Alloy and process design of thermo-mechanically processed multiphase ductile iron

Abstract

Abstract This work highlights the transformation kinetics, microstructure evolution, hardness and compression properties of four thermo-mechanically processed ductile irons (DIs) having from 0 to 1.7 wt.% aluminum. The DIs are subjected to different true strain values of 0, 0.3 and 0.5 by deformation in the austenite region. Additionally, four types of matrix were produced, namely martensitic, martensitic–ferritic, ausferritic and ferritic–ausferritic. The ferrite introduction is accomplished by isothermal holding in the intercritical region. Aluminum increase widened the intercritical region and shifted it to higher temperature range. The former effect rendered the intercritical annealing more controllable. The latter caused substantial discrepancy in the chemistry of the intercritical austenite by varying the aluminum content. The subsequent transformation kinetics, microstructure evolution and mechanical properties of the intercritically annealed DI are governed by the chemistry of the intercritical austenite. Whereas, those with fully martensitic and fully ausferritic matrices are governed by the aluminum variation. It is also shown that the kinetics of ausferrite formation is accelerated by both increasing the deformation and introducing ferrite to the matrix. The strength and hardness are increased by the former and declined by the latter factor. The fracture strain has not shown a continual increase by increasing the ferrite content.