel disc. No significant adhesive or abrasive wear was detected on the punch edges and punch edge corners after continuously fine blanking with 50 strokes. AISI304 gears were produced to have fully burnished surfaces. Their pitches, widths and circles were measured to evaluate their gear-grade balancing during the fine blanking process. The stabilized gear-grade balancing in JIS-9 to JIS-10 grades was attained for these as-blanked AISI304 gears without finishing processes.

Grain Growth during Mechanical Processing of Austenitic Stainless Steel AISI 321

The kinetics of austenite grain growth during thermomechanical treatment of AISI 321 steel with a relatively high content of carbon (0.07 wt. %) and titanium (0.50 wt. %) were studied. Hot deformation was carried out by the uniaxial compression of cylindrical specimens on a Gleeble 3800 thermomechanical simulator. A dependence is obtained for calculating the kinetics of austenite grain growth for a temperature range of 1150–1250 °C. The proposed dependence makes it possible to evaluate grain growth under non-isothermal conditions. The verification of the adequacy of the proposed dependence and the method for calculating the grain size at cooling rates 0.2, 1 and 5 °C/s showed its high convergence. The difference between the calculated and experimental grain size did not exceed 8%. The suppression of grain growth is due to the precipitation of titanium carbides and carbonitrides. Using the developed grain growth model, an analysis was made of the reasons for the formation of large grains in the shell after the elongating in the production process.

Evolution of the structure, texture and mechanical properties of a cold-swaged austenitic stainless steel during post-deformation annealing

In this work, we studied the effect of annealing temperature on the structure and texture, as well as the mechanical properties of the austenitic stainless steel AISI 316. Initially, the program material was subjected to cold rotary swaging with a reduction of 95%. Studies showed the formation of the structure and texture gradient during preliminary plastic deformation. Annealing at low temperatures (500-600°C) provoked polygonization, while the intensity of the and texture components remained unchanged. After annealing at 700°С, the onset of recrystallization was observed only in the subsurface layers of the rod. As a result of annealing at 800–900°C, static recrystallization occurred over the entire cross section of the rod, which caused dissipation of the texture gradient. Annealing at temperatures of 400–600°C was accompanied by an increase in the strength and hardness characteristics. Meanwhile, ductility also increased with the annealing temperature. Annealing at 700°C resulted in softening of the program material almost to the level of the initial cold-swaged state and a significant increase in ductility up to 16%.

Laser-Treated Steel Surfaces Gliding on Snow at Different Temperatures.

With the goal of substituting a hard metallic material for the soft Ultra High Molecular Weight Polyethylene (UHMWPE) presently used to make the bases of skis for alpine skiing, we used two non-thermodynamic equilibrium surface treatments with ultra-short (7-8 ps) laser pulses to modify the surface of square plates (50 × 50 mm2) made of austenitic stainless steel AISI 301H. By irradiating with linearly polarized pulses, we obtained Laser Induced Periodic Surface Structures (LIPSS). By laser machining, we produced a laser engraving on the surface. Both treatments produce a surface pattern parallel to one side of the sample. For both treatments, we measured with a dedicated snow tribometer the friction coefficient µ on compacted snow at different temperatures (-10 °C; -5 °C; -3 °C) for a gliding speed range between 1 and 6.1 ms-1. We compared the obtained µ values with those of untreated AISI 301H plates and of stone grinded, waxed UHMWPE plates. At the highest temperature (-3 °C), near the snow melting point, untreated AISI 301H shows the largest µ value (0.09), much higher than that of UHMWPE (0.04). Laser treatments on AISI 301H gave lower µ values approaching UHMWPE. We studied how the surface pattern disposition, with respect to the gliding direction of the sample on snow, affects the µ trend. For LIPSS with pattern, orientation perpendicular to the gliding direction on snow µ (0.05) is comparable with that of UHMWPE. We performed field tests on snow at high temperature (from -0.5 to 0 °C) using full-size skis equipped with bases made of the same materials used for the laboratory tests. We observed a moderate difference in performance between the untreated and the LIPSS treated bases; both performed worse than UHMWPE. Waxing improved the performance of all bases, especially LIPSS treated.

