Creep rupture strength and ductility of creep strength enhanced ferritic steels of Grades 23, 91, 92, and 122 was investigated with particular emphasis on remarkable drop in the long-term. Large difference in creep rupture strength and ductility was observed on three heats of Grade 23 steels. Remarkable drop of creep rupture strength in the long-term of T91 was comparable to those of Grades 92 and 122. Remarkable drop in creep rupture ductility in a stress regime below 50% of 0.2% offset yield stress was observed on Grade T23 steel, however, that of Grade P23 steel did not indicate any degradation of creep rupture ductility. Higher creep rupture ductility of Grade P23 steel was considered to be caused by its lower creep strength than that of T23 steels. Creep rupture ductility of Grades 92 and 122 steels indicated rapid and drastic decrease with decrease in stress at 50% of 0.2% offset yield stress. Stress dependence of creep rupture ductility of Grades 92 and 122 steels was well described by a ratio of stress to 0.2% offset yield stress, regardless of temperature. On the other hand, large drop in creep rupture ductility of Grade 91 steel was observed only in the very low-stress regime at 650 °C. Alloying elements including impurities and changes in precipitates may influence on creep rupture ductility, however, remarkable drop in ductility of the steels cannot be explained by chemical composition and precipitates. High ductility in the high-stress regime above 50% of 0.2% offset yield stress should be provided by easy plastic deformation, and it has been concluded that a remarkable drop in ductility in the low-stress regime is derived from a concentration of creep deformation into a tiny recovered region formed at the vicinity of grain boundary.

References

References
1.
Foldyna
,
V.
,
Kubon
,
Z.
,
Filip
,
M.
,
Mayer
,
K. H.
, and
Berger
,
C.
, 1996,
Steel Res.
,
67
, p.
375
.
2.
Kimura
,
K.
,
Kushima
,
H.
, and
Abe
,
F.
, 2000,
Key Eng. Mater.
,
171–174
, p.
483
.
3.
Hald
,
J.
, 2004,
Mater. High Temp.
,
21
, p.
41
.
4.
Strang
,
A.
, and
Vodarek
,
V.
, 1996,
Mater. Sci. Technol.
,
12
, p.
552
.
5.
Danielsen
,
H. K.
, and
Hald
,
J.
, 2006,
Energy Mater.
,
1
, p.
49
.
6.
Sawada
,
K.
,
Kushima
,
H.
,
Kimura
K.
, and
Tabuchi
,
M.
, 2007,
ISIJ Int.
,
47
, p.
733
.
7.
Kimura
,
K.
,
Kushima
,
H.
, and
Abe
,
F.
, 2002,
Proceedings of the International Conference on Advances in Life Assessment and Optimization of Fossil Power Plants
, Orlando, FL.
8.
Kimura
,
K.
,
Sawada
,
K.
,
Kubo
,
K.
, and
Kushima
,
H.
, 2004,
Proceedings of the 2004 ASME/JSME PVP Conference
, San Diego, CA, p.
11
.
9.
NIMS, 2008, “
Creep Data Sheet
,” NIMS, No. 54.
10.
Atlas of Creep Deformation Property, 2007, NIMS, No. D-1.
11.
NIMS, 2002, “
Creep Data Sheet
,” NIMS, No. 48.
12.
NIMS, 2006, “
Creep Data Sheet
,” NIMS, No. 51.
13.
Kimura
,
K.
,
Sawada
,
K.
,
Fujitsuka
,
M.
, and
Kushima
,
H.
, 2009,
Proceedings of the 2009 ASME PVP Conference
, Prague, Czech Republic, PVP2009-77485.
14.
R.Viswanathan
,
J.
, 1975,
Test. Eval.
,
3
, p.
93
.
15.
Suzuki
,
K.
,
Kumai
,
S.
,
Kushima
,
H.
,
Kimura
,
K.
, and
Abe
,
F.
, 2003,
Tetsu to Hagané
,
89
, p.
69
.
16.
Hald
,
J.
, 1996,
Steel Res.
,
67
, p.
369
.
17.
Sawada
,
K.
,
Kushima
,
H.
, and
Kimura
,
K.
, 2006,
ISIJ Int.
,
46
, p.
769
.
18.
Sawada
,
K.
(unpublished data).
19.
Matsuo
,
T.
,
Kimura
,
K.
,
Tanaka
,
R.
, and
Kikuchi
,
M.
, 1990,
Proceedings of the Fourth International Conference on Creep Fracture of Engineering Materials Structures
, Swansea, UK, p.
477
.
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