Ferritic Stainless Steel Research Articles

Constitutive Flow Equation for Cast Austenite–Ferrite Stainless Steels

Constitutive Flow Equation for Cast Austenite–Ferrite Stainless Steels

The effect of zinc addition on corrosion behavior of stainless steels with different phases in simulated PWR primary water

In this study, corrosion behaviors of commercial austenitic, ferritic stainless steels, and duplex stainless steel with B2-NiAl were investigated in simulated PWR primary water environments with and without zinc addition. In addition, electrochemical methods such as EIS and Mott-Schottky analyses were utilized to investigate oxide layers. Zinc was incorporated mainly into chromium-rich spinel. For austenitic stainless steel, improvement on corrosion was observed, however other stainless steels showed less effects by zinc addition. It was found that beneficial effect of zinc addition depends on chromium content of matrix and the presence of low chromium-containing phase reduced beneficial effect.

Characteristics of SEN clogging and adhesive behavior of oxide inclusion during continuous casting of Ti-stabilized ultra-pure ferritic stainless steels

Characteristics of SEN clogging and adhesive behavior of oxide inclusion during continuous casting of Ti-stabilized ultra-pure ferritic stainless steels

In-situ EBSD study of 409 L ferritic stainless steel during tensile testing

Two ferritic stainless steel (FSS) specimens, denoted as loading axis along the rolling direction(LR) and the transverse direction(LT) respectively, were produced to elucidate the mechanical anisotropyof409L FSS at grain scale. This approach was realized by the combination of in situ tensile test and field emission scanning electron microscopy (SEM) with electron backscattering diffraction (EBSD) at room temperature. Microstructure evolution, grain orientation rotation, and crystallographic slip were investigated in the tensile test. During tensile deformation, the tensile axis of LR specimens rotated towards the 〈101〉 direction, which is the stable end orientation of body-centered cubic (BCC) metals. However, the rotation of tensile axis towards 〈101〉 was restrained in LT specimens due to the operation of less favorable slip systems. {110}〈111〉 was the most favorable slip system in both specimens. The mechanical anisotropy in grain scale is due to different slip behaviors of LR and LT specimens.

Microstructure characteristics and mechanical properties of the thin-plate AISI 430 ferritic stainless steel joints by interrupted pulsed arc welding

The feasibility of the interrupted pulsed argon arc welding (IPAW) of the 0.5 mm-thick AISI 430 ferritic stainless steel (FSS) was studied. The results showed that the sound appearances of the butt joints were obtained by the IPAW under different welding parameters. Two joining modes were obtained: (1) typical fusion pool structure with continuous coarsen columnar grain by short interrupted time and low welding speed; (2) snowflake-shape melting pool structure with relatively independent radially grew columnar grain by long interrupted time and high welding speed. The fusion zone (FZ) and heat-affected zone (HAZ) of the joints showed higher microhardness compared to the base metal because of the carbide precipitation and martensite transformation. The joint with a typical fusion pool structure fractured at the fusion zone with a low tensile strength and elongation rate because the weak bonding region between the columnar grains was perpendicular to the tensile direction. The joint with the snowflake-shaped structure displayed a high tensile strength and elongation rate, which was fractured at the BM, as a result of the randomness of the intergranular bonding interface to the tensile direction caused by dendritic radial growth.

Isothermal hot tube material characterization – Forming limits and flow curves of stainless steel tubes at elevated temperatures

A new isothermal hot-tube-bulge test as well as a modified pressurized-tube-tensile test are presented to characterize forming limits of tubular materials at elevated temperatures – up to 1000 °C. By controlling temperature, internal pressure, and axial force the complete forming limit curve is determined under isothermal, frictionless conditions and nearly linear strain paths. In the hot-tube-bulge test, a tangential localization forms before failure, marking a forming limit. In the pressurized-tube-tensile test, an axial localization occurs. For the former, a new method for estimating the forming limit was developed whereas the later can be evaluated by standardized methods. The resulting forming limits are at comparable levels to those known from literature, while the new hot-tube-bulge test overcomes the uncertainty which arises from friction in other test setups. The materials used for the investigations are the ferritic and martensitic stainless steels X2CrTiNb18 and X12Cr13, respectively. The hot-tube-bulge test is examined for its suitability in determining flow curves. An empirical-analytical model is introduced to determine the stress components. It is based on tangential and meridional force equilibria, taking the internal pressure and the projected effective areas into account. Flow curves up to effective plastic strains of 0.5 are determined, exceeding the maximum strain of common hot tensile-test by a factor of 2. The strain-rate dependent stress-strain data was used to identify the parameters of a simplified Hensel-Spittel approach. This allows the prediction of isothermal flow curves with varying strains and strain rates at a temperature of 1000 °C.

