Reclassification of Spheroidal Graphite Ductile Cast Irons Grades According to Design Needs

AbstractThe 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

Heat treatment cycle optimization for A707L5 copper-nickel steel

The mechanical properties of the A707L5 steel grade were studied as a function of the applied aging temperature. The results obtained are discussed on the basis of the microstructure analysis and precipitates were identified on the fracture surfaces observed by scanning electron microscopy assisted by a field emission gun (FEG-SEM). This steel grade appears to be particularly sensitive to the aging time-temperature, which significantly affected the precipitation phenomena. The annealing temperature and solution quenching involved in the thermal cycle significantly affect the perlite formation, the grain size and the ε-Cu precipitates that represent the main factors of influence ruling the mechanical properties

Ultrasound-guided epidural catheter placement with a new technique: preliminary cadaveric study.

Several methods are described in veterinary medicine to perform and assess correct epidural needle placement to provide effective epidural analgesia (Adami et al 2017). The aim of this study is to evaluate the feasibility of an ultrasound longitudinal sagittal approach to epidural catheter placement using a biopsy needle guide. Seven dog cadavers were used in the study. With the cadaver in sternal recumbence, a 5-8 MHz microconvex transducer provided with a 16-gauge biopsy guide was positioned to obtain a longitudinal sagittal scan of the spinal process of L7 and the sacral crest; the epidural space was identified between two parallel hyperechoic lines and, as the trajectory of the biopsy guide crossed them, a 17G Tuohy needle was used to insert a 19G epidural catheter. Correct catheter placement was visualised through a resection of the column between L2 and L3. Firstly, an expert echographist (operator C1) visualised the ultrasonographic landmarks, while catheter placement was performed by an expert anaesthetist (operator A), a student (operator B) and another expert echographist (operator C2) (double-operator technique); secondly, operator A and C2 performed alone the whole procedure (single-operator technique); lastly all operators performed a blind procedure (Jones 2001). Operator A failed 2/7 single-operator procedures; time to perform the blind technique was statistically lower than the double-operator technique (75 ± 132.4 vs 91.6 ± 79.3 seconds). Operator C2 failed 3/7 blind procedures, scoring the higher total time of performance (329.3 ± 271.2 seconds), but was able to perform both the double- and single-operator technique without significant difference with operator A, despite a faster time in positioning the probe. Operator B showed a higher repositioning attempts of the needle with the double-operator procedure compared to the blind one. Ultrasound guidance appears to be a promising technique to ease catheter placement also by operators inexperienced of locoregional techniques

The Influence of Thermomechanical Processing Conditions on the Evolution of Microstructure and Crystallographic Textures and the Mechanical Properties of Deformed Mild Steels in the Intercritical Region

Rolling temperature and rolling reduction intensively influence the formation of Luder lines and fluting marks in mild steels. They govern these effects through control of strain aging. In order to enhance the strain aging resistance and the consequent reduction of yield point elongation and fluting intensity, warm rolling without using the skin pass process is applied. The development of microstructure and crystallographic textures during deformation process and the determination of fluting intensity and mechanical properties consisting of tensile and formability properties in terms of different thermomechanical conditions (RT and RR%) were investigated in this study. These properties are determined through the use of bending, tensile tests, optical microscope, and EBSD analysis

Impact of warm rolling process parameters on crystallographic textures, microstructure and mechanical properties of low-carbon boron-bearing steels

The effect of the warm rolling process on the microstructure and the mechanical properties of low-carbon high-boron steels are studied in this work. To investigate these effects, boron-bearing low-carbon steel, subjected to roll at three different temperatures, was studied symmetrically and asymmetrically. The results of the experimental trials achieved by mechanical and microstructural analysis revealed that the use of warm rolling can represent a favorable method to suppress strain aging completely, and to eliminate the fluting effect and yield point elongation. In addition, the tensile and elongation properties are modified with the formation of boron nitride precipitates and dislocations in different thermomechanical conditions

Isothermal austenite-Ferrite phase transformations and microstructural evolution during annealing in super duplex stainless steels

Super Duplex Stainless Steels (SDSSs) are composed of α-ferrite and γ-austenite grains, the simultaneous presence of which forms an optimal microstructure to achieve the best combination of mechanical and corrosion resistance properties. Moreover, international quality standards are strict about the phase fraction ratio. The purpose of this work is the achievement of a better description of the phase ratio evolution taking place during annealing at 1080°C in the super duplex stainless steels F53â\u80\u93S32750 and F55â\u80\u93S32760. The experimental results show a damped sinusoidal trend in the α/γ phase ratio evolution with the increase of the soaking time of thermal treatment. This can be described by coupling both the competitive coarsening growth regime and the concept of the local equilibrium phase transformations, pointing out a good correspondence with the experimental data. Further, recrystallization phenomena also play a major role. Finally, the additivity character of the observed processes has been proven