The Effect of Strain Rate on Hydrogen-Assisted Deformation Behavior and Microstructure in AISI 316L Austenitic Stainless Steel.

The influence of strain rate in the interval of (10-5-10-3) 1/s on room temperature tensile behavior, dislocation arrangement, deformation mechanisms, and fracture of austenitic stainless steel AISI 316L electrochemically charged with hydrogen was investigated. Independently on strain rate, hydrogen charging provides the increase in the yield strength of the specimens due to a solid solution hardening of austenite, but it slightly influences deformation behavior and strain hardening of the steel. Simultaneously, hydrogen charging assists surface embrittlement of the specimens during straining and reduces an elongation to failure, which both are strain rate-dependent parameters. Hydrogen embrittlement index decreases with increase in strain rate, which testifies the importance of hydrogen transport with dislocations during plastic deformation. The stress-relaxation tests directly confirm the hydrogen-enhanced increase in the dislocation dynamics at low strain rates. The interaction of the hydrogen atoms with dislocations and hydrogen-associated plastic flow are discussed.

Influence of nitrogen content on the corrosion fatigue behavior of additively manufactured AISI 316L stainless steel in chloride solution

The characterization of the corrosion fatigue behavior is detrimental for steels manufactured by laser beam powder bed fusion (PBF-LB). In this study, the corrosion and corrosion fatigue behavior of the austenitic stainless steel AISI 316L processed via PBF-LB with and without increased nitrogen content is investigated. The nitrogen alloyed steel shows improved pitting corrosion and fatigue behavior. A fracture mechanical approach was used for the fatigue data as surface defects lead to a high scatter in the results which not only allowed to separate the influence of defects but also to identify the improved defect tolerance due to nitrogen alloying.

Nano-twinning and uncommon α´-martensite formation as a result of very high cycle fatigue of metastable austenitic stainless steel at 573 K

Microstructural changes were investigated regarding the existence of the true endurance limit of a cyclic loaded metastable austenitic stainless steel AISI 347 in the very high cycle regime at 573 K. The fatigue tests were performed in stress control with a stress load ration R = -1 using a servo-hydraulic testing system with a load frequency of 980 Hz. Local cyclic plastic deformation and slip bands formation were observed even in the specimens that achieved the endurance limit at 5 × 108 cycles. Moreover, in these specimens further microstructural effects like nano-twins and α´-martensite formation were detected by transmission electron microscopy. While nano-twin formation takes place in the bulk material, the α´-martensite nucleates at the specimen's surface. Therefore, the α´-martensitic transformation is not the main mechanism responsible for the true endurance limit observed in the investigated AISI 347 at 573 K.

Complex Interdependency of Microstructure, Mechanical Properties, Fatigue Resistance, and Residual Stress of Austenitic Stainless Steels AISI 304L.

Stainless steels are important in various industries due to their unique properties and durable life cycle. However, with increasing demands for prolonged life cycles, better mechanical properties, and improved residual stresses, new treatment techniques, such as deep cryogenic treatment (DCT), are on the rise to further push the improvement in stainless steels. This study focuses on the effect of DCT on austenitic stainless steel AISI 304L, while also considering the influence of solution annealing temperature on DCT effectiveness. Both aspects are assessed through the research of microstructure, selected mechanical properties (hardness, fracture and impact toughness, compressive and tensile strength, strain-hardening exponent, and fatigue resistance), and residual stresses by comparing the DCT state with conventionally treated counterparts. The results indicate the complex interdependency of investigated microstructural characteristics and residual stress states, which is the main reason for induced changes in mechanical properties. The results show both the significant and insignificant effects of DCT on individual properties of AISI 304L. Overall, solution annealing at a higher temperature (1080 °C) showed more prominent results in combination with DCT, which can be utilized for different manufacturing procedures of austenitic stainless steels for various applications.

