Divorced eutectoid transformation in high-Al added steels due to heterogenous nucleation of κ-carbide

Abstract

A low density1.25C-5Al-1.5Cr steel involving both cementite and κ-carbide in the divorced eutectoid transformation (DET) led to successful softening from 416 ± 3 HV20 to 285 ± 1 HV20. The planar disregistry between two carbides was calculated to be 5.26%, which suggested that the undissolved cementite particles dispersed in the steel provided heterogeneous nucleation site for κ-carbides during the DET process. The orientation relationship (OR) between κ-carbide and cementite are (100)κ//(11¯0)θ and [011]κ//[111]θ. The study also revealed that only cementite was retained during intercritical austenitization and was effective as nucleating agent for κ-carbide during cooling. Finally, spheroidal κ-carbide was connected to cementite and dispersed in the ferrite matrix and was present after the DET reaction. An orientation relationship (OR) between κ-carbide and cementite is defined for the first time.