Selected Phenomena of the In-Mold Nodularization Process of Cast Iron That Influence the Quality of Cast Machine Parts

Abstract

This paper discusses a problem connected with the production process of ductile iron castings made using the in-mold method. The study results are presented showing that this method compromises the quality of the cast machine parts and of the equipment itself. Specifics of the nodularization process using the in-mold method do not provide the proper conditions for removal of chemical reaction products to the slag, i.e., the products stay in the mold cavity and they also decrease the quality of the casting. In this work, corrosion-type defects were diagnosed mostly on the surface of the casting and some compounds in the near-surface layer-i.e., fayalite (Fe 2 SiO 4 ) and forsterite (Mg 2 SiO 4 )-which cause discontinuities in the metal matrix. The results presented here were selected based on experimental melts of ductile iron. The elements of the mold used in this study, the shape of the mixing chamber, charge materials, method of melting, temperature of liquid metal, etc. were directly related to the production conditions. An analysis was conducted of the chemical composition using a Leco GDS500A spectrometer and a carbon and sulfur Leco CS125 analyzer. Metallographic examinations were conducted using a Phenom-ProX scanning electron microscope with an EDS system.

Bifilm Inclusions in High Alloyed Cast Iron

“…The presence of oxides (MgO, SiO 2 , Fe 2 O 3 , MnO) or silicates (Mg 2 SiO 4 , Fe 2 SiO 4 ) in liquid ductile iron or the slag bound within has been documented [ 10 , 23 ]. Complex compounds, such as (Mg 2 SiO 4 , Fe 2 SiO 4 ) have been recognized in cast iron [ 24 ]. Campbell proposed that these oxides are not taut marbles, cubes, rods, etc., but rather films or bifilms with a lower Stokes velocity, which lets them remain in the alloy suspension for a long time.…”

Effect of Mo Addition on the Chemical Corrosion Process of SiMo Cast Iron

“…Penetrating oxygen reaches the area enriched with silicon and forms compounds with it (e.g., SiO2) creating a tight barrier to the propagation of corrosive phenomena. Of course, a SiO2 compound can react with Fe, O, and FeO, forming a fayalite Fe2SiO4 [8,17]. The characteristic phenomenon of these alloys is their ability to perform so-called "self-healing".…”

“…Simultaneously, SiO 2 can react with O, Fe, and FeO. The result of these reactions may be the formation of fayalite, Fe 2 SiO 4 [6][7][8]. In the paper [9], the author writes that the oxide layer on the surface of SiMo cast iron is composed of the following sub-layers situated from the outside to the inside of the material: Fe 2 O 3 , Fe 3 O 4 , FeO, FeO + Fe 2 SiO 4 .…”

The Importance of the Geometry of the Down Sprue in the Gravity Casting Process

“…Such analyses have been carried out not only for typical gravity castings but also for high-pressure die casting [ 33 ], investment casting [ 34 ], and the lost foam process [ 35 ] with and without filters in the gating system [ 36 ]. In some cases, the geometry of the gating system, mostly the sprue, can significantly affect the processes occurring in the casting mold, for example, ductile cast iron casting manufacturing using the in-mold nodularization method [ 37 ].…”