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Thin AISI 430 ferritic stainless steel sheets containing 18% Cr were hardened by continuous-wave laser beams under different conditions. A symmetric double laser treatment platform was developed to operate two lasers simultaneously in order to achieve a homogenous microstructure through the specimen and avoid the overheating associated with single laser treatments on one surface. The influence of linear energy density and shielding gas on microstructure and hardness is investigated for both single and double laser treatments. Tensile behavior and oxidation effect during treatment are also studied. With a peak temperature around Tm, the single-track laser yields local microhardness that is 90% higher than the base material, while samples completely treated by the multi-track laser present a 60% increase in yield stress and 45.8% in ultimate tensile stress. These improvements in mechanical behaviors are driven by the formation of martensite and chromium carbides upon rapid cooling despite poor carbon content and dramatic grain coarsening. These results could be useful in order to locally modify the behavior of medium chrome ferritic stainless steel to meet industrial requirements. ANR JCJC SCOLASTIC 16-CE08-0009

The influence of inclusion size and number density on high-temperature urea corrosion (HTUC) behavior of ferritic stainless steels was investigated in a simulated working environment of selective catalytic reduction (SCR) system in commercial vehicles. There is a positive correlation between the control level of inclusions and the resistance of HTUC. By slightly increasing the content of Nb in ferritic stainless steels, the inclusions, especially TiN, were significantly refined, and thus displayed an improvement in HTUC resistance. The interface between inclusions and the matrix becomes a fast channel for chromium precipitation during high-temperature nitriding induced by the decomposition of urea. Chromium nitrides will precipitate around the inclusions and wrap the inclusions, which will decrease the chromium equivalent of the matrix and reduce the resistance of ferritic stainless steels to HTUC. In addition, the high-temperature oxidation accompanied with thermal fatigue also makes the inclusions more likely to become the crack nucleation source, which can accelerate the material thinning and reduce its service life.

A comparison between the niobium-stabilized type ASTM 430, 430Nb, and niobium-titanium-stabilized ASTM 439 ferritic stainless steels with respect to their microstructure and texture at the different stages of recrystallization was performed. The annealed samples were subjected to tensile test and Swift test for evaluation of mechanical behavior and deep drawability, respectively. The heat treatment was carried out on lab-scale cold rolled sheets with 85% thickness reduction as an attempt to mimic the industrial process. Recrystallization occurred first for 430Nb steel with smaller recrystallized grain sizes, less pronounced γ-fiber texture, lower average normal anisotropy coefficient, R¯, and limit drawing ratio, LDR. On the other hand, ASTM 439 showed higher yield stress but better drawability. These results are presented and discussed based on microtexture evolution, precipitate characteristics and grain boundary character distributions. Keywords: Ferritic stainless steel, Texture, EBSD, Mechanical behavior, Drawability, Microstructure

Localised-in-the-edge oxidation of four AISI 430 alloys was investigated after an industrial bright annealing process. The oxidised surface of each specimen was characterised by X-ray photoelectron spectroscopy (XPS), Raman-spectroscopy and SEM. The results showed that the selective oxidation of Cr and Mn took place at the coil edges of AISI 430. This led to the formation of an oxide scale based on Cr2O3 and MnCr2O4. On the other hand, the formation of Cr(OH)(3) and MnOOH in the outer part of the oxide scale was related to the effect of the H-2-N-2 environment on the annealing furnace. The results concluded that the composition of Cr and Mn in the alloy determined the composition of the oxidation products. However, the effect of annealing time was minor in this oxidation mechanism, which slightly contributed to an increase in the cation diffusion from the steel to the oxide. Finally, the results obtained indicate that the colouration of the coil edges displayed in each studied material varies according to the alloy chemical composition and annealing time., This research was funded by the "Proyectos de I+D Individuales" programme, Centro para el Desarrollo Tecnologico Industrial (CDTI), Ministerio de Economia y Competitividad from the Spanish Government-project "FERRINOP".

Flux activated tungsten inert gas (ATIG) welding is a variant of tungsten inert gas (TIG) welding process with high production efficiency, high quality, low energy consumption, and low cost. The study of activating flux mechanism by increasing weld penetration has direct significance in developing flux and welding process. This study has been conducted on 430 ferritic stainless steel alloy. Design of experiment is used to get the best formulation of flux. Based on Minitab17 software, nineteen compositions of flux were prepared using the mixing method. Fluxes are combinations of three oxides (MoO3-TiO2-SiO2). Using the optimizer module available in Minitab 17 software, the best formulation was obtained to achieve the best weld depth. Hence, the obtained depth is twice greater than that achieved by conventional TIG welding. Moreover, mechanical properties and corrosion resistance have been investigated for TIG and ATIG welds respectively in tensile, impact, and hardness tests, and in potentiodynamic polarization measurement test.

The solidification structure of ferritic stainless steel can be refined by controlling the contents of Ti, O, and N in the liquid steel through the thermodynamic analysis and high-temperature experiment. It is found by the scanning electron microscopy technology, in which the composite core of Ti nitride-enwrapping Ti oxide can be formed in the solidification front, which promotes the nucleation of δ iron and refines the solidification structure. Meanwhile, the structure analysis of the composite core by the transmission electron microscope technology proves that the Ti oxide that exists in the centre of the composite core is Ti2O3 and the Ti nitride that exists in the outer layer of the composite core is TiN.

Planar solid oxide fuel cell (SOFC) systems often employ metallic interconnects, which separate and connect individual cells in electrical series to create a stack. Coated and uncoated ferritic stainless steels (FSSs), are reported among the most promising materials currently being investigated for interconnect applications. In this study, FSS AISI 441 samples coated with electroless nickel (∼25 μm) were subjected to intermediate temperature IT-SOFC operating conditions at 700 °C for 500 h with and without the application of electrical current (0.5 Acm−2). The application of the electric current promotes Fe migration on both the cathode and the anode side. This phenomenon results in the formation of a ∼4 μm thick Fe2O3 on the anode side responsible for increased ASR values. Comparative analyses of the current and no current exposures and resultant surface oxide layers, along with suspected mechanisms and implications are presented and discussed.

