Austenitic Materials Research Articles

Comparative analysis of the manufacturing processes for 316L material

Abstract The present work focuses on the investigation of a comparative analysis of the manufacturing processes for 316L material. It aims to highlighting the advantages but also the disadvantages offered by conventional and additional manufacturing methods. This analysis was developed for the austenitic material, stainless steel 316L (1.4404). Due to its properties, this material is used in an ample range of applications spread across various industries (automotive, medicine and medical devices, chemical, biomedical) by using the additive manufacturing techniques (AM).

The modified Swift constitutive model of 304L stainless steel at the cryogenic temperature based on the Olson–Cohen model

The nonlinear behavior of austenitic stainless steel (ASS) is significantly affected by the temperature and strain during plastic deformation. However, the conventional constitutive model is often inadequate to accurately describe its mechanical properties, particularly at cryogenic temperatures. Therefore, the development of a constitutive model for ASS at cryogenic temperatures is of paramount importance in order to fully understanding the performance of liquefied natural gas (LNG) membrane tank structures under such conditions. In this study, we have derived a modified constitutive model using 304L stainless steel that incorporates a phase transition model through theoretical derivations. First, the stress and strain data for 304L stainless steel within the range of 108–293 K have obtained from quasi-static tensile experiments. Subsequently, the XRD test results are utilized to calculate the volume fraction of martensite across various temperatures and strains. Next, a modified constitutive model is proposed by combining the Olson–Cohen phase transition model and the Swift constitutive model. Finally, the accuracy of the modified Swift constitutive model is verified through experimental data. The results demonstrate that the modified Swift constitutive model is precise for characterizing the properties of 304L stainless steel across a wide range of temperatures. Furthermore, multiple case studies have proven the feasibility of using the modified Swift constitutive model to predict the properties of various austenitic materials. By incorporating the Olson-Cohen phase transition model, the modified Swift constitutive model showcases its wide applicability and potential in designing and assessing the safety of ASS structures.

Corrosion behavior of austenitic stainless steel and nickel-based welded joints in underwater wet welding

Marine structures such as ports, bridges, pipelines, vessels, and platforms are an essential part of modern infrastructure, where the use of higher-strength steel provides savings in logistics and construction. However, the repair of higher-strength steels can be challenging, especially underwater. Wet shielded metal arc welding is the most widely used and least expensive method for underwater welding repairs, but is very susceptible to hydrogen-induced cracking. Thus, researchers and welding engineers aim to reduce the amount of hydrogen in the weld material. Recent success has been achieved through the use of austenitic welding consumables, such as austenitic stainless steel and nickel-based electrodes. The use of these consumables drastically reduces the amount of diffusible hydrogen in the weld metal. However, these austenitic materials usually have different corrosion potential as compared to the structural steel the weld beads are applied to. This creates the risk of severe galvanic corrosion. In the presented study, the corrosion behavior of welds created with austenitic stainless steel and nickel-based electrodes were studied. Samples were aged for 1.5 years in the Baltic Sea. Simultaneously, the effectiveness of corrosion protection systems such as coating and Impressed Current Cathodic Protection (ICCP) were evaluated. Localized corrosion occurred in the heat-affected zone when austenitic electrodes were used in the corrosive environment. The localized corrosion depth after 1.5 years in the Baltic Sea and in the salt spray layer was approximately 250 µm and 390 µm, respectively. The ICCP system and the use of a coating were effective in preventing localized corrosion. The low pitting corrosion density of 2.5 × 103 m−2 corresponds to grade A1 according to the standard and was found to be negligible as compared to the localized corrosion in the heat-affect zone.

Stretch-forming characteristics of austenitic material stainless steel 304 at hot working temperatures

Abstract The need for sheet metal forming using highly resistant materials such as titanium alloys and stainless steel has increased recently. These materials possess elevated mean flow stress values, which make them difficult to draw at room temperature. To achieve a homogeneous distribution of strain in the stretched component, reduce the load required for plastic deformation, and greatly improve material formability, hot forming is helpful. The goal of the current study is to conduct stretch-forming experiments to investigate the forming characteristics of Austenitic material Stainless Steel (ASS) 304 at Hot working temperatures. Stretch forming experiments have been conducted on the Servo electrical sheet press test machine at 650 and 800°C. The formability has been estimated by constructing a Fracture forming diagram (FFLD), limiting the height of the dome (LDH) and the distribution of the strain of stretched cups. It has been discovered that the limit of forming bounds rises with the temperature reaching 800°C, while the DSA effect causes the necking region – the area between the safe and fracture limits ‒ to decrease with additional temperature rise from 800 to 900°C. Within the experimental limitations, it has been considered that the Hot forming of ASS 304 at 650°C gives the highest strain forming limits with a uniform strain distribution in the stretched cups. From the Formability limit diagram, dome height, and strain distribution, it can be observed that ASS 304 has good limiting strain up to 800°C with lower load application.

