Basic refractories from indigenous chrome ores

For manufacture of basic refractories of chrome-magnesite type use of high grade chrome ores with low SiO2, (<4%) and iron oxide (18–20% max) has been recommended. Such chrome ores are not readily available in India. As such, the possibility of utilising indigenous chrome ores with varying amounts of SiO2 and iron oxide for manufacture of chrome magnesite type of refractories has been discussed in this paper. Laboratory results indicate that chrome ores with even 8 to 10% SiO2 could be used and chrome concentrate with 7% SiO2 may be utilised. The ratio of chrome and magnesite varies with the quality of chrome ores used. Proper adjustment of grain sizes is an important factor. © 1964 Taylor & Francis Group, LLC

Metallography of explosive welds

Explosive welding is one of the industrially important techniques employing high energies derived from explosives. This technique produces sound metallurgical bonding between a wide variety of similar as well as dissimilar metals and alloys like aluminium, brass, stainless steel, invar, titanium, etc. which are not normally weldable by conventional methods. In this process a weighed amount of explosive is spread over a protecting plate placed on the cladding plate, which is spot-welded at a certain angle to the base plate. The included angle between the cladding and base plates and the amount of explosive used are critical for obtaining sound welds. These weld composites successfully withstand the normal metal-working processes. They find extensive use in bimetal industry, coinage, chemical process equipment, pressure vessel manufacture, rocket technology, etc. Collapse of the cladding plates during explosion generates a pressure wave moving ahead of the collision front and the material forming the colliding surfaces flows forward and is ejected in the form of a jet. Thus the surface jetting normally associated with this process gives rise to wavy interface as noticed in a number of weld combinations. High pressures are generated at the collision front resulting in localised severe plastic deformation. In order to develop sound explosive welds with good shear resistance, it is essential to understand the mechanism of bond formation between the two component metals and also the nature and composition of the interface regions. Techniques like optical and electron metallography, hot-stage microscopy, electron probe microanalysis, microhardness testing, etc. have been employed to investigate the metallurgical aspects of the explosive welds. Bond interface and the adjoining regions reveal many unusual microstructuralfeatures like complex pattern of plastic flow, formation of solidified melt zones, presence of shock-twins, entrapment of metal pockets, etc. Columnar grain structures, characteristic of cast metals, within the mixture zones indicate localised melting and subsequent rapid solidification starting from either side. High microhardness values of these zones could possibly be attributed to the high rates of cooling bringing in large amounts of microstresses and also possible leading to the formation of some non-equilibrium phases similar to those obtained in liquisol-quenched samples. Sets of fine recrystallized grains noticed at regions adjoining the interface indicate the presence of heat-affected zones. Hot stage microscopic examination of mild steel-stainless steel explosive welds shows features like the formation of parallel banded contours, presence of substructure within the twin bands, formation of decarburised layer in mild steel, diffusion of elements across the interface, etc. Electron probe analysis has also been used for the study of these welds by scanning the bond zones for elemental distribution and also by conducting point analysis for their composition. These studies generally indicate an alloy series midway between the two component metals. However, chance combinations of elements approximating to the composition of some intermetallic compounds could also occur. The normal diffusion does not seem to be operative in the explosive welding process, as sharp changes in concentrations have been reported in almost all the weld combinations. A number of explosive welds have also been investigated at our Defence Metallurgical Research Laboratory; some of the results of which are incorporated in this paper

Electron-metallographic studies of precipitation in an aluminium-zinc-magnesium alloy

The mechanism of sub-microscopic precipitation in an Al-Zn-Mg alloy selected for its maximum response to ageing has been studied by a standardized oxide-replica technique in a 100 kV. Philips Electron Microscope. Contrary to earlier conclusions, examination of the oxide replicas has been shown to reveal details of the precipitation process almost as clearly as the thin-foil transmission technique. The reported formation of spherical Guinier-Preston zones followed by the development of a Widmanstaetten pattern of precipitated platelets has been confirmed. The zones have, however, been shown to grow into the platelets and not to dissolve in the matrix as reported earlier. The precipitation process has been correlated with the Hardness/Ageing Time curve and the structure of the precipitates has also been discussed

Salt tolerance in rice varieties

In a water culture experiment, two dwarf (Hamsa & TN1) and two tall (MCM2 & HR12) indica varieties of rice were tested for salt tolerance at 1, 2, 3, 4, 5 and 10 mmhos salt concentration supplied through binary mixture of sodium chloride and calcium chloride. The results indicated that rice plant, irrespective of variety, tolerated salt concentration up to 3 mmhos. At 4.5 mmhos level, there was a reduction In yield from 25 to 35 per cent, The per cent sterility was about 30 in Hamsa, TNI and HR12 upto 5 mmhos salt concentration. But in the case of MCM2, the sterility gradually increased from about 30 to 47 per cent. At 10 mmhos level, the sterility was to the tune of 66 per cent for all the varieties