The intention of the present study is to review and compare the effect of various well-studied alloying elements on the microstructure and soft magnetic properties of the Fe-based ...amorphous/nanocrystalline system. The state-of-the-art Fe-based amorphous/nanocrystalline alloys have been developed because of their unique soft magnetic properties such as low core loss, high permeability(104–105 at 1kHz) and low magnetostriction (<10ppm) as compared to conventional silicon steels which are also called electrical steels. In Fe-based amorphous/nanocrystalline system, the chemical composition and microstructural features particularly grain size play an indispensable role on the saturated magnetization (Bs) and coercivity (Hc) values. An ideal Fe-based soft magnetic material is defined as a material possessing higher Bs and lower Hc. The problem of the new material is its low Bs value (for commercial material is 1.4T) than silicon steels (≈2T). In addition to Bs content of new material, many attempts have been made to reduce the Hc value which could be achieved via a decrease of grain size (<50nm). To reach this goal (Bs↑ and Hc↓), the effect of a variety of elements on the microstructure, crystallization process and soft magnetic properties of the Fe-based amorphous/nanocrystalline alloys has been investigated so far. The aim of all these studies is to find an appropriate replacement for conventional silicon steels because of their high core loss and low permeability. Effect of alloying elements including Si, B, Cu, Nb, Zr, N-doping, P, Ni, Co, H-doping, Ge and W on the microstructure and magnetic properties is the main subject of this study in order to shed light on the dependence of magnetic properties with composition and grain size.
•N-doped alloys showedsuperior soft magnetic properties.•Cu and Nb are the most effective elements in refining grain size.•Soft magnetic properties highly depends on the primary composition and grain size.
The intention of the present study is to investigate the effect of laser energy density on the microstructure, post-heat treatment response, and wear properties of additively manufactured 17-4 P H ...stainless steel. Microstructural characterisation techniques such as Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Electro Back Scatter Diffraction (EBSD) and thermal analysis methods such as Differential Scanning Calorimetry (DSC) and Dilatometry (DIL) were employed to attain the quantitative information about the microstructural evolution and phase transformation before and after conventional heat treatment (solution + aging). It was shown that applying higher energy density resulted in a slightly more retained austenite perhaps due to the lower cooling rate. The response of the 3D printed material to post-thermal treatment was affected by the initial energy density enabling us to control the final volume fraction of austenite. Significant grain refinement was observed in the heat-treated specimens. Solution treatment at 1040 °C led to the formation of retained austenite and precipitation of M23C6/M7C3 carbides (M = Cr, Mo) and NbC carbides. The increase of solution time from 1hr to 4 hrs increased the volume fraction of carbides (NbC, M23C6 and/or M7C3) precipitated during solution treatment and decreased the volume fraction of retained austenite due to the localised change in the chemical composition of the matrix around carbides and rise of Ms temperature. Subsequent aging at 472 °C for 1hr led to the precipitation of further carbides (and Cu-rich clusters) in the matrix forming Ni-rich regions promoting the formation of reverse austenite in the matrix. The amount of the precipitated carbides and reverse austenite was more severe in those samples solutionised at 1040 °C for 1hr rather than 4 hrs regardless of the initial energy density. The indentation results showed that the sample subjected to the lower energy density did not respond well to the conventional heat treatment on 17-4 PH stainless steels as expected; however, the increase of energy density improved the post-thermal treatment response. The reciprocating dry sliding wear resistance of the as-printed sample subjected to the energy density of 53.12 J/mm3 was considerably better than that of 73.40 J/mm3. We showed that the initial energy density of the additively manufactured samples could have a significant influence on the wear resistance of post-thermally treated samples and results in different wear behaviour. The main wear mechanism was oxidation and delamination of the iron oxide layer from the surface.
•The initial energy density has a significant influence on the post-thermal treatment response.•Conventional heat treatment resulted in the precipitation of carbides and formation austenite.•Thermal history and ratio of austenite to carbides control the wear behaviour.•The formation and delamination of oxide film was the main wear mechanism and led to lower coefficient of friction.
The present study was conducted to investigate the root cause failure analysis of 316L stainless steel air tube inlets at the weld joint in a High-Speed Power turbine (HSPT). Fractography analysis ...revealed ratchet marks and striations on the fracture surfaces, indictive of vibration-induced fatigue in the heat affected zone of the tube-to-flange weld joint, resulting from the rotation of the HSPT at high speed, identified as the primary cause of failure. Additionally, radiography and visual inspection unveiled a sharp interface between the weld metal and parent metal within the inner wall, acting as a stress riser. X-ray diffraction analysis demonstrated that the parent metal predominantly consisted of austenite (γ), while the weld metal comprised a mix of austenite (γ, ≈ 90%) and delta ferrite (δ, ≈ %10). Hardness readings in the weld zone ranged from 260–302 HV, compared to ≈ 140 HV in the parent metal. Microstructural examination showed inclusions and impurities rich in manganese, and silicon, likely introduced during manufacturing and/or welding processes. Conclusively, the study attributes failure to the use of low-quality materials and consumables, poor welding practices, and insufficient vibration condition monitoring.
