methods for the determination of the purity of steel during the schmelzprozesses or after opening as a batch control

摘要

The use of a differentiated solidification curve for determn. of impurities, esp. oxygen and sulphur, in molten steel during refining in arc- or open hearth furnaces. During melting, or after tilting, a sample of 1-2 litres of steel is drawn off to form an even-sectioned test-piece (e.g. a cube or a cylinder where the height is equal to the dia.) in a mould surrounded by an inert material to retard the cooling rate. A thermocouple is inserted in the centre of the molten sample and a differentiated cooling curve obtd. The growth of dendrites stops after a period of time, indicated by a discontinuity in the curve, and after this interval solidification continues. By sectioning the test-pieces and comparing the structure with the cooling curves it is found that primary dendritic formation ceases at the discontinuity and random solidification occurs after this point. The time which elapses before the discontinuity occurs is related to the amt. of impurities in the melt, esp. oxygen and sulphur, an increase in impurities causing a redn. in the time and vice versa. The cooling curves can thus be correlated with the purity of the molten steel and the size of the test-piece can be related to the size of castings produced.