Ferritic Steel Research Articles

High‐Temperature Oxidation Response of 444 Ferritic Stainless Steel in a Synthetic Automotive Exhaust Gas

The high‐temperature oxidation behavior of 444 ferritic stainless steel has been studied in cyclic oxidation experiments using synthetic automotive exhaust gas atmospheres at 950 and 1050 °C. The weight gain per unit area of the 444 ferritic stainless steel following oxidation at 950 °C for 100 h iss 85.7% lower than recorded at 1050 °C. The oxide scale at both temperatures consisted of Fe–Cr and Mn–Cr spinels in the outer layer and Cr2O3 in the inner layer. Nodule formation and spallation of the oxide scale are identified as the main causes of breakaway oxidation. The depth of the internal oxides gradually increases with the oxidation time. The nucleation and growth of internal SiO2 result in the formation of metal protrusions, which are eventually consumed in the formation of a SiO2 layer. The SiO2 layer is formed at the interface between the oxide scale and the substrate at 1050 °C. The nucleation and growth of internal SiO2, in combination with lateral growth of SiO2 at the Cr2O3 layer/substrate interface contributed to the formation of the SiO2 layer.

Corrosion behavior of austenitic and ferritic steels in alkaline and water-salt solutions

The paper presents the results of studies of the corrosion behavior of austenitic and ferritic steels in alkaline, sulfide, and chloride environments. Structural changes on the surface when the steels are kept in solutions at room temperature are shown. The chemical composition of the steels was determined, and the exact phase-structural composition was theoretically predicted and metallographically determined. It was found that austenitic steel is almost not subject to sulfide corrosion at room temperature and chlorine-containing substances. At the same time, ferritic steel, under the same conditions, has significant corrosion damage on the surface, especially in places of mechanical damage.

Hardening mechanism and thermal-solid coupling model of laminar plasma surface hardening of 65 Mn steel

In the present work, the laminar plasma surface hardening method is employed to enhance the service life of metal components fabricated from 65 Mn steel. The mechanical and wear behaviors of the laminar plasma surface hardened 65 Mn steel were analyzed. The martensite transition transformation of the temperature of the laminar plasma-hardened 65 ferrite Mn steel was determined by a thermal-solid coupling model. Based on the orthogonal experimental results, the optimal hardening parameters were confirmed. The scanning velocity, quenching distance and arc current are 130 mm/min, 50 mm and 120 A, respectively. The pearlites and ferrites are transformed into martensites in the hardened zone, while the ratio of martensite in the heat-affected zone decreases with the increase in the hardening depth. Compared to the untreated 65 Mn steel, the average hardness increases from 220 HV0.2 to 920 HV0.2 in the hardened zone and the corresponding absorbed power increases from 118.7 J to 175.5 J. At the same time, the average coefficient of friction (COF) decreases from 0.763 to 0.546, and the wear rate decreases from 5.39×10−6 mm3/(N·m) to 2.95×10−6 mm3/(N·m), indicating that the wear resistance of 65 Mn steel could be significantly improved by using laminar surface hardening. With the same hardening parameters, the depth and width of the hardened zone predicted by the thermal-solid coupling model are 1.85 mm and 11.20 mm, respectively, which are in accordance with the experimental results; depth is 1.83 mm and width is 11.15 mm. In addition, the predicted hardness distributions of the simulation model are in accordance with the experimental results. These results indicate that the simulation model could effectively predict the microstructure characteristics of 65 Mn steel.

