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Within the scoop of environmental sustainability, the elaboration of efficient inhibitors using biomaterials was investigated. Beginning with careful extraction of lignin from raw Alfa fibers. Following this, the study examined the synthesis and characterization of a new generation of corrosion inhibitors based on clays and lignin biopolymer. A comprehensive characterization of powder samples sepiolite-lignin (SP-L) and bentonite-lignin (BN-L) was executed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) analysis and scanning electron microscopy (SEM) images. Electrochemical impedance spectroscopy and potentiodynamic polarization measurements were conducted on carbon steel immersed in 3%NaCl solution containing SP-L and BN-L composites, showing an interesting inhibition efficiency of 92.0% and 90.2%, respectively. The surface characterization of carbon steel, subsequent to immersion in 3%NaCl solution without and with SP-L or BN-L was conducted using XRD, FT-IR and SEM coupled with energy-dispersive X-ray spectroscopy analysis. Interestingly, the results of the blank sample revealed a deposition of corrosion products; mainly FeO(OH), Fe3O4 and iron carbonate (FeCO3), while SP-L and BN-L samples revealed an organic layer adsorbed onto the CS surface acting as a protective barrier. [ABSTRACT FROM AUTHOR]

The purpose of this research is to investigate the influence of SO42− in aerobic/anaerobic environment and its interaction with HCO3− on the corrosion behavior of Q345 carbon steel using potentiodynamic polarization, X-ray diffraction, white-light interferometer, electrochemical impedance spectroscopy and scanning electron microscopy methods. It was found that the corrosion rates of Q345 carbon steel are faster in aerobic environment under the synergistic effects of SO42− and dissolved oxygen compared to that in the absence of oxygen. In solutions containing SO42− and HCO3− in anaerobic environment, a high proportion of HCO3−/SO42− leads to the passivation of Q345 carbon steel sample as a result of the competitive adsorption of HCO3− on substrate surface with smaller radius. As the ratio of HCO3−/SO42− decreases, the presence of SO42− can enhance the dissolution of Fe matrix, thereby resulting in the corrosion of specimens. High concentration of HCO3− also exhibits the suppression on corrosion because of the formation of dense corrosion products. [ABSTRACT FROM AUTHOR]

The influence of grain growth inhibition by pearlite on hydrogen embrittlement (HE) behavior of ultra-low carbon ferritic steels was studied. The Fe-0.02C alloy has a considerable sensitivity to HE, while the Fe and Fe-0.1C materials have lower HE sensitivity. The high fraction of high-angle grain boundaries (HAGB) is responsible for the shift of the peak to a higher temperature in the Fe-0.1C alloy. The trapping of hydrogen by HAGBs was observed by hydrogen mapping. Higher density of HAGBs contributes to higher trap density in Fe-0.1C alloy and lower H diffusion coefficient. The coexistence of hydrogen enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP) mechanisms was identified and discussed. The results indicate that HEDE is active in the initial stage of the tensile loading during crack initiation and HELP in the rest of tensile testing duration that controls the crack propagation. Due to the reduction in grain size caused by the addition of pearlite, the normalized hydrogen content per HAGB length is significantly lower than Fe-0.1C, which means that the critical amount of local hydrogen required for crack initiation is less likely to accumulate due to the weakening of cohesive interatomic strength. In Fe-0.02C alloy, the ciritcal local content was built up at HAGBs, and resulting in activation of HEDE mechanism for crack initiation. In Fe-0.1C, a lower possibility of accumulating the critical H concentration at HAGBs, resulting in limited activation of HEDE-based crack initiation at HAGB and less crack propagation events based on the HELP mechanism. [ABSTRACT FROM AUTHOR]

A newly designed smart self-healing epoxy coating system comprised of modified halloysite nanotubes (HNTs) having capping is proposed for corrosion protection of steel. In the first step, HNTs were loaded with 8-hydroxyquinoline (8HQ), used as a corrosion inhibitor. Then the HNTs were sealed/capped using cobalt (II), aiming for an efficient and controlled release of the loaded inhibitor. The smart coatings were developed by reinforcing loaded HNTs into the epoxy matrix. The structural, thermal, mechanical, and electrochemical properties of capped modified HNTs and smart coatings were studied using various techniques. UV–Vis analysis depicted that the capping of the metal-inhibitor complex was decomposed at acidic pH resulting in a controlled release of the loaded inhibitor into HNTs. Electrochemical impedance spectroscopic (EIS) analysis of blank and smart coatings demonstrated that the low-frequency impedance modulus of smart coatings is 109 Ω.cm2 for 20 days compared to blank coatings (105 Ω.cm2), reflecting their excellent corrosion inhibition performance. The superior corrosion protection properties of these smart coatings can be ascribed to the controlled and efficient release of the loaded inhibitor from the capped HNTs. Finally, X-ray photoelectron spectroscopy (XPS) analysis of the steel substrate after the corrosion analysis revealed the adsorption of 8HQ on the steel surface, confirming the formation of iron complex due to the release of loaded inhibitor. This work demonstrated the adeptness of 8HQ in mitigating the corrosion due to the controlled and effective release of the inhibitor from capped HNTs because of dissociation of the metal-inhibitor complex (Co-8HQ).Kindly check and confirm the authors names are correctly identified.Checked [ABSTRACT FROM AUTHOR]

