Nickel-Iron-Chromium Alloys are Designed to Resist Oxidation and Carburization with Higher Creep and Stress Rupture Properties than Alloy 800 (UNS N08800).
General Properties
Alloy 800H has good
creep-rupture properties at temperatures above 1100°F (600°C). It remains
ductile during long-term use at temperatures below 1290°F (700°C) due to a
maximum titanium and aluminum content of 0.7%. Alloy 800 with a standard anneal
is recommended for service below 1100°F (600°C). Alloy 800H resists reducing,
oxidizing and nitriding atmospheres, as well as, atmospheres that alternate
between reducing and oxidizing. The alloy remains stable in long-term high-temperature
service.
Alloy 800HT has excellent
creep strength at temperatures above 1290°F (700°C). If the application
involves frequent temperature excursions under 1290°F (700°C) or parts of are
permanently exposed to a temperature below 1290°F (700°C), Alloy 800H should be
utilized. The high temperature resistance of Alloy 800HT is comparable to Alloy
800H. It also remains stable in long term high temperature service.
Alloys 800H and 800HT are
easily welded and processed by standard shop fabrication practices.
Applications
- Chemical and Petrochemical Processing—process
equipment for the production of ethylene, ethylene dichloride, acetic
anhydride, ketene, nitric acid and oxy-alcohol
- Petroleum Refining—steam/hydrocarbon
reformers and hydrodealkylation units
- Power Generation—steam super-heaters
and high temperature heat exchangers in gas-cooled nuclear reactors, heat
exchangers and piping systems in coal-fired power plants
- Thermal Processing Fixtures—radiant
tubes, muffles, retorts and fixtures for heat-treating furnaces
Standards
ASTM..................B 409
ASME..................SB
409
AMS
...................5871
Chemical Analysis
Weight % (all values are
maximum unless a range is otherwise indicated)
|
Element |
800H |
800HT |
|
Nickel |
30.0
min.-35.0 max. |
30.0
min.-35.0 max. |
|
Chromium |
19.0
min.-23.0 max. |
19.0
min.-23.0 max. |
|
Iron |
39.5 |
39.5 |
|
Carbon |
0.05
min.-0.10 max. |
0.06
min.-0.10 max. |
|
Manganese |
1.50 |
1.50 |
|
Phosphorus |
0.045 |
0.045 |
|
Sulfur |
0.015 |
0.015 |
|
Silicon |
1.0 |
1.0 |
|
Aluminum |
0.15
min.-0.60 max. |
0.25
min.-0.60 max. |
|
Titanium |
0.15
min.-0.60 max. |
0.25
min.-0.60 max. |
|
Aluminum & Titanium |
0.30
min.-1.20 max. |
0.85
min.-1.20 max. |
Physical Properties
Density
0.287 lbs/in3
7.94 g/cm3
Specific Heat
0.11 BTU/lb-°F (32-212°F)
460 J/kg-°K (0-100°C)
Modulus of Elasticity
28.5 x 106 psi
196.5 Gpa
Thermal Conductivity
212°F (100°C)
10.6 BTU/hr/ft2/ft/°F
18.3 W/m-°K
Melting Range
2475 – 2525°F
1357 – 1385°C
Electrical Resistivity
59.5 Microhm-in at 68°C
99 Microhm-cm at 20°C
|
Mean
Coefficient of Thermal Expansion |
|||
|
°F |
°C |
in/in/°F |
cm/cm°C |
|
200 |
93 |
7.9 x 10-6 |
14.4 x 10-6 |
|
400 |
204 |
8.8 x 10-6 |
15.9 x 10-6 |
|
600 |
316 |
9.0 x 10-6 |
16.2 x 10-6 |
|
800 |
427 |
9.2 x 10-6 |
16.5 x 10-6 |
|
1000 |
538 |
9.4 x 10-6 |
16.8 x 10-6 |
|
1200 |
649 |
9.6 x 10-6 |
17.1 x 10-6 |
|
1400 |
760 |
9.9 x 10-6 |
17.5 x 10-6 |
|
1600 |
871 |
10.2 x 10-6 |
18.0 x 10-6 |
Mechanical Properties
Typicals Values at 70°F
(21°C)
|
Yield Strength |
Ultimate Tensile |
Elongation |
Hardness |
||
|
psi (min.) |
(MPa) |
psi (min.) |
(MPa) |
% (min.) |
(max.) |
|
29,000 |
200 |
77,000 |
531 |
52 |
126 Brinell |
Creep and Rupture
Properties
The tight chemistry control and solution annealing heat treatment were designed to provide optimum creep and rupture properties for Alloys 800H and 800HT. The following charts detail the outstanding creep and rupture properties of these alloys.
