Fragmented structure of niobium carbide particles in as-cast modified HP alloys

Phase transformations in Fe–Ni–Cr heat-resistant alloys for reformer tube applications

“…Consistent results have been reported in HP alloys, i.e. an intragranular secondary precipitation of M 23 C 6 carbides after aging at typical service temperatures [4,9,13,21,23]. An increase in both nucleation and growth was found when the carbon content increases [5].…”

“…Different carbides precipitate in HP alloys during solidification [4,5,7,[13][14][15][16][17][18][19][20][21][22], their nature and structure evolving during long thermal exposures [6,9,16,[18][19][20][21][22][23][24][25]. Carbides and carbonitrides of different types can be found, e.g.…”

“…Along with MX carbonitrides -or MC carbides-, eutectic M 7 C 3 has mainly been reported to form at grain boundaries during solidification, whereas M 23 C 6 have also been reported to precipitate inside grains if carbon is supersaturated in the γ austenite matrix [1]. Other phases, like nitrides or silicides, can also be found [6,9,16,[18][19][20][21][22][23][24][25]27]. However, although carbide formation during solidification and subsequent cooling has been documented in Nibase superalloys and often found to follow the sequence MC-M 7 C 3 -M 23 C 6 , the identification of carbides in HP alloys in the as-cast condition has led to various conclusions.…”

“…In addition, the correct identification of interdendritic carbides is difficult and has been the object of experimental developments. For instance, using a combination of experimental methods such as scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron back-scatter diffraction and/or wavelength dispersive spectroscopy (WDS), a strict identification of intergranular carbides was made possible showing the presence, in addition to MC carbides, of M 7 C 3 in the as-cast condition and of M 23 C 6 after aging at typical service temperatures [21,23,24], for instance after 100 h at 1223 K (950°C) [15] or at 1423 K (1150°C) [21]. Therefore, if for instance M 7 C 3 must transform into M 23 C 6 during heat exposure, it may also happen that a rather slow cooling from casting temperature leads to such a transformation, explaining why some authors found M 23 C 6 in the as-cast condition instead of M 7 C 3 .…”

Characterisation of tensile deformation behaviour of Fe–25Cr–35Ni-based alloy at high temperature

“…At high temperature, Fe-Cr-Ni-based alloy has excellent mechanical properties and good corrosion resistance. And it is the most important material for many high temperature applications, which is widely adopted as high temperature materials for gas turbine, reformer and cracking furnace tube, metallurgical industry and other high temperature load bearing components [1][2][3][4][5]. The reformer and cracking furnace tubes are often made by the casting Fe-25Cr-35Nibased alloy, which has excellent high temperature creep strength, good corrosion resistance and suitable welding performance [6][7][8].…”