Effect of Cr and W contents on Charpy impact properties of Fe–Cr–W oxide dispersion strengthened steels

Abstract

In this study, the effects of Cr and W contents on the microstructure and Charpy impact properties of Fe–Cr–W oxide dispersion strengthened (ODS) steels were investigated. ODS steels were fabricated by mechanical alloying followed by hot-rolling and tempering, and Charpy impact tests were conducted at −40 °C in both longitudinal-transverse (LT) and longitudinal-short transverse (LS) orientations. The high contents of Cr and W induced a significant <110> fiber texture in the elongated ferritic/martensitic matrix, which was associated with the high stability of ferrite at the hot-rolling temperature. This anisotropic microstructure caused the texture-induced delamination perpendicular to the notch base for the LT orientation and parallel to the notch base for the LS orientation. Such delamination in the LT specimens increased the tendency for ductile fracture, thereby resulting in the enhanced fracture propagation energy in a Charpy impact test. For the LS specimens, however, the Charpy impact energy exhibited enormous scatter depending on the formation of secondary delamination and the degree of plastic bending of the un-notched ligament after primary fracture. When the contents of Cr and W were relatively low, the equiaxed and fine grain structure without preferred orientation was obtained by the dynamic recrystallization of high-temperature austenite during hot-rolling. With this microstructure, the steel offered a high resistance to crack initiation, but the crack was propagated abruptly along the grain boundary decorated with coarse carbide particles.