Polypyrrole doped with phosphoric acid was electrochemically synthesized on carbon steel from acetonitrile medium, and then a coating of polypyrrole doped with a long carbon chain acid, dodecylbenzenesulfonic acid or lauric acid, was electrodeposited to form a bilayer. The more protective performance of the bilayers in relation to monolayers was explained in terms of adherence and low porous, as confirmed by scanning electron microscopy. The corrosion performance was also confirmed by electrochemical measurements of open-circuit potential, potentiodynamic polarization curves and electrochemical impedance spectroscopy in chloride solution. The polarization experiments indicated that the corrosion potential values for polypyrrole-bilayer-coated steel were shifted to the positive direction in relation to uncoated carbon steel, indicating anodic protection. Tafel plots also indicated that the anodic current densities were smaller for steel coated by polypyrrole-bilayer. In addition, the electrochemical impedance data showed that the charge transfer resistance values are associated with the resistance to electron exchange between the metal and the coating, and depend on the type of long carbon chain dopant used in the outer-layer. Thus, the suggested mechanism to explain the protection of carbon steel surfaces against corrosion was associated to the passivation and barrier effect of the polypyrrole-bilayer. Mechanism to corrosion protection of PPy-bilayer coated carbon steel. [ABSTRACT FROM AUTHOR]

The behavior characteristics of nano-inhibitors are meaningful to understand the inhibition mechanism and influencing factors of particles in large size. Given the accumulated charge in the outer layer of nanoparticles, the driving force in the electric field will be significantly different from that in traditional inhibitors, and the process of adsorption kinetic will be inevitably changed. In this study, the carbon dots (CDs) were used as the nano-inhibitor for carbon steel in 1 M HCl solution, and the effect of external parallel electric field (PEF) for inhibition performance had been investigated via the various measurements. The results revealed that CDs can effectively inhibit metal corrosion, and the inhibition efficiency reached 90% at only 5 mg/L. Chemisorption and chelation of polar groups in CDs lead to the accumulation, then forming the protective cover layer on metal surface. But the inhibition performance of CDs declined gradually with the increase of electric intensity of PEF, and inhibition efficiency decreased by about 20% according to the results in polarization curve when the electric intensity was in 2 × 105 V/m. The migration direction and aggregation concentration of CDs were affected by the electric field, and there was horizontal force during the adsorption of nanoparticles under PEF, thus the adsorbing performance at the interface weakening with the defective cover layer. [ABSTRACT FROM AUTHOR]

This study investigated the effect of ferrite band formation for preventing the diffusion of molten copper (Cu) into steel grain boundaries. To this end, the gas tungsten arc welding method was exploited for cladding ERCuAl-A2 and ERCuSi-A filler metals on plain carbon steel. Then, microstructure, cracks, and ferrite bands were characterized and the conditions for the formation of 4.20 wt.% Si in the ferrite band were evaluated using the design of experiments methodology. The results indicated that when cladding with 7.60 wt.% Si takes place with minimum heat input (0.9 kJ/mm), the penetration of the molten Cu will not occur in the grain boundaries of the heat-affected zone in the presence of the %overlap. [ABSTRACT FROM AUTHOR]

Lath martensitic high-strength steels are some of the most widely used materials in structural applications, and consequently, refining and controlling the lath martensitic morphology is of significant interest to expand the versatility of the steels and their associated range of applications. It is well known that the steel's carbon content has a pronounced effect on the lath martensitic morphology, its crystallography, and hierarchical structure, but the effect of other elements like Mn and Ni is still relatively unclear. This study provides a comprehensive investigation on the effect of Ni on the morphology, crystallography, microstructural refinement, internal transformational strain, and mechanical properties of lath martensite using advanced analytical tools at the meso-, nano-, and atomic scales to offer insights that have so far been lacking in the literature. The in situ alloying of Ni with the bulk microstructure triggered a relatively ideal martensitic transformation such that the majority of the austenite (γ) grains transformed into four martensitic packets (with each packet representing one of the four close-packed {111} planes in a given γ-grain) with a relatively homogenous distribution of the twenty-four martensitic variants that can potentially evolve in an γ-grain based on the Kurdjumov–Sachs (K–S) orientation relationship. The addition of Ni lowered the martensite start (Ms) temperature and strengthened the γ-matrix at lower temperatures, which resulted in the refinement of the packets and blocks due to an inherent need by the matrix to self-accommodate the transformational strain, whereby significantly decreasing the internal strain in the microstructure. The results of this study showed that alloying lath martensitic steels with Ni can prove to be an effective method to refine the hierarchical microstructure in a way that can be used to improve the mechanical properties of these steels. [ABSTRACT FROM AUTHOR]

The superhydrophobic surface with a high adhesive state (petal effect) has attracted considerable attention owing to its potential applications in fluid transportation. In this study, the preparation of a superhydrophobic surface with a highly adhesive state on carbon steel is reported. By the combination of electrochemical deposition and double glow plasma surface metallurgy (DGPSM), a hard CrFe alloy coating with a rose petal-like microscale structure is prepared. The water contact angle of CrFe alloy coating can reach 163° after modification with 1H,1H,2H,2H-Perfluorooctyltrichlorosilane (PFTEOS). Moreover, the surface exhibits excellent adhesive property with a petal effect. The linear abrasion test demonstrates that the superhydrophobic coating can resist 18 m abrasion distance under a 5 kPa pressure. In addition, electrochemical tests show that the superhydrophobic coating can prevent corrosion from carbon steel effectively. This study provides an effective method to prepare a robust superhydrophobic surface with a high adhesive state for potential industrial applications. [ABSTRACT FROM AUTHOR]