In this study, the kinetics of austenite layer growth on the surface of Fe-23Cr-2.4Mo ferritic stainless steel during solution nitriding and the effects of nitrogen adding on microstructure and hardness of the steel have been investigated. Steelplates of 2 mm thick were solution-nitrided at 1200˚C under nitrogen pressure of 0.25 MPa for 2, 3, 6, 9, 12 hours. Microstructure, the thickness of austenite layer and the hardnes of the nitrided samples, were investigated by using optical microscope, X-ray Diffraction (XRD) and microhardness measurements. The results showed that during solution nitriding, nitrogen diffuses through the lattice and grain boundaries and transforms ferrite to austenite phase, with average nitrogen diffusion coefficient of 6.54×10-5 mm2s-1. The thickness of the austenite layer formed on the samples surfaces increased proportional to the square root of the nitriding time, so that after 12 hours niriding, the whole thickness of the ferritic sample with hardness of 262 HV0.1 transformed to austenite with hardness of 420 HV0.1.

In the present study, the feasibility of laser surface melting (LSM) of AISI 430 ferritic stainless steel to minimize hydrogen embrittlement (HE) was investigated. LSM of AISI 430 steel was successfully achieved by a 2.3-kW high power diode laser (HPDL) with scanning speeds of 60 mm/s and 80 mm/s (the samples are designated as V60 and V80, respectively) at a power of 2 kW. To investigate the HE effect on the AISI 430 steel without and with LSM, hydrogen was introduced into specimens by cathodic charging in 0.1 M NaOH solution under galvanostatic conditions at a current density of 30 mA/cm2 and 25 &deg, C. Detail microstructural analysis was performed and the correlation of microstructure with HE was evaluated. By electron backscatter diffraction (EBSD) analysis, the austenite contents for the laser-surface melted specimens V60 and V80 are found to be 0.6 and 1.9 wt%, respectively. The amount of retained austenite in LSM specimens was reduced with lower laser scanning speed. The surface microhardness of the laser-surface melted AISI 430 steel (~280 HV0.2) is found to be increased by 56% as compared with that of the substrate (~180 HV0.2) because of the presence of martensite. The degree of embrittlement caused by hydrogen for the charged and non-charged AISI 430 steel was obtained using slow-strain-rate tensile (SSRT) test in air at a strain rate of 3 &times, 10&minus, 5 s&minus, 1. After hydrogen pre-charging, the ductility of as-received AISI 430 steel was reduced from 0.44 to 0.25 while the laser-surface melted AISI 430 steel showed similar tensile properties as the as-received one. After LSM, the value of HE susceptibility I&delta, decreases from 43.2% to 38.9% and 38.2% for V60 and V80, respectively, due to the presence of martensite.

The low-cost ferritic steel grades 441 and 430 are benchmarked against the specialty grade Crofer 22H as possible interconnect materials for intermediate temperature solid oxide fuel cells. The steels are either pre-oxidized or coated with MnCo2O4. The composition and growth rate of the oxide scales in air is evaluated over a period of 2000 h at 650, 700 and 750 °C. The MnCo2O4 coating is found to reduce the thickness of the oxide scale on all three steels at 700 and 750 °C. The greatest protective effect is achieved on Crofer 22H. A SiO2 scale is formed at the Cr2O3/steel interface after oxidation for all three steels, but it remains discontinuous during the evaluated period. The MnCo2O4 coating provides sufficient protection to make the low-cost steels 441 and 430 promising interconnect materials for operation at 650–700 °C. For higher operation temperatures, 441 is not applicable due to poor scale adhesion.

In this work, the effect of Nb addition on sensitization and pitting corrosion of welded AISI 430 ferritic stainless steel subjected to autogenous GTAW was investigated by microstructural characterization and electrochemical techniques. The three distinct regions of welding process, weld metal, heat affected zone and base metal of AISI 430 steel with and without Nb were evaluated. The degree of sensitization was measured by double loop electrochemical potentiodynamic reactivation and pitting corrosion was studied by potentiostatic polarization test. The microstructural analyses reported martensite network in the weld metal and heat affected zone of AISI 430 non stabilized. The electrochemical studies revealed that the highest degree of sensitization and the lowest pitting potential are in the weld metal of AISI 430 without Nb. Resumo Neste trabalho, o efeito da adição de Nb na sensitização e corrosão por pite de aço inoxidável ferrítico AISI 430 submetido à soldagem TIG foi investigado por caracterização microestrutural e técnicas eletroquímicas. As três regiões distintas do processo de soldagem, zona fundida, zona termicamente afetada e metal de base do aço AISI 430 com e sem Nb foram avaliadas. O grau de sensitização foi medido por reativação potenciodinâmica eletroquímica de “double loop” e a corrosão por pite foi estudada por testes de polarização potenciostática. As análises microestruturais revelaram uma fase martensítica na zona fundida e zona termicamente afetada do AISI 430 não estabilizado. Os estudos eletroquímicos mostraram que o maior grau de sensitização e o menor potencial de pite estão na zona fundida do aço sem adição de Nb.

The article describes the effect of alloyed additives in base material and filler metal on intergranular corrosion. Steel 1.2 mm thick, titanium-stabilized ferritic stainless steel and titanium and niobium-stabilized ferritic stainless steel have been surfacing method MAG (135). The specimens received was subjected to macro and microscopic tests, hardness tests and the intergranular corrosion resistance test. The study showed a higher corrosion resistance of niobium and titanium stabilized steel from titanium-stabilized steel. In addition, a ferritic fine-grain structure was found in the padding axis made with the use of filler metal with titanium and niobium microadditives.

