Corrosion Behavior of 12CrMoV Steel in Waste Incineration Environments: Hot Corrosion by Molten Chlorides

The corrosion resistance of a 12CrMoV alloy incontact with a molten mixture of (52-48)mol.%PbCl₂-KCl, similar to that found inwaste incineration plants, has been studied. Thecorrosion kinetics have been analyzed using continuous-currentelectrochemical techniques and electrochemical impedancespectroscopy (EIS). Studies were performed to determinethe influence that temperature and the presence of carbon in the salt have on the corrosion rate.Scanning electron microscopy (SEM) and electron-probemicroanalysis (EPMA) were used as additional analyticaltechniques to analyze the corrosion products in order to elucidate the corrosionmechanism.     

Silicon and Chromium Depletion During the Long-Term Oxidation of Thin-Sectioned Austenitic Steel

Electron-probe microanalysis (EPMA) measurementsare reported of the residual silicon and chromiumconcentrations in thin sections (0.38 mm) of a20Cr-25Ni-Nb-stabilized austenitic steel oxidized in aCO₂/1% CO environment for maximum periods of around40,000 hr at temperatures in the range 900 to 950°C.The depletion profiles obtained have been analyzed usingthe theoretical treatment of Whittle and Cowen-Webster. It is found that silicon depletion occursslowly because of the low rate of thickening of thesilica interlayer formed below the much-thicker,chromia-surface layer. This, coupled with relativelyrapid diffusion within the steel, leads to a flatdepletion profile. By contrast, the more rapid oxidationof chromium develops large concentration gradients ofthat element in the alloy in the vicinity of the oxidemetal interface. In each case, the soluteconcentration at this interface was very much largerthan that for equilibrium with the respective oxide,indicating that the oxidation kinetics were determined by transport within the oxide layer rather thanin the steel. In all the examples studied, thetheoretical analysis produced good agreement with thedepletion measurements using oxidation rate constants consistent with the metallographic measurementsand diffusion coefficients of similar value to thosereported in the literature.     

FE Simulation of Center Crack Occurrence in Tube Rounds During Two-Roll Rotary

With the aid of FE (finite element) code MSC.Superform 2005, 2-D coupled thermo-mechanical simulation of center-crack occurrence in round billet during 2-roll rotary rolling process was presented using Oyane ductile fracture criteria. A simple modeling is put forward based on the spiral motion of the workpiece as an essential characteristic in movement. The influence of the feed angle and the entry cone angle of the main roll on the process was taken into account in the modeling. The soundness for simplifying the 3-D rotary rolling into a 2-D problem was discussed. By adopting the parameters of Diescher piercer in 140mm mandrel mill of Bao Steel, the distribution and development of strain / stress were analyzed, and the eigen value of ductile fracture as well. The critical percentage of diameter reduction was obtained from the simulation. The result showed a good agreement with the experimental value, and therefore was of widely guiding significance to the practical process for rationally formulating the deformation parameters of steel tube piercing.     

Dark current suppression in HOT LWIR HgCdTe heterostructures operating in non-equilibrium mode

Typically,infrared detectors require cryogenic cooling to limit dark current w hich is directly dependent on Auger generation-recombination mechanism and highly influential in Hg Cd Te-narrow band gap material.The Auger suppressed architectures have an advantage over conventional detectors allow ing operation at elevated temperatures200 K.Architecture w ith combination of exclusion and extraction heterojunctions has been proposed to low er Auger contribution.The paper presents a new long-w ave(≈10μm)infrared Hg Cd Te architecture w ith graded gap/doping interfaces and extra barrier located in exclusion heterojunction to suppress dark current for high operating temperature conditions.Proper barrier implementation reduces dark current by more than 20 A/cm2for room temperature operation.     