The microstructure and properties of bainitic multiphase steels with bainitic ferrite as the main phase are the focus of the current research. In the work, multiphase microstructures of pre-formed martensite (PM), bainitic ferrite (BF), and retained austenite (RA) was obtained via austempering processes in medium carbon bainitic steel. The relationship between the multiphase characteristics and mechanical properties was analyzed quantitatively. The results show that the thickness of bainitic ferrite laths and the size of blocky retained austenite of the PM-BF-RA samples are smaller than those of the BF-RA samples. The dislocation density of bainitic ferrite and carbon content in retained austenite of the PM-BF-RA samples are higher. The PM-BF-RA samples obtain higher strength. The yield strength that was calculated by measured microstructural parameters is similar to the tested value. The dominant strengthening phases of PM-BF-RA samples are pre-formed martensite and bainitic ferrite dual phases, while those of the BF-RA samples are the bainitic ferrite. The main of the strengthening mechanism of bainitic ferrite is grain boundary strengthening, while it is solid solution strengthening for martensite and retained austenite. Small and stable retained austenite with high carbon content effectively ensures the high plasticity of PM-BF-RA samples. Moreover, the high toughness of PM-BF-RA samples can be attributed to fine bainitic ferrite and small blocky retained austenite. This study demonstrates that medium carbon bainitic multiphase steel with PM-BF-RA microstructure exhibits excellent combination of strength, plasticity, and toughness. [ABSTRACT FROM AUTHOR]

The effect of AC voltages, cathodic protection (CP) potentials and calcareous scale on the pitting corrosion of carbon steel 1010 was investigated by potentiostatic tests, electrochemical impedance spectroscopy (EIS) measurements and surface characterization techniques. Under the CP potential of − 1.12 VSCE, pitting corrosion increased with increasing AC voltage due to higher DC and AC current densities. The highest pitting severity was found at the highest AC current density over 4000 A/m2, facilitated by the utilization of microelectrodes. The presence of calcium and magnesium deposits reduced the pitting severity for all AC conditions acting as a barrier on the steel surface. Under constant high AC voltage, the dominant form of corrosion (uniform vs. pitting) depended on the applied CP potential and lowering the CP potential to − 1.5 VSCE promoted greater metal dissolution. It was also found that the presence of AC interference was not necessary for pit initiation, but it promoted pit growth. [ABSTRACT FROM AUTHOR]

Lath martensite substructures in as-quenched plain carbon steels exhibit dislocation-like contrast in the transmission electron microscope. More recent observations reported internal twins and nanoscale auto-tempered intra-lath carbides as additional lath substructures in ultra-low-C binary Fe–C steels. Modern microalloyed steels often have similar ultra-low C contents besides microalloying elements like Ti, Nb or V and, more recently, Mo, to achieve high strength, toughness and weldability. Nonetheless, little is known about the lath substructure evolution in the as-quenched state of microalloyed steels. This study investigates the hierarchical martensite substructure evolution post-quenching of microalloyed Nb and NbMo steels with 0.1 wt% C. Hierarchical microstructure characterization was done using scanning and transmission electron microscopy, and electron backscatter diffraction methods including parent grain reconstructions with MTEX. Thermokinetic simulations using MatCalc to determine the carbide evolution during auto-tempering were corroborated with site-specific transmission electron microscopy. Mo addition led to lowering of the martensite start temperature, yet the Nb steel showed a finer hierarchical microstructure. Finer laths with in-lath dislocations, short and long twins, and lath boundary decoration of carbides were found in the Nb steel. Conversely, laths in the NbMo were wider, with frequent intra-lath auto-tempered precipitates in the vicinity of dislocations, without twins. [ABSTRACT FROM AUTHOR]

In this study, the crack initiation and propagation behaviors of the γ' layer in nitrided ultra-low carbon steel subjected to monotonic and cyclic tensile tests were investigated to comprehensively understand the deformation and fracture behavior of the Fe4N (γ') phase. A γ' layer with a grain size of approximately 2 μm was successfully formed on the ferrite matrix through nitriding treatment by controlling the nitriding potential. After the monotonic tensile test until fracture, numerous microcracks were generated in the γ' layer, and a few macrocracks were detected in the ferrite matrix propagated from the γ' layer. The microcracks were initiated from the γ' layer/ferrite matrix boundary and propagated to the surface along the {100}γ' in the grain or grain boundary during the monotonic tensile test. During the cyclic tensile test, after applying yield stress up to 105 cycles, microcracks were initiated from the voids around the surface and propagated to inside of the specimen along {111}γ' in the grain or grain boundary. The results demonstrated that, in the γ' layer, the cracks propagated with the cleavage fracture on {100}γ' during the monotonic tensile test, and slipping-off occurred as a result of activating {111} < 1–10 > slip systems during the cyclic tensile test. It is most likely that the macrocracks propagate in the ferrite grain where {100}α is parallel to the microcrack plane in the γ' layer and lies in the direction perpendicular to the tensile direction. [ABSTRACT FROM AUTHOR]

Extension of corrosion inhibitors from traditional molecular-scale to nanoscale will not only be significant to develop green and efficient inhibitors, but also supplement the discipline system of corrosion inhibitors. However, many research on the interfacial behavior of nano-inhibitors have ignored the special colloidal properties of nanoparticles and show no obvious differences with traditional inhibitors. In this study, graphene oxide (GO) was functionalized with polydopamine (PDA) via covalent modifications and self-polymerization, and GO-PDA was studied as a corrosion inhibitor of carbon steel in HCl solution. Diversified measurements confirmed that GO-PDA can effectively protect carbon steel from corrosion, and the inhibition efficiency almost reached 90% at 100 mg/L. Interfering factors including immersion time and concentration were investigated. The lamellar nanoparticles adsorbed on the surface of carbon steel have formed a hydrophobic film in micro-nano structures. The transition from a negative charge on the GO surface to a positively charged GO-PDA contributed to adsorption at the interface. An initial model of nano-inhibitor was established to explicate the inhibition mechanism. [ABSTRACT FROM AUTHOR]