Direct utilization of gaseous fuels in metal supported solid oxide fuel cells

Direct utilization and internal reforming of gaseous fuels is investigated on symmetric-architecture metal supported solid oxide fuel cells (MS-SOFCs) with thin ceramic electrolyte and scaffold backbone layers, and low cost ferritic stainless steel supports on both sides. Infiltrated Pr-oxide and Ni/samarium-doped ceria catalysts are added to the cathode and anode electrodes, respectively. Initial performance and durability is evaluated for MS-SOFCs operating with natural gas, propane, ammonia, and dimethyl ether at 700 °C. Cells for natural gas and propane utilize a novel high entropy alloy (HEA) catalyst for internal reforming with performance and degradation rates similar to H2 (0.5 W cm−2 and ∼12%/100 h). Initial testing with sulfur shows reversible degradation for levels found in natural gas and irreversible degradation for higher levels found in commercial propane. Overall, MS-SOFCs show successful fuel flexibility.

Grain growth and precipitation behaviour of AISI 430 ferritic stainless steel subjected to pulsed laser beam welding using free-form pulse shaping

Ferritic stainless steels are prone to grain coarsening and precipitation of chromium-rich grain boundary phases during fusion welding, which increase intergranular corrosion susceptibility. State-of-the-art techniques to overcome these challenges mainly feature heterogeneous nucleating agents with regard to grain coarsening or alternating alloy concepts as well as post-weld heat treatments as for restoration of intergranular corrosion resistance. The present investigation seeks to depart from these traditional approaches through the use of a tailored heat input during pulsed laser beam welding by means of free-form pulse shaping. Grain size analysis using electron backscatter diffraction shows a substantial reduction of grain size as compared to continuous-wave lasers due to a distinctive columnar to equiaxed transition. Moreover, phase analyses reveal the overcoming of chromium carbide precipitation within the heat-affected zone. As corrosion tests demonstrate, intergranular attack is therefore concentrated on the weld metal. In comparison to continuous-wave laser beam welding, intergranular corrosion susceptibility is substantially reduced for very short pulse durations. From these results, it can be derived that pulsed laser beam welding using free-form pulse shaping enables direct control of heat input and, thus, tailored grain growth and precipitation formation properties.

The Effect of Holding Time on Dissimilar Transient Liquid-Phase-Bonded Properties of Super-Ferritic Stainless Steel 446 to Martensitic Stainless Steel 410 Using a Nickel-Based Interlayer.

The dissimilar joining of martensitic and ferritic stainless steels have been developed that needs corrosion resistance and enhanced mechanical properties. In this study, the transient liquid-phase bonding of martensitic stainless steel 410 and super-ferritic stainless steel 446 was conducted with a nickel-based amorphous interlayer (BNi-2) at constant temperature (1050 °C) and increasing times of 1, 15, 30, 45, and 60 min. For characterization of the TLP-bonded samples, optical microscopy and scanning emission microscopy equipped with energy-dispersive X-ray spectroscopy were used. To investigate the mechanical properties of TLP-bonded samples, the shear strength test method was used. Finally, the X-ray diffraction method was used for microstructural investigation and phase identification. The microstructural study showed that the microstructure of base metals changed: the martensitic structure transited to tempered martensite, including ferrite + cementite colonies, and the delta phase in super-ferritic stainless steel dissolved in the matrix. During the transient liquid-phase bonding, the aggregation of boron due to its diffusion to base metals resulted in the precipitation of a secondary phase, including iron-chromium-rich borides with blocky and needle-like morphologies at the interface of the molten interlayer and base metals. On the other hand, the segregation of boron in the bonding zone resulted from a low solubility limit, and the distribution coefficient has induced some destructive and brittle phases, such as nickel-rich (Ni3B) and chromium-rich boride (CrB/Cr2B). By increasing the time, significant amounts of boron have been diffused to a base metal, and diffusion-induced isothermal solidification has happened, such that the isothermal solidification of the assembly has been completed under the 1050 °C/60 min condition. The distribution of the hardness profile is relatively uniform at the bonding zone after completing isothermal solidification, except the diffusion-affected zone, which has a higher hardness. The shear strength test showed that increasing the holding time was effective in achieving the strength near the base metals such that the maximum shear strength of about 472 MPa was achieved.

