Precipitation behavior of novel 1 GPa ferritic advanced high strength steels

Abstract

<div lang="en" class="abs"><p class="abs_header">Abstract</p><p>The precipitation of nanosized carbides in the hot-deformed low-alloy Ti-Mo-V-Nb and Ti-Mo-V- steels during the isothermal dwell at three different temperatures (590 °C, 630 °C, and 680 °C) was investigated. Scanning transmission electron microscopy (STEM) revealed that the formation of regularly and irregularly distributed interphase precipitates (IP) and their orientation relationship with the polygonal ferrite matrix depended strongly on steel chemistry, dwelling time, and temperature. Results also showed that precipitation occurred not only at the austenite/ferrite phase boundary during the phase transformation, but nanosized precipitates also formed within the supersaturated polygonal ferrite grains after the phase transformation. Interpretation of the results suggested that finely dispersed interphase precipitated V(<em>Mo</em>)C carbides, formed rows in which the spacing and the size of the precipitates grew slightly during the isothermal dwell time in the Ti-Mo-V-Nb steel at the temperatures of 680 °C and 630 °C, whereas spherical V(<em>Mo</em>)C carbides formed within the supersaturated ferrite matrix at all temperatures. In the case of the Ti-Mo-V steel, the formation of the interphase precipitated Ti(<em>Mo,V</em>)C carbides occurred only at the highest dwell temperature of 680 °C. No IPs was detected at the other dwell temperatures in this steel, but an irregular carbide distribution consisting mostly of spherical Ti(<em>Mo,V</em>)C carbides was formed within the supersaturated polygonal ferrite matrix.</p></div>