1,721,104 research outputs found
Mechanical and microstructural characterization of metals and alloys
Full text linkIn order to design a fully functional manufactured component the designer needs a deep understanding of the materials behavior, which includes not only its in-service performance but also the effect of the processing routine. This knowledge is essential for the efficient use of resources, which can give positive fallout, both economic and environmental.
Material properties are usually investigated through laboratory testing, but this practice can be unfit to mimic actual working conditions, so it is crucial not only to describe the materials’ response on a laboratory scale, but also to explore the underlying active mechanisms on a physical basis. This task can be accomplished if the materials’ properties are interpreted in the light of microstructure analysis.
In reference [1], the authors face a biocompatibility issue regarding implant materials. The performance of the base material, the relatively common Ti-6Al-4V, was measured in terms of corrosion resistance in Ringer’s solution, and significant improvements were observed after a heat treatment routine which enhanced the β-phase content. The presence of this phase was detected through X-ray diffraction analysis and scanning electron microscopy observations. Therefore, a process-related feature (namely, heat treatment) led to a higher performance, and microstructural analyses explained why it happened.
Another example of the complex relationship between the desired properties and the process routine can be found in reference [2]. A Co-Cr-Mo alloy can be a good option as a biomaterial because of its excellent mechanical properties, corrosion resistance, and biocompatibility. These features are limited by limited workability, which makes it difficult to achieve the desired shape. This can be done with a novel technique, developed by the authors, and already used with other high melting point materials with low workability.
In reference [3], the authors focused on the optimal solution to the problem of joining a high entropy alloy, a relatively new class of materials with outstanding properties, with a 316 stainless steel through brazing. The authors found an effective way to join a “new” material to an “old” one, which could lead to new applications.
The examples here provided show that, with the aid given by laboratory analyses, it is possible to understand not only what the best solutions are, but also why they are so. In this process, new ideas may arise, in a continuous effort towards improvement
Ni-Based CW6MC: Effect of the Internal Revert Recycle on the Soundness of the Alloy
Full text linkThe CW6MC alloy is a nickel-based alloy used to withstand acidic environments, especially in the oil and gas industry where it is used in the production of valves, impellers, and pipes. This alloy is the foundry counterpart of the best known A625 for plastic deformation. Regarding nickel-based alloys, a scrap market like that in the case of steel has not yet been established, therefore, especially in the case of foundries, scrap generally comes from internal recycling (casting waste, feeders, sprues, runners, etc.) to be certain of the origin and quality of the material. In this work, four castings with different percentage of recycled content (0%, 30%, 70%, 100%) were produced in accordance with the technical specifications and analysed to evaluate the effect of scrap on the final chemical composition, the microstructure, the mechanical properties and corrosion resistance. Following the analyses carried out, it was determined that the amount of acceptable scrap content (of those analysed) without compromising the material properties corresponds to 30%
An overview of austenitic stainless-steel rock anchors damage in an environment rich with chlorides
No full textThe failure of rock anchors in exotic beaches can change a fun climbing holiday into a tragedy: austenitic stainless-steel bolts can break because of an underhand and insidious form of corrosion that does not show itself before it is too late.The failure analyses performed in this study on corroded bolts, the huge amount of information reported in literature and the presence of three unmistakable conditions (material, stress and environment) lead us to think that the eventual damages are due to stress corrosion cracking (SCC), in turn due to an unlucky combination of events.After analysing the corrosion, excluding production mistakes in the base material (e.g. steel sensitization) or during installation into the rock (e.g. galvanic connection), we have characterized commercial AISI 304 L expansion bolts and conducted focused experiments in order to understand the main factors involved with the aim to explain the origin of SCC. After this preliminary part, a specific SCC test has been set up to understand the susceptibility of the commercial bolts. The discriminating factor is the process route in terms of resulting surface finishing and hardness; however, all the bolts show more or less the same resistance to corrosion
