Stabilization of retained austenite by the two-step intercritical heat treatment and its effect on the toughness of a low alloyed steel
Journal
Materials and Design
Journal Volume
59
Pages
193-198
Date Issued
2014
Author(s)
Abstract
Fine film-like stable retained austenite was obtained in a Fe-0.08C-0.5Si-2.4Mn-0.5Ni in weight percent (wt.%) steel by the two-step intercritical heat treatment. The first step of intercritical annealing creates a mixed microstructure of preliminary alloy-enriched martensite and lean alloyed intercritical ferrite, which is called as "reverted structure" and "un-reverted structure", respectively. The second step of intercritical tempering is beneficial for producing film-like stable reverted austenite along the reverted structure. The stabilization of retained austenite was studied by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), dilatometry and X-ray diffraction (XRD) analysis. The two-step austenite reverted transformation associated with intercritical partition of C, Mn and Ni is believed to be the underlying basis for stabilization of retained austenite during the two-step intercritical heat treatment. Stable retained austenite is not only beneficial for high ductility, but also for low temperature toughness by restricting brittle fracture. With 10% (volume fraction) of retained austenite in the steel, high low temperature toughness with average Charpy impact energy of 65. J at -80. °C was obtained. © 2014 Elsevier Ltd.
Type
journal article