COMPACTED GRAPHITE CAST IRON

摘要

A method for casting cast iron product with compacted (vermicular) graphite by preparing a cast iron melt comprising 3.6-4.0 % carbon and 1.4-2.5 % silicon and with a CE less than 4.4 by adding structure modifying agent and inoculants in amounts which gives the casted product a structure containing compacted graphite. The amount of addition is determined by extracting a sample of the melt and register the value for the temperature curve measured near the wall in a sample device and near the centre of a sample device, registering thereafter in connection to the eutectic reaction the maximum difference between the undercooling occurent at the outer boundary of sample melt and the calibrated temperature for eutectic reaction at steady state, defined as the electromotive force of 47.171 mV for type K (chromel-alumed) thermocouples and corresponding to a temperature of 1155°C, ΔTw, the time derivative of the subsequently recorded rise in temperature at the boundary of said sample melt, (dT/dτ)w, the corresponding time derivative of the temperature rise in the centre of the sample melt, (dT/dτ)c; and the difference between the maximum temperature after recalescence of the centre of the sample melt and the calibrated temperature for eutectic reaction at steady state, ΔTc. Inoculant and modifying agent fading curves significant of the plant apparatus and process used are calibrated to determine the amount of inoculant ΔY and modifier ΔM that must be added per unit of time in order to maintain constant solidification characteristics. Thereafter, greater or smaller quantities of inoculant and/or modifier than is required to achieve said constant solidification characteristics are added, said modification being made on the basis of the digital values obtained when processing the temperature recording; increasing the amount of inoculant and modifying agent respectively without exceeding the CE value 4.4 and correcting the composition until the ΔTw falls within the range 19-29 K, (dT/dτ)w is > 0.4 Ks-1, (dT/dτ)c is > 0.5 Ks-1 and ΔTc < 10 K at the casting of the melt.