Mechanical Response of Ni-Based CU5MCuC Alloy to Different Stabilization Thermal Treatments
Full text linkThe Ni–Fe–Cr system is the basis of a series of commercial alloys featuring chemical–physical characteristics that allow them to be used in a variety of fields where excellent resistance to aggressive environments is required. In this scenario, the CU5MCuC alloy, the foundry counterpart of Alloy 825, is proving successful in the petrochemical field thanks to its good corrosion resistance in acidic and highly oxidizing environments. Intergranular corrosion resistance, critical for this material, is ensured by the stabilization treatment that allows precipitation of Nb carbides. Strengthening of this alloy takes place only via a solid solution. Therefore, its mechanical properties depend on the solution annealing treatment: often this treatment alone does not make it possible to reach the UTS imposed by the ASTM-A494 standard. In this work, the possibility of using stabilization treatment to increase mechanical strength as well was considered. Treatments, with different combinations of time and temperature, were carried out in order to modify the material’s microstructure. After the thermal treatments, microstructural analyses, mechanical tests and (pitting and intergranular) corrosion and resistance tests were carried out to identify optimal treatment parameters in order to promote the evolution of microstructural constituents capable of improving mechanical strength without decreasing corrosion resistance. The treatment that achieves the best compromise between mechanical properties and corrosion resistance is stabilization at 970 °C for 4 h
Reclassification of Spheroidal Graphite Ductile Cast Irons Grades According to Design Needs
Full text linkThe classification of grades inside a material family should be based on the properties required by design procedures. This paper proposes a reclassification of spheroidal graphite ferritic pearlitic and ausferritic (ADI) ductile cast irons grades based on yield strength (YS), strength ratio (SR) UTS/YS and elongation at fracture (EF). In fact, these parameters are fundamental for the static assessment according to the procedures FKM Guideline and BS 7910:2005. Static assessment at room temperature, involving plastic deformation and depending on the wall thickness and stress state triaxiality, is here proposed as the most significant for the material classification. All other properties (e.g., fatigue under cyclic loads, high strain rates and temperature effect, etc.) should be reported with reference to the classification mentioned above. SR and EF control the plastic deformation at the notch tip, where maximum calculated elastic stress is redistributed. Minimum YS is usually assumed as the basic parameter for static and cyclic loading design. Because of the inverse relationship that exists between strength and ductility, Brinell hardness control and material quality index should be adopted as Material Quality Control tools, preventing from a too low EF. Fracture Toughness and its ratio with YS must be considered for preventing brittle fracture due to the presence of flaws. Fracture toughness definitions and available data are not sufficiently consistent for a correct comparison between different material grades. A surrogate Charpy energy measurement is indicated for an indirect estimate of toughness
Jarosite wastes reduction through blast furnace sludges for cast iron production
No full textJarosite is a dangerous waste derived from the hydrometallurgical route of zinc production, and it cannot be safely disposed of due to its acidic pH and the risk of toxic metal leaching. A new process at laboratory scale for the utilization of jarosite sludges is proposed, with the aim to obtain cast iron and an inert slag, using blast furnace sludges as reducing agent. Jarosite-reducing agent mixes were reduced in a muffle furnace at 1500 °C for 15 min. Two reducing agents were used: pure graphite (as control) and blast furnace sludges. Two CaO concentrations (5, 15%wt. on jarosite mass) and four equivalent C concentrations (7.5, 15, 30, 60%wt. on jarosite mass) were analysed. Cast iron was obtained from all of the mixes, but the highest reduction yield was obtained at 15%wt. equivalent C. The slag obtained from the control batch had a fully crystalline structure, while the one related to the sample with BF sludges showed an incipient vitrified structure, that could prevent the leaching of hazardous elements. The best process parameters to profitably obtain cast iron and a glassy slag are 15% of equivalent C, 5% CaO and blast furnace sludges as reducing agent
Lack of correlation between serum ferritin and liver iron concentration in beta-zero thalassemia intermedia
No full textWeldability Investigation on Lightweight Steels
