Experimental Study Regarding the Possibility of Blocking the Diffusion of Sulfur at Casting-Mold Interface in Ductile Iron Castings

Abstract

The main objective of this work is to investigate the mechanism of sulfur diffusion from the mold (sand resin P-toluol sulfonic acid mold, sulfur-containing acid) in liquid cast iron in order to limit the graphite degeneration in the surface layer of iron castings. A pyramid trunk with square section samples was cast. On the opposite side of the feed canal of the samples, steel sheets with different thicknesses (0.5, 1, and 3 mm) were inserted with the intention of blocking the diffusion of sulfur from the mold into the cast sample during solidification. The structure evaluation (graphite and matrix) in the surface layer and the casting body was recorded. The experimental results revealed that by blocking the direct diffusion of sulfur at the mold-casting interface, a decrease of the demodified layer thickness (for 0.5 mm steel sheet thickness) is obtained until its disappearance (for steel sheet thicknesses of more than 1 mm). The paper contains data that may be useful in elucidating the mechanism of graphite degeneration in the superficial layer of ductile iron castings. Based on the obtained results, we recommend using such barriers on the metal-mold interface, which are able to limit sulfur diffusion from the mold/core materials into the iron castings, in order to limit or even cease graphite degeneration in the Mg-treated surface iron casting layer. The paper presents additional data related to the interaction of sulfur at the ductile iron casting-mold interface previously analyzed.

Evaluation of the Metallurgical Quality of Nodular Cast Iron in the Production Conditions of a Foundry

“…They can be divided into base materials that make up the base material of the alloy, auxiliary materials that are used to adjust the chemical composition or that carry alloying elements, and materials that are used to remove contaminants. For melting ductile iron, a typical charge has the following structure: pig iron, steel scrap, returned scrap of ductile iron and ferroalloy and carburizer [7][8][9][10][11][12].…”

Archives of Foundry Engineering

“…The following factors control the thickness of the deformed surface layer in ductile iron castings: high content of sulphur hardener, which distorts the shape of graphite particles, high pouring temperature, which increases the thickness of the layer, heavy and massive design of the casting, which makes it more prone to this effect, and high content of reclaim in moulding sand, which increases the thickness of the layer. Increasing the addition of a spheroidizer allows the thickness of the deformed layer to be reduced but not totally eliminated [13][14][15][16].…”