Thermo-mechanically processed dual matrix ductile iron produced by continuous cooling transformation

Abstract

Ductile irons with dual matrix structure were attained by controlled cooling in the austenite+ferrite region, after austenitization. Afterwards, the ductile irons were quenched to either 375°C, so as to transform the austenite into ausferrite or to room temperature to transform austenite to martensite. Fully ausferritic and fully martensitic matrices were also produced by direct quenching from the austenite region. Furthermore, three different deformations with true-strain values of 0, 0.3 and 0.5 have been applied in the austenite region. The structures were produced in three ductile irons with aluminum contents of 0.31wt.%, 0.96wt.% and 1.7wt.%. The different microstructures were produced in a thermo-mechanical simulator equipped with a dilatometry system. Dilatometry was used to monitor the structure development throughout the thermo-mechanical processes. The microstructural changes and hardness property exhibited by the produced structures were investigated. Increasing the aluminum widened the intercritical region making the control of the pro-eutectoid ferrite volume fraction easier. The quenching temperature in the intercritical region was shifted to higher value by both increasing the aluminum content and increasing the deformation. This shift resulted in a higher carbon level saturating the intercritical austenite which resulted in fundamental effects on the subsequent transformation kinetics.