Fabrication and characterization of austenite-ferrite stainless steel bimetals by twin wire arc additive manufacturing

In this work, gas metal arc welding (GMAW) based twin wire arc additive manufacturing (TWAAM) system has been employed to deposit to wire materials simultaneously to fabricate austenite-ferrite stainless steel (AFSS) bimetal of austenite stainless steel (SS304L) and ferrite stainless steel (SS430L). A combination of high voltage and wire feed with low torch speed and gas flow resulted in optimal deposition as determined through response surface analysis based on experimental data of single-track bimetal bead on plate depositions. Mechanical and microstructural characterization of the AFSS bimetal was carried out using tensile test, hardness tests, fractography, SEM with EDS, and phase analysis. Tensile properties of the AFSS bimetal were seen to improved with the yield strength of 343 MPa, ultimate strength of 613 MPa and elongation of 67%, and a hardness value of 225 HV. The interface of the AFSS bimetal was found defects free and microstructures contained both austenite and ferrite phases with higher amounts of Ni-content. The fracture morphology of the fabricated AFSS bimetal was seen to contain dimple sizes lying between that of individual steels and resulted in higher elongation than that of the pure ferrite steel. This study demonstrated defects free fabrication of bimetallic structures with unique microstructural features and enhanced mechanical properties.

Development of glass sealants for proton conducting ceramic cells: materials, concepts and challenges

In this study, we have successfully developed and tested sealing concepts for symmetrical, planar proton-conducting ceramic cells (PCCCs). Three glass sealants from the field of solid oxide cells were investigated as potential compatible sealing materials for PCCCs. The most promising results were obtained with a SiO2-MgO-CaO-Na2O-Al2O3-ZrO2-B2O3 glass, which provided a dense, crack-free sealant between the proton-conducting ceramic cells and the Al2O3-coated ferritic steels. During the sealing process, a reaction layer between the interface of the BaCe0.2Zr0.7Y0.1O3-δ contained in the PCCCs and the glass–ceramic, occurred. Here, we propose a reaction mechanism for this interaction and discuss its impact on potential applications. Moreover, next to evaluating potential glass sealants, we have successfully designed and demonstrated a new sealing geometry that prevents a potential gas crossover in the symmetrical proton-conducting ceramic cell.

Assessment of the impact behavior of CLF-1 steel with Charpy V-notch testing and miniature Charpy V-notch testing

China Low-activation Ferrite steel (CLF-1), as one of the structural materials developed in China for fusion reactors, is a Reduced activation Ferritic/Martensitic (RAFM) steel modeled after the traditional T91 steel (9Cr-1Mo-0.2V-0.08Nb). For fusion reactor materials, the Charpy impact testing is an important method to assess their notch sensitivity. In this study, Charpy impact tests were conducted on CLF-1 steel using Charpy V-notch specimens (CVN) and Miniature Charpy V-notch specimens (Kleinstprobe, KLST) to assess the impact behavior of CLF-1 steel, and data normalization was performed on the KLST specimen. The results show that as the specimen size of CLF-1 steel decreased, the curves of impact absorbed energy, lateral expansion, and shear fracture appearance shifted towards lower temperatures, and the impact absorbed energy significantly decreased. Both the macroscopic and microscopic characteristics of the specimens obtained from the experiments indicated that KLST specimens could achieve the same fracture characteristics as CVN specimens. Additionally, at the same experimental temperature, KLST specimens exhibited a higher proportion of ductile fracture regions.

Microstructural Evolution and High‐Temperature Tensile Properties of 15Cr‐Reduced Activation Ferritic Steel Processed by Hot Powder Forging of Mechanically Alloyed Powders

Reduced activation ferritic steels are being explored as possible cladding tube materials for nuclear reactors because of their low activation and excellent irradiation resistance. In the current investigation, reduced activation ferritic steel (Fe–15Cr–2W) is processed by mechanical alloying of elemental powders followed by hot powder forging. Mechanical alloying is carried out in a Simoloyer attritor mill (Zoz GmbH), after which the powders are placed in a mild steel can and forged at 1200 °C in H2 atmosphere. X‐ray diffraction and transmission electron microscopy (TEM) investigation reveal that 10 h of mechanical alloying is required to achieve complete dissolution of Cr and W in the Fe matrix powder. The relative density and hardness distribution of the forged slab is evaluated in longitudinal as well as transverse direction to optimize the powder forging operation. Electron backscatter diffraction analysis showed dynamic recrystallization to take place during the course of hot powder forging. Tensile tests are performed at room temperature as well as at elevated temperatures (600 and 700 °C). The yield strength and ultimate tensile strength at room temperature as well as at elevated temperatures are found to be higher than those reported in literature for reduced activation ferritic steels consolidated by other techniques.

