Study of Selective Oxidation Behavior of a 1.2Si-1.5Mn TRIP Steel during Intercritical Annealing

Abstract

The present study aims at clarifying the oxides that form on the surface of a 1.2Si-1.5Mn (in wt%) transformation-induced plasticity (TRIP) steel during intercritical annealing. X-ray photoelectron spectroscopy and transmission electron microscopy were employed as complementary tools for analyzing the oxides. The results indicate that both the dew point of the annealing atmosphere and the soaking time play important roles in the oxides forming on the surface. Regarding the steel annealed at 800°C in a low dew point (dp) atmosphere of −70°C, the surface oxides were initially amorphous and were composed of a mixture of SiO2 and xMnO·SiO2 (x<0.7). After soaking for 60 s, a small amount of Mn2SiO4 precipitated in xMnO·SiO2. The steel annealed at 800°C at dp = 0°C showed significant internal oxidation. Initially, a mixture of SiO2, xMnO·SiO2 and Mn2SiO4 formed on the surface. After soaking for 60 s, SiO2 and Mn2SiO4 transformed to xMnO·SiO2 and MnSiO3, respectively. However, some Mn2SiO4 still remained at the grain boundaries.