The TIG Dressing technique has been widely used for repairing cracks in welded structures when subjected to mechanical forces that induce localized fatigue, leading to the collapse during operation. However, this technique has not been used for studies in structures susceptible to corrosion. In addition to changing the microstructure, it is expected that this technique increases the corrosion resistance of the edge of the weld bead which is a vulnerable region to corrosion. Moreover, the machining technique has been widely used to improve the workpieces finishing and/or structures that have been subjected to repair by welding, improving the surface roughness, increasing the corrosion resistance of these structures when subjected to aggressive environments. Thus, this work will study the effects of finishing techniques using machining and welding on the edge of the weld bead joints of 410D ferritic stainless steels, making an evaluation by mass loss in the samples which will be subjected to corrosion by immersion in NaCl containing medium. It is expected that the finishing techniques can relieve tensile stresses increasing the corrosion resistance.

The addition of rare earth element Ce in ferritic stainless steel can improve the high temperature performance to meet the service requirements of automobile exhaust systems at high temperatures. Automobile exhaust systems are generally applied as welded pipes, so it is necessary to study the effect of Ce on the weldability of ferritic stainless steel. In this study, the Trans-varestraint test method was used to test the solidification crack sensitivities of 441 and 441Ce ferritic stainless steel. The 441Ce steel, which has added Ce, showed poor resistance to weld solidification cracking. Using Thermo-Calc software, Ce was observed to expand the solidification temperature range of 441 ferritic stainless steel, increase the time for solid&ndash, liquid coexistence during solidification, and increase the sensitivity of solidification cracking. Further, from scanning electron microscopy and energy dispersive spectrometer analysis, the addition of Ce was found to reduce high temperature precipitation (Ti,Nb)(C,N), reduce or even eliminate the &ldquo, pinning&rdquo, effect during solidification, and increase solidification crack sensitivity of 441 ferritic stainless steel.

Role of microstructure in susceptibility of 18Cr ferritic stainless steel to hydrogen embrittlement was studied. Specimens of the studied steel were charged with hydrogen electrochemically from 0.1 N H 2 SO 4 solution under controlled cathodic potential providing a homogeneous hydrogen distribution over the specimen cross-sections. Thermal desorption spectroscopy analyses were carried out investigating the uptake, trapping and diffusion of hydrogen in the ferritic stainless steel. Microstructural change caused by heat-treatment at 1050 °C and 1200 °C associated preferably with grain size growth from 18 µm to 65 µm and 349 µm, respectively, resulting in significant degradation of the mechanical properties of the studied steel. The effect of the grain size growth on hydrogen susceptibility was studied with constant extension rate test (CERT) performed under continuous hydrogen charging. It is found that hydrogen has a remarkable effect on the elongation to fracture of the Fe-Cr ferrite: in the presence of H elongation to fracture of the steel reduces up to 75% compared to the H-free counterpart. In general, the hydrogen sensitivity of the mechanical properties increases with increase of the mean grain size of the studied ferritic stainless steel. However, the detailed analysis reveals a complicated, non-linear behavior of the hydrogen sensitivity. Scanning electron microscopy (SEM) of the fracture surfaces of the tensile specimens tested during continuous hydrogen charging reveals a quasi-cleavage fracture surface morphology. Hydrogen-induced cracking in the studied 18Cr ferritic steel was studied using electron backscatter diffraction (EBSD) analysis from the side surfaces of the tensile tested specimens.

Development of efficient design guidance for stainless steel structures is key for the increased use of this corrosion-resistant material by considering both nonlinear behaviour and strain hardening into resistance prediction expressions, together with the moment redistribution in indeterminate structures. With the aim of analysing the bending moment redistribution capacity of ferritic stainless steel beams, a comprehensive experimental programme on continuous beams is presented. These tests contribute to the assessment of EN1993-1-4 specifications, where no plastic design is allowed, and the classical and new plastic design methods available in the literature for indeterminate stainless steel structures. Four three-point and eight four-point bending tests are also reported for the assessment of current codified and revised cross-sectional classification limits, analysing the different methods for the prediction of the ultimate bending capacities of ferritic hollow sections. Additional test results reported by other authors in different stainless steel grades and carbon steel are also studied and presented. The analysis indicates that Class 1 cross-sectional classification limits are too optimistic for ferritic stainless steels and further research is needed for the extension of plastic design to these grades, although promising predictions of ultimate loads are obtained for austenitic and lean duplex stainless steels.

Ferritic stainless steels, with their lower nickel content, supplement the desirable features offered by different stainless steel grades with a more controlled and lower initial investment requirements, which have encouraged the use of these materials in construction. The nonlinear behaviour of stainless steel grades is not usually considered when extending design expressions codified for carbon steel to these alloyed materials, leading to overconservative design approaches and the applicability of the different design expressions initially developed for carbon steel needs to be adjusted for every stainless steel grade. The study of stainless steel elements subjected to combined flexural buckling and bending moment loading conditions only covers the most usual austenitic, duplex and lean duplex grades, but experimental results on ferritic grades are still necessary to complete the analysis. Hence, an experimental programme on ferritic stainless steel RHS and SHS pin-ended elements has been conducted where the flexural buckling and beam-column behaviour of these elements has been investigated. Furthermore, the assessment of the different design approaches for flexural buckling and interaction expressions for combined loading has been derived from the obtained experimental results, and current specifications provided in Standards have been found to be, in general, safe but overconservative.

