Ferritic Stainless Steel Research Articles

Synthesis and Characterization of Innovative Fe–Cr–Mn Ferritic Stainless Steel by Laser Powder Bed Fusion

Crack development for laser‐fused metallic materials is one major challenge for laser‐based powder bed fusion (LPBF). The cracks are manifested in two forms, i.e., macrocracks along building layers due to spalling and microcracks along the high‐angle grain boundaries. To mitigate the crack formation, a new type of ferritic stainless steel Fe–Cr–Mn are synthesized by LPBF. The well‐developed columnar ferrite grains with an enhanced fine acicular austenite precipitation, which possess Nishiyama–Wassermann (N–W) orientation relationship with the ferrite matrix, can be readily produced when the laser energy density is beyond 100 J mm−3. Porosity can be further reduced below 0.5% by optimizing the laser power and scanning speed. It is found that laser rescanning may eliminate the cracks without modifying the grain morphology, crystallographic texture, and phase distribution.

The effect of cold rolling reduction ratio on the microstructure and mechanical properties of ferritic stainless steel 430

The effect of cold rolling reduction ratio on the microstructure and mechanical properties of ferritic stainless steel 430

Effects of cooling manner on Laves phase precipitation and mechanical properties of Al modified super ferritic stainless steels

The solution treating and cooling experiments were conducted to study the microstructure and mechanical properties of Al modified super ferritic stainless steels with various cooling methods. The results demonstrated that the grain was characterized by the stratified distribution. The grain coarsened gradually with the decrease in cooling rate. And the surface grain coarsened obviously, Nb (C, N) particles were precipitated in the samples in different cooling manners. However, the Laves phase was distributed both at the grain boundaries and in the grains in the furnace-cooled specimen, and the area fraction of Laves phase increased significantly with the increase of Al content. With the cooling rate decreased, the yield strength, ultimate tensile strength and Vickers hardness of the Al-free samples increased, while the elongation decreased, and the furnace-cooled specimens showed brittle fracture during the tensile test. The addition of Al also increased yield strength, ultimate tensile strength and Vickers hardness and deteriorated plasticity of samples with different cooling manners. Meanwhile, the plasticity of furnace-cooled samples was more sensitive to addition of Al than water-quenched and air-cooled specimens. The analysis results showed that the plastic deterioration of furnace-cooled samples was mainly related to the coarsening of Laves phase at grain boundaries. Hence, the precipitation of large size Laves phase at grain boundaries should be inhibited in the process of industrial production.

Cross-section resistance and design of stainless steel CHS and EHS at elevated temperatures

The structural behaviour and design of stainless steel circular hollow sections (CHS) and elliptical hollow sections (EHS) at elevated temperatures are investigated in this paper. Shell finite element models of stainless steel CHS and EHS are created and validated against experimental results from the literature, which are subsequently used to generate benchmark structural performance data. Parametric studies are performed on a large number of cold-formed and hot-rolled austenitic, duplex and ferritic stainless steel CHS and EHS subjected to (i) pure axial compression, (ii) pure bending, (iii) combined axial compression and bending and (iv) combined bending and shear at elevated temperatures; the studied cases comprise 24,495 stainless steel CHS and EHS in fire and cover a wide range of cross-section slendernesses and elevated temperature levels. Calibrated against the benchmark structural performance data obtained from the numerical parametric studies, new design proposals for predicting the cross-section resistances of stainless steel CHS and EHS in fire are put forward. The accuracy, safety and reliability of the new design proposals are assessed. It is shown that in comparison to the design provisions of the European structural steel fire design standard EN 1993-1-2, the proposed design methods provide more accurate and safe-sided cross-section resistance predictions for stainless steel CHS and EHS at elevated temperatures.