Two kinds of Fe-18Ni-12Cr-based alumina-forming austenitic (AFA) steels with ultralow carbon content were prepared by vacuum induction melting. Creep rupture tests were carried out with the applied stress range between 80 and 180 MPa at the target application temperature of 700 °C. Microstructure evolution was characterized using glancing X-ray diffraction, scanning electron microscopy equipped with a detector of electron backscatter diffraction and transmission electron microscope. Compared with 18-12-Al, 18-12-AlNb exhibited superior creep properties including ten times longer creep rupture life ( t rup ) and one magnitude smaller minimum creep rate ( ε ˙ min ). For example, the ε ˙ min at the applied stress of 140 MPa was 4.4 × 10–5 and 2.1 × 10–4 h–1 for 18-12-AlNb and 18-12-Al, respectively. The strengthening effect of B2-NiAl would weaken at 700 °C due to its ductile-to-brittle transition. The addition of Nb not only promoted the formation of Laves-Fe2(Mo,Nb), but also resulted in formation of nanoscale NbC. The GB Laves-Fe2(Mo,Nb) did not impair the creep ductility by strengthening GBs, and all the creep ruptured AFA steels exhibited typical ductile fracture mode. The GB Laves-Fe2(Mo,Nb) and NbC precipitates contributed to the superior creep resistance of 18-12-AlNb. [ABSTRACT FROM AUTHOR]

Radiation fields occur in nuclear power plant primary circuits, and decontamination is needed before the permanent shutdown of a reactor. Radiation field reduction in the primary coolant system of water-cooled reactors can be achieved by using a decontamination solution. As part of this, the corrosion behavior and characterization of oxide layers formed on different kinds of metal should be examined. In this study, NiFe2O4 thin film was deposited on substrates of stainless steel, inconel and carbon steel via electron beam evaporation. The reaction between nickel ferrite and different metal ions results in varying compositions of oxide layers. The phase, structure and morphology of materials were confirmed by SEM, XRD and XPS analysis, and the magnetic properties of each deposited sample were observed by using vibrating sample magnetometer (VSM). The characteristics of the surface-coated metals are the main focus of this work. [ABSTRACT FROM AUTHOR]

This study examined the controlling factors for the quenching crack sensitivity of ultra-strong martensitic steel with a tensile strength exceeding 1.8 GPa. Two factors, the content of carbon alloyed in the steel and the type of quenchant used in the quenching process, were evaluated in terms of the strain level and diffusible hydrogen concentration, which were measured by electron backscattered diffraction-kernel average misorientation and thermal desorption spectroscopy, respectively. This study demonstrated that specimens with a higher carbon content exhibited larger lattice distortion and a higher dislocation density during the quenching process and may be more susceptible to cracks propagating along the prior-γ grain boundaries. The decrease in quenching rate and diffusible hydrogen concentration can be effective technical strategies for improving the mechanical toughness and mitigating the quench cracking of ultra-strong steels with a tensile strength of 2.0 GPa. [ABSTRACT FROM AUTHOR]

Decreasing processing time of a quench and temper heat treatment is of high interest for industry due to the possibility of cost reduction. One option to reduce processing time is to shorten the austenitizing cycle by applying high heating rates and minimum holding times. However, due to the high heating rates, the analysis of their influences on the formation kinetics of austenite and its crystallographic parameters is challenging. Thus, this work concentrates on the in situ analysis of the austenitization process by means of high-energy X-ray diffraction to study a range of heating rates applied to ferritic–pearlitic and soft annealed initial microstructures. The transformation kinetics from ferrite/pearlite and soft annealed state to austenite, the cementite dissolution behavior and the homogeneity of the freshly formed austenite were analyzed. The results indicate three distinct steps of austenite formation independent of initial microstructure and heating rate: (1) nucleation of carbon-rich austenite at cementite–ferrite interfaces, (2) growth of austenite phase fraction accompanied by a reduction of the carbon content, until reaching the mean carbon content of the steel, followed by growth of the austenite grain size, (3) regarding austenite homogeneity, the combination of austenitization temperature and initial microstructure are the main influencing factors. [ABSTRACT FROM AUTHOR]

Dual-phase high-carbon steels are of significant interest in mining industries particularly in comminution and rock handling applications where the strain rate varies from very low to very high. The effect of quasi-static strain rate on the deformation behaviour of austenite-martensite high-carbon low-alloy steel is investigated for compression loading in this paper. Experiments were conducted at different compressive strain rates (2.56 × 10−4 to 2.56 × 10−1 s−1), and the subsequent microstructural evolution was characterised by optical microscopy, X-ray diffraction (XRD), scanning electron microscopy and electron backscatter diffraction (EBSD) techniques to establish the structure-property correlation. The experimental results indicated an increase in the yield strength (σy) with the increase in the strain rate due to the rate-dependent dislocation velocities. The strain hardening rate of the material exhibited a decreasing trend with an increase in the true strain values for all the applied strain rates. XRD results indicated the phenomenon of deformation-induced martensitic transformation (DIMT) to be rate dependent, whereas EBSD results showed an increase in the Kernel average misorientation values with increase in the strain rate. The volume fraction of retained austenite was observed to be decreasing with an increase in the engineering strain values irrespective of the applied strain rate. The microscopic features of the fracture surfaces showed the presence of transgranular cracking at low strain rates, whereas predominant intergranular cracks were found at higher strain rates. TEM results indicated the decrease in the lath martensites with increase in the strain rate. [ABSTRACT FROM AUTHOR]

