Herein, industrial-scale extruded profiles of aluminum alloy (AA) 7108 with rectangular cross-sections of dimensions 25.60 mm x 15.95 mm were used to investigate the effect of number of passes and strain rate on their crystallographic texture. After the initial microstructural and textural characterization, the samples were solution-annealed and cold-rolled using different numbers of passes to achieve the same degree of reduction. The samples that were cold-rolled for a few number of passes exhibited a remaining Cube texture component {001} <001> (similar to that observed in the AA 7108 as-received bars), a Goss component {011} <001>, and a Brass component {011} <211>. In contrast, the samples rolled for a high number of passes demonstrated only a strong Goss component {011} <001>.

This research investigates the influence of carbon content on the cavitation erosion behavior of three cast Fe-25Cr-5Ni duplex alloys containing 0.02, 0.12, and 0.37

Aged maraging steels offer unique strength and toughness via the presence of finely dispersed precipitates, allowing the material to reach values of up to 2400 MPa in yield strength in the case of 18Ni350. However, when aging heat treatments above 550°C are conducted, simultaneous precipitation and austenite reversion can occur changing the mechanical behavior of the material. Although many studies related to the physical metallurgy of maraging steels have already been published, less attention has been given to a detailed understanding of the initial formation of austenite and its relationship with the precipitates. In this study, undeformed and cold rolled commercial 18Ni350 maraging steel samples were submitted to short aging heat treatments of 1800 s at 600, 650, and 700 °C. The influence of the initial microstructure on subsequent phase evolution was studied using in-situ synchrotron X-ray diffraction and final microstructural products using transmission electron microscopy and atom probe tomography. Results show that cold rolled samples did not present faster kinetics of transformation of reverted austenite as expected, but this condition presented austenite in a different morphology than the undeformed condition. However, cold rolling changed the morphology of reverted austenite from elongated (undeformed case) to equiaxed; and induced a higher density of smaller Ni3Ti and Fe2Mo precipitates, especially after low-temperature aging. Besides, the deformation extinguished retained austenite, which influenced the reverted austenite formation, concluding that the simple increase in dislocation density is not a unique and direct factor to increase the reverted austenite kinetics.

In this research, the microstructure of three melt-spinning ribbons with a weight-based composition of Fe-25Cr-5Ni and varying carbon contents (0.02, 0.10, and 0.38 wt%) is evaluated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used for microstructural characterization. SEM analyses consist of image acquisition and electron backscatter diffraction. TEM analyses consist of bright-field image acquisition, selected area electron diffraction, high-resolution TEM, and local chemical composition measurements by energy-dispersive X-ray spectrometry. According to the results, the ribbons show different microstructures resulting from different solidification paths. The ribbon containing 0.02%C presents a predominantly ferritic microstructure, and austenite solid-state precipitation is not suppressed. It occurs as grain-boundaries allotriomorphs and secondary Widmanst & auml;tten side plates. As a result of carbon additions, the ribbon containing 0.10%C shows a microstructure composed of nearly equal parts ferrite and austenite, along with M23C6 (M = Cr15.6Fe7.4) nanometric carbides. The cube-on-cube orientation relationship is found between M23C6 and austenite. Lastly, the ribbon containing 0.38%C exhibits austenitic microstructure with islands of ferrite surrounded by M7C3 (M = Cr4.14Fe2.86) carbides.

Maraging steels are one of the highest strength steels commercially available. The new versions are known as ultra-high strength maraging (UHSM) steels and can offer yield strength values over 3 GPa. The aim of this investigation was evaluating the electrochemical behavior of three non-commercial/laboratory UHSM steels containing 13Ni–15Co and Mo content variations (7.5, 11 and 15 wt%). The UHSM steels were annealed at 1000 °C and studied at different conditions (non-aged and aged at 480 °C for 3 h and 6 h). As reference material, a commercial maraging steel (18Ni–9Co–5Mo) heat treated according to typical recommendations (annealed at 820 °C for 1 h and aged at 480 °C for 4 h) was used. The UHSM presented considerable higher hardness than commercial maraging. Comparing between the UHSM steels, the samples treated for 6 h do not contribute to increase the hardness when compared to those of 3 h. The electrochemical tests in hydrochloric aqueous solution showed that commercial maraging steel and the UHSM containing most Mo (11 wt%) aged by 6 h presented the worst corrosion resistance while the best performance was obtained by the samples with 7.5 and 11 wt% Mo aged for 3 h.

Although delta ferrite is a very common phase in most austenitic stainless steels, studies about its formation and evolution during slab processing from industrial heats of tens of tons are scarce. The main objective of this research is to study the evolution of delta ferrite (quantity, chemical composition, morphology, and distribution) along the production route from the cast slab to the coil of an industrial heat of 80 tons of 304 stainless steel. Samples were extracted after the following processing steps: continuous casting, first and second hot-rolling pass, and solution-heat-treating, arriving at the final commercial condition. Sample analyses were carried out with several complementary microstructural characterization techniques: optical microscopy, scanning electron microscopy with energy dispersive spectroscopy (EDS), X-ray diffraction, and magnetic measurements of delta ferrite content (feritscope). Thermocalc® indicates that the present continuous cast slab solidifes according to the FA (ferrite-austenite) mode and the final microstructure should be completely austenitic in equilibrium conditions. Nevertheless, delta ferrite is detected along the processing steps, indicating that the steel is out of phase equilibrium. The ferrite content measured after solidification varies significantly across the as-cast slab thickness. Lower values are detected on the surfaces, followed by a gradual increase when moving into the slab, reaching a peak, and finally decreasing at the slab center. This pattern of delta ferrite content is named "M type" distribution. The average content of delta ferrite decreases after each subsequent processing step, namely the two hot-rolling passes and the solution heat-treating.