Representative
Rupture-Strength Values for Alloys 800H/800HT
|
Temperature |
10,000 h |
30,000 h |
50,000 h |
100,000 h |
|||||
|
°F |
°C |
ksi |
MPa |
ksi |
MPa |
ksi |
MPa |
ksi |
MPa |
|
1200 |
650 |
17.5 |
121 |
15.0 |
103 |
14.0 |
97 |
13.0 |
90 |
|
1300 |
705 |
11.0 |
76 |
9.5 |
66 |
8.8 |
61 |
8.0 |
55 |
|
1400 |
760 |
7.3 |
50 |
6.3 |
43 |
5.8 |
40 |
5.3 |
37 |
|
1500 |
815 |
5.2 |
36 |
4.4 |
30 |
4.1 |
28 |
3.7 |
26 |
|
1600 |
870 |
3.5 |
24 |
3.0 |
21 |
2.8 |
19 |
2.5 |
17 |
|
1700 |
925 |
1.9 |
13 |
1.6 |
11 |
1.4 |
10 |
1.2 |
8.3 |
|
1800 |
980 |
1.2 |
8.3 |
1.0 |
6.9 |
0.9 |
6.2 |
0.8 |
5.5 |
Oxidation Resistance
The combination of the high nickel and chromium content in alloys 800H and 800HT provides excellent oxidation resistance properties to both alloys. The results of cyclic oxidation tests at both 1800°F (980°C) and 2000°F (1095°C) are shown below.
Corrosion Resistance
The high nickel and
chromium content of Alloys 800H and 800HT generally means they will have very
similar aqueous corrosion resistance. The alloys have corrosion resistance that
is comparable to 304 when used in nitric and organic acid service. The alloys
should not be used in sulfuric acid service. They are subject to chromium
carbide precipitation if in service for prolonged exposure in the 1000-1400°F
(538-760°C) temperature range.
Since Alloys 800H and
800HT were developed primarily for hightemperature strength, corrosive
environments to which these grades are exposed normally involve high
temperature reactions such as oxidation and carburization.
Fabrication Data
Alloys 800H and 800HT can
be easily welded and processed by standard shop fabrication practices. However,
because of the high strength of the alloys, they require higher powered process
equipment than standard austenitic stainless steels.
Hot Forming
The hot-working
temperature range for Alloy 800H and 800HT is 1740–2190°F (950–1200°C) if
deformation is 5 percent or greater. If the degree of hot deformation is less
than 5 percent a hot working temperature range between 1560–1920°F (850–1050°C)
is recommended. If the hot working metal temperature falls below the minimum
working temperature, the piece must be re-heated. The alloys should be water
quenched or rapid air cooled through the temperature range of 1000–1400°F
(540–760°C). Alloys 800H and 800HT require solution annealing after hot working
to ensure optimal creep resistance and properties.
Cold Forming
The alloys should be in
the annealed condition prior to cold forming. Work hardening rates are higher
than the austenitic stainless steels. This should be taken into account when
selecting process equipment. An intermediate heat treatment may be necessary
with a high degree of cold working or with more than 10 percent deformation.
Welding
Alloys 800H and 800HT can
be readily welded by most standard processes including GTAW (TIG), PLASMA, GMAW
(MIG/MAG), and SMAW (MMA). The material should be in the solution annealed
condition, and free from grease, markings or scale. A post-weld heat treatment
is not necessary. Brushing with a stainless steel wire brush after welding will
remove the heat tint and produce a surface area that does not require
additional pickling.
Machining
Alloys 800H and 800HT
should preferably be machined in the annealed condition. Since the alloys are
prone to work–hardening, only low cutting speeds should be used and the cutting
tool should be engaged at all times. Adequate cut depth is necessary to assure
avoiding contact with the previously formed work-hardened zone.