Effect of Aggressive Anions on the Stress Corrosion Cracking of Stainless Steel in Hot Pressurized Alkaline Water

Abstract U-bend stress corrosion cracking (SCC) testing of low Cr ferritic (Type 409) and austenitic (Type 304L) stainless steel was conducted in a hot pressured alkaline water to study the effect of aggressive anions (Cl− and HS−) on the relative susceptibility. SCC was only observed in Type 304L when immersed in the solution that contained both aggressive anions. Critical factors were identified based on cross-section examination of the U-bends after exposure using complementary electron microscopy techniques. These factors include: (i) preferential oxidation of deformation bands (arising from cold working), (ii) Ni-S compound formation at the oxide/metal interface and (iii) S and Cl incorporation into the inward growing Cr-rich oxide. These critical factors were considered within an overall slip dissolution-type mechanism to account for the SCC observed.

Rapid α-Al2O3 Growth on an Iron Aluminide Coating at 600 °C in the Presence of O2, H2O, and KCl.

In this work, a slurry iron aluminide-coated ferritic steel SVM12 was subjected to a laboratory experiment mimicking superheater corrosion in a biomass-fired power boiler. The samples were exposed under model Cl-rich biomass conditions, in a KCl + O2 + H2O environment at 600 °C for 168, 2000, and 8000 h. The morphology of corrosion and the composition of the oxide scale and the coating were investigated by a combination of advanced analytical techniques such as FESEM/EDS, SEM/EBSD, and XRD. Even after short-term exposure, the coating developed a very fast-growing and up to 50 μm thick α-Al2O3 scale in contrast to the spontaneous formation of a protective, thin, dense, slow-growing, and very adhesive α-Al2O3 layer usually formed on metallic materials after high-temperature oxidation. In view of the literature on the formation of oxide scales on alloys and coatings, the formation of an α-Al2O3 scale at this relatively low temperature is very surprising in itself. The thick alumina scale was not protective as its formation resulted in fast degradation of the coating and rapid Fe2Al5 → FeAl phase transformation, which in turn generated porosity inside the coating. In all cases, the resulting thick Al2O3 scale was porous and consisted of both equiaxed α-Al2O3 grains and randomly oriented aggregated alumina whiskers. Potassium is concentrated in the outer part of the Al2O3 scale, while chlorine is concentrated close to the scale/aluminide interface. The unexpected formation of rapidly growing α-Al2O3 at relatively low temperature is attributed to the hydrolysis of aluminum chloride generated in the corrosion process.

Effect of Al Addition on Thermal Fatigue Deformation Morphology in High Heat-resistant Ferritic Stainless Steel SUS444

Effect of Al Addition on Thermal Fatigue Deformation Morphology in High Heat-resistant Ferritic Stainless Steel SUS444

Electrophoretic Deposition and Physicochemical Properties of Ni- and Fe-Doped Cu–Mn Spinel Coatings Enhanced with Ce0.9Y0.1O2 Nanoparticles on Fe16Cr Ferritic Stainless Steel Interconnects for SOEC Applications

AbstractCu- and Mn-based spinel coatings are currently among the most promising materials for solid oxide electrolyzer cell (SOEC) interconnects due to their high electrical conductivity and ability to eliminate environmentally hazardous cobalt, which is included in the most widely used coatings. However, their properties are affected by the presence of the Cr2O3 scale and high-temperature corrosion, and to mitigate this they could be doped with elements such as Ni and Fe. In addition, the electrical properties of such steel/shell layered systems can be further improved using rare-earth element nanoparticles (Ce0.9Y0.1O2). In this work, low-chromium steel was modified using nanoparticles and/or spinel coatings and oxidized in air atmosphere at 800 °C for 2000 hours. The oxidized systems were then characterized using diffraction studies, microstructural observations and electrical measurements. Electrical studies in particular showed a significant reduction in area-specific resistance for steels modified using a combination of both nanoparticles and spinel coatings.

