Description
The austenitic grade 800 comprises of nickel-chromium-iron as its major constituent and is specifically used for applications at elevated temperatures. It can suitably resist oxidation and partially resist cyclic oxidation, carburization and nitride environments, all while keeping its strength at elevated temperatures. For achieving optimum properties at high temperatures, the grade 800 gets a slight modification in its chemical composition and is certified as grade 800H and grade 800HT.
The 800H & 800HT are heat treated for desired grade properties. They go through annealing to acquire fine grain structure. Both the grades have increased level of carbon which makes them conducive for applications at elevated temperature. The grade 800HT has extra levels of aluminium and titanium content. A close control on the addition of carbon, aluminium and titanium content is maintained.
The modification made gives the alloy its use in high-temperature structural applications. They remain ductile during long-term use due to their composition. The grade 800 is efficiently used below 590°C. For usage above 590°C, alloy 800H and alloy 800HT are used. These grades show exceptional creep resistance properties without failing even after long exposure to high temperature. These grades are also used in the sigma phase temperature range since they effectively resist embrittlement due to their composition and the titanium content stabilizes the carbides. The presence of aluminium in grade 800HT might be used to form intermetallic compounds during precipitation, this would subsequently increase the strength of the metal. Aluminium also helps in improving oxidation resistance.
The alloy grades can be conveniently hot worked as well as cold worked. Hot working needs to be done with precision. If the deformation is under 5%, the temperature range needs to be done around 850-1100°C, if the deformation is more, the temperature range needs to be around 950-1200°C. Less than the required temperature might make the metal lose its strength, with subsequent heat treatment required to retain its normal state. After this process, the alloys are gone through rapid air cooling or water quenching. Followed by annealing, to properly retain its strength and corrosion as well as creep resistance properties. The grade has a high work hardening rate and it should be considered before cold working. After cold working, if the deformation is still high, the metal needs to be annealed properly to remove brittleness.
Chemical Properties
| Grade | Ni | C | Cr | Mn | Si | Cu | Al | S | Fe | Ti | |
| Incoloy 800 | Min. | 30 | – | 19 | – | – | – | 0.15 | – | 39.5 | 0.15 |
| Max. | 35 | 0.1 | 23 | 1.5 | 1 | 0.75 | 0.6 | 0.015 | – | 0.60A | |
| Incoloy 800H | Min. | 30 | 0.5 | 19 | – | – | – | 0.15 | – | 39.5 | 0.15 |
| Max. | 35 | 0.1 | 23 | 1.5 | 1 | 0.75 | 0.6 | 0.015 | – | 0.60A | |
| Incoloy 800HT | Min. | 30 | 0.6 | 19 | – | – | – | 0.15 | – | 39.5 | 0.15 |
| Max. | 35 | 0.1 | 23 | 1.5 | 1 | 0.75 | 0.6 | 0.015 | – | 0.60A |
Physical Properties
| Density | 0.287 lb/in3 / 7.94 g/cm3 |
| Melting Point | 2475 – 2525 °F/ 1357 – 1385 °C |
| Specific Heat @ 70°F | 0.11 BTU/lb-°F (32 – 212°F) 460 J/kg-°K (0 –100°C) |
| Thermal Conductivity @ 212°F | 10.6 BTU/hr/ft2/ft/°F 18.3 W/m-°K |
| Elastic Modulus | 28.5 x 106 psi 196.5 GPa |
| Electrical Resistivity | 59.5 Microhm-in at 68°F 99 Microhm-cm at 20°C |
| Annealing | 983 – 1038 °C / 1800 – 1900 °F |
| Quench | Rapid Air |
| Permeability @ 70°F Annealed | 1.014 (200 Oersted) |
| Curie Temperature | -115 °C/ -175 °F |
General Data
| Standard | Incoloy 800 | Incoloy 800H | Incoloy 800HT |
| UNS | N08800 | N08810 | N08811 |
