Metallurgical Engineering

Based on very early occurring ruptures found in the first stage high pressure turbine blades of a turbo reactor in a local aviation company, this study has the aim to determine their safe life. The first stage blades are subjected to simultaneous action of gas pressure coming from the combustion chamber, centrifugal forces in the case of the rotor blades and to important temperatures transients, which progress in a very aggressive environment due to hot gases. These combined parameters cause a high state of stress involving several complex mechanisms of damage, such as: fatigue caused by mechanical stress fluctuations, thermo-mechanical fatigue caused by temperature variations and corrosion caused on the stressed elements. Life cycle determination asks for stress evaluation of blades regarding several variables which are approached deterministically in the study. Heat exchange between combustion gases and metal blades is considered. The total stress on two kinds of blades is calculated by the addition of the thermal effect and the mechanical loading. The stress cycle is then calculated for different steps of the engine function during the operation by considering the variation of the thermal and the mechanical properties of the system. Safe life determination is done by two different approaches: the safe life approach by the initiation model and the damage tolerance approach considering the defect growth mechanics and considering the pitting corrosion effect. The calculation is applied for stator and rotor blades of an aero engine high pressure turbine made of NI 738. Since these parts are high risk components from the point of view of potential failure consequences, the risk is assessed as well. The results obtained are studied to determine the solution to the problem, and to propose a safe decision to be taken about the design or maintenance procedures.

Sampling is a key component in mineral processing. It is the art of securing a small weight or fraction that is representative of a relatively large mass to ascertain the true value of a desired property of the material through its sample. Normally, it is prone to a lot of errors which can be brought about by the sampling technique used. Thus, it is important to know which method is the most applicable and reliable to use. In this experiment, two sampling techniques were used – Coning and Quartering and Jones Riffle Splitting to sample a mixture of white and black pebbles and the composition of the mixture was determined. Through coning and quartering, the mixture was estimated to be 58.84265% white pebbles in terms of quantity and 48.79815% by weight while through Jones Riffle sampling, the mixture was estimated to be 57.08796% white pebbles by quantity and 48.80276% by weight.

Solder dross containing Sn, Ni, Cu, Zn, Fe and other impurities was leached with 0.1-1.0
M citric acid at 60 °C for 24 hours stirring times. Parameter affecting the tin recovery of suggested
method such as acid concentration, stirring time and temperature were investigated. Results
obtained revealed that the optimum leaching parameter were achieved using 250ml of citric acid
(C6H8O7)and 10 acid/g drossfor 24 hours at 60°Cof solution temperature. Recovery of tin from
solder dross was 99.0%.

The common failures mechanisms of boiler components at elevated temperatures and monitoring techniques used in power plants to detect damaging or failures are generally well described in literature. Despite of different classification concerning the principal failure mechanisms of boiler thermal power plant components, it is necessary to emphasize that essential difference between these classification does not exist. Concerning the different failures mechanisms it is obvious that the most of them are completely explained and clear in physical sense of process but some of them are not still so explicit. Therefore, until today there is a great interest to investigate the failures of power plant boiler components especially having in mind the all peculiarities of particular events. This efforts are necessary while a full assessment of the failure mechanism(s) is required to prevent further failures due to the same causes. The numerous case studies presented in this paper were done as a contribution to this efforts.

Hydrogen embrittlement (HE) of steels is extremely interesting topic in many industrial applications, while a predictive physical model still does not exist. A number of studies carried out in the world are unambiguous confirmation of that statement. Bearing in mind multiple effects of hydrogen in certain metals, the specific mechanism of hydrogen embrittlement is manifested, depending on the experimental conditions. In this paper structural, low carbon steel, for pressure purposes, grade 20 - St.20 (GOST 1050-88) was investigated. Numerous tested samples were cut out from the boiler tubes of fossil fuel power plant, damaged due to high temperature hydrogen attack and HE during service, as a result of the development of hydrogen-induced corrosion process. Samples were prepared for the chemical composition analysis, hardness measurement, impact strength testing (on instrumented Charpy machine) and microstructural characterization by optical and scanning electron microscopy - SEM/EDX. Based on multi-scale special approach, applied in experimental investigations, the results, presented in this paper, indicate the simultaneous action of the hydrogen-enhanced decohesion (HEDE) and hydrogen enhanced localized plasticity (HELP) mechanisms of HE, depending on the local concentration of hydrogen in investigated steel. These results are consistent with some models proposed in literature, about a possible simultaneous action of the HELP and HEDE mechanisms in metallic materials.

The world yearly production of Silicon and Ferrosilicon is estimated in 2,4 1 and 8,2 mio 1 of tons respectively. China is responsible for 55% (Si) and 66% (FeSi) of the world production. The total amount of Submerged Arc Furnaces that could be used to produce Silicon in different grades (metallurgical for Aluminium Industry, chemical for Polysilicon and Silicones Industries, mainly) are estimate in 295 furnaces 2 divided between the main producers of Silicon product along Chinese country. Based on the updated marketing information, there are 64 of that Submerged Arc Furnaces 3 in the Northeast china region, which around 13 SAF 3 are in normal operation by the first quarter of 2016. The Silicon and Ferrosilicon processes have some similarities in terms of equipment. Since the raw material handling system, the batching and feeding process, stocking process in the top of the furnace, the main smelting process, the tapping, refining and casting as well as the crushing, milling, grinding, screening and packaging process have different environmental emissions, qualitatively and quantitatively speaking. The target of this technical article is to provide a review of the different techniques applied in the metallurgical industry towards reducing those environmental emissions, via efficiency increase or new process and equipment implementation. Also to give a general ideal about return on investment for each separated system. The outcome of those optimization and assets improvement are the positive environmental profile plants increase that could be capitalized via the microsilica quality increase, the NOx and SOx and other gas emissions reduction and the increase of the overall plant efficiency. Although there is an analogy of this article and the direction of the 13 th Five Year Plan (2016-2020), the coverage of the initiatives mentioned are applicable in any Silicon/FeSi plant worldwide; iincluding within the general context of the efficiency drive sustainable practices to all production process through an environmental management system. The global geographic distribution of production plants for ferrosilicon and metallurgical grade silicon is typically a function of the availability of low (and clean) electric energy, as well as the possibility of a long term contract with the local utility company; logistic access to the raw material such as the iron and silicon ore, carbon source (reducing agent called as " reductant ") and also access to potential customers and for example, regional off-takers within the respective processing industries which use Ferrosilicon and Silicon as feedstock. In the case of Ferrosilicon, mainly Carbon and others alloys, iron casting, magnesium industry (die casting for example and primary production process) and Stainless Steel are responsible for more than 99% of FeSi usage. In the case of Silicon, the main industries are respectively Chemical Industry (Silicones and Polysilicon) and Aluminium Industry, responsible together for more than 99% too. Besides the typical oscillation into those markets (due to the economic crisis in 2008 and lower demand in 2015), the forecast for both sectors are positively evaluated by the industry worldwide. For the case of Silicon production, better than Ferrosilicon: