Graphitization in chromium cast iron

peer reviewedSome trials with graphite Hi-Cr iron rolls have been done mainly in Japan, for the rolling of stainless steel. This material could lead to good compromise between oxidation, wear and thermal behaviour. By using thermal analysis and resistometry, the conditions for secondary graphite formation have been studied. The amount and volume of free graphite may be strongly increased by a suitable heat treatment, allowing a good thermal conductivity as well as high wear and mechanical properties

Corrosion studies of different ferrous alloys for rolling cylinders

peer reviewedThe aim of this work is to study the corrosion behaviour in chloride media of a high chromium iron alloy. The influence of the surface finishing as well as the heat treatment was analysed. The technique employed for measuring the corrosion behaviour was the Electrochemical Impedance Spectroscopy, an electrochemical technique that allows the observation not only of the corrosion rates but also the changes on the corrosion mechanism of the alloy. The results showed that it is worth performing a double tempering and a having smoother surface finishing only for long exposure periods. A comparison between different oxidising conditions was also performed simulating the life in service of the hot rolling cylinders and revealed an increase in the protective properties as the oxidising time increased due to the chromium present on the alloy (18%). (c) 2005 Elsevier Ltd. All rights reserved

Thermal Treatments of AlSi10Mg Processed by Laser Beam Melting

Recent studies have shown that AlSi10Mg processed by Laser Beam Melting (LBM) exhibits a much finer microstructure when compared to its cast counterpart as a consequence of the much faster cooling rates imposed in the LBM process. Such microstructural refinement causes a significant increase in strength and hardness, to such an extent that as-fabricated LBM AlSi10Mg was reported to present hardness value of 127 ± 3 Hv0.5, similar to the hardness of high pressure die cast AlSi10Mg in the aged condition (i.e. 130-133 Hv). Yet, little attention has been given so far to the influence of thermal treatments on the microstructure and mechanical behavior of LBM AlSi10Mg. The present work hence aims to investigate the effect of two different types of heat treatments – i.e. (i) stress relief and (ii) solutionizing and ageing − on the microstructure, hardness and tensile properties of LBM AlSi10Mg.Mechanical Engineerin

Effect of alumina and titanium nitrides inclusions on mechanical properties in high alloyed steels

peer reviewedevery commercial steel product in varying amounts. Since inclusions significantly influence properties and behaviour of materials and at the same time give indications on the quality of the steel, it is quite interesting to precise their nature and their origin. In this paper concerning a project involved in the COST 517 framework, studied alloys are high alloy steels. The raw materials were obtained from the conventionally electrical cast ingot and the Electro Slag Refining processes. The purpose is to compare various inclusions produced by these different processes and their effect on the mechanical properties. The raw material because of the melting processes themselves, leads to a product with a good to a great cleanliness, and tiny inclusions, which are haphazardly distributed. The actual ASTM E45 chart seems to be inappropriate, as the inclusions founded are too small in size. Therefore, we manage to develop a specific procedure for the study of such inclusions. The different types of inclusions encountered are oxides, titanium nitrides, and manganese sulphides. Studying the effect on mechanical properties, oxides often seem to initiate fatigue fracture

Electron microscopical investigations of hexagonal phase precipitation in Zn---12 wt% Al---1 wt% Cu and Zn---27 wt% Al---2 wt% Cu alloys

