Creep and Fatigue at Elevated Temperatures. Development of 18Cr-9Ni-W-Nb-V-N Austenitic Stainless Steel Tube for Thermal Power Boilers.

High temperature low cycle fatigue properties of a HF30-type cast austenitic stainless steel

“…(1) relied on the applied strain rates [10][11][12][13]. Indeed, numerous studies examined the phase transformation behavior and the associated effects of the alloying elements and mechanical properties of various wrought austenitic stainless steels [12][13][14][15][16][17][18][19][20][21][22][23]. However, although both wrought and cast austenitic stainless steels are used in many applications, cast steels have received little attention.…”

On precipitates in Fe–Ni base alloys used for USC boilers

“…The grain boundary may slide during deformation at elevated temperatures and has been considered as the weakness site especially for the alloy serviced between 600 and 800uC. Carbide precipitated discontinuously 7 Calculated phase diagram of Cr-Ni-Fe-7W system 35 8 Effect of precipitates on rupture strength 37,77,93,94 a ductility comparison; 57,99 b strength comparison 98,100 9 Comparison between Z phase adopted alloy along the interface of grain boundaries and may pin the boundary sliding and improve its strength. However, carbide suffers from faster growth rate at elevated temperature, especially at locations with the absence of stabilising elements (e.g.…”

“…57,[98][99][100] The researcher suggests that high strength is achieved for the vanadium addition, which stabilised the Z phase during high temperature. 100 Nevertheless, the lack of the strengthening precipitates at grain boundary may induce the weakness of strength at higher temperature, and it may be the main reason for XA704 showing lower strength when it is compared with NF709 at the temperature above 700uC (Fig. 9b).…”

“…9b). 98,100 Laves phase seems to be an option to further improve the grain boundary strength, in which extensive precipitates along the grain boundary in HR6W has been observed. 33 The tensile test shows that HR6W has good ductility at 973 K. This is quite different from that in GH2984; an alloy has similar dominant ingredient but solely strengthened by carbide at grain boundary, which suffers from the intermediate temperature brittleness at the same temperature.…”

Niobium carbo-nitride precipitation behavior in a high nitrogen 15Cr-15Ni heat resistant austenitic stainless steel

“…TiC and NbC have been employed for strengthening in earlier austenitic grades with lower creep properties [5]. The addition of Nb in combination with V to an ultra-low carbon high nitrogen 18Cr-9Ni austenitic alloy has resulted in significant improvement of creep strength due to the formation of a fine dispersion of (Nb,V)N precipitates [8]. Nb(C,N) or (Nb,Cr)N, which possess good thermal stability at 700°C, or even at higher temperatures, have been widely used in the most advanced commercial austenitic alloys developed recently such as NF709 or Sanicro25 [5,9].…”