Al–Si alloy is widely utilized in automobile pistons and cylinders due to good castability, high strength-to-weight ratio, excellent thermal conductivity, good resistance to corrosion/oxidation, and ...acceptable wear resistance. To increase the efficiency of engine motor, it is imperative to modify and engineer the microstructure of Al–Si alloy to enhance the high-temperature behavior. For this reason, in the current study, different concentration of Ni (0.8% and 2%) was doped into Al–Si alloy during casting to generate various Ni-rich intermetallic compounds within the alloy matrix. AlNiCu, AlCu, AlFeSi, and Mg
2
Si were found to be the main intermetallic compounds precipitated within the dendritic and interdendritic regions, which could enhance the thermal stability and high-temperature performance. High-temperature compression test at high temperatures ranging from 400 to 550 °C and at different strain rates ranging from 10
−3
to 1 s
−1
was carried out to develop high-temperature processing map and optimize the hot workability parameters of Ni-doped Al–Si alloy. The maximum power dissipation efficiency (
η
) was observed within the temperature range of 450–500 °C and strain rate of 0.05–0.08 s
−1
(lower strain rate) for Al–Si–0.8%Ni alloy and within the temperature range of 450–500 °C and strain rate of 0.3–1 s
−1
(medium to high strain rate) for Al–Si–2%Ni alloy. Dynamic recrystallization was found to be the primary softening mechanism at high temperatures (
T
> 450 °C).
Graphic abstract
The present study was undertaken to determine the amount of residual stress on the surface subjected to Tungsten Inert Gas (TIG) welding process in different protective gas environments (Ar-xN2, ...x = 20, 30 and 40 volume percent). It was shown that the increase of volume fraction of N2 gas in the welding environment led to more residual stress mainly due to the higher heat input. Nanoindentation technique was employed to obtain the variations of residual stress when Ar-40N2 protective gas was in use. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) method were used for microstructural study and phase identification. It was shown that applying higher heat input followed by quenching induced fully martensitic structure with very little amount of retained austenite. In addition, the magnitude of the residual stress in the TIG-treated area was measured to be ≈ 381 MPa using nanoindentation technique which was higher than the base metal. The type of residual stress was compressive which could be helpful for enhancing the surface properties and wear resistance of the alloy as a hip implant.
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•TIG welding introduced large number of defects providing nucleation sites for ε martensite embryos.•Nanoindentation showed the generation of compressive residual stress within the TIG-affected zone.•Fcc .→ hcp phase transformation was completed under Ar-40%N2 atmosphere due to the increase of thermal conductivity,•ε martensite and compressive residual stress led to higher hardness and better wear resistance.
Al–Si eutectic alloys could be an alternative for gray and compacted graphite cast iron engine blocks due to their excellent thermal conductivity, low density (resulting in weight reduction and fuel ...efficiency), and good combination of strength and ductility. However, microstructural softening at service temperature (170–250 °C) due to coarsening/coalescence of metastable precipitates and low wear resistance are a stumbling block limiting their usage in engine components. To meet endless demands for fuel-efficient car engine (i.e. higher temperature and pressure in combustion chamber), optimization of current chemical composition seems to be essential. For this reason and in the present study, different concentration of Ni (from 0.8% to 3.5%) was doped into a eutectic Al–Si alloy to investigate tribological, corrosion, and hot deformation properties. It was pointed out that Al–Si eutectic alloy containing 2–2.6% Ni had the highest wear resistance due to uniform dispersion, skeleton-type morphology of Ni-rich intermetallic compounds, and their better bonding with the matrix. Oxidation and delamination of oxide layer was shown to be the main wear mechanism. The presence of (Ni,Cu)-rich intermetallic compounds increased the corrosion rate by ≈ 60%; however, the repassivation potential was found to be slightly higher in 2.6%Ni sample indicative of easier repassivation of micropits. To better understand the high temperature behavior of Ni-containing Al–Si alloy, hot compression test was carried out within the temperature range of 400–550 °C and strain rates of 0.001 to 1s−1 and constitutive equations were used to develop hot deformation processing maps. The presence of Ni-rich intermetallic compounds enhanced the hot deformation behavior and increased the activation energy for hot deformation. Dynamic recrystallization was found to be the main softening mechanism during hot deformation. At true strain of 0.6, the maximum power dissipation efficiency (≈54%) was obtained at 400 °C and a strain rate of 0.01s−1.
The present study aimed to delve into the root cause failure analysis of a carbon steel member (Grade Q235C) within a high-voltage transmission tower which was subject to self-weight (approximately ...43 kg) and wind load only (calculated at 2787.35 Pa). Examination of the fracture surface revealed the presence of beach marks and ratchet marks which indicates that the carbon steel member (a square hollow section equipped with two bolted supporting plates positioned 1.7 meters away from the failed welded plate) experienced failure attributed to wind-induced fatigue along the weld joint. No abnormalities were observed in the microstructure and the weld zone predominantly featured a ferrite phase and grain boundary pearlite. However, the finite element analysis conducted using Abaqus software demonstrated that the steel member at the weld joint should not have failed under normal circumstances. The critical finding was that the failure occurred due to the loosening of bolted supporting plates located within a distance of 1.7 meters from the welded joint. As a consequence of the supporting bolted joint becoming loosened, a Von Mises stress of approximately 400 MPa manifested at the welded joint, resulting in an abrupt failure.
