Search Results (2,662)

This study presents a systematic investigation of laser surface hardening of 9CrSi tool steel with the aim of establishing the relationships between processing parameters, microstructural evolution, and resulting mechanical and tribological properties under the applied laser conditions. The influence of laser power, modulation frequency, and scanning speed on the hardened layer depth, microstructure, and surface properties was analyzed. Laser treatment produced a martensitic surface layer with varying fractions of retained austenite, while the transition zone consisted of martensite, granular pearlite, and carbide particles. X-ray diffraction identified the presence of α′-Fe, γ-Fe, and Fe₃C phases, with peak broadening associated with increased lattice microstrain induced by rapid self-quenching. The surface microhardness increased from approximately 220 HV_0.1 in the untreated state to 950–1000 HV_0.1 after laser hardening, with hardened layer thicknesses ranging from about 500 to 750 µm depending on the processing regime. Instrumented indentation showed higher elastic modulus values for all hardened conditions. Tribological tests under dry sliding conditions revealed reduced coefficients of friction and more than an order-of-magnitude decrease in wear rate compared with untreated steel. The results provide a parameter–microstructure–performance map for laser-hardened 9CrSi steel, demonstrating how variations in laser processing conditions affect hardened layer characteristics and functional performance. Full article

Long-distance natural gas pipelines with internal corrosion defects are susceptible to fatigue failure under operational pressure fluctuations, posing significant risks to infrastructure integrity and safety. To address this, the present study employs a finite element methodology, utilizing Ansys Workbench to model pipelines of various specifications with parametrically defined corrosion defects, and nCode DesignLife to predict fatigue life based on Miner’s linear cumulative damage theory. The S-N curve for X70 steel was directly adopted, while a power-function model was fitted for X80 steel based on standards. A cleaned real-world pressure-time history was used as the load spectrum. Parametric analysis reveals that defect depth is the most influential factor, with a depth coefficient increase from 0.05 to 0.25, reducing fatigue life by up to 67.5%, while the influence of defect width is minimal. An empirical formula for fatigue life prediction was subsequently developed via multiple linear regression, demonstrating good agreement with simulation results and providing a practical tool for the residual life assessment and maintenance planning of in-service pipelines. Full article

ZnAl and ZnAlCe layered double hydroxide (LDH) conversion layers modified with picolinoyl N4-phenylthiosemicarbazide (HL) are fabricated on hot-dip galvanized steel (HDG) to improve corrosion protection. X-ray diffraction (XRD) confirms that HL molecules are not intercalated within the LDH interlayers, whereas Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDS) analyses reveal their surface adsorption. Moreover, scanning electron microscopy (FE-SEM) observations reveal that HL modification induces changes in surface morphology. After 168 h in 0.1 M NaCl, the LDH structure remains intact, and N and S signals are still detected, confirming the persistence of both the LDH layer and adsorbed HL molecules under corrosive conditions. During 168 h immersion in NaCl, electrochemical measurements indicate that the modified LDH layers exhibit higher corrosion resistance than the unmodified ones, with the ZnAlCe LDH/HL coating providing the most effective protection. Full article

Grouting technology can be employed to repair cracks in an aquifer to maintain its stability; however, existing grouting materials tend to come with problems such as low flexural strength, poor cracking resistance, and the coupled effects of fiber reinforcement and sulfoaluminate cement (SAC) addition on hydrate evolution, and pore-refinement and crack-resistance mechanisms in coal-based solid-waste cementitious grouts remain insufficiently understood. In this paper, fiber-modified coal-based solid-waste grouting (F-CWG) materials were prepared by mixing different contents of sulfoaluminate cement (SAC) and different fibers. The mechanical strength, microstructure, hydration products, and pore evolution characteristics were analyzed by means of mechanical property tests, energy-dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR). The results show that the mechanical strength decreases at first due to insufficient early-stage hydration products. Specifically, the 28 d compressive and flexural strengths decrease from 15.34 MPa and 4.55 MPa at 0% SAC to 8.18 MPa and 2.99 MPa at 40% SAC but increase again to 13.36 MPa and 3.79 MPa at 60% SAC as the formation of ettringite (AFt) and C–S–H is promoted with higher SAC content. Among the tested fibers, a dosage of 0.6% generally improves mechanical strength and refines pore structure, with PVA and steel fibers showing the most pronounced effects. Our results reveal the mechanism behind the enhancement of cracking resistance in F-CWG materials, providing a scientific basis for grouting and water-preservation mining, and are of great significance in improving the utilization rate of coal-based solid waste. Full article

