Effect of Second Phase on the Deformation and Fracture Behavior of Multiphase Low-Density Steels

The effects of the second-phase characteristics on the deformation and fracture behavior in low-density steel are investigated in Fe-0.2C-(4, 8)Mn-5Al-1Si alloys, where the second phase can be retained austenite or a mixture of kappa-carbide and ferrite depending on the processing condition. With austenite as second phase, the mechanical stability of the austenite is critical regarding ductility because the fracture is likely to occur before the onset of necking when the austenite transforms into martensite in the early stage of deformation. In the case of the mixture of ferrite and kappa-carbide, the round shape of kappa-carbide is more favorable than the dense lamellar structure. The prominent influence of the second phase on the deformation and fracture behavior is attributable to the propensity of matrix ferrite for cleavage fracture due to its large aluminum concentration.