Effects of grain boundary characteristics changing with cold rolling deformation on intergranular corrosion resistance of 443 ultra-pure ferritic stainless steel

The relationship between evolution in grain boundary characteristics and intergranular corrosion properties of cold rolled 443 ultra-pure ferritic stainless steel was investigated. The results showed that low-angle (LA) grain boundaries, special grain boundaries (SGB), and high-angle (HA) grain boundaries had a high intergranular corrosion sensitivity after cold deformation in reducing acid medium. In oxidative acid medium, the LA and SGB boundaries had a high intergranular corrosion resistance in comparison to HA boundaries, and their inhibitory effect on the corrosion continuance of the dynamic recrystallization high-angle (RHA) grain boundaries can improve the corrosion resistance of the RHA grain boundaries.

Remote laser spot welding of AISI 430 sheets by fiber lasers—A phenomenal effect in refining weld microstructure with nanosecond pulses

In the present work, we have compared the results of microstructural and mechanical property characterization of AISI 430 ferritic stainless steel spot welds made remotely using a repetitive nanosecond pulsed fiber laser and a CW fiber laser. Optical/electron microscopy, microhardness test, and tensile shear tests were performed for evaluation of the welds. Welds made by the pulsed nanosecond laser were found to be superior due to the presence of the very narrow heat-affected zone along with finer grains in the fusion zone. The welds were also found to withstand more load before fracture and were more ductile. Use of short duration laser pulses with lower heat input were found to be responsible for the refinement of grains in the fusion zone and improvement of mechanical properties of nanosecond laser weld specimens.

Synergism between wear and corrosion of Cr26Mo1 ferrite stainless steels in 0.5 mol/L of sulfuric acid

In this paper, the tribocorrosion behavior of an ultra-pure high-chromium ferrite stainless-steel Cr26Mo1 in a 0.5 mol/L H2SO4 solution was investigated. Results show that the slight damage caused by PEEK to Cr26Mo1 is mainly scratching, micro-furrow, and micro-peeling, while the severe damage caused by Al2O3 to Cr26Mo1 is mainly furrow, peeling, and plastic deformation. The deformed layer in the subsurface of the wear track is closely related to the shear stress applied to the material. Geometrically necessary dislocations and the rotation of crystals greatly contribute to the deformation. The microdefects on the surface and subsurface caused by wear may accelerate corrosion, and the decline of microhardness and H adsorption in the surface layer caused by corrosion could deteriorate wear.

Extreme high-speed-rate laser directed energy deposition of high strength low carbon stainless steel coating with layered heterogeneous structure

In this work, a ferritic stainless steel coating was manufactured via extreme high-speed-rate directed energy deposition (EHLDED). Microstructural features and tensile behavior were investigated and analyzed. The microstructural analysis confirmed that EHLDED coating was characterized by alternating patterns of columnar dendrites and fine equiaxed dendrites. The average size of the dendrites was less than 1 μm. High-resolution transmission electron microscopy showed that there were a large number of dislocation lines (DLs) and dislocation tangles (DTs) enriched at inter-dendritic solidification structures attributed to the ultrahigh cooling and solidification as well as molten pool movement. In addition, a small percentage of predominantly nanosize carbides with the size ranging from 50 to 90 nm were also observed in dendrites and inter-dendritic solidification structures. The EHLDED coating sample manufactured at the deposition speed of 40 m/min showed a higher strength of 1084 MPa with the ductility 1.27%. Results reveal that the ultra-fine dendrites accompanied with nanosize carbides prepared by EHLDED contributed to achieving high strength of low carbon stainless steel coatings.

Tailoring the Process Parameters for Ti-Stabilized 439 Ferritic Stainless Steel Welds by Cold Metal Transfer Process

Tailoring the Process Parameters for Ti-Stabilized 439 Ferritic Stainless Steel Welds by Cold Metal Transfer Process

Study of the Role of Titanium and Iron Cathodic Cages on Plasma-Nitrided AISI 430 Ferritic Stainless Steel.