Welding Processing of Medium-Manganese Austenitic Steels for Cryogenic Applications

Abstract For several years, the significance of gaseous energy sources (e. g. liquified natural gas and hydrogen) has been increasing worldwide due to environmental and climate policy requirements. Storage and transportation of the liquids occur under cryogenic conditions. This results in specific requirements for the mechanical properties of the materials used at cryogenic temperatures. Nowadays, cold-tough, high-nickel austenites and martensitic steels of type X8Ni9 are used for such purposes. While austenitic materials offer good processing properties, they are not attractive due to their comparatively low strength and high costs. Welding martensitic steel with commonly used nickel-based additives significantly impacts processing quality and process automation due to high magnetic remanence. Additionally, the increased requirements for the storage of liquid hydrogen regarding low-temperature toughness push the conventional low-temperature materials to their limits. A potential solution to the identified challenges can be achieved by using medium- and high-manganese austenitic steels. Within the scope of this work, the medium-manganese steel X2CrMnNiN1775 (1.4371) is investigated as an economical substitute for the conventionally used materials in cryogenic applications. Considering the relevant qualification requirements for welded joints and welding additives, submerged arc welded joints are investigated and their applicability under cryogenic operating temperatures is demonstrated.

FEM model optimization study of mechanical properties and material selection in stamping process

Abstract This paper establishes a finite element model of stamping and forming and proposes solution algorithms for static and dynamic forces. The finite element simulation of the hot stamping process is carried out to analyze the thermophysical parameters of BR1500HS ultra-high-strength steel sheet material and H13 steel mold material. Set the temperatures of austenitic material in the transfer process and molding process, obtain the rheological stress data of BR1500HS ultra-high-strength steel plate during plastic deformation at high temperature, and determine the basic mechanical properties of the material at high temperature. A geometric finite element model of thermal-force-phase coupling of the hot stamping and forming process is established to simulate the temperature field change of the steel plate during the hot stamping and forming process by combining the process conditions and process parameters. At the same time, the ultra-high-strength boron steel 22MnB5 is selected to simulate the hot forming and tempering process of U-shaped parts made of high-strength steel sheet material, and the feasibility of the finite element model is verified. Different hot stamping process parameters are set to analyze the forming quality of both BR1500HS ultra-high strength steel and ultra-high-strength boron steel 22MnB5. When the stamping speed is increased from 50mm/s to 100mm/s, the maximum equivalent force of BR1500HS ultra-high strength steel decreases, and thus, when the stamping speed is 100mm/s and the holding time is 5s, the part forming performance is better, which meets the requirements of the gradient performance hot stamping process.

A Numerical and Experimental Sensitivity Analysis on Electrochemical Neutral Pickling for Stainless Steel Using Secondary Current Distribution

Electrochemical neutral pickling (ENP) is an extended process used in the stainless steel industry to remove the oxide surface layer formed during the annealing process. The absence of strong acids such as nitric acid results in a minimum loss of base material, improve operators working conditions, and reduces the pickling environmental impact, while keeping relatively low operation and maintenance costs. However, despite its multiple benefits, ENP may become the bottleneck for integrated annealing and pickling line, especially when processing thin austenitic and duplex steels. Fortunately, there is room for improvement as the total Faradaic efficiency of the process in typical operation is in general low (around 20 – 30 % for austenitic materials) [1]–[3], while estimations of the energy efficiency are as low as to 1 - 2 % [4].This work provides guidelines to the design and operation of ENP cells to increase the oxide removal rate. We focus on the effect of the geometry and some operational parameters, using secondary current distribution. The simulations are validated against experimental, and a sensitivity analysis of the oxide removal rate with respect to the geometry and some key operational parameters is performed. The electrode-to-strip and the inter-electrode distances were found to have a determining effect on the total cell resistance and on its so-called geometric efficiency (relative current reaching the strip). Moreover, an optimal range for the ratio of these distances is proposed. In addition, the strip thickness and width were found to significantly affect the cell performance, especially for the thinnest gauges.