The development of multiphase steels to obtain an optimum balance between strength and ductility is a very active topic of research. In particular, carbide-free bainitic steels have shown promising mechanical properties, making them good candidates for replacing well-established first-generation steels in the automotive industry. In this work, a detailed analysis of the microstructures attainable through overaging treatments is tackled in two bainitic steels with different Si contents. The focus has been put onto the mechanical characterization, via nanoindentation, of the phases that are generated as a consequence of the change in the bainitic treatment conditions and the final cooling to room temperature. The results show the suitability of the nanoindentation technique for gaining knowledge about the underlying transformation-related phenomena and for measuring the relative difference in hardness of the various micro-constituents. The latter is a key factor in understanding the origin of the damage in this kind of steels. [ABSTRACT FROM AUTHOR]

A novel nanocontainer using graphene oxide nanoscrolls (GONS) as shell and benzotriazole (BTA) as core is proposed and embedded in epoxy coating for the corrosion protection of carbon steel. BTA/GONS nanocontainer is effectively fabricated by a modified shock-cooling approach. The hybrid material takes the specific shape of graphene oxide sheet spirally wrapped into scroll structure, acting as favorable physical barrier to afford encapsulation performance. A high uptake and storage of BTA in GONS is achieved, showing a loading capacity of 78.40%. The fantastically scrolled structure also provides an effective network to well control the BTA liberation during long-term immersion. The transport of BTA is diverse with pH values. The maximum release capacity of BTA occurs in neutral condition, larger than that in acid or alkaline environment. The liberation for up to 456 h exhibits the steady releasing characteristics of the containers. The corrosion inhibition performance of BTA/GNOS containers was mainly evaluated by electrochemical impedance spectroscopy. In comparison with, the reference epoxy coating, the one modified by BTA/GNOS nanocontainers demonstrate more excellent anticorrosion ability. The successful embedding and homogeneous distribution of BTA-loaded GNOS nanocontainers in epoxy film contributes to the improvement in the corrosion resistance of Q235 carbon steel and the self-healing performance of the coating. [ABSTRACT FROM AUTHOR]

Synchrotron X-ray fluorescence mapping and micro-XANES were employed to characterize the spatial distribution of individual elements and the speciation of Cr on the cross section of various tubes that were exposed to oxy-fuel flue gas at 650 °C, 1 bar for 50 h. The gas composition tested is close to the flue gas produced from oxy-firing of low-rank coal in pilot-scale tests. Multi-layered scales with an uneven distribution were observed for individual elements on both the top surface and spalled layer of carbon steel SS400. Oxidation is the major reaction causing the scaling of the tube, whereas the other reactions such as sulphidation and chlorination led to the buckling of tube surface. The use of Cr, even at a low concentration of 1.2 wt% in 12Cr1MoVG, is essential and can considerably reduce the tube corrosion rate, as well as minimize the difference between oxy-fuel and air-firing flue gases on the tube mass loss rate. The CO2 cycle with the involvement of oxidation (mainly of iron) and carburisation (of chromium) took place simultaneously for the Cr-bearing alloy, even under the coexistence of CO2 and a number of oxidizers in the flue gas tested here. The fast diffusion of CO2 and its derivatives facilitated a preferential occurrence of carburisation under the oxide scale. However, upon the closure of gas passage channels in the oxide scale of a high-Cr tube such as austenite SUS304, the reductants CO and carbon can flow back to tube top surface, causing the formation of carbide on the most outer scale that further fragments into fugitive pieces. Carburisation is also the major cause of corrosion of high-Cr tubes. In contrast, for a tube with medium Cr content, such as high-chrome T91 tube with 9 wt% Cr, it undergoes both oxidation and carburisation successively on the metal/oxide interface. The gas passage channels mostly remain open, and hence, the resultant carbide and carbon precipitate penetrated deep inside the tube. [ABSTRACT FROM AUTHOR]

The first high-performance electroactive benzoxazine with an aniline dimer in its structure has been synthesized from 4-aminodiphenylamine (aniline dimer), paraformaldehyde, and phenol. FT-IR and 1H NMR are used to characterize the molecular structure of the electroactive benzoxazine monomer (PH-BA). The reversible one-electron transfer between the neutral form and the radical-cation form takes place in the redox reaction of PH-BA and its corresponding polymer (pPH-BA). The pPH-BA exhibits oxidation and reduction currents of 0.122 and 0.128 mA cm-2, respectively, which are higher than the published benzoxazine/ aniline oliogomer blend. The current value of the redox peaks of pPH-BA doubles when compared with PH-BA, which might be attributed to the formation of the electron-donating hydroxyl groups during the thermally induced ring-opening polymerization and the hydrogen bonding interactions between phenolic-OH groups and aniline units in pPH-BA network. The pPH-BA coating exhibits outstanding corrosion resistance properties with a corrosion rate of 0.0091 mm per year for carbon steel Q235, which is significantly lower than that of non-electroactive polybenzoxazines. pPH-BA can further facilitate the formation of a metal oxide layer composed of Fe2O3 on the steel surface and was characterized by SEM, Raman, and XPS. [ABSTRACT FROM AUTHOR]

The kinetics of cementite coarsening in tempered martensite AISI 4340 steel system has been investigated in order to understand over-tempering behavior. Microstructural response during tempering at 550 and 650 °C has been recorded, analyzed, and modeled. A statistical analysis of metallographic sections was performed to yield measurements such as average particle size, volume fraction, morphology, volume number density. The coarsening behavior of this multicomponent alloy system has been modeled with the classical coarsening theory for multicomponent alloys. These results highlight the remarkable coarsening resistance of 4340 steel even for prolonged tempering. [ABSTRACT FROM AUTHOR]

