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Oxidation Resistance

HAYNES® 556® alloy exhibits good resistance to both air and combustion gas oxidizing environments, and can be used for long-term exposure at temperatures up to 2000°F (1095°C). For exposures of short duration, 556® alloy can be used at higher temperatures.

Comparative Oxidation Resistance in Flowing Air*

Comparative Oxidation Resistance in Flowing Air*, 1008 Hours
Alloy 1800°F (980°C) 2000°F (1095°C)
Average Metal Affected** Metal Loss Average Metal Affected** Metal Loss
mils μm mils μm mils μm mils μm
X 1.5 38 0.2 5 4.4 112 1.3 33
601 1.7 43 0.4 10 3.8 97 1.3 33
556® 2.3 58 0.4 10 6.9 175 1.5 38
446 SS 2.3 60 1.3 35 14.4 366 13.0 330
RA330 3.0 76 0.3 8 6.7 170 0.8 20
800HT 4.1 104 0.5 13 11.6 295 7.6 193
304 SS 8.1 206 5.5 140 > 19.6 > 498 N/A N/A
316 SS 14.2 361 12.3 312 > 17.5 > 445 N/A N/A

*Flowing air at a velocity of 7.0 ft/min (213.4 cm/min) past the samples.
Samples cycled to room temperature once per week.
**Average Metal Affected = Metal Loss + Average Internal Penetration

Metallographic Technique used for Evaluating Environmental Tests

556 - Metallographic Technique used for Evaluating Environmental Tests

Comparative Oxidation in Flowing Air 1800°F (980°C) for 1008 Hours

Microstructures shown are for coupons exposed for 1008 hours at 1800°F (980°C) in air flowing 7.0 feet/minute (212.0 cm/minute) past the samples. Samples were descaled by cathodically charging the coupons while they were immersed in a molten salt solution. The black area shown at the top of each picture represents actual metal loss due to oxidation. The data clearly show HAYNES® 556® alloy to be superior to both RA330® alloy and Type 304 stainless steel as well as the other iron-base alloys shown in the table on the previous page.

556 - Oxidation in Flowing Air 1800°F (980°C) for 1008 Hours

HAYNES® 556® alloy
Average Metal Affected
= 2.3 mils (58 µm)

RA330 alloy - Oxidation in Flowing Air 1800°F (980°C) for 1008 Hours

RA330 alloy
Average Metal Affected
= 3.0 mils (76 µm)

304 Stainless Steel - Oxidation in Flowing Air 1800°F (980°C) for 1008 Hours

Type 304 Stainless Steel
Average Metal Affected
= 8.1 mils (206 µm)

Oxidation Test Parameters

Burner rig oxidation tests were conducted by exposing, in a rotating holder, samples 0.375 inch x 2.5 inches x thickness (9.5mm x 64mm x thickness) to the products of combustion of fuel oil (2 parts No. 1 and 1 part No. 2) burned at a ratio of air to fuel of about 50:1. (Gas velocity was about 0.3 mach). Samples were automatically removed from the gas stream every 30 minutes and fan cooled to less than 500°F (260°C) and then reinserted into the flame tunnel.

Comparative Dynamic Oxidation

Alloy 1600°F (870°C), 2000 h, 30-min cycles 1800°F (980°C), 1000 h, 30-min cycles 2000°F (1090°C), 500 h, 30-min cycles 2100°F (1150°C), 200 h, 30-min cycles
Metal Loss Average Metal Affected Metal Loss Average Metal Affected Metal Loss Average Metal Affected Metal Loss Average Metal Affected
mils µm mils µm mils µm mils µm mils µm mils µm mils µm mils µm
188 1.1 28 2.9 74 1.1 28 3.2 81 10.9 277 13.1 333 8 203 9.7 246
230 0.9 23 3.9 99 2.8 71 5.6 142 7.1 180 9.9 251 6.4 163 13.1 333
617 2 51 7.8 198 2.4 61 5.7 145 13.3 338 20.9 531 13.8 351 15.3 389
625 1.2 30 2.2 56 3.7 94 6 152 - - Consumed - - - -
556® 1.5 38 3.9 99 4.1 104 6.7 170 9.9 251 12.1 307 11.5 292 14 356
X 1.7 43 5.3 135 4.3 109 7.3 185 11.6 295 14 356 13.9 353 15.9 404
HR-120® - - - - 6.3 160 8.3 211 - - - - - - - -
RA330 2.5 64 5 127 8.7 221 10.5 267 15.4 391 17.9 455 11.5 292 13 330
HR-160® - - - - 5.4 137 11.9 302 12.5 18.1 460 8.7 221 15.5 394
310SS 6 152 7.9 201 16 406 18.3 465 - - - - - - Consumed
800H 3.9 99 9.4 239 22.9 582 Through Thickness - - Consumed after 300 h - - Consumed

Amount of metal affected for high‐temperature sheet (0.060 ‐0.125”) alloys exposed for 360 days (8,640‐h) in flowing air.*

Alloy 1600°F (870°C) 1800°F (980°C) 2000°F (1090°C)
Metal Loss** Average Metal Affected*** Metal Loss** Average Metal Affected*** Metal Loss** Average Metal Affected***
mils μm mils μm mils μm mils μm mils μm mils μm
230 0.2 5 1.4 36 0.1 3 2.5 64 3.4 86 11 279
HR-120® 0.3 8 1.6 41 0.5 13 3.3 84 18.1 460 23.2 589
188 0.2 5 1.8 46 - - - - - - - -
556® 0.3 8 1.9 48 0.5 13 6.2 157 15 381 24.1 612
X 0.3 8 2.2 56 0.2 5 2.8 71 17.1 434 26.2 665
800HT 0.4 10 2.9 74 - - - - - - - -

*Flowing air at a velocity of 7.0 ft/min (213.4 cm/min) past the samples.  Samples cycled to room temperature once per month.
** Metal loss was calculated from final and initial metal thicknesses; i.e. ML = (OMT – FMT) /2
***Average Metal Affected is sum of Metal Loss and Average Internal Penetration

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