Progress in Evaluation of Deep Artificial Defects from Sweep-Frequency Eddy-Current Testing Signals.

The article discusses the practical application of the method of electromagnetic non-destructive investigation of austenitic materials. To identify and evaluate deep artificial defects, the sweep-frequency eddy current method with harmonic excitation is used. The objects of interest are the surface electric-discharged machined notches, with a defined geometry, fabricated in a plate with a thickness of 30 mm. An innovative eddy current probe with a separate excitation and detection circuit is used for the investigation. The achieved results clearly demonstrate the robustness and potential of the method, especially for deep defects in thick material. By using the fifth probe in connection with the frequency sweeping of eddy currents, it is possible to reliably detect artificial defects up to 24 ± 0.5 mm deep by using low-frequency excitation signals. An important fact is that the measuring probe does not have to be placed directly above the examined defect. The experimental results achieved are presented and discussed in this paper. The conducted study can serve, for example, as an input database of defect signals with a defined geometry to increase the convergence of learning networks and for the prediction of the geometry of real (fatigue and stress-corrosion) defects.

Deformation-induced martensite transformation and variant selection in AISI 316L austenitic stainless steel during uniaxial tensile deformation

Present work has investigated the orientation dependence of deformation-induced martensite (DIM) transformation and contemporaneous variant selection in AISI 316L austenitic stainless steel during uniaxial tensile loading. The combined effect of slip and deformation-induced martensite transformation have been analysed comprehensively using experimental macrotexture analysis, visco-plastic self-consistent (VPSC) simulation and reconstruction of prior-austenite orientations from electron backscatter diffraction (EBSD) data. It has been shown that when the polycrystalline austenitic material is deformed, grains with orientations like Brass, Rot-Goss, Rot-Cu undergo plastic deformation by slip and rotate towards {110}<111> orientation. Grains of this orientation eventually undergo DIM transformation at sufficiently higher engineering strain (≥69%) levels. Variant selection during DIM transformation from {110}<111> component of austenite has been critically examined using a model developed based on the phenomenological theory of martensite crystallography (PTMC). It has been observed that in general, variants with higher interaction energies are preferred over the others. The results in turn indicate that Patel-Cohen theory, which is believed to be valid for stress-induced martensite (i.e. during elastic deformation), holds equally good for strain-induced martensite (i.e. during plastic deformation) as well.

Non-destructive characterization of strain induced surface hardness increase by measuring magnetic properties of AISI 304

The goal of this work is to establish a correlation between the surface integrity and magnetic properties of stainless steels like AISI 304 (X5CrNi18-10). In metastable austenitic stainless steels, a phase transformation from the austenitic to the martensitic phase can occur even at room temperature. In this work, machine hammer peening (MHP) is used to selectively introduce the activation energy required for martensite formation on discrete areas of the surface. The phase transformation is confirmed by electron back scatter diffraction (EBSD) and micrographs. A correlation between the energy input by MHP, magnetic properties, and surface hardness is established. Using this approach, characterization of the surface integrity by measuring magnetic properties can be achieved. In addition, a novel solution to code and encode information with high information density onto metastable austenitic materials is proposed.

&lt;i&gt;Cocos nucifera&lt;/i&gt; Surfactant Performance on Stainless Steel in Hcl and H&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt; Solutions

The corrosion inhibition effect of Cocos nucifera (CN) surfactant inhibitor, has been inspected on 316L steel in 5 M HCl and H2SO4 solutions by weight loss (WL) method. The results revealed that the presence of alkanols, glycosides, steroids and terpenoids in CN surfactant supported the inhibitor by retarding corrosion effect to give an optimum inhibition efficiency of 93.71% in HCl and 89.66% in H2SO4 solutions after 504 h. Also, the regression values for both acidic solutions were close to unity after obeying Langmuir isotherm adsorption mechanism with 0.9971 for HCl and 0.9882 for H2SO4 solution. The result confirms that CN surfactant inhibitor performed better in HCl solution than in H2SO4 solution. Keywords: Corrosion inhibitor; active components; austenitic 316L material; weight loss method; adsorption isotherm.

