high speed steels. That steel presented a great advantage over high carbon steels, which had been largelyHigh speed steels are ferrous based alloys of the applied so far in cutting tools, since it became hard Fe-C-X multicomponent system where X represents a group of alloying elements when air cooled from a temperature from which most comprising mainly Cr, W or Mo, V, and Co. These steels required water quenching for hardening.2-4 The steels are mainly used for cutting tools, since they most important development during the following are characterised by their capacity to retain a high with a view to leaner alloy contents and cheaper alloying elements, mainly substituting for tungsten

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I I r J t I ABSTRACTA sensor was developed to measure the cool ing curves inside a ferrous alloy during its solidification as centrifugally cast tubes. The temperature evolution at some points within the alloy is necessary to evaluate the heat transfer through the outer surface of the tube during the centrifugal casting process. Serious difficulties exist in this type of measurement. because of the rotation of the mold and the relatively high temperature at which the ferrous 3110y is poured.The sensor consists of sheathed thermocouples positioned by a convenient support internally to the rotating mold, within the metal layer. Although 'the sensor is subjected to thermal and mechanical stresses during the melt pouring and solidification. it must maintain its mechanical and thermal characteristics to temperatures of the order of the melting point of the ferrous alloy. Therefore. the thermocouple sheaths and support have been made of refractory metals. namely, tantalum and niobium, to resist the high temperature. Moreover, the sensor was designed to have low thermal inertia. allowing its temperature to increase above the liquidus temperature of the alloy before solidification of the surrounding liquid metal. Because the sensor is embedded in the solidified tube after solidification, a special design was necessary to allow stripping the tube out of the mold without disturbing the system.

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