The effect of production variables on the properties and performance of ingot mould cast iron.

It is extremely difficult to determine the effect of microstructure on the cracking resistance of cast iron by conventional mechanical tests. It has been established that a three point bend test may be used to rank irons of different microstructure in terms of cracking susceptibility.Experimental test block material has been produced and the effect of various production practices on cracking resistance assessed using the bend test. Production ingot moulds have also been examined to determine the relationship between production process, microstructure, mechanical properties and ingot mould performance.It has been established that high (>0.12%) phosphorus levels may cause premature mould cracking due to increased segregation of phosphide/carbide eutectic to the eutectic cell boundaries. This effect is enhanced by increased cooling rates and by increased residual levels. Titanium acts as a graphitiser and offsets the deleterious effects of increased residual levels by increasing cracking resistance. Too high a titanium level (>0.06%) produces a weak iron making the mould prone to torn seats. The effects of titanium are altered depending on the redox conditions. A ductility trough has been found at 0.03 to 0.05% titanium. Compacted graphite is not, necessarily, deleterious to performance. Its formation has been linked with high residual levels. Nitrogen has not been found to be contributory and has little effect on cracking resistance although levels above 0.014% promote pinholing.High residual levels cause a marked decrease in cracking resistance by promoting a cell boundary network of carbides. Slow solidification rates promote this effect by increasing the amount of segregation.Reduced casting temperatures cause a reduction in eutectic cell size with a corresponding increase in cracking resistance. In practice, reduced casting temperatures give reduced performance because of cold shuts in slab moulds and poor crazing resistance in small moulds.