| WERKSTOFF NR. | 1.4876 | 1.4958 / 1.4876 | 1.4859 / 1.4876 |
| EN | X10NiCrAlTi32-20 | X5NiCrAlTi31-20 | X8NiCrAlTi32-21 |
| BS | NA 15 | NA 15(H) | NA 15(HT) |
| OR | XH32T | XH32T | XH32T |
| GOST | ЭИ670 | ЭИ670 | ЭИ670 |
| JIS | NCF 800 | NCF 800H | NCF 800HT |
| AFNOR | Z8NC32-21 | Z8NC33-21 | – |
Standards Specifications
PIPES & TUBES
| Summary | Standards |
| Standard Specification for Seamless Nickel and Nickel Alloy Condenser and Heat-Exchanger Tubes | ASTM B163 |
| Standard Specification for Nickel-Iron-Chromium Alloy Seamless Pipe and Tube | ASTM B407 |
| Standard Specification for Welded Nickel-Iron-Chromium Alloy Pipe | ASTM B514 |
| Standard Specification for Welded UNS N08120, UNS N08800, UNS N08810, and UNS N08811 Alloy Tubes | ASTM B515 |
| Standard Specification for Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes | ASTM A213 |
| Standard Specification for Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes | ASTM A312 |
| Standard Specification for Electric-Fusion-Welded Austenitic Chromium-Nickel Stainless Steel Pipe for High-Temperature Service and General Applications | ASTM A358 |
FITTINGS & FLANGES
| Summary | Standards |
| Standard Specification for Factory-Made Wrought Nickel and Nickel Alloy Fittings | ASTM B366 |
| Standard Specification for Nickel Alloy Forgings | ASTM B564 |
| Standard Specification for Wrought Austenitic Stainless Steel Piping Fittings | ASTM A403 |
Forms of Supply
Pipe and tubing, fittings and flanges, washers.
Corrosion Resistance
The grade has exceptional resistance to general corrosion at elevated temperatures. The modified grade 800/800HT have excellent creep resistance properties and show enough strength even after long exposure to high temperature. The grades can show creep rupture strength of 120 MPa at a temperature of 650°C for an exposure of 10000 hours. The grades also show fine resistance to cyclic oxidation. After conducting cyclic oxidation test on the grades with 15 minutes heating and then cooling for 1000 hours, the grade showed very less change in weight (in mg/cm^2), close to alloy 600, and better than 300 series alloys. However, sulphuric acid environments are not recommended for the grade. Both the grades have similar and adequate aqueous corrosion resistance.
Heat Treatment
The grade has high rate of work hardening. Hence, after cold working to remove brittleness, the grade needs to annealed. Annealing is done by heating the grade about 980°C for about 15 minutes, and then air cooling.
Weldability
The grade can be readily welded by common welding techniques like gas tungsten arc welding, shielded metal arc welding, metal inert gas welding, etc. Post-weld annealing might not be required. The grade can be appropriately brushed for impurities and heat tint is removed after welding.
Machining
Since the metal has high work hardening rate, proper machining techniques are required. Slow cutting speeds, proper depth of cut, rigid tooling, powerful machinery shall be required.
Applications
Heat exchangers, heating elements, carburising equipment, power generation equipment, petroleum refining equipment, chemical and petrochemical processing, ammonia effluent cooler, process piping, furnace components, hydrocarbon cracking, pressure vessels.
Possible grade alternatives
INCONEL 600
| Grade | Ni | C | Cr | Mn | Si | Fe | S | Cu | N | P | |
| Inconel 600 | Min. | 72 | – | 14 | – | – | 6 | – | – | – | – |
| Max. | – | 0.15 | 17 | 1 | 0.5 | 10 | 0.015 | 0.5 | – | – |
GRADE 304
| Grade | Ni | C | Cr | Mn | Si | Fe | S | Cu | N | P | |
| Inconel 304 | Min. | 8 | – | 18 | – | – | – | – | – | – | – |
| Max. | 10.5 | 0.08 | 20 | 2 | 0.75 | BAL. | 0.03 | – | 0.1 | 0.045 |