Chemical composition dependence of the strength and ductility enhancement by solute hydrogen in Fe–Cr–Ni-based austenitic alloys

Tensile tests of five commercial Fe–Cr–Ni-based austenitic alloys were conducted after thermal hydrogen precharging in a pressurized gaseous environment. The divergence in Cr and Ni concentrations affected the hydrogen solubility significantly as well as the impacts of dissolved hydrogen on the mechanical performance of the alloy. Hydrogen solubility increased with increasing Cr content and Cr/Ni compositional ratio, bringing about an escalating solid-solution hardening with a magnitude of ≈ G/1000 (G: shear modulus) per atomic percent of solute hydrogen. Furthermore, hydrogen facilitated deformation twinning in alloys with relatively low stacking fault energy (lower Ni content), in which deformation twinning occurred even in a nonhydrogenated state. Augmenting the twin density enhanced the work-hardening capability at the later deformation stage, giving rise to the improvement of uniform elongation via retarded onset of plastic instability. Consolidating the experimental results and hitherto-understood hypothesis on the response to hydrogen of other austenitic materials, the essential conditions for promoting hydrogen-related strengthening and ductilization were deduced.

Hydrogen Isotopes Permeation in Clean or Unoxidized FeCrAl Alloys: A Review

The US Department of Energy is working with fuel vendors to develop accident tolerant fuels (ATF) for the current fleet of light water reactors (LWRs). The ATF should be more resilient to loss of coolant accident scenarios and help extending the life of the operating LWRs. One of the proposed ATF concepts is to use iron-chromium-aluminum (FeCrAl) alloys for the cladding of the fuel. A concern in using ferritic FeCrAl is that this type of cladding may result in an increase in the concentration of tritium in the coolant. The objective of the current critical review is to collect and assess information from the literature regarding diffusion or permeation of hydrogen (H) and its isotopes deuterium (D) and Tritium (T) across industrial alloys (including FeCrAl) used or intended for the nuclear industry. Over a hundred years of data reviewed shows that the solubility of hydrogen in ferritic alloys is lower than in austenitic alloys but hydrogen permeates faster through a ferritic material than through austenitic materials. The tritium permeation rates in FeCrAl alloys are between those in austenitic stainless steels and in ferritic FeCr steels. The activation energy for hydrogen permeation is approximately 30 pct higher in the austenitic alloys compared with the ferritic (typically ∼ 50 kJ/mol in ferritic vs. ∼ 65 kJ/mol in the austenitic). None of the major elements in FeCrAl alloys react with hydrogen to form detrimental hydride phases. The effect of surface oxides on FeCrAl delaying hydrogen entrance into FeCrAl alloy is not part of this review.

Fatigue damage evaluation of stainless AISI 347 steel by advanced microstructure-sensitive NDT analysis

There is an increasing need to test and evaluate the integrity of ageing components and structures in nuclear engineering. Since materials for nuclear applications are subjected to thermal, corrosive, tensile, and fatigue loads during their service life, a deep understanding of microstructural degradation is desirable, as it can be gained by nondestructive testing (NDT) methods.In this study, an innovative fatigue testing setup and NDT methods are combined to develop new, efficient and reliable concepts to evaluate fatigue life and damage mechanisms. For this purpose, specimens of metastable austenitic stainless AISI 347 (X6CrNiNb18-10, 1.4550) steel, relevant for pipe components, are tested in a setup allowing in-situ measurement of temperature, micromagnetic, electric and electrochemical NDT parameters. Strain-controlled constant amplitude and strain-increase tests were performed and various physical measurements were applied for a fatigue life analysis by short-time evaluation procedures. In-situ NDT parameters are linked to the microstructural evolution of the metastable austenite during cyclic loading. Extensive microstructural analysis through methods like electron backscatter diffraction have been performed in initial condition to help understanding data development versus life time. It is shown that an advanced test setup based on micromagnetic and electrochemical measurements is suitable to indicate fatigue damage-related mechanisms in a metastable austenitic material. In the future, these methods and findings could enable mobile testing systems to evaluate components in service regarding their remaining fatigue life.

Study on the mechanical properties of NPR steel bars and the bonding properties with marine concrete

Negative Poisson's Ratio (NPR) steel bar is a new type of high-strength, high-ductility and corrosion-resistant steel. In this paper, the chemical composition, metallographic structure, mechanical properties of NPR bar and its bond properties with marine concrete are studied and analyzed, and compared with ordinary (HRB400) steel bar. The metallographic structure of the NPR bar shows that it is the fully austenitic material. Furthermore, the mechanical properties such as yield strength, tensile strength, elongation after fracture, and total elongation at maximum force of NPR bar are significantly higher than ordinary steel bars. The results of central pull-out test show that the shape of ribs on the surface of the bar influences directly on the bond strength, and the bond strength of NPR reinforcement is lower than ordinary reinforcement. Moreover, the bond strength of NPR reinforcement increases with the decrease of bond length and the increase of strength grade of marine concrete. Finally, based on bond stress-slip curve obtained from the test, the bond stress-slip constitutive model between NPR reinforcement and marine concrete are proposed, and the calculated values are compared with the measured values. This results of study can provide a theoretical basis for the promotion and application of NPR new type reinforcement.