Nowadays, there is an increasing demand for the use of joining dissimilar metals in various industrial applications owing to the economic benefits and better joint performance. Ferritic stainless steel grades is a good alternative for austenitic ones in several applications as they display higher ductility and strength as well as better corrosion resistance in chloride environments. However, the poor ductility and low impact toughness of ferritic stainless-steel welded joints limit their wide-spread application. Thus, the demand for joining dissimilar ferritic and austenitic stainless steels is ever increasing in several engineering applications in various industries such as nuclear power plants, coal fired boilers, automobile manufacturing industry, chemistry and petro-chemistry industries, etc. Therefore, successful joining of these two different types of stainless steel grades using conventional fusion welding methods is rather important. In this study, the weldability of AISI 430 ferritic and AISI 304 austenitic steel plates using gas metal arc welding and the effect of heat input on microstructure and the mechanical properties were investigated. For this purpose, AISI 430 and AISI 304 plates with a thickness of 5 mm were joined using different heat input values. The microstructures evolved in the weld region of the joints and their mechanical properties were determined by detailed optical microscopy investigations, micro-hardness measurements and tensile tests. Thus, the influence of the heat input on the weldability of these two different stainless-steel plates using gas metal arc welding was also studied.

The use of composite floor slabs is well established and provides an opportunity to promote the use of visually exposed composite slabs. Stainless steels, with the combination of good mechanical properties and excellent corrosion resistance, are key to this strategy, specially ferritic stainless steels, whose price is lower and more stable than that corresponding to the more widely used austenitic grades, due to their low nickel content whilst still maintaining good mechanical properties and aesthetic appeal. In addition, the emissivity of these grades contributes to lowering the heating and cooling requirements of buildings, reducing the costs associated to maintenance. Generally used as cold-formed members with high resistance-to-weight ratios, stainless steel decks are slender and highly sensitive to buckling phenomena and so the study of the structural performance of composite slabs using ferritic stainless steel decking is required due to the complex nonlinear behaviour of stainless steels, which is very different from that exhibited by carbon steel. Thus, this paper presents a comprehensive experimental programme on ferritic stainless steel trapezoidal decks for composite slabs under several structural configurations occurring during construction stage: simply supported decks under positive and negative bending moment, continuous decks and internal and end support tests. All the experimental results have been compared with the predicted ultimate loads in EN 1993-1-4, which remits to EN 1993-1-3 for carbon steel, and also with some previous tests on galvanized carbon steel decks. The paper concludes that EN 1993-1-3 provisions are applicable to ferritic stainless steels.

The intergranular corrosion behavior of the low-chromium ferritic stainless steel without Cr-carbide precipitation was investigated by the methods of qualitative and quantitative corrosion testing and microstructural analysis. The intergranular corrosion susceptibility of the aged stainless steels can be attributed to the Cr-depleted zone formation induced by Cr-C co-segregation to grain boundaries before Cr-carbide nucleation. The change of intergranular corrosion morphology after aging at 450 °C from discontinuous (aged for 2 h) to semi-continuous (aged for 20 h) and to continuous (aged for 200 h) is discussed in detail.

The passivation behavior of AISI 430 ferritic stainless steel was investigated in concentrated alkaline solutions in relation to several test parameters, using electrochemical techniques. Increasing solution pH (varying from 11.5 to 14.0) leads to an increase in the corrosion rate of the alloy. Mott–Schottky analysis revealed that passive films formed on AISI 430 ferritic stainless steel behave as n-type semiconductor and the donor densities increased with pH. Electrochemical impedance spectroscopy (EIS) results showed that the reciprocal capacitance of the passive film is directly proportional to its thickness, which decreases with pH increase. The results revealed that for this ferritic stainless steel in concentrated alkaline solutions, decreasing the solution pH offers better conditions for forming passive films with higher protection behavior, due to the growth of a much thicker and less defective film.

Ferritic stainless steels are used in specific applications where corrosion resistance, oxidation resistance and a high mechanical resistance are required. Shot peening is a process applied to add residual compression stresses in metallic surfaces with the intent of improving the material when exposed to corrosion due to stress and fatigue. Some studies about the effect of the shot peening process on the fatigue resistance, bending fatigue behavior, and residual surface stress in the ferritic stainless steels have been performed. However, the effect of the shot peening process on the corrosion and oxidation resistance of the stainless steel is not well known. In this context, the purpose of this study is to evaluate the effect of the shot peening process on these superficial properties of ferritic AISI430 stainless steel. The obtained results showed that the ferritic AISI430 stainless steel samples treated with shot peening presented a significant modification on the surface morphology and an important decrease of oxidation and corrosion resistance, evidencing that the shot peening process compromises the chemical and physical properties of the surface.

The Bosch Group, a leading global supplier of technology and services develops reliable and efficient fuel cell components for future mobility solutions. This work studies the fatigue behavior of ferritic stainless steel 1.4005IA optimized for electromagnetic properties under varying environmental conditions. Fatigue-life of air-tested specimens are compared to specimens which are electrochemically hydrogen precharged and loaded in a pressurized gaseous hydrogen atmosphere. The fracture surfaces of broken specimens are investigated using optical microscope and SEM in order to analyze the failure mechanisms. Furthermore, the hydrogen contents of specimens before and after static and cyclic testing in gaseous hydrogen are measured. Based on strain controlled fatigue tests using unnotched specimens, the influence of hydrogen on cyclic material parameters is determined. Using these parameters, a fatigue-life estimation for notched specimens based on the local strain approach is carried out. Different estimation approaches are evaluated, by comparing experimental data and predicted fatigue-lifes. A modified material model, based on the four-parameter equation according to Manson, Coffin and Morrow is proposed to prescribe the influence of hydrogen on cyclic behavior of ferritic stainless steel in low gas pressure applications (up to 1 MPa). The proposed approach including the modified material model is in a good agreement to the experimental data. This opens a pathway for a reliable component design process for industrial applications.

