Papers by Keyword: Chromium

Abstract: The early stages of precipitation of Cr rich precipitates were investigated by Atom Probe Tomography (APT) in a Cu-1Cr-0.1Zr (wt.%). This way, quantitative data were obtained about their size, 3D shape, density, composition and volume fraction. Surprisingly, in the early stage of precipitation, nanoscaled precipitates exhibit various shapes (spherical, plates and ellipsoid) and contain a large amount of Cu (up to 50%), in contradiction with the equilibrium Cu-Cr phase diagram. APT data also show that some impurities (Fe) segregate along Cu/Cr interfaces. A precipitation sequence is proposed and the relationship between mechanical properties and microstructure is discussed.

Abstract: Due to their adequate properties, zirconium alloys are the reference materials for the nuclear fuel cladding tubes of Light Water Reactors (LWR). During some hypothetical accidental High Temperature (HT) transients, the materials should experience heavy steam oxidation and deep metallurgical evolutions. This promotes Alpha-Beta phase transformations and an associated strong partitioning of oxygen/hydrogen and of the main chemical alloying elements (Nb, Sn, Fe and Cr). Moreover, it has been shown quite recently that such chemical elements partitioning during on-cooling Beta-to-Alpha transformation can strongly impact the residual mechanical properties of HT oxidized materials. Thus, it appeared that it was important to better quantify and, if possible, to compute the quite complex phase equilibrium that occurs in multi-alloyed zirconium materials in the presence of both oxygen and hydrogen. For that, systematic studies have been performed on industrial alloys, charged with oxygen and/or hydrogen. After applying different heating/cooling scenarii, both Electron Microprobe using Wave Dispersive Spectrometry (WDS) and Nuclear Microprobe using Elastic Recoil Detection Analysis (ERDA) have been applied. Finally, to support the observed chemical elements partitioning between the Alpha and Beta allotropic phases, some thermodynamic calculations have been performed thanks to the development and the use of a specific thermodynamic database for zirconium alloys called “Zircobase".

Abstract: In allusion to facility corrosion problem in caustic soda industry five types of ni-Cr-cu alloy cast irons were developed. The corrosion rates of ni-Cr-cu alloy cast irons in hot concentrated alkali solution were measured by using self-made dynamic corrosion experiment equipment; the microstructures and surface corrosion morphology of alloy cast irons were observed by means of the optical microscope and SEM; the composition was analyzed using XES. Corrosion resistance mechanism were discussed detailedly. the experimental results showed that ni-Cr-cu cast iron was uniform corrosion macroscopically in the dense caustic soda at high temperature and there was ni, cu enrichment microcosmically. The Ni and Cu enriched in the matrix , which increase in local electrode voltage of the matrix,are advantageous to the improvement of caustic corrosion resistances of that zone. The higher Ni content,the better alkali corrosion resistance performance with high temperature.

Abstract: The stainless steel slag contains chromium and iron as well as significant levels of heavy metals, such as Cr(VI). Therefore, to efficiently recovery the valuable components in the stainless steel slag has potential environment and economic profit. In this paper, the physical and chemical properties as well as the leaching properties of the stainless steel slag were summarized. In addition, the treatment processes which can recovery or utilize the valuables in the slag and other potential measures to reduce the environmental pollution of the stainless steel slag were also discussed.

Abstract: A theoretical investigation of 52Cr atomic beam in optical traps was reported, the Doppler and sub-Doppler laser cooling forces were discussed and some characteristics of these forces were shown based on the semi-classical theory. The simulative results indicate that the atomic beam can be collimated by these laser cooling forces, especially by sub-Doppler laser cooling force.

Abstract: Mechanical properties, microstructure and fracture of Fe-3Cr-0.5Mo-xMn steels sintered laboratory at 1250°C and industrially at 1180°C, and of Fe-3Cr-0.3Mo-0.3V-xMn steels laboratory sintered at 1200°C are presented; all steels with 0.24% C. The highest tensile strength of 806 and 856 MPa attained the steels with 2% Mn based on Fe-3Cr-0.5Mo powder and of 929 MPa the Fe-3Cr-0.3Mo-0.3V-1.5Mn-0.24C steels. Linear increase of hardness and relatively linear decrease of impact energy in dependence on Mn addition was recorded. Tested steels exhibited lower heterogeneity of the microstructures. The fracture of steel containing vanadium with 2% Mn showed more metallic inclusions adversely affecting the strength properties.

Abstract: Nano-calcium titanate-based coated aluminum oxide (ACCTO) was successfully prepared by the citrate acid sol-gel method and characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Its application in speciation of Cr(III) and Cr(VI) from water was studied. The conditions of adsorption and elution were investigated. The results show that nanometer calcium titanate could be immobilized on the aluminum oxide firmly, becoming a composite adsorbent. Two forms of chromium showed different adsorption capability at different pH values, Cr (III) selectively retained at pH 8-14, whereas Cr (VI) retained at pH≤2. So separation of the Cr(III) and Cr(VI) is possible. Retained species were eluted with 5mL of 1 mol•L-1 HCl and NaOH. The Cr(III) and Cr(VI) concentration was measured by atomic absorption spectroscopy. The adsorption agent has a promising prospect in removal or enriching and separation of Cr(III) and Cr(VI) in water.

Abstract: The different dilatometric curves of continuous cooling transformation with the different cooling rates were determined by means of Gleeble-2000 thermal simulation machine. The CCT curve of heavy rail steel was obtained by measuring the dilatometric curves and metallographic analysis. And the effects and mechanisms of chromium on the phases transformation of heavy rail steel were investigated. It is found that, the heavy rail steel only takes place pearlite and martensite transformation during continuous cooling. The CCT curve of heavy rail steel is moved right with increasing chromium content, which indicates that chromium can obviously improve the stability of super cooled austenite and delay the pearlite transformation. When the content of chromium is increased from 0.21% to 0.40%, the shortest incubation time of pearlite transformation is increased from 25s to 52s. When the cooling rate ≤ 5°C s^-1, with increasing chromium content, both starting and finishing temperatures of pearlite transformation are decreased at different extent, meanwhile the pearlite is refined. In addition, when the content of chromium is increased from 0.21% to 0.40%, the critical cooling rate of quenching is decreased from 15°C s^-1 to 7°C s^-1.

Abstract: In order to develop low carbon bainitic Cr-B steel, experimental procedures including melting, thermal simulation study and laboratory hot rolling were adopted. The dynamic CCT diagram was established, microstructure and properties of experimental steel were also analyzed. The transformation temperature of experimental steel lies between 650～400°C and final microstructure changes fromquasi-polygonal ferrite, granular bainite to lath bainite as cooling rate increases from 0.2 to 50°C.s-1. The microstructure of steel plates, air cooled or water cooled to 530°C then air cooled, is mainly composed of granular bainite and quasi-polygonal ferrite, and the large size islands in granular bainite are responsible for the low strength and poor toughness. However, steel plate with lath bainite, water cooled to roomtemperature, boasts high yield strength (672MPa) and superior impact toughness (127J at -20°C). Therefore, it is feasible to produce low carbon bainitic Cr-B steel with high strength and good toughness through controlling cooling parameters.