Effect of arc remelting on microstructure and pitting corrosion resistance of 441 ferritic stainless steel

Effect of arc remelting on microstructure and pitting corrosion resistance of 441 ferritic stainless steel

Dependence of strengthing and toughening on retained austenite of quenched and partitioned AISI 430 ferritic stainless steel

The quenching and partitioning (Q&P) process was applied to AISI 430 ferritic stainless steel (FSS). As a comparison, the quenching and tempering (Q&T) process was also applied to the experimental steel. This study evaluated the selection of the optimal interrupted quenching temperature. Through the combination of experiments and theoretical calculations, the functional relationship between the microstructure and the quenching temperature was qualitatively and quantitatively analyzed. When the quenching temperature was close to the intermediate temperature between the martensite start (Ms) point and the Martensite finish (Mf) point, there were more retained austenite could be preserved at room temperature. The model of the microstructure evolution was obtained and carbon diffusion behavior was discussed. The diffusion of carbon to austenite and to precipitation is a competing reaction. The diffusion of carbon into the precipitation can be suppressed by changing the quenching temperature. The effect of quenching temperature on mechanical properties was analyzed by tensile test. The result indicates that the sample quenched at 160 °C exhibits superior tensile properties, with the product of strength and elongation (PSE) of 16.87 GPa%. With the increase of quenching temperature, the yield strength decreased gradually, and the plasticity and PSE first increased and then decreased. Initial fraction and mechanical stability of retained austenite jointly affect ductility. In addition, the quenching temperature affected the formation of the yield platform of the tensile curve, which was mainly related to whether there were enough interstitial carbon atoms in the matrix for pinning dislocations.

Characterization of Acalypha Wilkesiana Leaf Extract by FT-IR and GC–MS as Green Inhibitor for Ferritic Stainless Steel in 1 M Nacl

Characterization of Acalypha Wilkesiana Leaf Extract by FT-IR and GC–MS as Green Inhibitor for Ferritic Stainless Steel in 1 M Nacl

Experimental review of the performances of protective coatings for interconnects in solid oxide fuel cells

Ferritic stainless steel interconnects are used in solid oxide fuel cells; however, coatings are required to improve their performance. Although several types of coatings have been proposed, they have been scarcely investigated under similar conditions. This study compares the characteristics of uncoated Crofer 22 APU and eight different coatings on Crofer 22 APU for up to 3000 h at 800 °C. The coatings were deposited at various research laboratories around the world, and the experiments were performed at Chalmers University of Technology, Sweden. Cross-sections of the samples were analysed using scanning electron microscopy and energy-dispersive x-ray spectroscopy. The (Co,Mn)-based coated steels showed more than 50-fold lower chromium evaporation and at least 3 times thinner Cr2O3 scale thickness compared to uncoated steel. The coated steel samples showed lower area-specific resistance (ASR) values than the uncoated steel after 3000 h of exposure, irrespective of the coating thickness, composition and deposition method.

PTA-Welded Coatings with Saturation Magnetization above 1.3 T Using FeCrBSi Powders with Chemical Composition Similar to AISI 430 Ferrite Stainless Steel

Fe-Cr-based soft magnetic alloy (SMA) monolayer coatings with high saturation magnetization (Ms) above 1.3 T were deposited onto AISI 1010 substrate by co-axial powder feeding plasma transferred arc (PTA) welding, using FeCrBSi self-fluxing powders Fe313, which have a similar chemical composition to AISI 430 ferritic stainless steel (FSS). The effect of welding parameters on the phase assemblage, microstructure, hardness and magnetic performance of the coatings was investigated. The results show that the coating’s maximum width and the welding surplus height increased with the rise in welding heat input and powder distribution density, respectively. The coating’s Ms increased sharply, but its coercivity (Hc) decreased with the growth in the substrate dilution ratio. The coating’s Hc increased whereas its Ms decreased with the increment in welding heat input. The as-welded coating C3 with optimum magnetic performance had a dendrites–eutectics composite structure, where the columnar or equiaxed sorbitic pearlite dendritic cores surrounded by network-like eutectics α(Fe,Cr) + (Fe1−xCrx)2B were the main contents. Moreover, (Fe,Cr)7C3 and CrB had also been detected, and they were mainly distributed in the interdendritic regions. The body-centered cubic (b.c.c.) α(Fe,Cr) multi-element solid solution contributes to a high Ms of 1.61 T, and the borides (Fe1−xCrx)2B and CrB as well as (Fe,Cr)7C3 and other carbides cause a high Hc of 58.6 Oe and hardness HV0.3 of 4.90 ± 0.06 GPa, much higher than that of AISI 430 FSS (HV < 1.8 GPa). The current work verifies the feasibility of fabricating Ni- and Co-free FeCrBSi SMA coatings with high Ms and high hardness via PTA welding, and since the feedstock powders have chemical composition similar to AISI 430 FSS, the work may bring about novel applications for AISI 430 FSS in particular cases where the considerable wear-resistant performance as well as superior soft magnetic and anti-corrosive properties are required.