Empirical approaches alone have significant limitations for accurate estimation of the fracture toughness of welds in gas line pipes being considered for repurposing to hydrogen service. These problems arise because most samples machined from ex-service welds contain a range of microstructures. The different microstructural zones have different properties and even when compact tension samples with side grooves are utilized, it is unlikely that plane strain conditions are achieved during laboratory testing. Thus, the measured toughness may not be directly relevant to assessing in-service performance. The present research has been undertaken as part of an integrated series of projects seeking to define a robust protocol for assessing the damage tolerance of piping used for the transmission of hydrogen, especially when considering repurposing existing infrastructure. The key work described in this paper involved establishing heat treatments which produced microstructures relevant to the constituents found in ex-service welds of X46 type steel. Following comprehensive microstructural characterization, these heat treatments were applied to steel sections which allowed for the fabrication of standard compact tension specimens, which were subsequently tested in hydrogen to measure fracture toughness. The results obtained showed that the fracture behavior varied for different microstructures. To identify the influence that hydrogen gas has on the performance of pipeline steels, it is important to assess microstructures relevant to the welds present, as testing only on base metal may not provide conservative information. However, the results from well-planned and carefully executed programs can be used to identify the relative performance in hydrogen. The data can also be used as critical input to models which form part of an integrated approach to structural integrity assessment. Full article

Among corrosive environments, Cl⁻ is one of the most aggressive anions which can cause electrochemical corrosion and the resultant failures of alloys, and the increase in Cl⁻ concentration will further deteriorate the passive film in many conventional alloys. Here, we report single-phase Nb₂₅Mo₂₅Ta₂₅Ti₂₀W₅C_x (x = 0.1, 0.3, 0.8 at.%) refractory high-entropy alloys (RHEAs) with excellent corrosion resistance in high-concentration NaCl solutions. According to potentiodynamic polarization, electrochemical impedance spectroscopy, corroded morphology and the current–time results, the RHEAs demonstrate even better corrosion resistance with the increase in NaCl concentration to 23.5 wt.%, significantly superior to 304 L stainless steel. Typically, the corrosion current density (i_corr) and over-passivation potential (E_t) reached the lowest and highest value, respectively, in the 23.5 wt.% NaCl solution, and the i_corr (2.36 × 10⁻⁷ A/cm²) of Nb₂₅Mo₂₅Ta₂₅Ti₂₀W₅C_0.1 alloy is nearly two orders lower than that of 304 L stainless steel (1.75 × 10⁻⁵ A/cm²). The excellent corrosion resistance results from the formation of passive films with fewer defects and more stable oxides. Moreover, with the addition of the appropriate C element, the RHEAs also demonstrated improved strength and plasticity simultaneously, for example, the Nb₂₅Mo₂₅Ta₂₅Ti₂₀W₅C_0.3 alloy exhibited an average yield strength of 1368 MPa and a plastic strain of 19.7%. The present findings provide useful guidance to address the conflict between the excellent corrosion resistance and high strength of advanced alloys. Full article

