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

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.
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.
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