The objective of this work is to investigate the influence of the crystallographic texture on the corrosion resistance of 16% Cr ferritic stainless steel. Samples of ASTM S43000 ferritic stainless steel, both niobium-stabilised and non-stabilised, were used. The samples were subjected to crystallographic characterisation (EBSD) and analysed using an inverse pole figure (IPF) and a crystalline orientation distribution function (CODF). The samples also underwent anodic potentiodynamic polarisation tests (deaeration by high-purity argon gas) in 3.56% NaCl and 1N H2SO4 solutions, and the surface was examined by SEM after the tests. The results showed a clear influence of the crystallographic texture on the corrosion resistance. The niobium decreases the amount of the preferred orientation and thus the influence of the texture on the corrosion resistance, although the corrosion resistance of the stainless steel is increased as niobium carbides are formed.

The effect of annealing treatment on the deep drawability and ridging resistance in a Sn-containing ferritic stainless steel was studied by average plasticity strain ratio r-value measuring, X-ray diffraction (XRD) and electron back scatter diffraction (EBSD) analysis after carried out tensile tests. The results indicate that the average plastic strain ratio (r-value) increased as the annealing temperature and keeping time increased, which reached up to 1.82 after annealing treated at 900 °C for 4 min. However, ridges became obvious as the temperature increased. When the annealing temperature increased from 860 to 920 °C for 2 min, the fraction of the recrystallization texture component of γ-fiber in the center of the tested sheet increased from 40% to 70%, while the root-mean-square deviation of the profile (Rq value) increased from 1.179 to 1.783 μm. In the tensile tests of the annealed samples with half-thickness of the sheet, the ridging morphology in the center was more obvious than that on the surface. The experiments show that the inhomogeneous distribution of grain clusters of γ-fiber texture formed during recrystallization in the center layer of the sheet is a significant cause of ridging in the sheet, the textures on the surface distributes homogeneously relatively, which is beneficial to reduce the manifestation of ridging.

The effect of grain refining elements such as titanium (Ti) on mechanical properties of AISI 430 ferritic stainless steel welds through gas tungsten arc welding process was studied. Titanium powder of -100 μm mesh was added in the range from 1 g to 3 g between the butt joint of ferritic stainless steel. In order to investigate the influence of post- weld heat treatment on the microstructure and mechanical properties of welds, post-weld annealing was adopted at 830 °C, 30 min holding followed by water quenching. Residual stresses and corrosion behaviour of ferritic stainless steel welds was also studied. From this investigation, it is observed that the joints made by the addition of 2 g Ti (0.7 wt %) in post-weld annealed condition led to improved strength and ductility. The observed mechanical properties have been correlated with microstructure, fracture features, residual stresses and corrosion behaviour of ferritic stainless steel weldments.

International audience; Several compositions of metal cored filler wire were manufactured to define the best welding conditions for homogeneous welding, by Gas Metal Arc Welding (GMAW) process, of a modified AISI 444 ferritic stainless steel dedicated to automotive exhaust manifold applications. The patented grade is know under APERAM trade name K44X and has been developed to present improved high temperature fatigue properties. All filler wires investigated contained 19%Cr and 1.8%Mo, equivalent to the base metal K44X chemistry, but various titanium and niobium contents. Chemical analyses and microstructural observations of fusion zones revealed the need of a minimum Ti content of 0.15% to obtain a completely equiaxed grain structure. This structure conferred on the fusion zone a good ductility even in the as-welded state at room temperature. Unfortunately, titanium additions decreased the oxidation resistance at 950°C if no significant Nb complementary alloying was made. The combined high Ti and Nb additions made it possible to obtain for the welded structure, after optimized heat treatment, high temperature tensile strengths and ductility for the fusion zones and assemblies, rather close to those of the base metal. 950°C aging heat treatment was necessary to restore significantly the ductility of the as welded structure. Both fusion zone and base metal presented rather homogenized properties. Finally, with the optimized composition of the cored filler wire - 0.3 Ti minimum (i.e. 0.15% in the fusion zone) and high Nb complementary additions, the properties, including the thermal fatigue strength, of the K44X assemblies are excellent.

International audience; Seven compositions of metal cored filler wires for Gas Metal Arc Welding (GMAW), containing the same weight percent of chromium (Cr) and molybdenum (Mo) as 444 steel, but with different titanium (Ti) and niobium (Nb) contents were investigated. Experimental results pointed out that the filler wire Ti content required to be twice time more than the amount expected in the deposited metal. This was due to the low Ti transfer ratio during arc welding. Moreover, Ti increased the wetting angle and promoted penetration. It was supposed that Ti affected the weld pool surface tension what led to inward Marangoni convection. Columnar to equiaxed grain transiton (CET) was also promoted thanks to the precipitation in the weld pool of Ti rich refractory compounds which act as heterogeneous nucleation sites for equiaxed grains. A minimum 0.3% Ti was required in the filler wire to form a completely equiaxed grain structure in the fusion zone. Niobium in the filler wire did not seem to have any effect on penetration, wetting and grain structure of the fusion zone.

The influence of grain refining elements such as copper (Cu) and aluminium (Al) on mechanical properties of AISI 430 ferritic stainless steel welds through gas tungsten arc welding process was studied. Cu (foil form) and Al powder of −100 μm mesh was added in the range from 1 to 3 g between the butt joint of ferritic stainless steel. In order to investigate the influence of post-weld heat treatment on the microstructure and mechanical properties of welds, post-weld annealing was adopted at 830 °C, 30 min holding followed by water quenching. Corrosion behaviour of ferritic stainless steel welds was also studied. From this investigation, it is observed that the joints made by the addition of 2 g Al (2.4 wt.%) in post-weld annealed condition led to improved strength. There is a marginal improvement in the ductility and pitting corrosion resistance of ferritic stainless steel welds by the addition of 2 g Cu (0.18 wt.%) in post-weld annealed condition. The observed mechanical properties have been correlated with microstructure, fracture features and corrosion behaviour of ferritic stainless steel weldments.

