Microstructure of Compacted Graphite Iron Near Critical Shrinkage Areas in Cylinder Blocks

Abstract

To study the microstructure of CGI near areas prone to shrinkage, a special sample was developed that resembles critical areas in cylinder blocks. Foundry trials were conducted with different magnesium contents and inoculation amounts. Using color etching techniques to follow the solidification sequence, four areas were observed with different macrostructure: (i) direct chill and columnar region near the surface; (ii) small eutectic cells and small intercellular space; (iii) large eutectic cells and large intercellular space; and (iv) eutectic cells with carbides in the last to freeze area. By increasing the amount of inoculation, the size of the eutectic cells in the zone with large eutectic cells (iii) is reduced, and the eutectic cells are now smaller and more evenly distributed through the section. Increasing the magnesium content brings a similar effect. In zone (iv), the samples with less inverse chill formation show smaller shrinkage porosities, which are located in the same regions where the inverse chill are, between the eutectic cells, in the last to freeze areas; they also have higher amounts of spheroidal graphite in the last-to-freeze areas. The amount of inverse chill carbides observed in zone (iv) did not present any clear relation with inoculation levels or magnesium content variations used in the experiments.

Data-Driven Model Selection for Compacted Graphite Iron Microstructure Prediction

“…It is much more difficult to find examples of research using ML tools in the analysis of CGI properties. The latest publications on this material use either qualitative analysis [42][43][44] or the traditional statistical approach to search for dependencies and build linear regression models [45,46].…”

Mechanism of Shrinkage in Compacted Graphite Iron and Prediction of Shrinkage Tendency

“…Boeri et al [ 11 ] designed three different shapes of stepped specimens to evaluate the compacted graphite iron, and it was found that the shrinkage was mainly generated at the interstices of the dendritic arms. Ramos et al [ 12 ] observed the microstructure of compacted graphite iron near the shrinkage zone and found that the eutectic undercooling plays a key role in the microstructure of compacted graphite iron, as well as in the generation of shrinkage, and it was found that a decrease in the eutectic undercooling could reduce the generation of shrinkage.…”

Evolution of inoculation thermal analysis and solidification morphology of compacted graphite iron

“…In CGI production, the goal is to get as close to the eutectic solidification point as possible to get as much carbon precipitating in the form of graphite as possible to fill out the shrinkage porosity without getting any cementite or exploded graphite [4]. The narrow production process window of CGI and the unexpected parameter changes may lead to a large deviation in the treating effect of one-step graphite vermicularization.…”

“…As the last adjustment of molten iron state, inoculation will have an independent or even contradictory effect on the actual solidification morphology of the melt and the nodularity rate of graphite particles [5][6][7]. Due to a lack of knowledge about actual solidification behavior and inoculation mechanism in CGI, it is more difficult to produce sound cast components, mainly due to the control of shrinkage porosity defects [4,8]. Therefore, in CGI foundry, it is often seen that there are shrinkage porosity defects and unqualified graphite shape castings.…”