Abstract
The improvement in the combination between strength and ductility of austempered ductile iron with dual matrix structure was investigated in two ductile irons having different silicon contents, namely 2.6 wt% and 4.0 wt%. The structure was produced in a thermo-mechanical simulator, equipped with a dilatometry system. The effect of silicon content on the transformation kinetics and mechanical properties was studied. For both ductile irons, the influence of introducing ferrite into the matrix on the structure development and mechanical properties was investigated and compared to those of completely ausferritic matrix. Increasing the Si-content widened the intercritical region and shifted it to higher temperature range. The former effect renders the intercritical annealing process more controllable. The introduction of the ferrite phase accelerated the ausferrite transformation kinetics and improved both the ductility and the formability index (ductility × ultimate strength), while both yield and ultimate strength declined.
Highlights
The dual-phase matrix (DPM) ADI is a novel grade of ADI with optimal combination of strength/ductility properties that was developed with a matrix structure of a soft phase, which is the ferrite and a hard phase which is either martensite (DMS-M) 1,2 or ausferrite.[3,4,5,6,7,8,9]
It should be noted that, contrary to the conventional ADI, where the austempering time and temperature have the major effect on mechanical properties, intercritical austenitizing time and temperature of IADI significantly effect the mechanical properties since these determine the ratio of c/a as well as the amount of carbon and other alloying elements into solid solution in c
The ferrite grain size is insignificantly affected by increasing the silicon
Summary
It should be noted that, contrary to the conventional ADI, where the austempering time and temperature have the major effect on mechanical properties, intercritical austenitizing time and temperature of IADI significantly effect the mechanical properties since these determine the ratio of c/a as well as the amount of carbon and other alloying elements into solid solution in c. The hot deformation of ductile iron attracts attention, because it refines the austenite structures, closes up the internal shrinkage cavities and gas porosity, and reduces the segregations of alloying elements. It increases the dimensional accuracy and surface finish of the products which would reduce the manufacturing cost. Forged ductile iron products have been promoted as replacements for some types of steel forgings.[11]
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