In contrast to austenitic and martensitic stainless steels, ferritic stainless steels have a lower hardness and wear resistance but exhibit excellent corrosion resistance. Due to this fact, their use in the aerospace, automobile, and house construction industries is restricted. Several methods have been utilized to enhance the tribological characteristics of ferritic stainless steels. In this work, titanium nitride coating has been carried out by using a cathodic cage of titanium material, and later on, the titanium cathodic cage is replaced by an AISI-304 cathodic cage in a CCPN chamber to form iron nitride coating on AISI-430 ferritic stainless steel coupons through a plasma nitriding process for 4 h at a fixed temperature of 400 °C. The microstructures and mechanical traits of all processed and control coupons were analyzed using scanning electron microscopy, X-ray diffraction, ball-on-disc wear tester, and microhardness tester techniques. The results showed that hardness increased up to 1489 HV with the titanium cage, which is much higher than the hardness of the base material (270 HV). The titanium cage-treated coupons have high layer thickness, smooth surface morphology, and a minimum crystallite size of 2.2 nm. The wear rate was reduced up to 50% over the base material after the titanium cage plasma treatment. The base coupon exhibited severe abrasive wear, whereas nitrided coupons exhibited dominant adhesive wear. In the iron nitride coatings, this effect is also important, owing to the more influential cleaning process in a glow discharge, and the better adhesion with enhanced interlayer thickness is attributed to the fact that the compliance of the interlayer minimizes shear stresses at the coating–substrate interface. The use of a graded interface improves adhesion compared with the case where no interlayer is used but a titanium interlayer of comparable thickness provides a significant increase in measured adhesion. For both titanium and iron nitride films, there is a reduction in wear volume which is a function of interlayer thickness; this will have a substantial effect on wear lifetime. Thus by careful control of the interlayer thickness and composition, it should be possible to improve coating performance in tribological applications.

Flower-like Superhydrophobic Surfaces Fabricated on Stainless Steel as a Barrier against Corrosion in Simulated Acid Rain.

Functionalisation of the metal surface of low-carbon ferritic stainless steel (from hydrophilic to hydrophobic properties) was achieved by flower-like hierarchical structures on a steel substrate prepared by a low-cost immersion method. The flower-like structured hydrophobic layers on the steel substrate were obtained by immersing the samples in an ethanolic solution of stearic acid with the addition of various concentrations of expired vitamin E ((+)α-tocopherol). The stability and corrosion-inhibiting effect of the hierarchically structured (such as natural cornflower) hydrophobic layers were studied systematically during short and long immersion tests, 120 h (five days) in an acidic environment (pH = 3) using potentiodynamic measurements, electrochemical impedance spectroscopy and chronopotentiometry. The surfaces of the samples, their wettability, surface morphology and chemical composition were characterised by contact angle measurements, SEM, ATR-FTIR and EDAX. After 120 h of immersion, the inhibition efficiency of the flower-like structured hydrophobic layers on the steel substrate in the selected corrosion medium remained above 99%, and the hierarchical structure (flower-like structure) was also retained on the surface.

An analysis of microstructure and mechanical properties of ferritic stainless steel 430 during cold rolling and subsequent annealing

Systematic study on the microstructural evolution and mechanical properties of ferritic stainless steel (FSS) 430 with different annealing processes was carried out in the present work. The results show that microstructural refinement can be achieved by optimization of annealing processes, improving elongation, yield strength, and tensile strength of FSS 430. An optimal annealing temperature of 950 ℃ is found with better homogeneity and enhanced mechanical properties among the cold-rolled and annealed FSSs. During annealing processes, the fraction of high-angle grain boundaries of FSS 430 annealed at 950 ℃ is found to be the highest, indicating that a homogeneous microstructure with high recrystallization rate is formed inside the FSS 430 strips. In addition, high fraction of the hard grains (SF < 0.4) and low fraction of the soft grains are found inside FSS 430 annealed at 950 ℃, improving the plasticity of material. Overall, the optimization of annealing processes benefits the microstructural refinement of FSS and thereby improving the mechanical properties of materials.

Effect of Manganese Concentration in Cerium Oxide Dispersed Ferritic Stainless Steels on Oxidation Behavior for Metallic Interconnect Material of Solid Oxide Fuel Cell

The ferritic stainless steel is used as interconnect materials of planar solid oxide fuel cell (SOFC) stack designs. However, the formation of a Cr2O3 oxide layer on the metallic interconnect is inevitable in the SOFC cathodic environment, and the formed layer decreases its electrical conductivity. In this study, we have investigated the effect of manganese (Mn) concentration in the cerium oxide (CeO2) dispersed ferritic stainless steels on oxidation behavior of SOFC metallic interconnect. The mixed powders with various Mn concentrations of 0.5 to 2wt.% were prepared by high-energy ball milling (HEBM), and subsequently were pelletized and sintered at 1400oC in reduction atmosphere. The area specific resistance (ASR) tests were carried out for 1,000 hrs. in air at 800 oC. The material characterization and morphology analysis of the tested samples were performed. After oxidation test, the oxide scale formed on the surface of the sample with Mn was confirmed as a Mn-Cr spinel structure. The thickness of the oxide scales increased with Mn concentration of the samples. Among the various Mn compositions, the sample with 1wt.% Mn had the lowest area specific resistance. The results show that the Mn in the ferritic stainless steel has great influence on the oxidation behavior. In this talk, we will discuss these results as related the requirements of the SOFC metallic interconnect.