First-principles study on the failure and doping strengthening mechanisms at the interface of high-alumina ferritic heat-resistant steel/oxide film

This study employs first-principles calculations based on density functional theory to explore the failure mechanisms and enhancement strategies for the interface between high-aluminum ferritic heat-resistant steel and oxide film (α-Fe/Al₂O₃ interface). Establishing an interface model at the lowest-energy densely packed plane and performing tensile tests determined that fracture behavior manifests as ductile fracture at the interface. Further analysis of the charge density and differential charge density maps for various doped models confirmed the feasibility of strengthening the α-Fe/Al₂O₃ interface structure through alloy element doping. The results demonstrate that effective dopant elements (such as V, Mn, and Mo) can induce more electrons to transfer to the interface, increase electron concentration, and alter the chemical bonding nature of the interface, thereby significantly enhancing its bonding performance. This study proposes a method to enhance the interface of high-aluminum ferritic heat-resistant steel through doping, providing a theoretical foundation for further research on similar heat-resistant steel surfaces with Al₂O₃ films.

Effect of rare earth Ce treatment on the microstructure and properties of 430 ferritic stainless steel bearing Sn and Cu

The effects of rare earth Ce on purifying molten steel, modifying inclusions and micro-alloying in 430 ferritic stainless-steel bearings with Sn and Cu has been studied in this paper. The results demonstrate that Ce can purify molten steel, modify inclusions, enhance the mechanical properties and improve the pitting and corrosion resistance of the experimental steel. Ce effectively purifies the molten steel, reducing the total oxygen (T. O) content to as low as 0.00086 wt.% and sulphur (S) content to 0.0020 wt.%. The transformation of inclusions in the steel follows the sequence of MnS·Al2O3 → CeAlO3 → Ce2O2S → Ce2O3 with increasing Ce content. The number of inclusions initially decreases and then increases, with the experimental steel containing 0.012 wt.% Ce showing the best cleaning effect. Additionally, Ce treatment only slightly improves the mechanical properties of the experimental steel, but significantly enhances its pitting corrosion resistance and intergranular corrosion resistance by changing the enrichment state of carbides and impurity elements at the grain boundaries. In detail, Ce can partially inhibit the precipitation of M23C6 type carbides at grain boundaries, thereby improving the intergranular corrosion resistance of the experimental steel.

Wire arc direct energy deposited multiphase steel through in situ micropowder alloying: mechanical and metallurgical studies

Purpose This study aims to investigate the effect of copper and titanium micropowder addition on the mechanical and metallurgical properties of additively manufactured low-carbon steel, aiming to produce a modified (multiphase) steel with ferritic low-carbon steel using in situ micropowder addition during wire arc direct energy deposition (WA-DED). Design/methodology/approach A robotic arm equipped with a GMA welding source deposited ER70S6 filler wire on AISI S235 substrate steel using WA-DED. Cu and Ti micropowders were interspersed between layers for microstructural modifications. Microscopy, spectroscopy, diffraction and mechanical testing were used to evaluate the properties of the deposited samples. Findings Incorporating Cu and Ti micropowders significantly enhanced the yield and tensile strength of the deposited material, showing an 83% increase in yield strength and a 33% increase in tensile strength. Microstructural analysis identified key phases such as ferrite, pearlite, bainite, retained austenite and martensite/austenite, with Cu and Ti acting as grain refiners. Nanoscaled Cu precipitates contribute to enhanced low-temperature toughness and a 150% improvement in impact strength at −30°C. Originality/value This study presents a novel approach to overcome the limitations of the available alloys (filler materials). This can be achieved by introducing in situ micropowder alloying during the WA-DED process. The micropowder addition allows altering the properties of the deposited material without changing the parent filler material itself, achieving the desired composition. With this approach, there is no need to manufacture the filler material with the preferred alloy composition separately and then carry out the deposition process.