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•Root cause failure analysis of studs using experimental and computational methods.•Studs failed due to corrosion-fatigue mechanism.•The presence of corrosive agents such as sulphur ...and chlorine may have accelerated the corrosion rate.•Finite Element Analysis (FEA) determined the critical crack size to be 2C = 0.6 mm, and a = 0.5 mm.
The objective of this study is to conduct a root cause failure analysis on wind turbine fasteners constructed from carbon steel Grade 10.9. The presence of corrosion pits at the thread root, as well as beach and ratchet marks on the fracture surface, suggests that the fastener failed due to a corrosion-fatigue mechanism. The microstructure of the failed fastener predominantly consisted of 98 % tempered martensite, with some bainite and a small amount of chromium carbides, which is characteristic of quenched and tempered low alloy steel. Magnetic particle testing revealed similar crack marks on other fasteners in similar locations, indicating the points of maximum stress in these fasteners. Furthermore, finite element analysis using Abaqus software demonstrated that for a corrosion pit to grow, it required a minimum pit length and depth of 0.5 mm and 0.6 mm, respectively.
•1- FFS assessment was conducted on a gas separator pressure vessel containing using finite element analysis (FEA)•2- Different load scenarios were considered using elastic-perfectly plastic stress ...analysis.•3- Level III assessment considered the influence of residual welding stresses on both longitudinal and circumferential cracks.•4- The HIC affected area fell within the acceptable region of the failure assessment diagram (FAD) during the evaluation in level III.
Hydrogen-induced cracking is the cracking of carbon steel or low-alloy steel in a wet H2S environment, driven by the diffusion of hydrogen atoms into the steel due to corrosion reaction. The formation of blisters and hydrogen-induced cracks in pressurized components in the oil and gas or petrochemical industries imposes a serious risk to personnel safety and production continuity. In this study, a fitness-for-service assessment of a gas separator pressure vessel containing 3.76 % H2S and 3.47 % CO2 was analyzed using finite element analysis as required by level III assessment in API 579–1/ASME FFS-1 2021. Different load scenarios, including internal pressure, static head from liquid, dead weight, and wind loads, were considered using elastic-perfectly plastic stress analysis. The hydrogen-induced affected area, with dimensions of 2650 mm × 900 mm, was shown to sustain an internal pressure of 14.8 MPa, which is above 1.35 times the design pressure (i.e., 12.1 MPa). The assessment of API 579–1/ASME FFS-1 in level I and II failed due to the presence of a hydrogen-induced crack near the weldment. However, the evaluation in level III assessment considered the influence of residual welding stresses on both longitudinal and circumferential cracks in their as-welded state. The findings indicated that the affected area fell within the acceptable region of the failure assessment diagram, thereby confirming the continued safe operation of the HIC damaged pressure vessel while accounting for welding residual stresses.
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•Fitness-for-service assessment (FFS) using API 579 methodology was used to examine the condition of the crack.•Finite element analysis (FEM) using Abaqus software showed the ...distribution of residual stress after welding.•Fatigue striations were observed on the fracture surfaces emanating from multiple areas.•Poor welding joint and steam hammering led to vibration-induced fatigue and caused premature failure.
Fitness-for-service assessment (FFS) is employed in oil and gas refiners to assess the structural integrity of an in-service pressure vessels and storage tanks that may contain a flaw or damage. API 579/ASME FFS-1 standard provides guidance for conducting FFS assessments using methodologies specifically prepared for pressurized equipment. In the present investigation, FFS assessment (level 3, based on the Failure Assessment Diagram (FAD)) carried out on a 304 demineralized water stainless steel pipeline containing a crack at weldment eleven months before the failure is explained in detail. Despite the FFS assessment and acceptance of the pipeline, failure occurred eleven months after the FFS assessment. The distribution of the residual thermal stress introduced during welding was estimated by means of Finite Element Analysis (FEA) using Abaqus software. Further investigation revealed that the operating condition of the DM pipeline deviated from the date of FFS assessment and the failed pipeline had been under vibration. Defects such as inclusions and porosities and irregular shape of weld bead were observed in weld joint showing lack of proper quality control (QC) during welding and installation of the pipeline. The heat affected zone (HAZ) region was found to be sensitized (perhaps due to the improper welding procedure during installation) and severe precipitation of chromium carbides was observed on the grain boundaries. Further investigation showed the transgranular nature of the crack propagated perpendicular to the weld metal as a result of the dynamic loading caused by steam hammering effect leading to the vibration-induced fatigue. The Scanning Electron Microscopy (SEM) of the fracture surfaces showed that the fracture surfaces consist mostly of fatigue striations and quasi-cleavage fracture.
