Effects of furnace atmosphere on selective oxidation behaviour of Si-added transformation-induced plasticity steels

The selective oxidation behaviours of Si-added transformation-induced plasticity (TRIP) steels were investigated by controlling the furnace atmosphere, dew point, and annealing temperature. Two steels were used for the study: a sample 2 of 1.6 wt% Mn and 1.5 wt% Si and a sample 1 of 2.4 wt% Mn and 1.0 wt% Si. As the annealing temperature increased, the surface enrichment of Si and Mn increased for a sample 1. However, the surface enrichment of Mn decreased above 1073 K for sample 2. This was correlated with the deterioration of galvanized coating quality. The over-aging at 773 K showed a different trend of Mn enrichment as a function of Si and Mn contents. For sample 1, Mn was enriched continuously at relatively low temperatures (773 K) during the over-aging process, as well as at high temperatures (1073 K) during soaking. This could mean that Mn enrichment increased due to the formation of selective oxides Mn2SiO4 at low temperature. However, Mn enrichment was not dominant for sample 2 during the overaging process.