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Thermal Stability

HAYNES® 188 alloy is similar to the solid-solution-strengthened superalloys, such as alloy 625 or HASTELLOY® X alloy,  which will precipitate deleterious phases upon such long-term exposure. In this case. the phase in question is a CO2W laves phase.  which serves to impair both tensile ductility and impact strength. The behavior of 188 alloy is significantly better in this regard than HAYNES® 25 alloy, which it replaced; but for applications where thermal stability is important, 230® alloy is recommended.

188 alloy ThermalEx

Room-Temperature Properties of Plate after Thermal Exposure

Exposure Temperature - 0.2% Yield Strength Ultimate Tensile Strength Elongation Impact Strength
°F °C h ksi MPa ksi MPa % ft.- lbs. J
1200 650 0 65.0 450 140.0 965 56.0 143 194
8000 79.7 550 151.6 1045 29.1 23 31
1400 760 0 65.0 450 140.0 965 56.0 143 194
8000 74.0 510 147.9 1020 10.8 3 4
1600 870 0* 70.1 485 146.0 1005 50.4 143 194
1000 70.7 490 157.5 1085 28.7 10 13
4000 68.8 475 156.0 1075 26.6 10 13
8000* 64.5 445 147.4 1015 22.2 9 12
16000 63.8 440 146.1 1005 24.0 8 11

*Average of two test exposure. All other single exposures.

Comparative Impact Strength after 8000-Hour Exposures

Alloy Solution-Annealed Charpy
V-Notch Impact 		Charpy V-Notch Impact Following Exposure
For 8000 Hours at Temperatures
1200°F 650°C 1400°F 760°C 1600°F 870°C
- ft.-lbs. J ft.-lbs J ft.-lbs J ft.-lbs J
230® 54 73 30 41 21 28 21 28
188 143 194 23 31 3 4 9 12
X 54 73 15 20 8 11 15 20
625 81 110 5 7 5 7 15 20
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