Thermal Stability of High-temperature Alloys

 

Tensile Ductility after Thermal Exposure

Thermal stability is an important design characteristic for engineering materials used at elevated temperatures. It may be defined as the resistance of an alloy to degradation of ductility and toughness when subjected to long-term thermal exposure. One common measurement of thermal stability is residual room temperature tensile elongation following such exposure. The following are test results for both plate and sheet materials exposed for 6,000 to 8,000 hours at different temperatures. Data are averages of at least two tests.

Alloy Form Room Temperature Tensile Elongation Following 8,000 Hour Exposure at the Indicated Temperature (%)*
None 1200°F (650°C) 1400°F (760°C) 1600°F (870°C)
230® Plate 50 38 35 36
S Plate 54 50 46 53
625 Plate 46 18 13 26
X Plate 47 18 20 26
188 Plate 56 29 11 22
556® Plate 51 31 22 23
800H Plate 58 35
X Sheet 57 19 19 30
188 Sheet 62 32 9 15
S Sheet 58 54 54
600 Sheet 37 38 39* 41*
601 Sheet 47 30 41* 43*
800H Sheet 47 37 42* 40*

* Data for 6,000 hour exposures are indicated with an asterisk

Impact Strength after Thermal Exposure

Another common measurement of thermal stability is residual room temperature impact strength following long-term exposure at elevated temperatures. The following are results for impact tests performed upon samples exposed for 5,000 to 10,000 hours at different temperatures. The comparison includes values derived from multiple in-house tests and values taken from published data. Results are for Charpy V-Notch tests unless otherwise noted.

Alloy Room Temperature Tensile Elongation Following 8,000 Hour Exposure at the Indicated Temperature (%)*
None 1200°F (650°C) 1400°F (1150°C) 870°C (1600°F)
ft-lb J ft-lb J ft-lb J ft-lb J
230® 54 73 30 41 28 21 28 21
S 140 190 54 73 65 48 142 105
625 81 110 5 7 7 5 20 15
X 54 73 15 20 11 8 20 15
188 143 194 23 31 4 3 14 10
556® 177 240 18 24 8 6 7 5
800H 239 324 81 110
253MA 110 149
13(1)
18(1)
22(2)
16(2)
304* 91 123
47(3)
64(3)
316L* 80 108
21(3)
28(3)
310* 75 102
2(3)
3(3)
446 1 1
1(3)
1(3)

* Charpy Key Hole tests are indicated with an asterisk. All others are Charpy V-Notch tests.
(1) 5,000 Hour Exposure at 1292°F (700°C)
(2) 5,000 Hour Exposure at 1472°F (800°C)
(3) 10,000 Hour Exposures