Martensite has a body-centered tetragonal (bct) structure in high carbon steels. However, body-centered cubic (bcc) {112} 〈111〉-type twins instead of bct twins always be observed as the substructure of martensite in high carbon steels. In this paper, martensitic substructure in a quenched high carbon Fe-1.4C (wt%) alloy has been investigated in detail using selected area electron diffraction (SAED) technique in a conventional transmission electron microscopy. The reciprocal lattice of martensite has been built based on the experimental SAED patterns. Two sets of diffraction spots (one face-centered cubic lattice and one hexagonal lattice) in the built reciprocal lattice suggest that two crystalline phases with bcc (or α-Fe) and hexagonal (ω-Fe) structure actually coexist in the twinned martensite. The two-phase diffraction spot patterns from the reciprocal lattice can match perfectly with the experimental results. The fact that the {0001} diffraction spot at the 1/3{222} position and the {0002} at 2/3{222} can support the ω-Fe existence in the twinned martensite. [ABSTRACT FROM AUTHOR]

The paper presents the results of a study on the microstructure and mechanical properties of a medium-carbon steel (0.45 % C) processed by severe plastic deformation (SPD) via high-pressure torsion (HPT). Martensite quenching was first applied to the material, and then HPT processing was conducted at a temperature of 350 °C. As a result, a nanocomposite type microstructure is formed: an ultrafine-grained (UFG) ferrite matrix with fine cementite particles located predominantly at the boundaries of ferrite grains. The processed steel is characterized by a high-strength state, with an ultimate tensile strength over 2500 MPa. Special attention is given to analysis of the thermal stability of the microstructure and properties of the steel after HPT processing in comparison with quenching. It is shown that the thermal stability of the UFG structure produced by HPT is visibly higher than that of quenching-induced martensite. The origin of the enhanced strength and thermal stability of the UFG steel is discussed. [ABSTRACT FROM AUTHOR]

The Avrami kinetics of the dynamic recrystallization (DRX) of V-microalloyed medium carbon steel is studied by measuring the flow curves and evolution of grain size distribution (GSD) due to DRX and by modeling the flow softening kinetics and flow curves under various deformation conditions. The ε method is proposed as a new method of modeling the Avrami kinetics and is shown to be, unlike the conventional t method, capable of modeling the flow softening kinetics and flow curves with a single variable Z (= $$ {\dot{{\varepsilon }}} $$ exp( Q/RT)). The time exponent ' n' of the Avrami kinetics decreases from 2.3 to 1.4 with increasing Z, which results from a shift in the mode of necklace recrystallization from boundary migration dominant mode to nucleation dominant mode. The GSD method is proposed as a new method for estimating the DRX fraction in deformation conditions where it is difficult to distinguish recrystallized grains from un-recrystallized grains. The softening fractions estimated from the flow curves tend to overestimate the DRX fractions at a later stage of deformation, where DRX kinetics appear to be retarded by dynamic precipitation. [ABSTRACT FROM AUTHOR]

A new extended technique for 3D modelling of normal grain growth in low carbon steels is presented in this paper. This technique is based on real-valued cellular automata with the use of a local transition function that allows it to be applied to materials with both fcc and bcc lattices with the grain growth being easily simulated in ferrite as well as in austenite cases. The simulated data were calibrated with four sets of experimental data for isothermal grain coarsening in austenite, alpha- and delta-ferrites. The obtained results cogently demonstrate that there is a good agreement between simulated and experimental data across a wide range of temperatures. The new model developed in this paper, allows for the identification of two different mechanisms of grain growth in austenite. It is also shown in this paper that the newly presented approach can be used to extract additional parameters from the grain growth process, such as grain boundary velocity, mobility and driving force, which are hardly accessible even via real-time experiments. [ABSTRACT FROM AUTHOR]

The feasibility of using friction stir-processing technique as a microstructural refining method for preventing hydrogen-induced blisters of SK4 carbon steel alloy containing microstructure of hard cementite particles in a ductile ferrite matrix was examined. Amount and size of hydrogen-induced blisters decreased in the stirred layers with increasing rotation speed and completely disappeared when rotation speed attained 400 rpm because of the formation of a hard and fine microstructure consisting of pearlite, martensite, and retained austenite instead of that containing hard spheroidized cementite particles in a soft ferrite matrix. Interfaces between ferrite matrix and cementite particles were the preferential sites for the hydrogen blisters initiation. [ABSTRACT FROM AUTHOR]

Bi-metallic corrosion resistant steel pipes were produced through explosive welding process. The weldability window of the stainless steel pipe (inner pipe) and the carbon steel pipe (outer pipe) was determined by the use of available semi-empirical relations. The impact velocity of the pipes as the most important collision parameter was calculated by the finite element simulation. Direct effect of the explosive mass reduction on the bonding interface of the pipes was studied. Optical microscopy study showed that a transition from a wavy interface to a smooth one occurs with decrease in explosive load. [ABSTRACT FROM AUTHOR]

Three-dimensional atom probe was used to investigate solute carbon and other elements distributions during bake hardening process after pre-deformation and also to analyze their effect on bake hardening phenomenon of the steels. Two different kinds of bake hardening steels were prepared and annealed by water quenching. The as-received samples were pre-deformed at different levels (from 0 to 10%), and baked at 170 °C for 20 min. Distributions and concentrations of solute elements in the steels were characterized with three-dimensional atom probe. Bake hardening values of the steels were examined by tensile experiments. Three dimensional atom probe detection results indicate that C distribution changes little with the increase of pre-deformation in BH-Mn steel. In BH-P steel, however, with the increase of pre-deformation, more C clusters form in the matrix and C concentration decreases. Distribution patterns and the maximum separation distance method results prove that the C cluster is just C segregation or C together with P segregation rather than vanadium carbides precipitate. Moreover, bake hardening experiment results indicate that BH values are similar in the two BH steels and the BH values change only a little as the pre-deformation increases from 2 to 10%. The 4% pre-deformation induces the highest BH values in the two BH steels, and is considered to be the critical pre-deformation in making the balance of Cottrell atmosphere in the two BH steels. [ABSTRACT FROM AUTHOR]

