C. K. Gupta

Effect of serrated flow on deformation behaviour of AISI 403 stainless steel

Abstract AISI 403, a martensitic stainless steel in the quenched and tempered condition has been subjected to uni-axial tension test at a range of strain rates (2×10−5–10−2 s−1) and a range of temperatures (25–500°C) to investigate the effect of temperature and strain rate on its mechanical properties. Serrated flow behaviour, predominately of type A and B, has been observed in the temperature range of 250–375°C and at strain rates lower than 10−3 s−1, which suggests the presence of dynamic strain aging (DSA) in this parametric domain. In this domain, while an increase in ultimate tensile strength and work hardening have been observed, the yield strength has been found to be nearly independent of temperature. A loss in ductility, due to the presence of DSA has also been seen in this material. The solute responsible for serrated flow has been identified to be chromium, which is the major alloying addition in this material. McCormick’s method has been employed to determine the activation energy from the knowledge of critical strain for the appearance of serrations as a function of strain rate and temperature. The magnitude of activation energy is approximately 50% of that for bulk diffusion of chromium in body centered cubic iron suggesting that a mechanism other than volume diffusion is involved.

Base Metal Resource Processing by Chlorination

This paper is concerned with a review of published reports on the processing of oxide and sulphide resources of base metals by chlorination. The chlorination processes has been described principally under the categories of dry chlorination and aqueous chlorination. In dry chlorination, various processes involving use of different chlorinating agents such as elemental chlorine, gaseous hydrogen chloride, and chlorides of alkali or alkali earth metals are described. In the case of aqueous chlorination, the applications of chlorine, chlorine-oxygen, ferric chloride, ferrous chloride-oxygen, and copper chlorides as chlorinating agents are dealt with. Well accepted basic chemical reactions have been incorporated in the description of the various chlorinating processes.

Hot Working of Zirconium Alloys: Some Recent Developments

Abstract The published results on the hot deformation behaviour of zirconium and its alloys have been reviewed critically to ascertain the type of information available in the areas of hot workability and evolution of microstructure during hot deformation. It is observed that in a majority of these investigations, the emphasis was on the fundamental aspects of hot deformation such as identification of the rate controlling mechanisms, activation energy for hot working and identification of softening mechanisms. However, no systematic effort has been directed towards the optimization of hot workability and control of microstructure of these technologically important materials. In recent years efforts have been made to characterize the hot workability and development of microstructure during hot deformation by constructing power dissipation maps or processing maps and flow instability maps in the format of Dynamic Materials Model. The power dissipation maps and instability maps have been found very useful in optimizing the hot workability and controlling the microstructure during hot deformation of several zirconium alloys.

Investigations on Flowsheet Development for the Treatment of Niobium-Tantalum Bearing Cassiterite

Abstract The paper presents the results of experimental investigations carried out for developing a flowsheet for the treatment of niobium-tantalum bearing cassiterite containing about 23%of mixed niobium and tantalum oxide. Three different approaches viz. direct smelting of cassiterite to tin metal and niobium-tantalum bearing slag, reduction roasting-acid leaching and alkali fusion-leaching to separate tin from niobium-tantalum followed by recovery of tin as oxide and finally carbothcrmic reduction to tin metal have been examined on laboratory scale. It has been observed that alkali fusion—leaching—tin oxide smelting is quite attractive to obtain a good purity tin metal and also recover niobium and tantalum as mixed oxides.

Studies on Processing of Low Grade Indian Molybdenum Sulphide Concentrate

In India, a low grade molybdenum sulphide concentrate containing 25–30% molybdenum is recovered as a by-product of uranium operations at Jaduguda. This concentrate contains a high association of copper and nickel. If it is processed by the conventional route, both copper and nickel would decrease molybdenum recovery. Such concentrates need a different processing route. Various processes such as soda ash roasting, lime roasting, oxychlorination, and electro-oxidation have been studied. The processes aimed at converting molybdenum into a soluble form, then purified by chemical processing as well as by carbon adsorption-desorption route to yield pure molybdic oxide. The oxide was then reduced to metal with hydrogen. In an alternate scheme, molybdenum values in solution have been converted into molybdenum intermediates such as calcium molybdate/ferrimolybdate. This paper presents the result of these investigations.

Quantitative 3D characterisation of porous NiTi fabricated by self-propagating high temperature synthesis using X-ray microtomography

Abstract A porous NiTi specimen prepared by self-propagating high temperature synthesis for bone implant applications has been characterised by a laboratory X-ray microtomography instrument to reveal the three-dimensional (3D) structure of the internal porosity. The reconstructed slices obtained from the tomography scan showed open porosity as well as micropores in the matrix. The 3D renderings revealed that the open porosity is highly interconnected, tortuous structure. 3D quantitative estimates of the micropores in terms of their volume fraction, number density and size have been evaluated. Metrics have been developed based on skeletonised idealisation of the complex architecture of interconnected pores that reflect its structural properties.

Microstructure and dynamic strain aging phenomena in two structural steels

Abstract Two steels with bainitic and martensitic microstructures have been investigated with respect to the changes occurring in their uniaxial tensile properties in the temperature regime where they display dynamic strain aging (DSA) behaviour. The variations in yield strength, ultimate tensile strength, ductility and strain rate sensitivity in the case of martensitic steel have been found to vary in an embrittling manner as compared with those observed in the case of the bainitic steel within the DSA temperature regime. An attempt has been made to provide an insight into the difference in manifestations of DSA on the uniaxial behaviour of the two steels.

Analysis of flow behaviour of iron and steel using power law models

The tensile flow behaviour of mechanically milled iron and a low-alloy steel are analysed using power law models that describe the evolution of stress–strain during a tensile test. A new analytical power law equation is presented that is shown to be superior to the Hollomon and Ludwigson equation to describe the room temperature flow properties of the low-alloy steel over a wide strain rate range. It not only provides a better fit to the homogenous flow curve of the low-alloy steel but also predicts the maximum strength without the prior knowledge of the uniform strain. The new equation also fitted the flow curves of mechanically milled iron with grain sizes in nano to micrometer range.

Studies on Processing of Nickeliferrous Sources in India

Nickel requirement in India is met through imports although there are known deposits of nickel laterites. In addition, there are secondary sources such as nickel sulphide in multimetal sulphides associated with uranium ore, low grade nickel bearing lateritic overburden of chromite mining and industrial wastes, such as spent catalyst and grinding waste of alnico. The primary deposits are extensive but the grade is low. All the other sources are small and some of them are quite complex. Recovery of metal values from such sources is important on account of resource conservation. The paper reviews the studies carried out in different laboratories in India.

Beryllium Extraction—A Review

This paper reviews the current status of beryllium process metallurgy. Emphasis is laid on the extraction of beryllium metal from beryl ore. The resource position, demand and application of the metal and its alloys are also summarised.