Breakaway oxidation behaviour of ferritic stainless steels at 1150°C in humid air

Abstract

The breakaway oxidation behaviour of ferritic stainless steels 430, 443 and 445 has been investigatedat 1150•C in humid air. The oxidation kinetics exhibited significant differences among the three ferriticstainless steels. A uniform and steady growing oxide scale was developed on the 430 steel with an evensteel/oxide interface. Local breakdown of the initially protective oxide scale occurred and oxide noduleswere developed on the 443 and 445 stainless steels, resulting in irregular and rough steel/oxide interfaces. The breakaway oxidation behaviour was significantly influenced by the microstructure and thecomposition of the oxide scale. The Mn-Cr spinel oxide formed on top of the Cr2O3scale in Mo alloying445 steel can greatly minimise the Cr depletion.

Influence of Cr-Rich Oxide Scale on Sliding Wear Mechanism of Ferritic Stainless Steel at High Temperature

“…The formation of Mn-Cr oxide can reduce Cr activity, and Mn-Cr oxides are known to provide protection against oxidation [26][27][28][29].…”

“…Cr 2 O 3 has a corundum structure, which consists of an hcp array of oxygen with two-thirds of the octahedral sites occupied by the metal [26][27][28]. µm.…”

High Temperature Oxidation Behavior of Fe-Cr Steel in Air at 1000-1200 K

“…1 and 2). This could be related to breakaway oxidation [6,9], resulting in severe oxidation at higher oxidation temperature. Microstructure and phase composition of oxidized Fe-Cr steel Figure 3 shows the appearances of Fe-Cr steel before and after high temperature oxidation at 1000-1200 K for 72 ks.…”

“…In accordance to the results of XRD analysis, the oxide layer is composed of Fe2O3 and Cr1.3Fe0.7O3. The formation of thick oxide scale could be related to the transition from a protective chromia oxide to poorly protective Fe-rich oxide scale [9,10,13] due to Cr depletion on the steel surface. According to literature [21], at low temperature, the Cr2O3 provides a high protection to oxidation.…”

“…Nevertheless, due to a mechanical damage or insufficient amount of Cr content in the alloy, further later on the protective chromia oxide transforms into unprotective oxide scale by forming Fe-rich oxides on the steel surface [6,[8][9][10]. The degradation of chromia oxide can be caused by vaporization of the oxide by forming a volatile species of CrO3 or CrO2(OH)2, especially at high temperature and wet atmosphere [8,9,[11][12][13]. In addition, defects on the oxide scales as cracks and pores can enhance the anion diffusion to the substrate.…”