The failure of an AISI 316 austenitic stainless-steel pipe used in a hydrotreatment plant was investigated. Circumferential cracks starting from outside the pipe and parallel to the weld were identified in the pipe elbow. The failure occurred after three years of plant inactivity and exposure to the atmosphere. The pipe was operated regularly for 16 years at a temperature of 515 °C before failure, having undergone phase transformations that made the steel susceptible to intergranular attack, followed by stress corrosion cracking at room temperature. The preferential precipitation of chromium-rich M23C6 carbides at the grain boundaries allowed the occurrence of sensitization, which, associated with the residual tensile stresses caused by the welding process and the presence of chlorine from industrial atmosphere concentrated under insulation, were responsible for the failure by stress corrosion cracking.

This study offers valuable insights into the precipitation behavior of 13Ni maraging steels, emphasizing the role of molybdenum content in their microstructure, strengthening, and precipitate evolution. Precipitate morphology and crystallography were examined using a combination of high-resolution transmission electron microscopy and selected area electron diffraction. Strengthening mechanisms were assessed through Vickers hardness measurements. All the examined samples exhibited a lath martensite microstructure and displayed an increasing hardness over the aging time. The molybdenum content not only influenced the presence of retained austenite in the initial microstructure but also affected the type of precipitates formed during the early aging stages. Initially, Ni3Mo precipitates were formed, succeeded by the formation of more stable Fe2(Mo,Ti) Laves precipitates. The ultra-high strength of 13Ni maraging steels arises from the combination of the precipitate type and size distribution. The base composition of 13Ni maraging steels achieved a peak hardness of 798 HV1 through the precipitation of Laves Fe2(Mo,Ti) phases ranging from 3 to 14 nm in diameter.

The effects of forced convection on the microstructure, macrostructure and macrosegregation of impurities in cylindrical ingots obtained by directional solidification of metallurgical grade silicon were examined. Two experiments were carried out, one without and another with the forced convection induced by a disk at the melt top rotating at 120 rpm during solidification. In the two resulting ingots, two regions exist: (1) a lower region extending from the bottom of the ingot up to 8 mm (without rotation) or 75 mm (with rotation) of columnar grains with straight boundaries, aligned in the heat extraction direction and free from intermetallic particles (except SiC); (2) an upper region of columnar grains with serrated boundaries and intermetallic particles. The lower region, which increases from 8 to 75 mm with disk rotation, is purified and displays concentrations of metallic impurities (except Al) below the recommended limits for solar grade silicon feedstock. The macro/microstructures suggest that the lower region solidified with a planar solid–liquid interface, which changed to cellular/dendritic in the upper region. A mathematical model indicates that, although forced convection increases the growth velocity and decreases the temperature gradient in the liquid, which are detrimental to the stability of a planar solid–liquid interface, convection also decreases the concentration gradient in the liquid, increasing stability.

Young modulus and toughness (KIC) of bulk solar grade silicon (SoG-Si) obtained by directional solidification of metallurgical grade silicon were determined. The Young modulus was measured by the technique of impulse excitation of vibration and KIC was determined using the indentation method. Measurement values agree well with those available in the literature. The indentation method proved to be a reliable, relatively simple, inexpensive, and fast experimental method to measure KIC in SoG-Si.

Maraging steels are martensitic steels hardened by intermetallic compounds that precipitate during aging heat treatments. During aging of these steels complex phenomena involving nucleation and growth of several phases as well as changes in the precipitates, morphology and stoichiometry take place. The present work aims to study the kinetics of precipitation in a maraging 350 steel through the KJMA and Austin-Rickett (AR) equations. Analysed data were obtained from Vickers microhardness measurements carried out in samples heat-treated between 440 and 560 °C. Variation in the n-constant has been observed for both equations, indicating changes in the precipitation behavior. However, the n-constant values obtained from AR equation follow the microstructural changes observed in previous works on maraging steels. Interpretation of the n-constants using the AR equation was linked to the precipitation on dislocations at 440 °C, the growth of finite long cylinders in comparison to their separation at 480 °C, and general particle growth from small dimensions at 520, and 560 °C.