Mathematical modelling of molten steel flow in a whole degasser during RH refining process

Abstract

A three-dimensional mathematical model for molten steel flow in a whole degasser during the RH (Ruhrstahl–Heraeus) refining process is proposed. The model has been developed considering the physical characteristics of the process, particularly the behaviour of gas–liquid two phase flow in the up snorkel and the momentum exchange between the two phases. The fluid flow fields and gas holdups of liquid phases, among other parameters, in a 90 t RH degasser and a water model unit of one-fifth linear scale have been computed using this mathematical model. The results show that the flow pattern of molten steel in a whole RH degasser can be well represented by the mathematical model. Apart from the area close to the free surface and the zone between the two snorkels in the ladle, the molten steel in an RH degasser, especially in the vacuum vessel, is reasonably fully mixed during the refining process. However, there is a boundary layer between the descending liquid stream from the down snorkel and the surrounding liquid, which is typical liquid–liquid two phase flow, and the molten steel in the ladle is not perfectly mixed. The blown lifting gas ascends mostly near the up snorkel wall, which is more obvious under the conditions of an actual RH degasser, and the flow pattern of bubbles and molten steel in the up snorkel is closer to annular flow. Calculated circulation rates for the water model unit at various lifting gas rates are in good agreement with values determined by means of water modelling experiments.     

Production of injection moulded 316L stainless steels reinforced with TiC(N) particles

Abstract

Metal matrix composites, based on 316L stainless steel and reinforced with TiC and TiCN particles, were manufactured following a powder injection moulding route: mixing, preparation of feedstock, moulding, debinding and sintering. The 316L stainless steel and carbide powders were dry mixed and moulded with wax based binder. The critical powder loading for injection moulding was 62·5 vol.-% for all samples. Binder debinding was performed by solvent and thermal method. After debinding, the samples were sintered at 1250 and 1385°C for 1 h in pure H₂. Metallographic studies were conducted to extend densification and the corresponding microstructural changes. The sintered samples were characterised by measuring tensile strength, hardness and wear behaviour. Wear loss was determined for all samples after wear tests. All powder, fracture surfaces of moulded and sintered samples, and worn surfaces of all the samples, were examined using scanning electron microscope. The sintered density of injection moulded 316L stainless steel samples, reinforced and unreinforced, increases with increasing sintering temperature. The addition of TiC and TiCN improves the hardness and wear resistance with increasing sintering temperature.     

Grain refinement and superplastic behaviour of a modified 6061 aluminium alloy

Abstract

The superplastic properties and microstructure evolution of a 0.15%Zr and 0.7%Cu modified 6061 aluminium alloy were examined in tension at temperatures ranging from 475 to 600°C and strain rates ranging from 7 × 10^-6 to 2.8 × 10^-2 s^-1. The refined microstructure with an average grain size of about 11 μm was produced in thin sheets by a commercially viable thermomechanical process. It was shown that the modified 6061 alloy exhibits a moderate superplastic elongation of 580% in the entirely solid state at 570°C and ? = 2.8 × 10^-4 s^-1. Superior superplastic properties (elongation to failure of 1300% with a corresponding strain rate sensitivity coefficient m of about 0.65) were found at the same strain rate and a temperature of 590°C, which is higher than the incipient melting point of the 6061 alloy (~575°C). The microstructural evolution during superplastic deformation of the 6061 alloy has been studied quantitatively. The presence of a slight amount of liquid phase greatly promotes the superplastic properties of the 6061 alloy, reducing the cavitation level.     

高工作温度碲镉汞p-on-n中波1024×768焦平面探测器

提高红外探测器的工作温度对于减小红外系统的尺寸、重量和功耗至关重要，进而实现结构紧凑和成本低廉的红外系统。昆明物理研究所多年来对掺铟和砷离子注入技术的HgCdTe p-on-n技术进行了优化，实现了性能优异的中波红外探测器的研制。本文报道了高工作温度中波1024×768@10 μm红外焦平面阵列探测器的最新结果，并介绍了在150 K工作温度下的器件性能。结果标明，器件在150 K下截止波长为4.97 μm，并测得了不同工作温度下的NETD、暗电流和有效像元率。此外，还展示了在150 K的工作温度下焦平面器件的红外图像，并呈现了99.4%的有效像元率。