Development of precipitate size and volume fraction of niobium carbonitrides in stabilised stainless steel

Abstract

Niobium carbonitride (NbX) precipitates have been studied in a niobium stabilised austenitic stainless steel AISI type 347 with approximate nominal composition Fe–0.06C–17.5Cr–11.4Ni–0.8Nb. The steel was extruded to seamless tube, solution annealed at 1100°C for 3 min, water quenched, and subsequently isothermally aged at 700°C for times up to 70 000 h. Size distribution and volume fraction of the coarse distribution (1–10 µm) of NbX particles were measured using scanning electron microscopy (SEM). The fine distribution (～30 nm) was investigated using energy filtered transmission electron microscopy (EFTEM). Size distribution and volume fraction were determined using jump ratio images. Coarse NbX (～0.3% volume fraction) precipitates were formed during solidification and extrusion, and were little affected by solution annealing and isothermal aging. Fine NbX (～0.5% volume fraction) precipitates formed during solution annealing and grew during the first 800 h of aging. Precipitate size determination using EFTEM appears to give accurate results, while volume fraction determination requires homogeneous material for good results.     

Evaluation of green compressive strength of clay bonded moulding sand mix: neural network and neuro-fuzzy based approaches

Abstract

An attempt has been made to develop neural network and neuro-fuzzy based models to predict the green compressive strength of clay bonded moulding sand mixtures and to analyse the properties of the mixed sand. Data for the models were generated following standard experimental procedure in the sand laboratory. Process parameters such as clay content, moisture, coal dust and mulling time were varied. The collected data were used in developing these models. The predicted green compressive strengths by neural network and neuro-fuzzy based models have been found to be in good agreement with the experimental values. Furthermore, it has been observed from the results that the predicted values from the neuro-fuzzy model are more accurate than those predicted from the neural network model.     

XPS analysis of the coverage and composition of coatings on glass fibres

For a fundamental approach to glass fibres for composite applications, it is essential to develop efficient methods to analyse the composition and distribution of the sizing layer on the glass filaments. We have been investigating the use of X-ray photoelectron spectroscopy (XPS) as a tool for the rapid characterization of the sizing and interphase in glass fibre reinforcements. In this report we present and discuss a model, based on a patchy sizing overlayer hypothesis, to assist the data reduction of XPS spectra from glass fibres coated with organic sizings. We show how plots of atomic ratios can be used to estimate the surface coverage of the sizing on glass fibres and to obtain information on the stoichiometry of the sizing. The results generated using this model are in good agreement with previously published data. Using this model, we show that XPS results combined with the weight fraction of the sizing give a quantitative value for the coverage of the fibre surface by the sizing.     

Effect of state of sea on atmospheric corrosion in coastal zones

Abstract

Several studies in the literature have shown a considerable effect of wind on marine aerosol production and atmospheric corrosion when the wind speed exceeds some 3–5 m s^-1. However, the current work has shown that the wind effect is not so clear at the Tarragona testing station, on the Mediterranean coast of Spain, where marine winds are generally moderate. Apparently, factors other than marine wind speed at the coast exert a significant influence on the aerosol production. In addition to wind data, the study considers data on the state of the sea in the coast close to the Tarragona testing station obtained from records from an experimentation buoy. These latter data suggest a direct relationship between chloride aerosol deposition rate and the square of wave height. The effect of chloride deposition rate on atmospheric corrosion at the Tarragona testing station has also been studied. Using bimetallic ‘Climat’ type specimens a proportionality has been revealed between corrosion and atmospheric salinity.     

Oxidation Behavior of ODS Alloy MA 6000

MA 6000 is a mechanically alloyed, Ni-base ODSalloy. Excellent high-temperature strength makes it astrong candidate for application in high-temperatureindustrial processes. In order to assess its usefulness for high-temperature structural components,in-depth knowledge of its oxidation behavior,particularly long-term exposure, is necessary. Thepresent work deals with studies of the cyclic andisothermal oxidation of MA 6000 in the temperature range900-1050°C, with emphasis at 1050°C. A fewcomplementary studies have been carried out on the oxideintegrity under creep conditions for exposure times of up to 11,000 hr. The results have shown thatoxidation of MA 6000 involves rather complex mechanismsand alterations of the oxidation behavior still occurafter long-term exposure. Excellent oxidation resistance is based on the formation of an internalcontinuous Al₂O₃ layer.     