Usually niobium is added in ferritic stainless steels to avoid chromium carbides precipitation and then to improve corrosion resistance and to avoid embrittlemet. This study shows that a low Nb stabilization makes recrystallization nucleation much faster and prevents incomplete recrystallization. A qualitative interpretation, based on interaction with precipitates, is proposed and explains the main features of the softening kinetics as well as the microstructures obtained. Above a specific magnetizing frequency, the deformed state led to smaller losses than the recrystallized state. These results are believed to be attributed to a grain size effect. This leads to soft magnetic properties that makes 17%CrNb ferritic stainless steels a very interesting solution for the market of electromagnetic injection. Improving response-time of fuel injection valves is a great challenge for automotive industry in order to enhance car engine efficiency and to limit noxious gas emission. Normalmente o nióbio é adicionado aos aços inoxidáveis ferríticos para se evitar a precipitação de carbonetos de cromo e, em seguida, para se melhorar a resistência à corrosão e para se evitar a fragilização. Esse estudo mostra que a estabilização com baixo Nb baixo promove a nucleação da recristalização muito mais rapidamente e evita a recristalização incompleta. Uma interpretação qualitativa, baseada na interação com precipitados, é proposta. Nessa interpretação, explicam-se as principais características da cinética de amolecimento, bem como as microestruturas obtidas. Acima de uma frequência específica de magnetização, o estado deformado leva a perdas menores do que o estado recristalizado. Acredita-se que esses resultados podem ser atribuídos a um efeito de tamanho de grão. Isto leva a propriedades magnéticas macias, que faz dos aços inoxidáveis ferríticos 17% CrNb uma solução muito interessante para o mercado de injeção eletromagnética. Melhorar o tempo de resposta das válvulas de injeção de combustível é um grande desafio da indústria automobilística, a fim de se aumentar a eficiência dos motores, quanto às emissões de gases tóxicos.

According to previous studies the careful argon shielding of the weld is very important in order to achieve a ductile and formable laser weld of Ti-stabilized ferritic stainless steel. In practice it is often difficult to use the root gas shielding of the laser weld. The aim of this study was to determine the sufficient practise of gas shielding in order to achieve the ductile laser weld. According to Erichsen formability results the shielding gas nozzle in the post weld side must be used in order to reach the good formability of the laser weld. The single shielding gas pipe before the weld is not a sufficient method for the gas shielding. There is no need to use root gas in order to achieve a ductile weld. The single shielding gas pipe before the weld can cause a uptake blast in the key hole and further oxidize the weld metal.

cited By 0; International audience; Oxide dispersion-strengthened ferritic stainless steels are foreseen as fuel cladding tube materials for the new generation of sodium fast nuclear reactors. Those materials, which exhibit remarkable creep properties at high temperature, are reinforced by a dense precipitation of nanometric oxides. This precipitation is obtained by mechanical alloying of a powder and subsequent consolidation. Before consolidation, to obtain a fully dense material, the powder is vacuumed to outgas trapped gases and species adsorbed at the surface of the powder particles. This operation is commonly done at moderate to high temperature to evacuate as much as possible volatile species. This paper focuses on the influence of outgassing conditions on some properties of the further consolidated materials. Chemical composition and microstructural characterization of different materials obtained from various outgassing cycles are compared. Finally, impact toughness of those materials is evaluated by using Charpy testing. This study shows a significant influence of the outgassing conditions on the mechanical properties of the consolidated material. However, microstructure and oxygen contents seem poorly impacted by the various outgassing conditions. © 2017, The Minerals, Metals & Materials Society and ASM International.

International audience; A two step modeling for predicting the grain morphology − columnar or equiaxed − of the melting zone in welding is proposed. The first step consists in numerically compute, using the Finite Element Method, the thermal fields around the weld pool boundary, according to the welding parameters. The second step consists in a post-treatment of the thermal field in order to compute the undercooling in the liquid all along the solidification front of the columnar grains, and finally to compute the fraction of equiaxed grains formed in the undercooling zone. The modeling takes into account the effect of the convection phenomena on the undercooling, and is based on an heterogeneous nucleation model specially adapted to steels inoculated with titanium. The nucleation model involves the size distribution of Ti-rich refractory compounds formed in the weld pool, that act as heterogeneous nucleation sites. A method to identify this distribution is also presented. The comparison of the modeling with experimental results of welding with a Gas Tungsten Arc Welding process has proved its ability to predict the columnar to equiaxed transition of a ferritic stainless steel inoculated with Ti.

In the present study, the effects of the addition of Nb, W, and V alloying elements on the thermal fatigue properties of the ferritic stainless steel weld heat affected zone (HAZ) were investigated. Simulation of the weld HAZ and thermal fatigue testing were carried out using a metal thermal cycle simulator (MTCS) under a complete constraint force in the static jig. The fatigue life during cyclic heating and cooling in the temperature range of 200 to 900 °C was strongly related not only to precipitation and coarsening of MX type precipitates and Laves phase but also to the Nb content in the solid solution and grain coarsening. The thermal fatigue life increased with higher Nb and W contents due to more (Nb,Ti)C precipitates and a less coarsened Laves phase, respectively. Contrary to the results with Nb and W additions, there were no obvious effects on grain size and precipitation behavior associated with V addition.

When ferritic stainless steels are exposed to the temperature range of 400-550 °C, they undergo 475 °C embrittlement that could be attributed to the spinodal decomposition. In the present study, high-chromium ferritic stainless steel, type 447, was aged at 520 °C under both static and cyclic loading conditions and microstructure was analyzed using a transmission electron microscope (TEM). By aging under static condition, hardness and tensile strength were largely increased. TEM observation revealed the mottled contrast due to the typical spinodal decomposition of Cr phase. Under cyclic loading condition, increases in hardness and tensile strength were smaller than those under static condition. TEM micrographs of the specimens subjected to cyclic loading exhibited a lower contrast of the mottled pattern than those of the specimens aged under static condition, indicating that cyclic loading suppressed the spinodal decomposition, thus resulting in the lower increases in hardness and tensile strength.

