Formation of Laves Phase in Sanicro 25 Austenitic Steel During Creep-Rupture Test at 700 °C

Science and Technology of High Performance Ferritic (HiperFer) Stainless Steels

“…Having low solubility [19,20] and comparably high diffusion rate [21,22] in ferrite, Nb is a key element in the design of ferritic, stainless, intermetallic particle strengthened steel. It is a strong Lavesphase former [23] and in combined alloying with tungsten, for improved solid solution strengthening, and silicon to accelerate nucleation [24][25][26][27][28], forms a thermodynamically stable (Fe,Cr,Si)2(Nb,W)-Laves phase [16,29,30]. With Nb being a strong carbonitride former it is necessary to restrict C and N to a minimum (< 0.01 wt.-%), because even small contents of these species may decrease the amount of Nb available [28,[31][32][33] for Laves phase precipitation.…”

Microstructural Characterisation of Austenitic Heat Resistant Sanicro 25 Steel after Steam Oxidation

“…STEM-EDS results ( Figure 5 B–I) clearly indicate the presence of Cr, Nb, and N with 1:1 Cr to Nb ratio for Z-phase. The M 23 C 6 precipitates contain mainly Cr, with a minor amount of W. White precipitates on Figure 5 B consist of W, Fe, Cr, and Cu with stoichiometry close to (Fe,Cr,Cu) 2 W. Suo et al also found Laves phase in Sanicro 25 after creep tests [ 15 ] and proposed that the precipitation is promoted by stress. -Cu precipitates, having the unit cell similar to that of austenite, consist of pure Cu and coagulate with time [ 9 ].…”

“…Figure 5A, acquired at a higher magnification using the STEM-HAADF (high-angle annular dark-field) technique, shows part of bulk material, where bigger precipitate of primary Z-phase is encapsulated by those of M23C6, nucleated on the austenite/Z-phase interface. [15] and proposed that the precipitation is promoted by stress. ε-Cu precipitates, having the unit cell similar to that of austenite, consist of pure Cu and coagulate with time [9].…”

“…Therefore Z-phase is more stable at high temperature than MX precipitates. Sanicro 25 contains around 22% of Cr, making [15] and proposed that the precipitation is promoted by stress. ε-Cu precipitates, having the unit cell similar to that of austenite, consist of pure Cu and coagulate with time [9].…”

Science and Technology of High Performance Ferritic (HiperFer) Stainless Steels

“…Having low solubility [19,20] and comparably high diffusion rate [21,22] in ferrite, Nb is a key element in the design of ferritic, stainless, intermetallic particle strengthened steel. It is a strong Laves-phase former [23] and in combined alloying with tungsten, for improved solid solution strengthening, and silicon to accelerate nucleation [24][25][26][27][28], forms a thermodynamically stable (Fe,Cr,Si) 2 (Nb,W)-Laves phase [16,29,30]. With Nb being a strong carbonitride former it is necessary to restrict C and N to a minimum (< 0.01 wt.%), because even small contents of these species may decrease the amount of Nb available [28,[31][32][33] for Laves phase precipitation.…”