Technology of thin-walled ductile cast iron castings obtaining in coated metal moulds with the use of in-mold melt modifying

Abstract

The most common method of making ductile iron castings is green-sand casting. However, this method does not always allow to obtain the desired fine-grained structure in castings due to its relatively low cooling rate. The application of the coated metal mould casting method makes it possible to expand the range of casting cooling rate regulation by the change of sandresin coating layer thickness on the metal mould surface. The article presents results of studies on the distribution of chemical composition, structure parameters (diameter and number of nodular graphite particles, ferrite amount) and mechanical properties (tensile strength, yield strength, elongation) of ductile cast iron in castings of thin-walled shells obtained in coated metal moulds with the use of in-mold melt modifying. This technology allowed to obtain castings without the use of risers, increase the casting yield from 45 to 65 % and their dimensional accuracy. At the same time, the surface roughness and value of machining allowances are decreased, which increases the metal utilization rate from 43 up to 88 % and reduce the parts manufacturing labor intensity in 2.1 times. The developed technology provides high indicators of ductile cast iron mechanical properties (R m ≥ 515 MPa, R p0,2 ≥ 378 MPa, A ≥ 5.8 %) without carbides formation at crystallization. The castings obtained in this way are well processed by cutting without graphitizing annealing. It is established that the use of our developed ductile cast iron with silicon content 3.2-3.8 wt.% allows to increase the mechanical properties of cast metal (R m ≥ 600 MPa, R p0,2 ≥ 450 MPa, A ≥ 8 %). Ductile cast iron, in-mold modifying, coated metal mould, chemical composition, structure, mechanical properties, distribution, alloying.