Abstract
Dynamic testing methods, especially the Charpy V-notch testing at different temperatures, are commonly used to determine the impact response of metallic materials. However, in nodular cast iron this transition trend is characterized by scatter, which makes it difficult to precisely identify the influence of microstructural features on material response. In this paper the vertical surface roughness parameter RV obtained from fracture profiles is considered on the hypothesis that the surface topography is a sensitive indicator of the energy absorbed by plastic deformation and of the microstructure. Nodular cast irons having a range of microstructures were impact tested and the surface roughness determined. Transition trends of impact toughness and of RV are discussed.
Highlights
Nodular cast iron is preferred to grey cast iron in many engineering applications where high strength and high impact toughness are required, [1]
The role of ferrite in the matrix on the transition behavior of nodular cast iron is examined as obtained by Charpy V- notch impact tests at temperatures ranging from Ϫ10 °C to 180 °C
The classical sigmoidal equation is best fitted to all the experimental results and a value of 70 °C is found for the transition temperature T0, defined as the temperature associated to the average of the two asymptotic KCV values
Summary
Nodular cast iron is preferred to grey cast iron in many engineering applications where high strength and high impact toughness are required, [1]. Previous studies, [2, 3], showed that ductile iron has a pronounced ductile-to-brittle transition i.e. the change in fracture response from ductile to brittle with an increase in test temperature. Most alloying elements or impurities affect toughness indirectly through their effect on graphite morphology and matrix microstructure. The effect of graphite morphology is especially significant for upper-shelf toughness (ductile response) and very limited below the transition temperature, [4]. Addition of copper or tin favours the development of a pearlite matrix with an expected decrease in impact toughness
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