Ab initio informed solute drag assessment for ferritic steels

Linking atomistic information on solute interactions with microstructure evolution is a key challenge for predictive modelling of chemistry effects on material properties. The objective of the present work is to provide a link between grain boundary segregation energies with GB migration kinetics on the example of recrystallization in multi-component ferritic steels. For that purpose, the segregation of 64 elements from the periodic table to a representative grain boundary is computed with ab initio density functional theory. To connect this data to grain boundary migration kinetics, the solute trend parameter from a simplified solute drag treatment is employed. The solute trend parameter for individual solutes is presented, which highlights solutes with large impact on grain boundary migration. Furthermore, an extension of the solute trend parameter is introduced that allows to evaluate the solute drag potential of realistic steel compositions. The necessity to include solute co-segregation, site competition, and precipitation effects is shown in a comparison to experimental data on recrystallization kinetics. The comparison to experimental data demonstrates the qualitative predictability of recrystallization kinetics by the extended solute trend parameter.

Local heating at the running crack tip in bcc iron according to molecular dynamics

Abstract This study presents estimates of a possible temperature rise at the crack tip from three dimensional (3D) atomistic simulations of fracture via molecular dynamics (MD) technique. Simulations start from an initial temperature of 0 K. The pre-existing edge crack was loaded in tension mode I. Crack initiation in MD is accompanied by surface dislocation emissions and later by a cross slip of the emitted dislocations into other slip systems. This leads both to stress waves radiation and to local heating in the plastic zone created by these dislocations. The local heating at the crack tip in the surface layers reaches a level of 480–500 K at some atoms, but an average temperature in the plastic zone is lower and depends on a chosen crack tip zone size. In the bulk crystal, where no dislocation emission (i.e. no plastic zone) has been realized, no significant heating is observed at the crack tip. MD results at the free sample surface comply with experimental data for ferritic steels with a pre-existing notch, loaded (quasi-statically) in mode I, as well as with some continuum predictions.

Mechanical Behavior of Oxide Dispersion Strengthened Steel Directly Consolidated by Rotary Swaging.

Among the main benefits of powder-based materials is the possibility of combining different constituents to achieve enhanced properties of the fabricated bulk material. The presented study characterizes the micro- and sub-structures and related mechanical properties of ferritic steel strengthened with a fine dispersion of nano-sized Y2O3 oxide particles. Unlike the typical method of preparation via rolling, the material presented herein was fabricated by direct consolidation from a mixture of powders using the versatile method of hot rotary swaging. The mechanical properties were evaluated at room temperature and also at 1300 °C to document the suitability of the prepared steel for high-temperature applications. The results showed that the imposed shear strain, i.e., swaging ratio, is a crucial parameter influencing the microstructure and, thus, material behavior. The workpiece subjected to the swaging ratio of 1.4 already exhibited a sufficiently consolidated structure with ultra-fine grains and featured high room-temperature microhardness values (up to 690 HV0.5), as well as a relatively high maximum flow stress (~88 MPa) when deformed at the temperature of 1300 °C with the strain rate of 0.5 s-1. However, the dispersion of oxides within this sample exhibited local inhomogeneities. Increasing the swaging ratio to 2.5 substantially contributed to the homogenization of the distribution of the Y2O3 oxide particles, which resulted in increased homogeneity of mechanical properties (lower deviations from the average values), but their lower absolute values due to the occurrence of nucleating nano-sized recrystallized grains.

EVALUATION OF TECHNOLOGICAL PLASTICITY OF HIGH BORON CORROSION-RESISTANT STEEL DURING HOT DEFORMATION OF PIPES USED FOR SPENT NUCLEAR FUEL STORAGE

