Analysis of precipitation and dissolution of the microalloying elements by X-ray absorption spectroscopy (XAS)

Abstract

The dissolution of the microalloying elements in high strength low alloy steels is a cause of longer slab reheating time before hot forming processes compared with those for carbon steels. This is to ensure that all the necessary microalloying elements are dissolved and available for the precipitation hardening during and after the hot forming processes. In order to decrease the enormous amount of the reheating energy, which is the only heat required in the hot forming process, this works selects a high strength low alloy steel containing vanadium and analyses the dissolution kinetics by means of X-ray absorption spectroscopy (XAS). The XAS scans for other elements, i.e., titanium and nitrogen have been carried out and discussed for the possibility of the technique to investigate precipitates in microalloyed steels. Vanadium shows rapid dissolution kinetics that as soon as a lower reheating temperature of 1200 °C is reached, most of it is dissolved into the solid solution. This is opposite to titanium whose most fraction is still in TiN after long reheating time at higher temperature in accordance with the application of TiN for the grain boundary pinning during reheating. X-rays absorption near edge structure (XANES) analysis of nitrogen shows different form of spectra before and after the reheating process. This indicates that the change in the coordination around the central nitrogen atoms takes place during the reheating interval.