Kinetics of Secondary Carbides Precipitation in a High-Chromium White Iron

This work analyzes the rate of secondary carbides precipitation during the destabilization heat treatment of a 17%Cr white iron. The experimental iron was characterized in the as-cast conditions to have comparable parameters with the heat treated samples. Destabilization heat treatments were undertaken at temperatures of 900, 1000, and 1150 °C for between 5 min and 8 h; each sample was water quenched immediately after being taken out of the furnace. Characterization was carried out by optical and electron microscopy, image analysis, and energy dispersive spectroscopy (EDS) microanalysis; hardness and microhardness were also evaluated. It was found that most of the secondary carbides that precipitate (between 2-30% of the matrix volume) precipitated in less than 2 h for the lowest destabilization temperature (900 °C). The secondary carbides volume fraction was found to increase for lower destabilization temperatures and large soaking times. A very low carbide precipitation along with a stabilization of the austenite phase occurred for heat treatments at 1150 °C. The results are discussed in terms of the solubility of chromium and carbon in the austenite phase at the different treatment temperatures.