No full textA novel class of AHSS (Advanced High Strength Sheet) for the automotive sector is under development. Such steels are featured by high Mn and Al content, low density (16% lower than conventional stainless steel), and high mechanical properties (up to 800MPa of yield strength and up to 55% of elongation at break). Due to the sector of application also other properties must be controlled e.g., weldability. Due to the high content of alloying elements and their nature, it is possible to forecast criticalities in such a process, like abnormal grain growth, and κ-carbides excessive precipitation. Such carbides are exploited for their strengthening effect in the case of coherent carbide intragranular precipitation, but they have a detrimental effect in the case of intergranular precipitation. An austenitic lightweight steel alloy (X100MnAl30-9) has been tested with a standard welding technique and different material starting conditions. The microstructure and mechanical properties of the joints have been investigated. Sturdy joints have been obtained with microstructure and mechanical properties coherent with expected ones and no detrimental effect of the welding has been observed in HAZ
Characterization of dynamic recrystallization behavior of low carbon steel under flexible rolling process
No full textThe uplifting process of the flexible rolling causes different deformations at different positions of the rolled strip, which will affect the microstructure and dynamic recrystallization behavior of the material under the coupling effect of contact heat transfer and plastic deformation. The equivalent substitution method and the Gleeble-3800 thermal simulation experimental machine were used to study the effect of dynamic recrystallization behavior of a low carbon steel in the flexible rolling process at a temperature of 900–1100 °C, a strain rate of 0.01–10 s−1, and strains in the range 0.2–1.2. Firstly, the critical condition of dynamic recrystallization was determined by analyzing the flow stress curve at high temperature, and the Zener-Hollomon equation under the coupling interaction of stress, strain rate, and temperature was established. Secondly, the method of solving the dynamic recovery coefficient r is optimized, and the dynamic recrystallization volume fraction model is established based on the optimized model, and the experimental value is compared with the predicted value. Finally, the microstructure of the experimental steel was analyzed. Through the equivalent substitution method, it can be concluded that as the roll uplifting reduces the reduction of the strip during the flexible rolling process, the number of dynamically recrystallized grains decreases with the decrease of deformation degree
The influence of slag tapping method on the efficiency of stabilization treatment of electric arc furnace carbon steel slag (EAF-C)
Full text linkStudies conducted over the past 10 years have demonstrated the technical suitability of the electric arc furnace slag as an alternative to natural stone in several applications. Steel slag can be profitably used as a road surface layer, for foundations and embankments, or for concrete aggregates. However, a strong limitation to their use is due to the presence of toxic metals (Ba, Cr, V, Mo, etc.) that can be released into the environment in particular conditions, especially for unbound products in which the slag can come into contact with water. Recent studies have investigated the role of chemical composition and microstructure of slag on toxic metal leaching, allowing for the design of suitable stabilization treatments for hindering such leaching. In this work, four batches of electric arc furnace carbon steel slag underwent a stabilization treatment and the obtained results were compared. In two batches, the stabilizer was added directly in the slag pot and the slag was cooled down in the same pot. The other two batches were stabilized during the downfall from slag door to slag pit. Several slag samples were collected before and after the stabilization treatment and were characterized by means of ED-XRF, XRD, and SEM analysis. Leaching tests were carried out in agreement with EN 12457-2 standard on 4 mm granulated slag, and the leachate concentration was compared with the current Italian limits listed in D.M. 3 August 2005 N. 201 and D.M. 5 April 2006 N. 186. The results clearly indicated that the cooling in the slag pot improved the efficiency of the stabilization treatment, leading to a complete transformation of the microstructure by a full development of homogeneous gehlenite matrix and a coarsening of Cr-spinels, assuring better toxic metal retention behavior. On the contrary, stabilization in the slag-pit was rapid and reduced the interaction between slag and stabilizer, leading only to partial transformation of larnite into gehlenite, and also reducing the coarsening of Cr-spinel. In addition, a layering effect was observed, resulting in an inhomogeneous product from top to bottom in terms of chemical composition, microstructure, and leaching behavior
- …
