Effect of Boron Addition on the Oxide Scales Formed on 254SMO Super Austenitic Stainless Steels in High-Temperature Air

Abstract

Focusing on the serious volatilization of MoO3 in super austenitic stainless steel with a high Mo content, the influence of B on the formation of oxide film and the distribution of Cr and Mo was investigated at 900 °C and 1000 °C. Without the addition of B, Mo tends to diffuse to the surface, forming porous Cr/Mo-rich oxides, causing the volatilization of Mo. The addition of B can inhibit the diffusion of Mo to the surface, facilitate the diffusion of Cr to the surface and combines with O, providing conditions for the nucleation of Cr2O3. A large amount of Cr2O3 accumulated on the surface to form a dense passive film, which inhibited the diffusion of Mo to the surface, reduced the loss of Mo, and formed Mo/Cr-rich precipitates at grain boundaries that are close to the surface. However, it was difficult to form Mo-rich precipitates at the grain boundaries of a sample without B, which aggravated the volatilization of Mo from grain boundary to surface. Therefore, the addition of B can improve the oxidation resistance of 254SMO and inhibit the volatilization of Mo.

Effect of Nitrogen on the Corrosion Resistance of 6Mo Super Austenitic Stainless Steel

“…Behrens et al [5] found that the combination of high nickel content and nitrogen in 6Mo super austenitic stainless steel resulted in favorable low sigma solvent temperatures, and high chromium and molybdenum content resulted in resistance to common forms of corrosion and localized corrosion in chlorine-containing media. Ren et al [6] studied the effect of boron addition on the oxide skin of S31254 super austenitic stainless steel in high-temperature air, and the results showed that the addition of B could inhibit the diffusion of Mo to the surface and promote the diffusion of Cr to the surface to form a dense Cr 2 O 3 film. Yang et al [7] found that the grain boundary segregation of B and Ce had a significant inhibitory effect on precipitates, and the addition of B and Ce could greatly improve the corrosion resistance of S31254 SASS.…”

Effect of heat treatment on microstructure and properties of 10B21 cold-heading steel for fasteners

“…The alloying elements can improve the hardenability of steel mainly because they prevent the transformation of austenite into proeutectoid ferrite, pearlite or upper bainite during quenching. Dong et al [7,[11][12] explored Trace B is isolated at the boundary, occupies the appropriate nucleation position in advance, reduces the austenite grain boundary energy, inhibits the ferrite nucleation and delays the ferrite formation. At the same time, the boron atom on the grain boundary also blocks the diffusion of the grain boundary atom, and slows down the ferrite nucleation on the grain boundary, thus improving the thermoplasticity of the material.…”