Maraging steels are precipitation hardening alloys that can achieve an ultra-high yield strength (~3 GPa), however associated with low toughness. During exposure to high temperatures, an oxidation process occurs on the surface of these steels, generally, the oxides formed are hematite and/or magnetite. The aim of this study was to investigate oxidation on a maraging 13Ni15Co10Mo at annealing temperature of 900 °C. The bulk microstructure was investigated by several complementary techniques and the oxidized surface was characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and X-ray Diffraction (XRD). The results showed that the bulk microstructure, at annealed condition, consists of a lath martensite with a hardness of round 400 HV. The most external and oxidized surface contains the oxides hematite, magnetite and kamiokite. Finally, the presence of austenite was detected in the first 2 μm below the surface. Chemical microanalysis indicated that the austenite is stable at room temperature in this region due a composition gradient that makes this region rich in nickel and cobalt. The composition gradient is due atom diffusion during oxides formation. Austenite near to the surface is very convenient as it could avoid crack initiation and propagation, improving toughness.

In the present study four different precipitate extraction techniques were investigated on a 3003 aluminium alloy samples (twin-roll cast and homogenized conditions). The dissolution product was analyzed with the help of X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. The performance of four chemical solutions (iodine solution, perchloric acid, oxine solution, and phenol solution) was compared, and the phenol solution presented the best precipitate extraction results. The phases in the cast and homogenized microstructures were identified, explaining some aspects of the phase transformation during the homogenization.

The main objective of the present work was to characterize the phases that are present after solution annealing in the microstructure of the titanium stabilized austenitic stainless steel W.-Nr. 1.4970, developed as a candidate material for fast breeder reactor fuel cladding. The crystalline structure, chemical composition, quantity, size, morphology, and distribution of the phases present in the microstructure after solution annealing heat treatments were studied in detail with the help of several complementary techniques. Chemical dissolution of the matrix has been performed using the Berzelius solution and the extracted residue has been analyzed by X-ray diffraction in a high precision camera. Three phases have been observed and identified after solution annealing heat treatments performed in the 1090 to 1300 °C temperature range, namely: (Ti,Mo)C; Ti (N,C) and Ti4C2S2. The Ti-nitride and the Ti-carbosulfide did not dissolve in the steel matrix up to 1300 °C, on the other hand, the solubility of the (Ti,Mo)C raised strongly with temperature. A solution annealing heat treatment is recommended for the W. Nr. 1.4970 stainless steel.

Abstract This study evaluated the as-cast microstructure of three alloys based on Fe-25%Cr-5%Ni weight (wt.) composition whose carbon content is 0.02 wt.%, 0.12 wt.%, and 0.37 wt.%, respectively. Thermocalc was applied to predict the possible phases that could be formed during the cooling of each alloy and then the cross-sections of the ingots were characterized. The first alloy, with 0.02 wt.%C, presented a microstructure composed of ferrite and austenite, which was formed through solid-state precipitation. The second alloy, with 0.12 wt.%C, showed a microstructure formed by ferrite, austenite from the peritectic reaction (L + δ → γ) and M23C6 (M=Fe, Cr) carbide. Finally, the third alloy, with 0.37 wt.%C, exhibited a microstructure formed by dendrites of ferrite and austenite, also formed according to the peritectic reaction (L + δ → γ), with an M23C6 (M = Fe, Cr) and M7C3 (M = Fe, Cr) carbide network in the interdendritic regions.

Maraging steels are among the highest strength steels commercially available. Despite being relatively rare and expensive, they may present a yield strength around 3 GPa and are indispensable for various applications. In the present paper, several aspects will be reviewed related to maraging steels including a brief history of its development, microstructure and acting hardening mechanisms, loss of toughness with the tensile strength increase, resistance to oxidation, and corrosion, nitriding behavior, and future perspectives.

A Nb-50(wt.)%Ti alloy was melted and remelted in an electron beam furnace and the cast ingot was subsequently deformed into a bar by cold swaging, undergoing a maximum reduction in the area of 90%. Samples of the cold deformed bar were subjected to isochronous annealing cycles for 1 h in the temperature range between 250 and 1000 degrees C. The microstructural changes of the samples were monitored by optical microscopy, scanning electron microscopy with backscattered electron diffraction (EBSD), X-ray diffraction for pattern and texture determinations, and Vickers microhardness measurements. Recovery is the main softening mechanism in the samples annealed at temperatures up to 600 degrees C, but recrystallization is significant at temperatures equal to or above 750 degrees C and might also contribute to softening. Grain growth is also noted after annealing at the temperatures of 900 degrees C and 1000 degrees C. The microstructures of the cold deformed sample and of the samples annealed at temperatures up to 600 degrees C display a curly structure caused by deformation bands and their dislocation substructures. At the annealing temperatures of 900 degrees C and 1000 degrees C, complete recrystallization occurs and eliminates the deformation bands, but the curly pattern still exists and is probably due to a residue of the microsegregation of elements that occurs during solidification of the ingot. An intense fiber texture that is typical of cold swaging is observed in the cold deformed sample and in those annealed at temperatures up to 750 degrees C, but annealing at temperatures of 900 degrees C and 1000 degrees C weakens this texture owing to complete recrystallization. The results of the present work show the importance of the strong interactions among the phenomena of recovery, recrystallization, and micro segregation in determining the microstructure and texture of cold deformed and annealed Nb-Ti alloys. (c) 2021 Elsevier B.V. All rights reserved.