The Role of Carbon Content on the Microstructure of Rapidly Solidified Fe–Cr–Ni Duplex Steels

Abstract

In this research, the microstructure of three melt-spinning ribbons with a weight-based composition of Fe–25Cr–5Ni and varying carbon contents (0.02, 0.10, and 0.38 wt%) is evaluated. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used for microstructural characterization. SEM analyses consist of image acquisition and electron backscatter diffraction. TEM analyses consist of bright-field image acquisition, selected area electron diffraction, high-resolution TEM, and local chemical composition measurements by energy-dispersive X-ray spectrometry. According to the results, the ribbons show different microstructures resulting from different solidification paths. The ribbon containing 0.02%C presents a predominantly ferritic microstructure, and austenite solid-state precipitation is not suppressed. It occurs as grain-boundaries allotriomorphs and secondary Widmanstätten side plates. As a result of carbon additions, the ribbon containing 0.10%C shows a microstructure composed of nearly equal parts ferrite and austenite, along with M₂₃C₆ (M = Cr_15.6Fe_7.4) nanometric carbides. The cube-on-cube orientation relationship is found between M₂₃C₆ and austenite. Lastly, the ribbon containing 0.38%C exhibits austenitic microstructure with islands of ferrite surrounded by M₇C₃ (M = Cr_4.14Fe_2.86) carbides.