Solidification microstructure of centrifugally cast Inconel 625

Centrifugal casting is a foundry process allowing the production of near net-shaped axially symmetrical components. The present study focuses on the microstructural characterization of centrifugally cast alloys featuring different chemical compositions for the construction of spheres applied in valves made of alloy IN625 for operation at high pressure. Control of the solidification microstructure is needed to assure the reliability of the castings. Actually, a Ni-base superalloy such as this one should have an outstanding combination of mechanical properties, high temperature stability and corrosion resistance. Alloys such as IN625 are characterised by a large amount of alloying elements and a wide solidification range, so they can be affected by micro-porosity defects, related to the shrinkage difference between the matrix and the secondary reinforcing phases (Nb-rich carbides and Laves phase). In this study, the microstructure characterization was performed as a function of the applied heat treatments and it was coupled with a calorimetric analysis in order to understand the mechanism ruling the formation of micro-porosities that can assure alloy soundness. The obtained results show that the presence of micro-porosities is governed by morphology and by the size of the secondary phases, and the presence of the observed secondary phases is detrimental to corrosion resistance

Influence of Microstructure and Shot Peening Treatment on Corrosion Resistance of AISI F55-UNS S32760 Super Duplex Stainless Steel

Shot peening is a surface process commonly used in the aeronautic and automotive industries to improve fatigue resistance. Shot peening is proven to be beneficial in the fatigue behavior of components, but rarely has its influence on wear and pitting corrosion resistance been evaluated. In this work, shot peening was performed on AISI F55-UNS S32760 super-duplex stainless steel samples previously submitted to various thermal treatments, to obtain different initial microstructures and properties. Samples have been characterized in terms of microstructure morphology, local chemical composition, microhardness of each constituent phase, and energy dissipation modes. The enhanced properties provided by shot peening has been evaluated through residual stress depth profiles and Full Width at Half Maximum (FWHM) using X-ray diffraction (XRD), surface hardness, surface roughness, and corrosion resistance through salt spray fog tests. The 1400 °C solution thermal treatment was identified as the optimum initial condition, which maximizes the advantages of the shot peening treatment, even pitting corrosion resistance. These results are related to the uniformity of austenite and ferrite in terms of microstructure morphology, micromechanical properties, and alloying elements distribution

Hot-dip aluminizing on AISI F55-UNS S32760 super duplex stainless steel properties: Effect of thermal treatments

The behavior of super duplex stainless steels AISI F55-UNS S32760 in hot-dip aluminizing process has been studied, investigating the influence of cold working and of different initial microstructures obtained through a preliminary thermal treatment. The microstructural features examined are the secondary austenite precipitation, the static recovery of ferrite and the thermal dissolution of austenite within ferritic matrix. The hot-dip aluminizing temperature has been optimized through sessile drop tests. The treatment has been performed at 1100 °C for 300 s, 900 s and 2700 s. A strong chemical interaction occurs, generating intermetallic compounds at the interface. Molten aluminum interacts exclusively with the ferritic phase due to its much higher diffusivity in this phase coupled with its marked ferrite-stabilizer behavior. Thus, the influence of cold working is not remarkable, since the strains are mainly allocated by austenitic phase. The diffusivity of aluminum increases due to lattice defects thermally generated and, mainly, to influence given by grain boundaries, multiplied by secondary austenite precipitation, which act as short-circuit diffusion paths. Ni and Cr contents in the ferritic matrix have an influence but not highly relevant. Then, the best starting condition of the super duplex stainless steel substrates, to obtain a thick interfacial layer, are the thermal annealing at 1080 °C for 360 s/mm after a solution thermal treatment at 1300 °C for 60 s/mm

Surface Quality Improvement of AA6060 Aluminum Extruded Components through Liquid Nitrogen Mold Cooling

6xxx aluminum alloys are suitable for the realization of both structural applications and architectural decorative elements, thanks to the combination of high corrosion resistance and good surface finish. In areas where the aesthetic aspects are fundamental, further improvements in surface quality are significant. The cooling of the extrusion mold via internal liquid nitrogen fluxes is emerging as an important innovation in aluminum extrusion. Nowadays, this innovation is providing a large-scale solution to obtain high quality surface finishes in extruded aluminum semi-finished products. These results are also coupled to a significant increase in productivity. The aim of the work is to compare the surface quality of both cooled liquid nitrogen molds and classically extruded products. In this work, adhesion phenomena, occurring during the extrusion between the mold and the flowing material, have been detected as the main causes of the presence of surface defects. The analysis also highlighted a strong increase in the surface quality whenever the extrusion mold was cooled with liquid nitrogen fluxes. This improvement has further been confirmed by an analysis performed on the finished products, after painting and chromium plating. This work on the AA6060 alloy has moreover proceeded to roughness measurements and metallographic analyses, to investigate the eventual occurrence of other possible benefits stemming from this new extrusion mold cooling technology