The high temperature degradation of ferritic stainless steel in solid carbon atmospheres

Stainless steel is widely used for many components and parts in coal-fired thermal power plants. AISI 430 ferritic stainless steel (FSS) is one common grade to combat the degradation at high temperatures in coal combustion atmospheres containing flue gas, coal ash, and soot (impure solid carbon particles). However, the effect of the solid carbon particles on the degradation of FSS needs to be clarified. Graphite powder was used to simulate solid carbon atmospheres for investigating the degradation of AISI 430 at high temperatures of 1150℃ to 1350℃ in coal-fired boilers. After the carbothermic reduction, the mass gain of a pre-oxidized sample at 750℃ was approximately 0.0793 mg⸳cm-2 and increased when increasing the reduction temperature. The peak of Fe2O3 and Cr7C3 were detected by X˗ray diffraction (XRD) after the oxidation and reduction test, respectively. Besides, the degree of sensitivity (%DoS) of the samples was measured by double loop electrochemical potentiokinetic reactivation (DL-EPR) technique and increased around 30 times after heating the pre-oxidized sample to 1150℃.

Effect of anionic surfactants as pitting corrosion inhibitors for stainless steels

AbstractAlthough anionic surfactants have been widely introduced as inhibitors against uniform corrosion, their efficiency as pitting inhibitors remains unclear. Herein, fatty alcohol ether sulfate (FAES), linear alkylbenzene sulfonate (LAS), and palm kernel oil (PKO) were tested for a Ti‐stabilized (1.4510) and a nonstabilized grade (1.4016) of ferritic stainless steel in alkaline chloride solutions containing H2O2. Electrochemical impedance spectroscopy (EIS) measurements were performed to elucidate the adsorption of surfactants at OCP, followed by potentiodynamic polarization. For 1.4510, LAS and FAES did not significantly affect the EIS results but inhibited pitting initiation with identical efficiencies. In the case of 1.4016, Cr‐rich carbides acted as adsorption sites, where LAS showed higher efficiency than FAES. While LAS and FAES interact preferentially with pitting initiation sites, PKO appears to adsorb randomly on the passive film. Consequently, inhibition can reach a maximum due to the electrical neutralization of the surface. Finally, LAS can be effective as an inhibitor for stainless steel containing carbides that can lead to pitting initiation.

EFFECT OF ULTRAFAST HEATING ON AISI 441 FERRITIC STAINLESS STEEL

The use of the ultrafast heating (UFH) heat treatment process attracted great attention in the last few years, following the requirements of CO2 emissions reduction. The
 effect of ultrafast heating (UFH) treatment an AISI 441 ferritic stainless steels is reported in this paper. Results show that a minimum temperature of 975 °C is required in order to achieve a fully recrystallized microstructure. The study highlights the effect of ultrarapid annealing on grain size evolution as a function of different adopted process parameters. The obtained microstructure is related to mechanical properties in terms of ultimate tensile stress and hardness.

Investigation of Creep Properties and Fracture Mechanism of 430 Ferritic Stainless Steel at Elevated Temperature

Investigation of Creep Properties and Fracture Mechanism of 430 Ferritic Stainless Steel at Elevated Temperature

Fabrication of Mn–Co Alloys Electrodeposited on AISI 430 Ferritic Stainless Steel for SOFC Interconnect Applications

Mn–Co alloys were electroplated on AISI 430 stainless steel using an electrodeposition technique with the aim to reduce oxidation and chromium volatilization. The electroplating parameters were designed to improve the coating quality. The increased current density with decreased MnSO4 content resulted in a denser coating layer. A sample coated with 0.10 M CoSO4 and 0.50 MnSO4 at 350 mA cm−2 showed the best oxidation resistance after being oxidized at 800 °C for 90 h. The X-ray diffraction (XRD) result revealed that the oxide growth on the surface of the coated samples mainly formed oxides of MnCo2O4, MnCr2O4, and Cr2O3. The chromium volatilization was evaluated by exposing the coated samples to humidified synthetic air at 800 °C for 96 h. The mass flux of Cr volatilization was on the order of 10−11 g cm−2 s−1. Furthermore, different heat treatments in O2 and CO2 atmospheres were compared. Annealing in CO2 at 800 °C for 4 h helped increase the Mn–Co coating density. The relationship between the porosity and its failure behavior was also discussed.