peer reviewedIn Zn---12 wt% Al---1 wt% Cu and Zn---27 wt% Al---2 wt%Cu alloys aged at 100° and 250°C the precipitation of h.c.p. phases was studied by means of transmission electron microscopy. The presence of the metastable ηm and ηx-phases was established using the Moiré pattern method. The ηm → η phase transition was observed. Screw dislocations are visualized in (114) with b logical and {220} in η phase precipitates by means of Moiré fringes.On étudie, par microscopie électronique en transmission, la précipitation de phases H. C dans des alliages Zn-12% en poids Al---1% en poids Cu et Zn---27% en poids Al---2% en poids Cu. La Présence des phases métastables ηm et ηx est établie par la méthode des moirés. On observe la transition de phase ηm → η. Des dislocations vis avec b logical and •220• sont mises en évidence dans le plan (114βbr) des précipités de la phase η par la méthode des franges de moiré.Die Ausscheidung von hexagonalen Phasen in de Legierungen Zn---12 Al---1 Cu und Zn---27 Al---2 Cu (alles in Gew. —%), die bei 100 und 250°C ausgelagert worden waren, wird mittels Durchstrahlungselektronenmikroskopie studiert. Das Vorkommen der metasbilen Phasen ηm und ηx wird über die Auswertung von Moiré-Streifen bestätigt. Die Phasenumwandlung ηm → η wird beobachtet. In den η-Ausscheidungen werden mit Moiré-Streifen Schraubenversetzungen auf (βbr114) mit b mid left angle bracket220right-pointing angle bracket identifiziert

Influence of Alloying Elements on the Thixoformability of a Chromium Steel

This paper deals with the examination of the influence of alloying elements on the thixoformability of a chromium steel. It focuses on the liquid fraction curves of various chromium steels with and without modification of composition. The liquid fraction versus temperature has been obtained by MTData, a thermodynamic prediction package, and by Differential Thermal Analysis (DTA), limited to low heating rates. The correlation between liquid fraction and temperature has been studied. The effect of modifications of composition and of heating rate was observed. First, the thermodynamical calculations allow the study of the influence of alloying elements with variations in chemical composition. Secondly, the DTA tests offer the possibility to observe the influence of heating rate on liquid fraction curve parameters. All these results lead to the identification of the initial parameters necessary to perform inductive heating and quenching tests, and so to approach the industrial process

Research regarding the formation of micropores in a Ni-Ti-C alloy during directional solidification under vacuum

The aim of this experiment was to study the origin and formation of microporosities in a Ni-5% Ti-0.2% C alloy which has been solidified and quenched, and to compare it to the previously developed mathematical model. In the selected alloy, the porosity may result from gases formed during solidification (for example by chemical reaction). The results show that solidification conditions influence microporosity formation through the fraction eutectic and this suggests that it is possible to relate susceptibility to microporosity formation to the fraction eutectic. The results also confirm that for solid solution alloys such as Ni-5% Ti0.2% C, the fraction eutectic increases when the ratio G/R decreases

Structural investigations of HSS rolls for hot strip mill

peer reviewedHigh Speed Steel (HSS) cast rolls are used in front finishing stands of hot strip mills (HSM). Good wear resistance and hardness at high temperatures, are defining features of HSS. Previous experience has shown that HSS rolls containing mainly hard MC carbides have a high friction coefficient, which is detrimental for the rolling power consumption and for the strip surface quality. On the other hand, HSS rolls containing eutectic rod shaped carbides are brittle and more susceptible to spalling. To overcome these problems, a suitable grade, called HSS7, that gives the best compromise between a low friction coefficient and a high crack propagation and wear resistance was developed. That alloy contains well-dispersed hard VC carbides improving wear, and non-interconnected eutectic carbides of the M2C and M7C3 type, hindering crack propagation. All the metallurgical factors affecting the performance and damage of under rolling condition in front finishing stands are reviewed: wear resistance, friction coefficient, resistance to rolling incident, and oxide film formation. The effect of nature, morphology and amount was for each of the carbides studied and connected to the factor affecting the behaviour of the new grade developed. Different techniques are used such as: differential thermal analysis, optical and electron scanning microscopy and image analysis. A correlation with mechanical properties was also performed

Study of microporosity formation in nickel-base superalloys

peer reviewedThe susceptibility of nickel-base superalloys to microporosity formation is studied experimentally and theoretically. Analysis of a model introduced herein leads to formulation of a microporosity index, Ap*, which is expressed in terms of solidification parameters and alloy system properties. This index can be determined from information obtained by quantitative differential thermal analysis. The effect of composition on the formation of microporosity is evaluated. Thus, aluminum, titanium, and cobalt are found to increase, and chromium to decrease microporosity. The effect of carbon is beneficial or detrimental depending on the aluminum content in the alloy