Ferritic stainless steels can be attractive bipolar plate materials of proton exchange membrane fuel cells (PEMFC), provided that the stainless steels show sufficient corrosion resistance, for instance, by eliminating interstitial elements such as carbon and nitrogen. In the present study, thus, ferritic stainless steels (19Cr2Mo and 22Cr2Mo) with extra low interstitials (ELI) are evaluated to determine the required level of chromium content to apply them for PEMFC bipolar plates. In a simulated PEMFC environment (0.05 M SO 4 2− (pH 3.3) + 2 ppm F − solution at 353 K), the 22Cr2Mo stainless steel showed lower current density during the polarization in comparison with the 19Cr2Mo one. The polarization behavior of the 22Cr2Mo stainless steel resembles that of the type 316 one (17Cr12Ni2Mo). Similar values of interfacial contact resistance (ICR) are observed for both ferritic stainless steels. The 22Cr2Mo stainless steel bipolar plate is found to be stable throughout the cell operation, while the 19Cr2Mo stainless steel corroded within 1000 h. After the cell operation, the 22Cr2Mo stainless steel retains the chromium enriched passive film, while the chromium enriched surface film is not found for the 19Cr2Mo one, showing iron oxide/hydroxide based film. X-ray fluorescence (XRF) analysis of the membrane electrode assemblies (MEAs) after the cell operation indicates that the 22Cr2Mo stainless steel was less contaminated with iron species. The above results suggest that the 22Cr2Mo stainless steel can be applicable to bipolar plates for PEMFC, especially 22 mass% of chromium content in ferritic stainless steel with ELI system is, at least, demanded to ensure stable cell performance.

Stainless steels are used in architecture and building because of their good corrosion resistance and visual appearance. Despite all precautions localised corrosion has caused unexpected material failures in environments which should be harmless. These failures are associated to surface contamination with corrosive salt solutions that are formed when splash water concentrates due to evaporation. This paper reports on studies carried out to investigate the localised corrosion risk of stainless steels in concentrated salt solutions. A quantitative corrosion risk prediction approach based on the experimental corrosion studies and quantitative pitting corrosion models developed for evaluation of pitting corrosion risk are presented.

The high temperature oxidation behavior of two ferritic stainless steels type AISI 430A and AISI 430E is examined at low oxygen pressure and high temperatures. The AISI 430A steel is ferritic up to 860 °C. Above this temperature, this steel is bi-phased: presence of austenite and ferrite phases. The 430E steel is stabilized with Nb, and is ferritic at all temperatures. The oxidation experiments were performed in a thermobalance SETARAM TGDTA 92, in the range of 850-950 °C, in Ar/H2/H2O atmosphere, under oxygen partial pressures lower than 1.3 x 10-18 atm. The microstructure and the composition of the oxide scales were analysed by scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS). Different oxidation behaviors in AISI 430A and AISI 430E stainless steels were observed. At 850 °C, the oxidation of the 430A steel is greater than that of the 430E steel, but above 900 °C the oxidation of the 430A steels is lower than that of the 430E steel. The oxidation rate of the 430A steel shows low dependence on temperature, while the oxidation of the 430E follows an Arrhenius law, with an activation energy corresponding to the chromia scale growth.

The applications of stainless steel are one of the most reliable solutions in concrete structures to reduce chloride-induced corrosion problems and increase the structures service life, however, due to high prices of nickel, especially in many civil engineering projects, the austenitic stainless steel is replaced by the ferritic stainless steels. Compared with austenite stainless steel, the ferritic stainless steel is known to be extremely resistant of stress corrosion cracking and other properties. The good corrosion resistance of the stainless steel is due to the formation of passive film. While, there is little literature about the electrochemical and passive behavior of ferritic stainless steel in the concrete environments. So, here, we present the several corrosion testing methods, such as the potentiodynamic measurements, EIS and Mott–Schottky approach, and the surface analysis methods like XPS and AES to display the passivation behavior of 430 ferritic stainless steel in alkaline solution with the presence of chloride ions. These research results illustrated a simple and facile approach for studying the electrochemical and passivation behavior of stainless steel in the concrete pore environments.

Anodizing of ferritic stainless steel has been used for decoration purposes to obtain a barrier effect. The most commonly used electrolyte for this process is INCO (5M H2SO4 + 2,5M CrO3). INCO electrolyte with glycerin addition induces the formation of ordered porous structures, because glycerin reduces the electrolyte conductivity. Ferritic stainless steel was anodized in electrolyte composed by 2M H2SO4 with glycerin addition in different concentrations, without chromium oxide addition. It was observed that the addition of 90 v/v% glycerin promoted a reduction in the electrolyte conductivity, which caused an increase in the anodizing potential. The glycerin addition to the electrolyte diminished the oxide dissolution in the electrolytic solution, promoting the formation of an oxide with an ordered porous structure. La anodización de acero inoxidable ferrítico ha sido utilizada con fines decorativos, para obtener una capa de barrera. El electrólito más comúnmente utilizado para este proceso es el INCO (5M H2SO4 + 2,5M CrO3). Con adición de glicerina induce la formación de estructuras porosas ordenadas, pues la glicerina reduce la conductividad del electrólito. Se anodizaron muestras de acero inoxidable ferrítico, en electrólito de 2M H2SO4 con la adición de glicerina en diferentes concentraciones, sin adición de óxido de cromo. Se observa que la adición de glicerina en un 90 v/v % promovió la reducción de la conductividad del electrólito, lo que ocasionó un aumento del potencial de anodización. Los resultados muestran que la adición de glicerina al electrólito redujo la disolución del óxido en la solución electrolítica y promovió la formación de un óxido con una estructura porosa ordenada.

