Dendritic morphology and ultimate tensile strength of pearlitic lamellar graphite iron

Abstract: The continued development, of cylinder blocks and cylinder heads for heavy truck engines that are made of lamellar graphite iron (LGI) is focused on achieving high ultimate tensile strength (UTS) whilst conforming to environmental regulations. The purpose of this work is to further improve the tensile strength as well as the predictive engineering tools for optimization of LGI aimed to enhance the efforts for producing lighter and sustainable components without sacrificing performance.Varying the carbon content and solidification rate greatly influences the amount and the coarseness of the microstructure phases resulting in large variations of material properties. The experimental data set provided in this work covers a comprehensive range of microstructure and the UTS values aimed to be used in a holistic model for UTS prediction.In pearlitic LGI the primary austenite dendritic network reinforces the material while the distance between the pearlite grains defines the maximum continuous defect size. The novel parameter of Hydraulic Diameter of the Inter-dendritic Phase (DIPHyd) has been introduced in this work to express the amount and the coarseness of the space between the pearlite grains that have been solidified as primary austenite dendrites. The DIPHyd has proven to be the generic parameter that defines the maximum continuous defect size in the material, and hence it has been applied in modified Griffith and Hall-Petch models for prediction of UTS.Microstructure models have been developed for prediction of the key microstructure parameters that define the strength of LGI. These models have been combined with the modified Griffith and Hall-Petch equations and incorporated into casting simulation software to enable the strength prediction for pearlitic LGI alloys with various carbon contents. The results show that the developed models can be successfully applied, along with the simulation tools across a wide range of carbon content from eutectic to hypoeutectic composition, for the alloys solidified at various cooling rates typical for both thin and thick walled complex shaped iron castings.