Rotary friction welding of Inconel 718 – AISI 304 stainless steel dissimilar joint

Nickel-based superalloy Inconel 718 and austenitic stainless steel AISI 304 are joined by rotary friction welding. The changes in microstructure and mechanical properties of the dissimilar joint for solutionising, solutionising + aging, and post-weld aging treatment, with a prior solution heat treatment, are studied. Two distinct microstructural zones, the FDZ (fully deformed zone) and the TMAZ (thermo-mechanically affected zone) are observed in all weldments. The post-weld aged joint sample shows the highest tensile strength and hardness due to the precipitation of γ′ (Ni3(Ti, Al)) and γ″ (Ni3Nb) strengthening precipitates. The solution-treated sample shows the highest yield strength, while the solutionising + aging treatment is found to deteriorate the mechanical properties of the dissimilar joint. The observed changes in the mechanical properties are investigated based on microstructure and electron dispersive spectroscopy.

Influence of γ'N and ɛ'N phases on the properties of AISI 304L after low-temperature plasma nitrocarburizing

The surface of austenitic stainless steel AISI 304L has been hardened by adding nitrogen and carbon through the plasma nitrocarburizing process. Plasma nitrocarburizing at low temperatures eliminates the formation of nitrides and carbides of chromium, thereby increasing the surface hardness without compromising its corrosion resistance. This is attributed to the presence of a hard case consisting of a solid-solution of nitrogen and carbon occupying interstitial sites in an “expanded” austenite phase. The expanded austenite is further characterized as nitrogen-expanded austenite (γN) and carbon-expanded austenite (γC). In the present work, austenitic stainless steel AISI 304L samples were plasma nitrocarburized by varying the N2 content (%N2) in N2-H2-C2H2 feed gas mixture and treatment times (3, 5, and 7 h) at 673 K and 500 Pa. The samples were characterized by means of XRD, microindentation, XPS, EIS, and potentiodynamic polarization testing, for studying the microstructural, mechanical, and electrochemical properties. The XRD analysis revealed the presence of ɛ'N and γ'N in addition to γN and γC when treated with higher %N2 gas for 5 and 7 h. From XPS, the binding energies of undefined FexN were obtained which were found to lie very close to the defined FexN for higher %N2 gas. Surface hardness significantly improved after the plasma nitrocarburizing processes irrespective of the %N2 and treatment times compared to the untreated AISI 304L. The presence of CrN precipitation on the surface of samples treated with the 75% N2 for 5 and 7 h were observed from XPS, which caused higher corrosion rate. Among the treated samples, the process with 50% N2 and 5 h exhibited the best corrosion resistance with high surface hardness.

Region-wise evaluation of strength and creep behavior of AISI 904L weldments by small specimen testing techniques

Super austenitic stainless steel AISI 904L is a premium stainless steel renowned for its outstanding characteristics and the ability to be maintained even under harsh situations. This alloy is widely used in a variety of engineering applications, and hence generating creep and indentation data of the material will prove useful for those concerned. Our study investigates the impression creep (IC) and automated ball indentation (ABI) performance in activated tungsten inert gas (ATIG) and hot wire tungsten inert gas (HWTIG) weldments of 10 mm thick plates of AISI 904L. ABI-evaluated strength correlates well with the conventional uniaxial tensile test and hardness data. IC studies were performed on base metal and welds by applying a load of 60 kg on a 1 mm diameter flat-end cylindrical punch at 650 oC. Several cycles of loading followed by partial unloading were performed on ABI specimens at 25 °C using a 0.76 mm diameter tungsten carbide spherical indenter. The results indicated that the ATIG weld excelled over the HWTIG weld with higher creep resistance. During the ABI analysis, the heat-affected zone of HWTIG weldment displayed higher UTS and ABI hardness values of 499 MPa and 185 HB, respectively. Hardness values generated by the ABI analysis are 174 HB, 161 HB, and 177 HB for the base metal, ATIG weldment, and HWTIG weldment, respectively. This was found to be very much in agreement with conventional hardness test results. The results cemented the ability of IC and ABI analysis to precisely predict the creep and mechanical properties of the base metal and weldments. Data generated through this study will benefit industries and researchers associated with AISI 904L.