Statement of the problem. The sustainable development of the global nuclear power industry in the future depends on how effectively the problems of radiation safety and nuclear proliferation are addressed. Such problems occur, among other things, at the final stage of the nuclear fuel cycle – spent fuel management. This task is currently on the agenda of both the international community and national governments of countries that develop or intend to develop nuclear energy [1−3]. Today, in connection with ensuring the safety of nuclear energy, boron-containing steels are widely used in the world practice as a material for biological protection and for the manufacture of special equipment parts. This is due to the fact that the B10 isotope in steels provides neutron capture [4]. Hexagonal pipes made of high-boron steel were needed to shield the support cover of the compacted spent fuel storage facility at nuclear power plants. Corrosion-resistant steels alloyed with boron are widely used in the nuclear power industry due to their special nuclear properties. During the operation of nuclear power plants, fuel assemblies that have served their useful life must be stored in special storage facilities using containers – hexagonal tubes made of 04Сr14Ti3B2V steel. To reduce costs during in the construction and operation of NPPs, part of the spent nuclear fuel management should be performed at Ukrainian enterprises. This will provide a significant import substitution effect. To manufacture hexagonal tubes from 04Сr14Ti3B2V steel according to the ingot-hot deformation-profiling-heat treatment scheme, it is necessary to develop the parameters of hot deformation and subsequent technological operations. The use of these pipes in compacted spent fuel storage facilities of NPPs will allow to increase the storage capacity by 2 times, which will give a significant national economic effect Material and methods of research. Material used for the study was steel 04Сr14Ti3B2V (CS-82), smelted using two variants (vacuum-induction – “VI” and vacuum-induction followed by vacuum-arc remelting – (“VD”). Steel grade 04Сr14Ti3B2V belongs to high-alloy, corrosion-resistant ferritic steels with a high boron content of up to 2 %. The method of differential thermal analysis was used to study the phase transformation temperatures in the steel. X-ray diffraction and micro-X-ray spectral analysis were used to assess the phase state. The steel samples were tested for weldability After cooling, the welded samples were subjected to X-ray transmission [5]. Hot twisting tests and mechanical tests at high temperatures were also performed. The macro- and microstructure of the metal was studied. Results. The macro- and microstructure of steel was evaluated depending on the smelting method. The phase composition of the steel was studied. The study of the plastic properties of steel ChS-82 by means of penetration and hot twisting tests showed that the temperature range of maximum plasticity is in a wide range (from 1 025 to 1 150 0C) with a rather low resistance to deformation. During hot deformation in the temperature range of 1 175 0C and above, metal fracture was observed along the grain boundaries at the melting points of the Cr−Fe−B boride phase. The optimal temperature range for hot deformation of steel ChS-82 is 1 000−1 050 ⁰С. Scientific novelty. For corrosion-resistant high boron steel used for spent nuclear fuel storage, the temperature range of hot deformation was selected and the structural and phase composition was estimated, which will allow deforming the metal on the piercing mill and manufacturing pipes.

New insights into oxidation and creep characteristics of T91 heat-resistant steel in martensitic and ferritic states

This study systematically compared the oxidation and creep characteristics of T91 steel in both martensitic and ferritic states. Findings indicate the formation of mixed oxides, including Fe3O4, (Cr, Mn)2O3, and MnCr2O4, during the oxidation process. In the ferritic specimens, the oxygen diffusion channel is restricted due to the transition of M23C6 carbide. Moreover, the ferritic steel exhibits poor creep life, and a strong α fibre texture was observed. For T91 steel, appropriate thermomechanical treatment can lead to uniform distribution of M23C6 carbides within the matrix, achieving the optimal precipitation strengthening effect and resulting in improved high-temperature properties.

Thermo-mechanical fatigue analysis of ferritic stainless steel STS444LM for exhaust manifold application

This work presents thermo-mechanical fatigue (TMF) life analysis of ferritic stainless steel STS444LM recently developed to enhance the durability of the automotive exhaust manifolds. To determine cyclic material properties, isothermal tensile and low cycle fatigue (LCF) tests at temperature ranging from 200 °C to 900 °C under two different strain rates of 0.1 %/s and 0.01 %/s are performed. Based on these tests, the unified Chaboche visco-plasticity model is determined. Then, the TMF test using the V-shaped specimen subjected to the temperature cycle from 250 to 850 – 950 °C with three different dwell times at the maximum temperature is performed. An energy-based model based on the Morrow model is determined using TMF test data by incorporating effects of the dwelling time and maximum temperature.