Investigation of the Heat-Affected Zone Properties During Cladding of Power Equipment with Austenitic Materials Using Control Mechanical Impacts on the Strip Electrode

During cladding an austenitic layer on low-carbon and medium-alloyed steels, the properties of the heat-affected zone, along with the resistance of the surface layer to resist corrosion, largely determine the performance and durability of the surfaced product. The work is devoted to the study of the dependence of the properties of the heat-affected zone during cladding of power equipment with austenitic materials on the parameters of the control mechanical impacts on the strip electrode and determination of their optimal range, which ensures high values of the mechanical properties of the deposited layer.

Corrosion of construction materials of separator in molten carbonates of alkali metals

The mitigation of steels and alloys corrosion is one of the great challenges for application of high-temperature devices in contact with molten salts. The current research estimates corrosion resistance of the following construction materials: Crofer APU 22, austenitic steel 12Cr18Ni10Ti and two types of austenitic nickel-chromium alloy: CrNi78Ti, CrNi78Ti + 5% wt. W. The measurements are performed by exposition of samples within 24 h in the molten mixture of carbonates of lithium and potassium at 650 °C. The rates and mechanism of materials corrosion under these conditions are determined. The process occurring on the surface while contact of the materials and steels with carbonate melt are investigated.Accurate quantitative data on materials interaction with alkali carbonate melt have been obtained by gravimetrical and physico-chemical methods. The high-temperature corrosion of Fe and Ni austenitic materials has turned dramatically different from both their low-temperature corrosion and each other. There are mixed passivating oxide films on the surface of the only iron-based materials.In addition, the resulting layers of corrosion products are well bonded to the substrate and have protective properties and can be used as protective coatings in molten salts of other compositions, including alkali metal fluorides.

Mathematical Simulation of Microstructural Phase Transformations in the Course of Welding Heating for the Case of Cladding of Protective Layer in the WWER-1000 Reactor Vessel

By using the developed finite-element models, we perform the numerical investigation of nonstationary temperature fields and the kinetics of microstructural phase transformations in the base material of the WWER -1000 reactor vessel (15Kh2NMFА steel) under the conditions of submerged-arc cladding of protective anticorrosion layers of austenitic materials. We perform the comparative analysis of the results of simulation of microstructural phase transformations obtained by using two methods of prediction of the decomposition of austenite in the process of cooling. The first method is based on the application of regression equations and the characteristic cooling time Δ t8/5. The second method is based on the diagrams of isothermal decomposition of austenite, the Avrami equation, and the Koistinen–Marburger equation. As a result of simulation of microstructural transformations under cladding, we obtain the bainite-martensite composition in the heat-affected zone of the base material of reactor vessel, which is confirmed by results of the dilatometric analysis and metallography.

Dislocation creep modelling of Sanicro 25 based on microstructural evolution and particle hardening mechanism

A dislocation model for predicting creep deformation and long-term life of Sanicro 25 austenitic steel was proposed on the basis of microstructural evolution and particle hardening mechanism. This approach was integrated by four sub-models of (i) time- and strain-induced detachment stress model, (ii) Orowan strengthening model of two precipitates, (iii) void nucleation and growth model, and (iv) temperature-induced strain energy model. The validation of the proposed model was verified by the experimental data of different testing conditions of Sanicro 25. In addition, the microstructural fracture mechanism and the variation of detachment stress were discussed. The framework of the proposed model may provide a basis for evaluating the creep life of high temperature austenitic material.

Agglomerated flux for welding of corrosion-resistant high-strength nitrogen-containing steels

ABSTRACT The problems of Russian welding materials for welding highly alloyed austenitic steels that are not inclined to intergranular corrosion are considered. A new agglomerated flux for welding with austenitic welding materials is developed. Slag composition is selected that ensures a stable welding process, good separation of the slag crust and the formation of a seam. The possibility of introducing ferroalloys and metal powders through the flux ensures the necessary level of mechanical characteristics of the weld metal, and increases also the resistance of the weld metal to hot cracks and pore formation.