Elemental arsenic (As) is essential for diverse industrial applications. Most elemental As in China is produced by reducing gaseous arsenic trioxide (As₂O₃) with carbonaceous materials in steel reactors. This study aimed to extend the reactor lifespan through corrosion experiments and analysis. In this study, corroded regions of steel reactors were inspected after each production batch, and the corrosion process was examined. X-ray diffraction (XRD) was used to identify the major corrosion products, X-ray fluorescence (XRF) was used to measure the composition of corroded area, scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were used to inspect the features and elemental distributions of the corroded steel-plate cross-sections. The results revealed that the steel wall near the charcoal zone exhibited the highest corrosion rate. Tin (Sn), selenium (Se), and antimony (Sb) did not promote the corrosion process, whereas carbon (C) accelerated it by forming an Fe–As–C system at the grain boundaries of the steel matrix, characterized by a low melting temperature. The important source of C responsible for initiating corrosion was solid-state C particles originating from reused materials from previous batches. Additionally, owing to the high processing temperature, oxygen (O) was transferred to the inner side of the steel wall before the dramatical corrosion of the matrix by elemental As and C. Results of this study provide references to increase the lifespan of steel reactors for elemental As production. Full article

In this paper, a series of Co-free FeCr_0.6Ni_0.6(AlSi)_x (x = 0, 0.1, 0.12, 0.14, 0.16) high-entropy alloys (HEAs) were designed and fabricated by suction casting, and the effects of equi-molar (Al, Si) co-addition in these Fe-rich Fe-Cr-Ni-based HEAs on microstructure, mechanical properties, and corrosion resistance were systematically investigated. It is found that equi-molar (Al, Si) co-addition could cause the phase formation from FCC to FCC + BCC, while the morphologies of the phases change from dendrite-type to sideplate-type. Moreover, trade-off between strength and plasticity occurs with the increase in (Al, Si) co-addition, and the production of ultimate tensile strength and plasticity reaches the highest value when x = 0.12, while there exists a narrow region for x values to realize excellent comprehensive mechanical properties. In addition, similar corrosion resistance in 3.5 wt.% NaCl solution higher than 316L stainless steel could be realized in the HEAs with x = 0.12 and 0.14, while the latter one is slightly lower in pitting corrosion and the width of passive region, which is possibly caused by the increase in the density of phase boundaries. This work provides a novel insight on designing high-performance cost-effective Fe-rich and (Al, Si)-containing (Fe-Cr-Ni)-based HEAs combining high mechanical properties and corrosion resistance. Full article

In this study, the service behavior of an X65 oil and gas pipeline in seawater and production water environments was simulated by a corrosion experiment, and the influence of surface treatment (polishing and scratching) on its corrosion behavior was systematically analyzed. The corrosion resistance of the material was evaluated by means of scanning electron microscopy (SEM), an electrochemical test, and uniform corrosion rate calculations. The results show that the corrosion degree of X65 steel in an oilfield production water environment is significantly higher than that in a seawater environment. The uniform corrosion rate of the welding area is as high as 1.05 mm/y, which is more sensitive than that of the matrix material. The surface treatment has a significant effect on the corrosion behavior. The polishing treatment reduces the corrosion current density of the matrix material from 472.44 μA/cm² to 313.10 μA/cm², and the polarization resistance increases to 14.07 kΩ·cm², which effectively improves its corrosion resistance. The scratch treatment significantly reduces the corrosion resistance of the material, and the corrosion current density of the welding area at the scratch site is as high as 313.00 μA/cm², even more than that of the untreated matrix material. The study further points out that the scratches and welding areas generated during the pipeline cleaning process will significantly aggravate the tendency of local corrosion and pitting corrosion due to their microstructure heterogeneity. This study provides a clear theoretical basis and engineering guidance for the anti-corrosion design and maintenance of offshore oil and gas pipelines in complex water quality environments. Full article