Alloy design for microstructural-tailored boron-modified ferritic stainless steel to ensure corrosion and wear resistance

Ferritic stainless steels armored with borides had their endurance tested in demanding both abrasive and corrosive environment. The degradation was investigated through a very aggressive plate-on-cylinder wear test in water-based drilling mud containing chlorides, which was designed to simulate, in laboratorial scale, the corrosive tribosystem found in the wear of risers and casings used in deep water oil exploitation. A commercially-grade 430 ferritic stainless steel containing boron content far beyond its solubility limity, namely 1.2 and 3.5 wt.%, was processed by spray-forming to induce a ferritic stainless steel matrix protected by a boride skeleton. Additional corrosion assessment was performed by potentiodynamic polarization and electrochemical impedance spectroscopy in 0.27 M KCl solution, since KCl is a common clay swelling inhibitor. For comparison, API 5L X80 steel was also included since this material is used in risers and casings manufacture. The addition of boron (1.2 and 3.5 wt.%) led to the formation of microstructures composed of an α-ferrite matrix with homogeneously distributed M2B-type borides of different morphologies. Electrochemical tests revealed high corrosion resistance of the alloy with 1.2 wt.% B. However, the alloy with 3.5 wt.% B showed a considerable decrease in corrosion resistance due to Cr-depletion of the ferritic matrix given the M2B formation richer in Cr. Therefore, the alloy with 1.2 wt.% B offered the best tribocorrosion resistance.

Corrosion of 1.4016 Ferritic Steel by Urea at High Temperature

The corrosion behavior of a ferritic unstabilized stainless steel 1.4016 during decomposition of aqueous urea solution at high temperature has been investigated. Corrosion was obtained from 100 h of cyclic heating (from room temperature up to 600 °C) and injection of aqueous urea solution on the steel plate in a laboratory-scale test bench. The evaluation procedure covered the metallographic analysis of corroded steel samples by high-resolution scanning electron microscopy (HR-SEM) and transmission electron microscopy (TEM). Uniform corrosion underneath deposits was found as one of the drivers for degradation of the steel. Damage happened by high-temperature depassivation of stainless steel due to the excess of the aggressive medium. Besides uniform corrosion, a nitridation layer underneath surface oxides together with chromium carbonitride particles precipitated through the whole depth of the sample was identified resulting in intergranular attack.

Ferritic stainless steel thin sheet bolted connections failing by bearing–curling interaction: Testing, modelling and design

This paper presents experimental and numerical studies of ferritic stainless steel thin sheet bolted connections failing by bearing–curling interaction. An experimental programme was firstly conducted on fifteen ferritic stainless steel thin sheet bolted connection specimens, including eleven specimens designed with curling and four specimens designed without curling. The test setup and procedures as well as the key test results, including failure loads, failure modes, load–in-plane elongation curves and load–out-of-plane deformation curves, were reported. Following the experimental programme, a numerical modelling programme was performed, where finite element models were developed and validated against the test results and then used to perform parametric studies to generate further numerical data. Based on the obtained numerical data, the effects of various geometric parameters, including end distances, edge distances, longitudinal spacings and sheet thicknesses, on failure loads of ferritic stainless steel thin sheet bolted connections were discussed. Both the test and numerical data were then used to assess the codified design rules for ferritic stainless steel thin sheet bolted connections susceptible to bearing–curling interaction, as set out in the European code and American specification. On the basis of the assessment results, the European code and American specification were found to respectively underestimate the actual load-carrying capacities by 57% and 18%, on average. Besides, a relevant design method proposed for carbon steel thin sheet bolted connections was assessed for its applicability to ferritic stainless steel thin sheet bolted connections, with the results showing that it provided more consistent failure load predictions than the design codes, but the predicted failure loads were still conservative. Therefore, a revised design formula was proposed and shown to provide improved failure load predictions.

