The aim of this work is study on the recycling process of zirconium alloy chips and the results aiming the efficiency in the cleaning process; the quality control; the obtaining of the pressed electrodes and finally the melting in a Vac-uum Arc Remelting furnace (VAR). The recycling process begins with magnetic separation of possible ferrous al-loys chips contaminant, the washing of the cutting fluid that is soluble in water, washing with an industrial degreas-er, followed by a rinse with continuous flow of water under high pressure and drying with hot air. The first evalua-tion of the process was done by an Energy Dispersive X-rays Fluorescence Spectrometry (EDXRFS) showed the presence of 10 wt. % to 17 wt. % of impurities due the mixing with stainless steel machining chips. The chips were then pressed in a custom-made matrix of square section (40 x 40 mm - 500 mm in length), resulting in electrodes with 20% of apparent density of the original alloy. The electrode was then melted in a laboratory scale VAR furnace at the CCTM-IPEN, producing a massive ingot with 0.8 kg. It was observed that the samples obtained from In-dústrias Nucleares do Brasil (INB) are supposed to be secondary scrap and it is suggested careful separation in the generation of this material. The melting of the chips is possible and feasible in a VAR furnace which reduces the storage volume by up to 40 times of this material, however, it is necessary to correct the composition of the alloy for the melting of these ingots.
Thin plates of duplex stainless steel UNS S32304 were welded using the pulsed gas tungsten arc GTAW process (butt joint) without filler addition. The used shielding gas was pure argon and 98% argon plus 2% of nitrogen. The thermal cycles were acquired during welding, in regions near the melting pool. This alloy is candidate for the external clad of a cask for the transport of high activity radiopharmaceuticals substances. For the residual stress measurements in austenite phase an X-ray diffractometer was used in a Bragg-Brentano geometry with CuKα radiation (λ= 0.154 nm) and for ferrite phase was used a pseudo-parallel geometry with CrKα radiation (λ= 0.2291nm). The results of residual stress using sin2y methodology shown that the influence of the high welding temperature leads to compressive stresses for both phase of the duplex steels mainly in heat-affected zone. It was observed a high temperature peak and an increase of the mean residual stress after addition of nitrogen to the argon shielding gas.
ResumoCavacos de Zircaloy 4 são produzidos em larga escala durante a usinagem de tubos Zircaloy 4 para peças do elemento combustível de reatores PWR. Atualmente Zircaloy 4 é uma liga de zircônio importada para o Brasil e sua usinagem gera cavacos que são um desafio para a indústria da reciclagem. Esse trabalho apresenta o primeiro passo do processo de reciclagem e os resultados para a procura de uma maneira eficiente de limpeza, controle de qualidade e fabricação do eletrodo no VAR (Vacuum Arc Remelting). O processo começa com a lavagem do óleo de corte e é seguido pela prensagem dos cavacos limpos. A primeira avaliação do processo foi feita por testes de fluorescência de raio-X com o intuito de definir a qualidade dos cavacos. Os resultados indicaram que é preciso incluir a etapa de separação magnética no processo para extração de liga ferrosa presente nos cavacos. O processo de prensagem dos cavacos produziu um eletrodo de 1kg para ser fundido em um protótipo de forno VAR no CCTM. Os autores também concluem que as amostras obtidas da indústria de elementos combustíveis são de cavacos secundários e sugerem a eles um procedimento de estocagem de cavacos. AbstractZircaloy 4 chips are produced in large quantities during the machining of Zircaloy 4 rods for the PWR fuel elements parts. Currently Zircaloy 4 is a zirconium alloy imported into Brazil and the machining chips scraps poses a challenge to the recycling industry. This paper presents the first step on the recycling processes and the results for the search of an efficient way on the cleaning, quality control and Vacuum Arc Remelting (VAR) electrode fabrication. The process starts with cutting oil washout and is followed by the die pressing of the clean chips. Process evaluation was first made by means the X-ray fluorescence tests in order to define the quality of the scraps. Results indicates the need of the inclusion of a magnetic separation step in the process to withdraw the ferrous alloy present in the scraps. The die pressing of the scraps yield process adequate 1 kg electrodes to be melted in the CCTM prototype scale VAR furnace. The authors also conclude that the samples obtained from the fuel element industry are secondary scraps and suggest them a procedure for the scrap stocking.
The characterization of sintered valve seat inserts (VSIs) after being subjected to different heat treatment operations has been carried out. The VSIs were obtained from three different alloys by mixing iron powder with AISI M3:2, AISI M2 high-speed steels, and AISI D2 tool steel. After sintering, the VSI were quenched in air followed by double tempering at seven different temperatures. The cooling rate during air quenching was measured by means of a thermocouple type k attached to a data acquisition system. The characterization of the mechanical and physical properties of the VSIs was achieved by measuring relative density, apparent hardness and crush radial strength. The resulting microstructures for the sintered parts were interpreted using the isothermal and continuous cooling transformation diagrams for similar alloys. The VSI obtained with AISI M3:2 and AISI M2 high-speed steels after air quenching and double tempering at 600 ºC showed the best results in terms of apparent hardness and crush radial strength.
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