The Portevin-Le-Chatelier (PLC) effect manifests itself as serrated plastic flow in strain controlled tensile tests of dilute alloys. The effect causes most of the material qualities to suffer, including the ductility. Monitoring the effect is important since the induced loss of ductility can cause premature failures on structural materials under load. Surface potential fluctuations of AISI 1020 low carbon steel during its serrated flow was investigated by a combined set-up of an electrochemical cell and a slow strain tensile test. The steel was exposed to an aqueous electrolyte under a strain rate of 1.6 x 10/s, and the surface potential was monitored in situ during the creation, magnification, and annihilation phases of the serrated flow achieved by changing test temperatures stepwise between 50 and 85 °C. The serration amplitude showed strong correlations both with test temperatures and the surface potential. A rather large potential shift around 110 mV through active direction during the burst of serrations hinted that the slip bands, in addition to temperature and strain, could also be responsible for the charge release due to the dislocation domains carried in them. The study verifies a potential use of the set-up for monitoring the PLC events in aqueous environments where load cells, extensometers etc. are not utilizable. [ABSTRACT FROM AUTHOR]

In this study, a thermo-mechanical model was utilized to investigate the effects of welding parameters on the distribution of residual stresses in dissimilar TIG welds of low carbon and ferritic stainless steels. To solve the governing thermal and mechanical problems, a finite element program, ANSYS, was employed while the different aspects such as welding sequence and dilution were considered in the numerical solution. To validate the predictions, the model results were compared with the residual stresses measured by X-ray diffraction technique and a reasonable agreement was found. The results show that the magnitude of tensile residual stresses decrease as the welding current increases while lower residual stresses are produced in the longer samples. In addition, the magnitudes of residual stresses significantly decrease when a symmetric welding sequence is employed especially for the carbon steel part with the higher yield strength. [ABSTRACT FROM AUTHOR]

new kind of V-Ti-N high strength microalloyed medium carbon steel has been developed, which is used for fracture splitting connecting rod. In this article, the characteristics of this carbon steel and its production process were studied. The microstructure, precipitated phases and their effects on mechanical properties were investigated by optical microscope, SEM, and TEM. The results showed that the steel was constituted of ferrite and pearlite. By reducing the finish rolling temperature and accelerating the cooling rate after rolling, microstructure with fine grain ferrite and narrow lamellar space pearlite could be obtained in V-Ti-N microalloyed medium carbon, and a large number of precipitated phases distributed over ferrite. These led the tensile strength to be more than 1000 MPa, yield strength (YS) more than 750 MPa. The impact fractograph showed typically brittle fracture characteristic. [ABSTRACT FROM AUTHOR]

Isothermal stress–strain curves data from torsion tests conducted at high temperature (950–1200 °C) and strain rates (2–26 s−1) were analyzed in an ultrahigh carbon steel (UHCS) containing 1.3%C. The sine hyperbolic Garofalo equation was selected as an adequate constitutive equation for the entire range of the forming variables considered. The Garofalo parameters were assumed strain dependent allowing the prediction of stress–strain curves under transient and steady-state conditions. The average relative errors obtained were below 3% in stress. In addition, the creep deformation mechanisms in the UHCS were analyzed from the Garofalo equation parameters. For this aim, the stress exponent of the Garofalo equation was, for the first time, related to that of the power law equation. The results show that the controlled deformation mechanism at steady state is lattice diffusion-controlled slip creep. [ABSTRACT FROM AUTHOR]

Using the high pressure torsion (HPT) deformation method the medium carbon steel (AISI 1045) was the experimental material used to conduct the deformation process. The torsion deformation experiment was performed at increased temperature of 400 °C. The influence of deformation processing parameters, resolved shear strain γ (number of turns N = 1–6) and applied pressure p (constant pressure of 7 GPa), was evaluated by microstructure analysis and mechanical properties. The strength behaviour was assessed by microhardness measurements across the disc to detect the positional hardening, by tensile tests and in situ measured torque. In situ measurement of torque during deformation allows characterizing the changes in mechanical properties due to the large shear deformation developed across the disc. To obtain absolute values of strength the ultimate tensile strength was measured in radial direction with respect to the deformed sample. From each deformed disc two sub-sized tensile test specimens with gauge length of 2.5 mm were machined. The tensile strength in samples increased markedly with the number of turns. The hardness measured at disc edge gradually increases as straining increases until it saturates after 2–3 turns. However, the hardness values at edge were different from those measured in disc centre and for applied straining no saturation was reached across the disc. The SEM and TEM investigations were carried out to analyze the fine microstructure evolution regarding the strain introduced. To follow the difference in strain distribution across the deformed disc the microstructure analysis was performed at edge and central site of the disc in order to evaluate the effect of the strain distribution. TEM investigation confirmed the increasing misorientation even in very small grains, the fragmentation and dissolution of the cementite lamellae, (diffuse cementite/ferrite boundaries), the alignment of the fragments to the shear plane with increasing deformation. Indistinct deformation of ferrite and preserved cementite lamellae morphology were found at the centre of the disc. [ABSTRACT FROM AUTHOR]

