Microsegregation in nodular cast iron and its effect on mechanical properties

A review of the literature pertaining to the mechanical properties, solidification and segregation effects in nodular cast iron has been made. A series of investigations concerning the influence of microsegregation on mechanical properties of :pearlitic, ferritic and austenitic nodular cast iron have then been reported. The influence of section size on the tensile and impact properties of cornmercial purity and refined ferritic nodular cast iron has been studied. It has been shown. that an increase in section caused a decrease in impact transition temperature of the commercial purity material without greatly affecting the impact transition temperature of the purer material. This effect has been related to increased amounts of segregation effects such as cell boundary carbides in heavier sections of the commercial purity material. Microsegregation studies on the materials used in this thesis have been carried out using an electron probe microanalyser. This technique has shown that concentrations of chromium and manganese and depletions of nickel and silicon occurred at eutectic cell boundaries in nodular cast iron and were often associated with brittle carbides in these areas. These effects have been shown to be more prevalent in heavier sections. The nature of segregation during the solidification of nodular cast iron has been studied by quenching samples of nodular iron during the solidification process. Micro-analysis of such samples has shown that segregation of manganese and chromium occurs by a gradual build-up of these elements at the solid/liquid interface. The microstructures of the quenched specimens revealed carbide filaments connecting graphite nodules and areas of quenched liquid. These filaments have been used as evidence for a revised hypothesis for the solidification of nodular cast iron by a liquid diffusion mechanism. A similar series of experiments has been carried out on two high nickel austenitic irons containing 0.5 per cent manganese and 4 per cent manganese respectively. In both these materials a decrease in elongation was experienced with increasing section. This effect was more drastic in the 4 per cent manganese material which also contained much greater amounts of cell boundary carbide in heavy sections. Micro-analysis of samples of the 4 per cent manganese material quenched during solidification revealed that manganese concentrated in the liquid and that nickel concentrated in the solid during solidification. No segregation of silicon occurred in this material. Carbide filaments appeared in the microstructures of these specimens. A discussion of all the above effects in terms of current concepts is included.

Editorial

The year so far has been a slow start for many businesses, but at least we have not seen the collapse of as many businesses that we were seeing around two years ago. We are, however, still well and truly in the midst of a global recession. Interest rates are still at an all time low, UK house prices seem to be showing little signs of increase (except in London where everyone still seems to want to live!) and for the ardent shopper there are bargains to be had everywhere. It seems strange that prices on the high street do not seem to have increased in over ten years. Mobile phones, DVD players even furniture seems to be cheaper than they used to be. Whist much of this is down to cheaper manufacturing and the rest could probably be explained by competition within the market place. Does this mean that quality suffered too? Now that we live in a world when if a television is not working it is thrown away and replaced. There was a time when you would take it to some odd looking man that your father would know who could fix it for you. (I remember our local television fix-it man, with his thick rimmed bifocal spectacles and a poor comb-over; he had cardboard boxes full of resistors and electrical wires on the floor of his front room that smelt of soldering irons!) Is this consumerism at an extreme or has this move to disposability made us a better society? Before you think these are just ramblings there is a point to this. According to latest global figures of contact lens sales the vast majority of contact lenses fitted around the world are daily, fortnightly or monthly disposable hydrogel lenses. Certainly in the UK over 90% of lenses are disposable (with daily disposables being the most popular, having a market share of over 50%). This begs the question – is this a good thing? Maybe more importantly, do our patients benefit? I think it is worth reminding ourselves why we went down the disposability route with contact lenses in the first place, and unlike electrical goods it was not just so we did not have to take them for repair! There are the obvious advantages of overcoming problems of breakage and tearing of lenses and the lens deterioration with age. The lenses are less likely to be contaminated and the disinfection is either easier or not required at all (in the case of daily disposable lenses). Probably the landmark paper in the field was the work more commonly known as the ‘Gothenburg Study’. The paper, entitled ‘Strategies for minimizing the Ocular Effects of Extended Contact Lens Wear’ published in the American Journal of Optometry in 1987 (volume 64, pages 781-789) by Holden, B.A., Swarbrick, H.A., Sweeney, D.F., Ho, A., Efron, N., Vannas, A., Nilsson, K.T. They suggested that contact lens induced ocular effects were minimised by: •More frequently removed contact lenses •More regularly replaced contact lenses •A lens that was more mobile on the eye (to allow better removal of debris) •Better flow of oxygen through the lens All of these issues seem to be solved with disposability, except the oxygen issue which has been solved with the advent of silicone hydrogel materials. Newer issues have arisen and most can be solved in practice by the eye care practitioner. The emphasis now seems to be on making lenses more comfortable. The problems of contact lens related dry eyes symptoms seem to be ever present and maybe this would explain why in the UK we have a pretty constant contact lens wearing population of just over three million but every year we have over a million dropouts! That means we must be attracting a million new wearers every year (well done to the marketing departments!) but we are also losing a million wearers every year. We certainly are not losing them all to the refractive surgery clinics. We know that almost anyone can now wear a contact lens and we know that some lenses will solve problems of sharper vision, some will aid comfort, and some will be useful for patients with dry eyes. So if we still have so many dropouts then we must be doing something wrong! I think the take home message has to be ‘must try harder’! I must end with an apology for two errors in my editorial of issue 1 earlier this year. Firstly there was a typo in the first sentence; I meant to state that it was 40 years not 30 years since the first commercial soft lens was available in the UK. The second error was one that I was unaware of until colleagues Geoff Wilson (Birmingham, UK) and Tim Bowden (London, UK) wrote to me to explain that soft lenses were actually available in the UK before 1971 (please see their ‘Letters to the Editor’ in this issue). I am grateful to both of them for correcting the mistake.

