Oxide Film Structure and Formation Mechanism of TP347H Heat-resistant Steel Pipe under Supercritical Condition

The oxide film structure and formation mechanism of the burst TP347H heat-resistant steel pipe were studied. The results show that the oxide film was divided into three layers of outer layer, middle layer and inner layer. The outer layer was made of Fe2O3. The middle layer was made of Fe3O4 mainly and a small amount of spinel (FeCr2O4, NiFe2O4). The inner layer contained Cr-enriched oxide layer (FeCr2O4 and Cr2O3) and Ni-enriched metal layer. The iron ions in TP347H heat-resistant steel transported outward and reacted with the oxygen to form the outer Fe2O3 layer and the middle Fe3O4 layer. However, the formation of Cr-enriched oxide layer and Ni-enriched metal layer had relationship with the selective oxidation because of the different oxygen affinities of Cr and Ni.