This study was undertaken to propose a method of continuous shear drawing (CSD) for industrial applications to steel-wire manufacturing. The study compared the spheroidization behavior of medium carbon steel processed by CSD to that processed via conventional drawing. Microstructural observation revealed that the use of the CSD method was effective for deforming the pearlite colonies, resulting in wavy pearlitic cementites without noticeable cracks on the surface. After annealing treatment at a subcritical temperature of 973 K for 1 h, the CSD-deformed sample exhibited a uniform microstructure with a number of fine globular cementites that was greater in extent than that by drawing; this result was mainly due to the easy spheroidization triggered by the CSD strain. [ABSTRACT FROM AUTHOR]

Plastic deformation behavior was investigated in near fully dense nanostructured and ultrafine-grained bulk samples of carbon steel (0.55 wt% C) under compression and tension tests. The specimens were obtained by hot pressure from mechanically milled powder at 400 and 500 °C. Subsequent heat treatments at temperatures going from 600 to 900 °C produced samples with ferrite grain sizes from 30 nm to 17 μm. Nanocrystalline grained steel samples presented very high strength with low ductility. Once, in the ultrafine range, as the ferritic grain size was increased, the strength was decreased and the ductility was improved. The porosity and carbon atoms within the structure were analyzed in order to explain the results of strength and strain obtained. [ABSTRACT FROM AUTHOR]

In this study, effect of rolling speed on strain aging phenomena in warm rolling of a carbon steel has been investigated. For this purpose, by using a mathematical model and predicting temperature and strain rate fields, the possibility of occurrence of dynamic strain aging during the warm rolling was first evaluated. In the next stage, warm-rolled samples were aged up to 11 months at room temperature for studying the kinetics of static strain aging, while mechanical tests as well as microstructural evolutions have been performed to determine the effect of strain aging on material behavior. The results indicate that dynamic strain aging may not occur for the employed rolling program; however, static strain aging takes place after warm rolling leading to changes in the mechanical behavior of the warm-deformed samples. In addition, by increasing rolling speed, the aging time required to achieve the maximum hardness increases. [ABSTRACT FROM AUTHOR]

The mechanical properties and microstructure were evaluated and analyzed by optical microscopy (OM) and transmission electron microscopy (TEM) for micro-alloy carbon steel weld metal with and without Nb addition, respectively, under different heat treatment processes including stress relief annealing, normalizing, and no treatment after welding. The strength and elongation of the weld metal without treatment after welding were improved with the addition of Nb element, and the impact toughness was not affected obviously with the Nb addition. After stress relief annealing, the strength decreased for the Nb-free weld metal, while the elongation and impact toughness increased. However, for the Nb-bearing weld metal, stress relief annealing improved the strength of the weld metal significantly, and deteriorated the elongation and impact toughness. In the case of normalizing treatment to the weld metal, it was shown that with the increase of the holding time at the normalizing temperature of 920 °C, for both the weld metals with and without Nb addition, the microstructure of the columnar grain zone (CGZ) was transformed from one of columnar grain into one of equiaxed grain. The grain size of the equiaxed grain zone (EGZ) increased initially, then remained almost unchanged with the prolonging of the holding time. The mechanical properties of the weld metal with and without Nb addition showed no obvious change with the increasing holding time. With the increase of the normalizing temperature, the strength of the Nb-bearing weld metal increased, while the elongation and impact toughness decreased significantly. OM and TEM analysis found that the fine NbC particles were precipitated at the normalizing temperature of 920 °C, which refined the grains of the weld metal and increased the impact toughness. With the increase of the normalizing temperature, the content of widmanstatten ferrite (WF) in the Nb-bearing weld metal increased, whereas the quantity of the NbC particles decreased, which improved the strength and lowered the impact toughness. [ABSTRACT FROM AUTHOR]

The inhibition behavior of low carbon steel in 1 M HCl by l-tryptophan was investigated with weight loss experiment and Tafel polarization curve in the used temperature range (298–328 K). All the experimental results show that l-tryptophan has excellent corrosion inhibition performance and the most effective concentration of inhibitor is 1 × 10−2 mol L−1. The Tafel polarization curve results indicate that l-tryptophan acts more as a cathodic than anodic inhibitor. The adsorption of l-tryptophan on the surface of low carbon steel obeys the Langmuir adsorption isotherm, and the thermodynamic parameters were determined and discussed. The adsorption behavior of l-tryptophan at Fe surface (1 1 0) was also investigated by the molecule dynamics simulation method and density functional theory. The results indicated that the l-tryptophan could adsorb firmly on the Fe surface through the indole ring with π-electrons and nitrogen/oxygen atom with lone-pair electrons in its molecule. [ABSTRACT FROM AUTHOR]

An Mg–Li–Zn (designated as LAZ61) alloy containing about 6 wt% of Li has been prepared by melting and solidification in a carbon steel crucible, and extruded at a billet preheating temperature of 200 °C. The extruded plate was then cold-rolled to a final thickness of 0.6 mm with a total reduction of approximately 82%. Tensile tests were carried out in the rolling and transverse directions and at various temperatures to explore the effects of anisotropy and temperature on mechanical properties and strain-hardening behavior. Kocks–Mecking type plots were used to illustrate different stages of strain hardening. Anisotropic behavior of LZ61 sheet were observed in the mechanical properties at all test temperatures due to the development of texture in α phase during cold-rolling and a low content of BCC β phase. The cold-rolled LZ61 alloy sheet showed stage II and stage III strain-hardening behavior at test temperatures of room temperature and 100 °C. The specimens tested at 200 °C did not show stage II strain hardening. Higher initial strain-hardening rates were observed in the transverse direction as a result of the cold-rolled fibrous structure providing more strong barriers to the dislocation movement. [ABSTRACT FROM AUTHOR]