Analysis of zonal shrinkage in alloy steels

Abstract

Thermal behaviour of the solidifying steel structure is important for understanding of the defects during ingot solidification. During solidification and cooling, most metals shrink. As a consequence in upper part of solid ingot, pores and pipes of typical shapes and size are formed. Forming of pipes is closely related to the casting and solidification processing parameters. In the present paper the influence of liquid temperature, chemical composition and temperature gradient on the shrinkage intensity are investigated. The ratio of the pipe depth to total ingot height as a criterion of the pipe size is used. The values of the temperature gradients on the base of the numerical model solidification are obtained. The experimental measurements of temperature change have been carried out on laboratory steel ingot. The results by numerical model are compared with the experimental ones and showed a good agreement.     

Microstructure of electromagnetic stir cast grain refined iron base alloy

Abstract

Electromagnetic stirring using multiple induction coils has been investigated as a method of preparing semisolid FC20 alloy. The effects of additions of titanium, zirconium, and boron on the microstructure of the FC20 alloy have also been studied. The electromagnetic flux density increased with input voltage and was higher at the wall of the container than near the centre of the coil. The microstructure of the alloys varied with cooling rate: the higher the cooling rate, the smaller the particle size and the greater the degree of sphericity. The additions of titanium, zirconium, and boron also improved the alloy microstructure.     

Effects of Al content on porous Fe–Al alloys

Abstract

Porous Fe–Al alloys with the nominal composition ranging from Fe–20 wt-%Al to Fe–60 wt-%Al have been fabricated by Fe and Al elemental powder reactive synthesis. The effects of the Al content on the pore properties of resultant porous Fe–Al alloys were systematically studied. It has been found that the volume expansion, the open porosity and the permeability can be manipulated by varying the Al content and that their maximum values are reached at Fe–45 wt-%Al. Their mechanical properties suggest that they are strong enough for the filtration applications.     

Synthesis and characterisation of free standing,one­dimensional,Al–SiC based functionally gradient material

Abstract

In the present study, an aluminium–silicon carbide based functionally gradient material was successfully synthesised using a new technique termed here as gradient slurry disintegration and deposition process. The gradient of SiC was successfully established using this technique for 21 wt-%SiC. The results were confirmed using microstructural characterisation techniques, microhardness measurements, and wear rate determination. The results further revealed that an increase in the weight percentage of silicon carbide particulates along the deposition direction lead to a concurrent increase in porosity, degree of clustering, and microhardness while the nature of silicon carbide/aluminium interfacial integrity remained the same. The results of wear rate determination indicated that a difference of ～9.53 vol.-%SiC on the opposite faces of the functionally gradient material led to the wear resistance increasing to ～31.5× that of the high aluminium end. An attempt is made to interrelate the processing methodology, microstructure, microhardness, and wear rate results obtained in the present study.     

The effect of microstructure on pitting of stainless steel

Abstract

Using temperature as a pitting criterion, a critical pitting temperature has been defined for molybdenum-bearing austenitic stainless steels containing nominally 18% Cr which provides a quantitative measure of their pitting resistance. Single phase alloys had increasing resistance to pit initiation with increasing Mo content while the performance of duplex alloys was limited by the presence of Mo-rich second phase. The effects of heat-treatment and alloy additions on microstructure and pitting resistance are discussed

Résumé

Une température critique de piqûre a été définie pour des aciers austénitiques au molybdène contenant 18% de chrome. Ceci fournit une mesure quantitative de leur résistance à la piqûre.

La teneur en molybdène augmente la résistance au début de piqûre alors que la performance des alliages duplex est limitée par la présence d'une deuxième phase riche en molybdène.