Carburization effects on pig iron nugget making

The iron nugget process is an economical, environmentally friendly, cokeless, single-step pig iron making process. Residence-time dependent process requirements for the production of pig iron nuggets at a fixed furnace temperature (1,425°C) were investigated. Depending on the residence time in the furnace, three chemically and physically different products were produced. These products were direct reduced iron (DRI), transition direct reduced iron (TDRI) and pig iron nuggets (PIN). The increase in the carbon content of the structure as a function of residence time was detected by optical microscopy and microhardness measurements. Sufficient carbon dissolution for the production of pig iron nuggets was obtained after a residence time of 40 minutes. The pig iron nuggets produced had chemical and physical properties similar to blast furnace pig iron. They were liquid-state products, and the slag was completely separated from the metal. Copyright 2006, Society for Mining, Metallurgy, and Exploration, Inc

Early stages of spinodal decomposition in an aluminum-zinc alloy

A small-angle X-ray scattering study has been made of isothermal decomposition in an Al-Zn alloy containing 22 at.% Zn. The changes in the X-ray spectra in the early stages of the decomposition at 65°C were in accord with the theory of spinodal decomposition proposed by J.W. Cahn. [Acta Met. 9, 795 (1961).] The diffusion coefficient derived from the kinetics agreed with an extrapolation of high-temperature data and the measured value of the gradient-energy coefficient was (16 ± 3) × 10-6 erg cm-1. © 1967

The effect of heat treatment, mechanical deformation, and alloying element additions on the rate of bainite formation in austempered ductile irons

Several Alloys of Ductile Cast Iron containing various amounts of manganese, molybdenum, and nickel were austempered in the temperature range 316° to 427 °C. The rate and morphology of ferrite platelet formation (bainite reaction) were studied by optical metallography, x-ray diffraction, and hardness measurements. Austenitizing temperature, austempering temperature, and deformation by rolling were used as variables to control the kinetics of ferrite formation, stage I of the austempering reaction. Vickers hardness, austenite carbon content, and volume fraction all change rapidly during the formation of the ferrite platelets, reaching a plateau when stage I is completed. The rate of this reaction is increased dramatically by deformation of the austenite prior to the reaction, is retarded somewhat by alloy additions, and increases with decreasing austenitization temperature. In addition, as the rate of the bainite reaction increases, with its higher ferrite plate density, a more uniform microstructure results, thus minimizing the incidence of martensite in the higher-alloy-content interdendritic volumes. © 1985 American Society for Metals

The microstructure and mechanical properties of austempered ductile iron

This paper represents a summary of experimental results dealing with the time dependence of microstructure and mechanical properties during austempering, and with the austempering temperature dependence of microstructure and mechanical properties. Alloys with a nominal compositions of 3.7 C, 2.5 Si and various controlled amounts of manganese, molybdenum, and nickel were prepared in the MTU foundry. Austenitization at 927° C (1700°F) and 871°C (1600°F) was followed by austempering at temperatures between 230° C (446° F) and 420° C (788° F) at 10°C (18°F) intervals for one hour, and at 316°C (601°F) and 371°C (700° F) for various times from 2 min to 1440 min. Optical and electron microscopy as well as x-ray metallography were used to determine the kinetics and details of the transformations during stages I and II. It is shown that the carbon gradient within the austenite during the transformation controls the rate of Stage I and alloy content controls the rate of Stage II. Interdendritic segregation of alloying elements leads to the presence of significant quantities of untransformed austenite, especially at early austempering times. It is shown that these volumes constitute convenient crack paths, thereby reducing ductility. Minimizing the continuity of those volumes increases ductility, a job aided by a lower austenitizing temperature and a minimum alloy (especially manganese) content. A processing window concept used to optimize ductility at austempering temperatures in excess of 350° C (662° F) is defined by the times needed to avoid excessive untransformed austenite volume (UAV) (the minimum time) and to avoid excessive decomposition of austenite (the maximum time). Tensile strength and ductility are shown to be a function of austenite volume fraction, scale of the microstructure, alloy content, the presence of carbide formed during the austenite transformation, and the presence of intrinsic defects such as eutectic alloy carbides. © 1988 Springer-Verlag New York Inc