1,721,034 research outputs found
Heat treatment and impact toughness of the f55-grade steel
No full textLow-temperature impact tests are commonly performed to test the quality of industrial forgings in Duplex Stainless Steels (DSS). The F55 grade is a highly alloyed Super DSS characterized by excellent low-temperature toughness in the solution annealed condition. Because of the rich chemical composition, it is very prone to precipitation phenomena during quenching. This research investigates the effect of the material cooling rate on the impact toughness of a water-quenched F55 steel, characterized by the absence of s-phase. Furthermore, by elaborating the impact test data, the T45J [°C] and the KV-46°C [J] parameters have been identified. They are two indicators based on the austenite/ferrite ratio and the material cooling rate, useful for predicting the material impact behavior prior to testing
Metallurgical characterisation of a historical metal tie-rod from Milan Cathedral
No full textOne tie-rod from Milan Cathedral (15th century) recently broke in a defective cross-section. In order to infer the causes of failure, a metallurgical characterisation was performed, the results of which are discussed here. First, a visual inspection of the specimen was performed. Next, the fracture surface was analysed using a Scanning Electron Microscope (SEM) combined with Energy Dispersive X-Ray Spectrometry (EDXS) to detect the failure modes involved. A cross-section close to the failure surface was investigated by means of Stereoscopy, Light Optical Microscopy (LOM), SEM and EDXS in order to identify the microstructural compounds and characterise the slag inclusions. Vickers and Rockwell hardness tests were also carried out to correlate microstructural observations with mechanical properties. A strong relationship between failure and defects due to forging was observed, which is a particularly noteworthy result with regard to the representativeness of laboratory tests and the viability of in-situ inspection
Metallurgical Analysis as a Useful Method for Fire Investigation: the Case of Galvanized Steel Sheets
Full text linkIn this work, fire simulations were carried out on zinc-coated steel sheets usually employed for the structural parts of furniture, transformer rooms and aeration pipes. The thermal alteration induced by the fire was simulated by heating samples at 13 different temperatures (from 20° C to 1050° C) and for different exposure times (1 h and 6 h) in a laboratory furnace. The metallurgical investigation concerned the surface coloring by photographic analysis, the morphology and chemical composition of the surface oxides by SEM and EDS and the microstructure modifications as a function of the temperature by LOM. The influence of the different parameters was discussed by a statistical approach. The obtained results allowed to associate the temperature to one or more alteration of the steel microstructure and of the color, the morphology and the chemical composition of the surface oxides
Aging Treatment Of Selective Laser Melted Alloy 625: Mechanical Strength And Corrosion Resistance
No full textAdditive manufacturing is nowadays increasingly adopted to produce a large variety of components, especially with complex geometries. A deep investigation and optimization of the mechanical and corrosion performance of the selective laser melted Alloy 625 is extremely useful to support designers in the transition from the conventional to the additive manufacturing technology. Even though the selective laser melting technique is still associated with too high production costs and low productivity to enable a broader expansion, it permits to obtain excellent mechanical and corrosion properties compared to those of the conventionally manufactured alloy. Despite the additively produced material shows outstanding performance already in the as-built condition, aging treatments permit further strength improvement enabling possibility of reducing thicknesses, mass, resources consumption and environmental emissions. However, the balance between the mechanical and corrosion properties is critical and it requires a careful tuning of the heat treatment parameters
Correlazione tra ciclo produttivo proprietà meccaniche e microstruttura del composito 2124 rinforzato con particelle di SiC
No full text
Experimental measurement of residual stresses in Cr-Mo-V steel restrained welds with high thickness
No full textThis experimental work is focused on the residual stresses induced by multi-pass welding of thick components. Two samples were produced, inspired by the nozzle-vessel geometry, with Submerged Arc Welding buttwelding, performed according to the standard welding procedures employed by Belleli Energy CPE. The components were characterized by different sizes and groove positions. Measurements of residual stresses were carried out by hole drilling according to ASTM E837-13a, Standard Test Method for Determining Residual Stresses by the Hole-Drilling Strain-Gage Method, in different positions of the samples. The measurements were performed on welded, and Dehydrogenation Heat Treatment (350°C, 4h), and Intermediate Stress Relieving treatments. The obtained results allowed a discussion of the influence of the component size on the residual stresses and the effectiveness of an intermediate heat treatment for reducing the stress state
Deep cryogenic treatment of AA7050: tensile response and corrosion susceptibility
Full text linkCryogenic treatments represent an innovative technology developed with the aim of improving the performance of metallic alloys. The beneficial effects on steels are well documented in the literature, whereas their influence on other materials, such as aluminum alloys, is still not completely clarified. Even if the scientific literature reports conflicting data and conclusions, the industrial applications of such treatments are constantly growing. In the present experimental work, the mechanical and corrosion properties of a high-performance 7050 aluminum alloy plate were studied after cryogenic treatment at − 196 °C in liquid nitrogen. Tensile tests were performed on heat-treated samples, and intergranular corrosion tests were carried out on prismatic samples, according to ASTM G110-92 standard. The specimens were exposed to the corrosive environment and the effect of intergranular corrosion was measured by quantitative analysis using light-optical microscopy (LOM). Whereas trifling variation was observed in the mechanical resistance and plastic behavior, the corrosion tests showed a benefic effect of the cryogenic treatment. The microstructure was investigated by FEG-SEM analysis, revealing a different distribution of precipitates near the grain boundaries, which was able to reduce the electrochemical potential difference among these regions and the center-grain
The dilatometric technique for studying sigma phase precipitation kinetics in F55 steel grade
No full textSigma phase precipitation occurring during the exposure of duplex stainless steels in the temperature range from 800 to 900 °C deeply affects the material toughness and corrosion resistance. σ-Phase precipitation process is strongly influenced by many physical parameters, such as the specific chemical composition, the ferrite amount and its average grain size, and the entity of plastic deformation due to the previous technological process. The strong dependencies of σ-phase precipitation on all these factors justify the continuous study of the process kinetics. This paper focuses on the σ-phase precipitation kinetics in F55 steel grade. The investigation has been performed by an innovative experimental method, such as the anisothermal dilatometric technique. The application of the Kissinger’s method has been used for deriving the process activation energy and kinetics. The results have been compared with the ones obtained by metallographic analysis and hardness tests performed on isothermally aged samples, heat-treated in a laboratory furnace at 850 °C
- …