The effect of CO₂ laser treatment on the surface composition and properties of a woven fabric (polyester (PET) fiber (59 wt%)/cotton (CO) fiber (31 wt%)/stainless-steel (SS) metal fibers (10 wt%)) was investigated across a range of laser intensities (19.1 × 10⁶ to 615.0 × 10⁶ W/m²). Elemental analysis using wavelength-dispersive X-ray fluorescence (WD-XRF) revealed that for an intensity up to 225.4 × 10⁶ W/m², the carbon content on the fabric surface increased while the oxygen content decreased, indicating thermally induced surface modification. Fourier transform infrared (FT-IR) spectroscopy confirmed that no new chemical bonds were formed, suggesting that the changes observed were predominantly physical in nature. High-resolution scanning electron microscopy (HR-SEM) showed progressive fiber fusion and surface smoothing with increasing laser intensity, consistent with polyester melting. Tensile testing demonstrated a significant decline in peak load and elongation at peak load with rising laser fluence, indicating mechanical embrittlement. Overall, CO₂ laser treatment alters the morphology and elemental composition of the fabric surface without inducing major chemical decomposition, markedly reducing its mechanical strength. Full article

The chemical composition, mineral composition, and mineral distribution characteristics of steel slag were characterized through petrographic analysis, X-ray diffraction (XRD), and particle size analysis. Limestone, silica, and silicomanganese slag were blended with converter steel slag to fabricate a reconstructed steel slag. Through burden calculation, the chemical composition ratio of this reconstructed steel slag approximated the silicate phase region. The high-temperature reconstruction process outside the furnace was simulated through reheating. The composition, structure, and cementitious characteristics of the reconstructed steel slag were investigated through X-ray diffraction (XRD), FactSage software (FactSage version 7.0 (GTT-Technologies, Aachen, Germany, 2015))analysis, scanning electron microscopy–energy dispersive spectroscopy (SEM–EDS) analysis, setting time determination, compressive strength measurement, and thermodynamic computation. The findings indicated that the primary mineral compositions of the reconstructed steel slag were predominantly silicates, such as Ca₃Al₂O₆, Ca₂SiO₄, Ca₂MgSi₂O₇, Ca₂Al(AlSiO₇), Ca₂(SiO₄), and FeAlMgO₄. In comparison with the original steel slag, these compositions underwent substantial alterations. The α′-C₂S phase appears at 1100 K and gradually transforms into α-C₂S at 1650 K. The liquid phase begins to precipitate at approximately 1550 K. Spinel exists in the temperature range from 1300 to 1700 K, and Ca₃MgSi₂O₈ melts into the liquid phase at 1400 K. As the temperature increases to 1600 K, the minerals C₂AF, Ca₂Fe₂O₅, and Ca₂Al₂O₅ gradually melt into the liquid phase. Melilite melts into the liquid phase at 1700 K. It was observed that the initial and final setting times of the reconstructed steel slag exhibited reductions of 7 and 43 min, respectively, in comparison to those of the original steel slag. In comparison with steel slag, the compressive strength of the reconstructed steel slag exhibited an increase of 0.6 MPa at the 3-day strength stage, 1.6 MPa at the 7-day strength stage, and 3.4 MPa at the 28-day strength stage. The reduction in setting time and the enhancement in compressive strength verified the improved cementitious activity of the reconstructed steel slag. Thermodynamic calculations of the principal reactions of the reconstructed steel slag at elevated temperatures verified that the primary reaction at 1748 K is thermodynamically favorable. Full article

In order to explore the influence of different current forms on the protection effect of cathodic protection systems for intelligent test piles of oil and gas gathering and transportation pipelines, X80 steel was taken as the research object to simulate the soil corrosion environment, and cathodic protection performance test experiments were carried out under three current forms: direct current (DC), conventional pulse (P) and high-frequency pulse (HP). Through a polarization curve test, electrochemical impedance spectroscopy (EIS) analysis, surface morphology observation and corrosion rate test, the effects of three current forms on cathodic polarization effect, polarization resistance, corrosion product composition and protection efficiency were compared. The results show that high-frequency pulse current can make the pipeline steel reach the protection potential in a shorter time, and under the same average current density, its polarization resistance is 23.6% and 15.8% higher than that of DC and conventional pulse, respectively. The anti-interference ability of conventional pulse current is better than that of DC. In the presence of stray current, the fluctuation amplitude of protection potential is only 21.1% of DC. The protection stability of DC is good, but the polarization speed is slow, and the phenomenon of “over protection” easily occurs in the process of long-term protection. Combined with economic analysis, high-frequency pulse current has significant advantages in high-corrosion-risk environments. Conventional pulse is suitable for stray current interference areas, while DC is more suitable for long-distance pipeline protection with low corrosion risk. The research results can provide a theoretical basis and technical support for the selection of the current form of pipeline cathodic protection systems. Full article

