Abstract
Residual stresses in ferritic ductile iron castings have been studied for decades. However, little attention has traditionally been given to the local residual stresses which may arise in the microstructure as a result of the thermal contraction mismatch between the matrix and the graphite nodules during solid-state cooling. Recent synchrotron X-ray measurements performed by the authors have demonstrated that in the ferritic phase these local stresses can be in the order of 100-150 MPa, hence of the same order of magnitude as the material macroscopic yield stress. This suggests that they might have a significant influence on the mechanical properties of ductile iron components. However, no systematic research appears to have been conducted so far to investigate this aspect. The present work takes a first step in this direction by presenting an integrated theoretical analysis which addresses both the formation of these local residual stresses at the microscopic level and their role during mechanical loading at the macro-scale.
Highlights
Ductile iron (DI) is nowadays widely used in key industrial sectors like transport, marine, and energy production, accounting for as much as 25 % of the total casting production worldwide [1]
This composite microstructure provides a combination of strength, ductility and toughness which is quite unique within the cast iron family, and, together with the low price and excellent castability of the material, makes DI ideal for several advanced engineering applications [2]
The intrinsic composite nature of DI suggests that another type of residual stress may form, at much smaller length scales, as a consequence of the thermal contraction mismatch between the nodules and the matrix
Summary
Ductile iron (DI) is nowadays widely used in key industrial sectors like transport, marine, and energy production, accounting for as much as 25 % of the total casting production worldwide [1]. One of the main reasons for the great success of this material is its microstructure, which is formed by spheroidal graphite particles (nodules) embedded in a continuous metallic matrix This composite microstructure provides a combination of strength, ductility and toughness which is quite unique within the cast iron family, and, together with the low price and excellent castability of the material, makes DI ideal for several advanced engineering applications [2]. As with many other cast alloys, DI parts may contain macroscopic residual stresses which arise due to the presence of mechanical constraints that hinder the thermal contraction of the material during solidification and solid-state cooling This problem is well-known, and today reliable tools exist that allow predicting and coping with it in almost all practical cases. Any reliable theoretical estimate was prevented by the very large uncertainty existing on the mechanical properties of the nodules, which in some reports were considered as voids while in others were even regarded as rigid spheres
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
