METHOD FOR PRODUCING CAST-IRON, AND IN PARTICULAR CAST-IRON WHICH CONTAINS VERMICULAR GRAPHITE

摘要

The invention relates to a method for producing castings from cast-iron containing structure-modifying additives. There is prepared a molten cast-iron bath from which a sample is taken in a sampling and testing vessel. The sample and the vessel are brought to thermal equilibrium at a temperature above the crystallisation temperature of the molten bath and the sample is then permitted to solidify over a period of from 0.5 to 10 minutes. During the process of solidification the temperature is recorded simultaneously by two temperature responsive means, one of which is placed in the centre of the sample and the other in the immediate vicinity of the vessel wall. The dispersion degree of the graphite phase is assessed in relation to known reference values for the same sampling and testing method with respect to the finished castings with the aid of recorded values of supercooling in the molten sample at the vessel wall T*v, the recalescence at the vessel wall, rekv, the positive difference between the temperature and the vessel wall at the centre (.DELTA.T+) of the vessel, and the derivative of the temperature decrease at the vessel wall during the time of constant eutectic growth temperature at the centre of the molten sample , alternatively the maximum negative values (.DELTA.Tmax) of the temperature difference. When necessary, a graphite nucleating agent is added to the molten bath, or the degree of dispersion is lowered by implementing a holding time prior to casting. The morphology of graphite precipitation in relation to known reference values for the same sampling and testing method is assessed with the aid of supercooling at the centre (T*c) of the molten material, the recalescenee at the vessel centre (rekc) and the maximum growth temperature (Tcmax). The morphology is then corrected by changing the amount of structure-modifying agents present, so that the graphite precipitation takes a pre-determined, for example vermicular form upon solidification of the castiron melt subsequent to casting. The invention also relates to various embodiments of the sampling and testing vessel.