Abstract
A mathematical procedure based on the analysis of tensile flow curves has been proposed to assess the microstructure quality of several ductile irons (DIs). The procedure consists of a first diagram for the assessment of the ideal microstructure of DIs, that is, the matrix where mobile dislocations move, and a second diagram for the assessment of the casting integrity because of potential metallurgical discontinuities and defects in DIs. Both diagrams are based on the dislocation-density-related constitutive Voce equation that is used for modeling the tensile plastic behavior of DIs. The procedure stands on the fundamental assumption that the strain hardening behavior of DIs is not affected by the nature and the density of the potential metallurgical discontinuities and defects, which are expected to affect only the elongations to fracture. However, this fundamental assumption is not obvious, and so its validity was evaluated through tensile testing Isothermed Ductile Irons (IDIs) 800, showing a wide scatter of elongations to rupture. The analysis of the strain hardening behaviors supported by strain energy density calculations of IDIs tensile tests proved that the fundamental assumption was valid and the quality assessment procedure could be applied to IDIs. A modified Voce equation was also introduced to improve the fitting of the experimental tensile flow curves and the strain energy density calculations.
Highlights
Due to the demand of improving mechanical properties, new chemical compositions and production routes of Ductile Irons (DIs) have been explored to obtain different microstructures
A specific classification approach to properly weigh up these new generations of advanced ductile irons (DIs) is needed, which should be capable of taking into account increasing alloying elements content and new production routes, mainly through heat treatments resulting in complex microstructures, like ausferrite in Austempered DIs (ADIs) and perferrite in Isothermed Ductile Irons (IDIs)
A first matrix assessment diagram is for the classification of DIs ideal microstructure, that is, the matrix, identifying DIs with different silicon content and DIs produced through different routes and heat treatments
Summary
Due to the demand of improving mechanical properties, new chemical compositions and production routes of Ductile Irons (DIs) have been explored to obtain different microstructures. The current international standards were originally produced for classifying conventional DIs, where silicon content is almost constant (1.8–2.8 wt%) and the pearlite to ferrite ratio, changing because of alloying elements like copper, is the key microstructure parameter that increases yield and tensile strengths, and reduces elongations to rupture. A specific classification approach to properly weigh up these new generations of advanced DIs is needed, which should be capable of taking into account increasing alloying elements content and new production routes, mainly through heat treatments resulting in complex microstructures, like ausferrite in ADIs and perferrite in IDIs. Metals 2019, 9, 837; doi:10.3390/met9080837 www.mdpi.com/journal/metals
Sign-in/Register to view highlights & summary 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 callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