Multi-criteria optimization of TIG welding process parameters on AISI 409M stainless steel by Grey Taguchi method

AISI 409M ferritic stainless steel materials were examined in this study. TIG welding was utilized for the creation of butt welded joints in the construction of the L9 Taguchi orthogonal array experiment. A visual and X-ray examination of the joints followed the procedure. After the butt-joining, a slew of experiments were run to figure out the material’s specific properties. There has been an evaluation of the weld quality in terms of the specimens’ ultimate tensile strength (UTS) and percentage elongation (PE). Grey-Taguchi methodology was used to interpret, discuss and analyse the collected data. It appears that the investigation has led to some conclusive results.

Influence of filler wire on metallurgical, mechanical, and corrosion behaviour of 430 ferritic stainless steel using a fusion welding process

The advantage of ferritic stainless steels (FSS’s) over austenitic stainless steels is that they are less expensive alloys. This is due to low or negligible nickel in its alloying element which makes the steel affordable. This type of steel is highly recommended against chloride attack and is also machinable to produce various components for engineering applications. This study examines the effect of various fillers on 430 ferritic stainless steel (FSS). The austenitic (308) and ferritic (410) grades of filler were used to study the weldability, microstructure, mechanical properties, and corrosion resistance using tungsten inert gas welding. The findings showed the emergence of various complex phases in both the weld sample. The sample welded with 410 filler shows acicular ferrite, martensite and austenite. Whereas, austenite and vermicular ferrite are observed in the sample welded with 308 filler. Based on compositions and solidification modes, the mechanical properties of welded joints also vary. It was found that ferritic mode solidified welds dominated in terms of qualities, which was found in 410 filler. In the chloride solution, the behaviour of the pitting corrosion resistance of each weld varied. The sample welded with 410 was superior corrosion resistance. This is due to more δ-ferrite in the weld sample. Whereas, 308 showed poorer resistance against the simulated seawater solution. In 410 welds, a greater degree of sensitization was observed, as compared to 308 welds.

Thermal expansion of Crofer 22 APU steel used for SOFC interconnect using in-situ high temperature X-ray diffraction

Crofer 22 APU is ferritic stainless steel extensively used as metallic interconnect material in Solid Oxide Fuel Cell (SOFC) applications. The interconnects are exposed to both oxidizing and reducing atmospheres at high temperatures. As SOFCs are operated above 700 °C, understanding the thermal expansion behavior of the interconnect material with other components (anode, cathode, electrolyte) of the fuel cells is essential. Metallic interconnects should have a matchable thermal expansion to other ceramic materials such as anode, cathode, and solid electrolyte used in SOFCs. The present study evaluates the thermal expansion of Crofer 22 APU steel from 25 to 950 °C in a controlled atmosphere (10-4 mbar pressure) using in-situ high-temperature X-ray diffraction (XRD). The XRD patterns were analyzed using the ‘High Score Plus Software’ attached to the system, and the phases were identified using the standard Crystallographic Open Database (COD). The coefficient of thermal expansion (CTE) was determined based on the change in lattice parameter/peak shift to a lower 2θ value as a function of temperature. The normal XRD data showed no oxide formation on the Crofer steel after heating until 950 °C in in-situ high-temperature conditions.The peak shift to the lower 2θ degree observed in the XRD data was due to the relaxation of residual stress upon heating. The isothermal section and phase fraction of Crofer 22 APU alloys are analyzed with the help of thermo-calc with the iron database of TCFE7. The Fe-rich bcc phase was found to be stable up to high temperatures. The major phases are the Fe-rich bcc, Cr-rich BCC, and sigma phase in the solid state. The minor phases are FCC, M3P, TiC, Laves, and Ti4C2S2. The calculated lattice parameter of the Fe-rich BCC phase matches with the experimentally calculated data using XRD. The thermal expansion of Crofer 22 APU was found to be 11.9181 × 10-6 /°C at 950 °C. The in-situ high-temperature XRD technique has been an effective methodology for determining the thermal expansion behavior of the as-received Crofer steel.