Retificação plana tangencial dos ferros fundidos nodular, vermicular e cinzento em várias condições de corte

In a scenario of increasing competitiveness of the global industrial sector and with a consumer market increasingly demanding, there is an increased demand for new materials and, consequently, possibilities to explore new research and technological advances towards the development of new manufacturing methods or the improvement of existing technologies. In the case of cast irons, new grades of them have been developed so that their mechanical properties have been improved, making them more competitive with steel, expanding the applications and thus represents great economic gain for metallurgy and manufacturing sectors. This increases the interest and creates new opportunities to study these materials and identify how they respond in terms of the surface integrity, tool wear, cutting forces, among others, when machined by grinding operation. In this context, due to the lack of results from grinding of cast irons and studies comparing grindability among several grades of cast irons found in the literature, this work aims to generate scientific and technological contribution to the metallurgical and metal working sector through roughness results (Ra and Rz parameters) and evaluation and analysis of the subsurface integrity of three cast iron grades (gray, compacted graphite and nodular). The machining trials were performed on a surface grinding machine with silicon carbide grinding wheel at different cutting conditions. The input variables were the radial depth of cut (15 and 30 μm), worktable speed, vw (5 and 10 m/min) and the abrasive grain size of the grinding wheel. The results showed that surface roughness increased with the radial depth of cut for all materials tested; and the lowest values were obtained for gray cast iron. Also, roughness was sensitive to variation of worktable speed and the lowest values were obtained after machining with vw = 5 m/min. With respect to the abrasive grain size, as it decreased the roughness values increased to gray and nodular cast iron grades. Furthermore, grinding burns marks were observed on the surfaces of nodular cast iron and compacted graphite iron grades after grinding the smallest grain size, contrary to what is usually reported in literature. However, no evidence of severe thermal damages below the machined surfaces of all cast iron grades was observed after analyzing the results of hardness and the SEM micrograph images.

High school classes: small appliance repair class

Inscription: Verso: small appliance repair class: Eli Whitney Vocational High School, Brooklyn New York.

Potencialidade do sensor Worldview II na detecção de hematita e goethita em solos tropicais

Dissertação (mestrado)—Universidade de Brasília, Instituto de Geociências, Programa de Pós-Graduação Stricto Sensu em Geociências Aplicadas, 2016.

Espiritualidad y política: una propuesta tibetana para la transformación del orden mundial

La Revolución Espiritual promovida por el Dalai Lama plantea una unión entre espiritualidad y política. El proyecto de una ética universal, que se inscribe dentro de dicha Revolución, busca impactar la manera en que las relaciones internacionales se desarrollan, dándole prevalencia a los valores humanos. Sin embargo, esa proposición se encuentra ligada al contexto de exilio en el marco del conflicto sino-tibetano que afecta al continente asiático. Por esto, en la presente monografía, haciendo uso de los conceptos de marco de acción colectiva e identidad inscritos en la corriente de los movimientos sociales en la disciplina de las Relaciones Internacionales, se pretende determinar la relación entre identidad tibetana, marco de acción colectiva y la propuesta de una ética universal. Para ello se recurre, metodológicamente, a textos y a trabajo de campo en Bogotá. Así, se pretende establecer la relación entre espiritualidad y política como propuesta tibetana atravesada por el conflicto sino-tibetano.