This study examines the influence of build orientation on the mechanical behavior of 316 stainless steel components fabricated by selective laser melting (SLM). Additively manufactured tensile specimens produced in different build orientations were experimentally analyzed and compared with reference specimens obtained from conventionally hot-rolled material and laser-cut to identical geometries. Uniaxial tensile testing combined with digital image correlation (DIC) was employed to evaluate the mechanical response and full-field strain evolution. Microstructural features were investigated using scanning electron microscopy (SEM), while phase composition was assessed by X-ray diffraction (XRD). The results reveal a pronounced orientation-dependent mechanical anisotropy in the SLM specimens, reflected in variations in yield strength, ultimate tensile strength, and ductility. Specimens loaded perpendicular to the build directions exhibited higher strength but reduced ductility compared to those loaded parallel to the build direction, whereas the rolled material showed a more isotropic mechanical response. Although the XYZ and XZY samples feature similar deposition patterns, the XRD analysis revealed a the existence of a $\left[220\right]$ texture. Thus, the mechanical performances of XZY specimens are about $10\%$ lower compared to XYZ printed samples. The stress maximum–strain curves were extrapolated from the true data using the Swift model. The section dedicated to numerical modeling includes a failure model based on the traixility. The numerical models were validated for the range $\eta \in \left[0.33\dots 0.45\right]$ specific to uniaxial tension. Fractographic observations further confirmed the correlation between build orientation, microstructural features, and fracture behavior. The present study provides a multiscale experimental framework linking processing conditions, microstructure, and mechanical response in additively manufactured stainless steel. Full article

This work addresses the influence of Ni on the natural passivation process of stainless steels (SSs) in alkaline media simulating concrete pore solution by a combination of electrochemical and X-ray photoelectron spectroscopy (XPS) surface analysis. It was found that the involvement of Ni in the passive film on the SS promoted Fe depletion at the passive film/substrate interface and increased the content of Cr oxide during natural passivation, thereby enhancing the corrosion resistance of the passive film. The passive film with Ni has a higher breakdown potential and can be more easily re-passivated compared with a passive film without Ni. Full article

This study investigated the efficacy of electrochemical treatment of a water-soluble cutting fluid (SCF) solution using Al, Fe, and stainless steel (SUS304) scraps as three-dimensional (3D) electrode packing materials. The SCF solution had an initial COD_Cr of approximately 109,000 mg·L⁻¹, a TOC of approximately 25,000 mg·L⁻¹, and an initial pH of 9.65. During treatment, the pH remained in the alkaline range (9.99–10.67), and the solution conductivity was approximately 1000 μS·cm⁻¹. Using a conventional two-dimensional (2D) configuration, Al exhibited the highest removal efficiencies (TOC: 58.55%; COD_Cr: 57.12%). An applied current of 0.8 A, corresponding to a current density of 5.00 mA·cm⁻² based on the geometric electrode area, and an inter-electrode distance of 40 mm provided an optimal balance between treatment performance and energy consumption. Under these optimized conditions, the introduction of metal scraps as 3D packing media significantly enhanced treatment efficiency. Al scrap (20 g) achieved the highest TOC removal (69.55%), while Fe scrap showed superior COD_Cr removal (87.42% at 40 g) with the lowest specific energy consumption (0.27 kWh·kg⁻¹ COD_removed). The energy consumption of the baseline D system was 0.46 kWh·kg⁻¹ COD_removed(cage O) and 0.72 kWh·kg⁻¹ COD_removed(cage X). Overall, scrap-based 3D electrodes effectively improved organic removal and energy performance, demonstrating their potential as low-cost and sustainable electrode materials for the electrochemical pre-treatment of high-strength oily wastewater. Full article