Exhaust lines of cars have been strongly evolving during the last decade to meet the various requirements of the automotive industry and the new environment regulations. This development tends to favour stainless steel grades to replace cast iron for the exhaust manifold and aluminized low carbon steel for pipes and mufflers. Among the various stainless steel grades, the proportion of ferritic grade increases for the hot part of the exhaust system as its price is lower and more stable than austenitic or refractory grades, and as it exhibits a better resistance to cyclic oxidation. A large and rapid development of stainless ferritic grades has been based on Ti and Nb stabilization. Adding niobium presents many advantages for corrosion resistance, deep-drawability, and mainly creep resistance at high temperature. The paper is focused on stainless steel with 14 wt% chromium, stabilized with Nb. Intermetallic precipitation is studied after a 100 h holding time at different temperatures (sag tests). It is shown that, depending on the test temperature and on the chemical composition of the steel, Fe 2 Nb or Fe 2 Nb 3 intermetallic particles can precipitate, which affects the creep resistance: Fe 2 Nb 3 being more stable at higher temperature. Some impacts on the alloy design dedicated to exhaust line application are presented as a conclusion of the study.

The usage of stainless steel in construction has been increasing owing to its corrosion resistance, aesthetic appearance and favourable mechanical properties. The most common stainless steel grades used for structural applications are austenitic steels. The main drawback of these grades relies on their nickel content (around 8–10%), resulting in a relatively high initial material cost. Other stainless steel grades with lower nickel content such as the ferritic steels offer the benefits of stainless steels in terms of functional qualities and design butwithin a limited cost frame. Hence, ferritic stainless steels may be a viable alternative for structural applications. Given the fact that little experimental information on ferritic stainless steels is currently available, the purpose of this investigation is to report a series of material and cross-section tests on ferritic grade EN 1.4003 (similar to 3Cr12) stainless steel square and rectangular hollow sections to enable a better understanding of their material response and structural performance. Four different cross-section geometries have been tested under pure compression and in-plane bending. Measurements of geometric imperfections and material properties are also presented. The obtained test results are used to assess the adequacy of the slenderness limits and effective width formula given in EN 1993-1-4 to ferritic stainless steels, those proposed by Gardner and Theofanous and Zhou et al. design approach.

In this paper, friction stir welding technique was used to join ferritic stainless steels, AISI 430. Ferritic stainless steel sheets were successfully joined considering both, the appearance of the welding bead and the strength of the welded joint by selecting proper weld parameters and tool material. The weld parameters such as revolutions, traverse speeds, compressive tool forces and tool tilt angles influenced the tensile strength of welded joints. Genetic algorithm model was developed to perceive the stronger joints by selecting proper welding parameter combinations. The strong welded joint higher than base material was obtained with appropriate welding parameter combinations, having a revolution of 1,120 rpm, compressive tool force of 4.5 kN, traverse speed of 125 mm min−1, and tool tilt angle of 0°. Best welding parameter combinations resulted in ultra fine grain structures in the welding zone and high-quality welded joint. © 2014, Springer-Verlag London.

International audience; This study focuses on the characterization of the oxide scales formed after different exposure times in the range of 2.5-20 min. A commercially available ferritic steel grade AISI 441 was exposed to wet argon at 1100 °C with 5, 9 and 13% H2O. Raman microspectroscopy, XRD, EDS and XPS were used to fully characterize the oxide scale. For all samples exposed for over 4 min, the scale was constituted of three layers in this order: a thin top layer of spinel phases (Fe,Cr,Mn)3O4 with local outgrowths; a second and main layer of Cr2O3 + (Mn,Cr)3O4; and finally a bottom layer of SiO2. The uncommon presence of Fe in the top layer was also observed.

International audience; Strain controlled low cycle fatigue tests are performed at 300 °C under tension compression on an 18%Cr ferritic stainless steel using base metal and welded specimens. Changes in the microstructure and geometry of the weld bead have a negative impact on the specimens' lifetime. Digital image correlation is used to get information on strain gradient in specimens. Potential drop measurements as metallographic observations are used to monitor micro-cracking. The significance of the results is discussed using finite element computations of welded specimens and observations of fracture surfaces. A tentative rationale is proposed using an energy based micro-crack growth model.

International audience; The progress in designing high temperature components relies on more accurate viscoplastic constitutive models. The capability of various models under high temperature and variable temperature conditions is investigated for two body centred cubic alloys, cast iron and ferritic stainless steel. Improvements are shown to overcome problems encountered by standard viscoplastic models. Firstly a physically based modified flow equation predicts reliably the behaviour of cast iron under thermal-mechanical loading. Secondly further improvement is proposed drawing on dislocation models to describe static recovery effects in stainless steels. Good agreement is thus obtained between experiment and model prediction under various thermal mechanical loading path.

AISI 409 ferritic stainless steel samples were nitrided using the cathodic cage plasma nitriding technique (CCPN), with the addition of methane to reduce chromium precipitation, increase hardness and wear resistance and reduce the presence of nitrides when compared to plasma carbonitriding. Microhardness profiles and X-Ray analysis confirm the formation of a very hard layer containing mainly ε-Fe3N and expanded ferrite phases.

International audience; In the current context of fossil energy scarcity, car manufacturers have to optimize vehicles energy efficiency. This global and continuous improvement includes a change of the exhaust manifold design. Usually in cast iron, exhaust manifolds tend to be mechanically welded in order to fit new constraints such as lightness, durability, efficiency and small size. To achieve such requirements, ferritic stainless steels with high chromium content (19%) and molybdenum (2%) are developed. For the welding, the use of existing filler wire does not satisfy fully the application requirements. This leads to oxidation problems and / or thermal fatigue strength that drastically reduces assembly lifetime. New flux cored wires are developed in the context of this study in order to provide molten zone characteristics close to those of the base metal. Different chemical compositions are tested in order to highlight the influence of stabilizing element on microstructure. Welding tests revealed the major influence of titanium on the grain refinement in the molten zone. A minimum Ti content of 0.45 weight % in the filler wire is required to be efficient as grain refiner.