Experimental Investigation On The Melting Of Electrode And Liquid Metal Pool Shape In An Electro-slag Remelting Process

The entire melting process of electroslag remelting(ESR) contains extremely complex physical and chemical reactions with melting, the metal refining and purification and solidification, finally we get the desired ingot product. With the increasing demands of the production mechanical properties and service life, so how to obtain the ingot with higher purity, smooth surface and dense organization is our current main research. Compared with numerical simulation, small ESR experiment is difficult to control in operational aspects and difficult to get the datas, however, it is more realistic and has some guiding significance for industrial production of large ingots. This paper did appropriate research in single electrode ESR experiment.The main research topics are as follows:(1) In ESR experiments, magnetic flux density along radially outward electrode was measured by Gauss Meter at various slag thickness and loaded current, and the temperature of slag was measured by Thermometer at different current.(2) The shape of the electrode tip was photographed at a time under different current for different filling ratio. Among steady melting time, by recording the melting time of each length, we could calculate the melting rate in different current.(3) In order to clearly and effectively track the liquid metal pool shape variation throughout the whole melting process, the paper used Two-alloy tandem connection method, tracking the metal pool depth variation in different current.(4) In order to verify the not uniform temperature distribution in slag pool, the "true and false" electrode melting experiment has been done. The so-called "true" electrode is that one electrode loaded current, while the other without current, and keep insulation between the two electrodes.(5) In practical industrial applications, the production made from semi-manufactured goods in ESR, such as turbine totor, some alloying elements should be added along the longitudinal direction of it in order to meet the different mechanical properties in different parts. The paper studied the length of the nickel content transition section and its location of two-alloy ingot.The conclusions of this article:(1) The closer to the electrode axis, the larger and increased faster the magnetic flux density was. Under one loaded current, the height above top surface of mold had little effect on the magnetic flux density radially outward the electrode. Under the same height above top surface of mold, the larger loaded current was, the larger the magnetic flux density radially outward electrode was. The slag cap thickness was controlled as a single variation, with the increasing of slag cap thickness, the magnetic flux density increased, when the slag cap thickness increased to a certain value, the magnetic flux density changed a little.(2) All other parameters kept constant, the larger loaded current was, the greater the electrode melting rate was and the more pointed the electrode tip was, that the tip height was larger. In common section of the stable melting current, small filling ratio electrode tip was more pointed and larger tip height than large filling ratio electrode tip. The slag cap thickness was controlled as a single variation, within a certain range, with the increasing of slag cap thickness, the melting rate increased, while the slag cap thickness increased a certain value, the melting rate declined.(3) In experiment, the metal pool shape of entire melting process in ESR was clearly tracked by using two-alloy tandem connection method. At initial stage of melting, the ingot is very short, the main heat in metal pool was transferred to bottom tank and transfer rate was high, so the pool is very shallow. With the growth of the ingot, the heat transfer mainly occurred in the radial direction of mold, at this time, the heat transfer rate declined, the depth of the metal pool increased, when the process reached stable period, the shape and depth were substantially constant. All other parameters kept constant, the larger the current was, the larger metal pool depth at stable period was.(4) The "true and false" electrode experiment showed the temperature distribution in slag pool was not uniform. There was a high-temperature region just below the electrode, while the temperature was lower in other slag pool regions.(5) After two equal amounts of alloys were melted sequentially, the starting position of transition section was a little below the pool shape after etching, nickel content contours were consistent with the pool shapes, and the length of the transition section is approximately equal to the depth of metal pool.