The Feasibility of Using Bipolar Electrochemistry to Study Pitting and Crevice Corrosion of Stainless Steels in Cementitious Materials

The durability of carbon steel reinforced concrete infrastructure is often limited by rate of corrosion damage progression. Over the past couple of decades, corrosion-resistant alloys, such as stainless steels (SS), have garnered attention as a potential way to address the durability of reinforced concrete exposed to aggressive marine environments. However, there are currently no models available to accurately forecast corrosion of stainless-steel reinforced infrastructure and durability projections for carbon steel may not consider the necessary mechanistic steps.Traditional corrosion durability projections adopt the classic two stage model considering the time prior to and following corrosion initiation often distinguished by the point in time where enough chlorides have accumulated at the steel surface to exceed the chloride concentration required to initiate corrosion.[1] Such models do not consider the evolution of pitting or crevice corrosion and the potential for progression to more widespread corrosion. Therefore, research is required to first identify the expected corrosion damage morphology of stainless steels in concrete and then to formulate a theoretical framework that can be used to describe accurately its progression provided expected exposure conditions. This work attempts to develop an efficient yet informative method to study pitting corrosion evolution of steel in concrete with the objective of identifying the role of the cement pore structure on damage evolution and pit or crevice stability.Recently, bipolar electrochemistry has been used to identify potential-kinetic-corrosion damage mode relationships from single measurements on ferritic [2] and duplex stainless steels.[3] Bi-polar electrochemistry (BPE) comprises indirect dc polarization of a conductive element usually immersed in an electrolyte in cases where direct contact to the elements need to be avoided. In application to pitting corrosion studies, BPE followed by post exposure 3D surface metrology can provide pitting characteristics as a function of applied potential from a single experiment. In this work various BPE configurations including single and split electrodes are used to assess the feasible in applying a suitable potential distribution on steel plate specimens that have a thin cement overlay. A finite element model was developed to simulate the applied potential distribution considering the cell geometry and interfacial kinetics. The corrosion damage morphology and the pitting characteristics obtained will be compared to that of chloride-ponded SS reinforced concrete beams to uncover mechanistic insight on SS corrosion damage evolution. Tuutti, K: Corrosion of steel in concrete. 1982, Stockholm. Swedish Cement and Concrete Research Institute, ISSN 0346-6906. Royal Institute of Technology, Stockholm. Department of Building MaterialsZhou, Yiqi, and Dirk Lars Engelberg. "On the application of bipolar electrochemistry to characterise the localised corrosion behaviour of type 420 ferritic stainless steel." Metals10, no. 6 (2020): 794.Zhou, Yiqi, and Dirk Lars Engelberg. "Fast testing of ambient temperature pitting corrosion in type 2205 duplex stainless steel by bipolar electrochemistry experiments." Electrochemistry Communications117 (2020): 106779.

Effect of Cold-Rolling Reduction on Recrystallization Microstructure, Texture and Corrosion Properties of the X2CrNi12 Ferritic Stainless Steel.

X2CrNi12 ferritic stainless steel has a wide range of application prospects in the railway transportation, construction, and automobile fields due to its excellent properties. The properties of X2CrNi12 ferritic stainless steel can be further improved by cold-rolling and subsequent annealing treatment. The purpose of this work is to investigate the effect of cold-rolling reduction on the microstructure, texture and corrosion properties of the recrystallized X2CrNi12 ferritic stainless steel by using SEM, TEM, EBSD and electrochemical testing technology. The results show that the crystal orientation characteristics of the cold-rolled sheet could be inherited into the annealed sheet. The higher cold-rolling reduction could promote the deformed grains rotating into the {111}<uvw> orientation, increasing storage energy and driving force for recrystallization, which could reduce the recrystallized grain size. The orientation densities of α-fiber and γ-fiber were low at 50% cold-rolling reduction. After recrystallization annealing, a large number of grains with random orientation could be produced, and the texture strength was weakened. When the cold-rolling reduction rose to 90%, the γ-fiber texture at {111}<110> was strengthened and the α-fibers, particularly the {112}<110> component, were weakened after recrystallisation annealing, which could improve the formability of the steels. The proportions of special boundaries, i.e., low-angle grain boundaries and low-Σ CSL boundaries, among the grain boundary distribution of the recrystallized X2CrNi12 stainless steel were higher when the reduction was 90%, especially when the annealing temperature was 770 °C. Additionally, the proportion of LAGBs and low-Σ CSL boundaries were 53% and 7.43%, respectively, which improves the corrosion resistance of the matrix, showing the best corrosion resistance.