Nickel-based super alloy: Incoloy 800HT (UNS N08811/W.Nr. 1.4959)

What is Incoloy 800H?

Incoloy 800HT, also known as “Alloy 800HT”, is designated as UNS N08811 or DIN W.Nr. 1.4959. It is an iron-nickel-chromium alloy having the same basic composition as Incoloy 800 and Incoloy 800H but with significantly higher creep-rupture strength. The higher strength results from deliberate control of the carbon, aluminum, and titanium contents in conjunction with a high-temperature anneal. Used in chemical and petroleum processing, in power plants for superheater and reheater tubing, in industrial furnaces, and for heat treating equipment.

Incoloy800HT (N08811) is a kind of All-Austrian in the same series as Incoloy 800 a low-carbon nickel-iron-chromium alloy whose cobalt content can be strictly controlled below 0.01%. Incoloy 800HT (N08811) is resistant to corrosion by many corrosive media. Its high nickel content makes it have good stress corrosion cracking resistance under water-based corrosion conditions. The high chromium content makes it have better resistance to pitting corrosion and crevice corrosion cracking. The alloy has good corrosion resistance to nitric acid and organic acids, but has limited corrosion resistance in sulfuric acid and hydrochloric acid. 
In addition to the possibility of pitting corrosion in halides, it has good corrosion resistance in oxidizing and non-oxidizing salts. It also has good corrosion resistance in water, steam and mixtures of steam, air and carbon dioxide. Used in nitric acid condenser, resistant to nitric acid corrosion, steam heating, good mechanical properties, heating element tubes, good mechanical properties, etc. For applications up to 500℃, the alloy supply state is annealed state.

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incoloy 800ht rods - Nickel-based super alloy: Incoloy 800HT (UNS N08811/W.Nr. 1.4959)

ASTM B408 UNS N08811 (Incoloy 800HT) rods. O.D=52 mm.

Incoloy 800, 800H & 800HT have nearly identical chemical composition and physical properties. The major differences between these alloys are their mechanical properties which stem from the restricted compositions of alloys 800H and 800HT and the high-temperature anneals used for these alloys. In general, alloy 800 has higher mechanical properties at room temperature and during short-time exposure to elevated temperatures, whereas alloys 800H and 800HT have superior creep and rupture strength during extended high-temperature exposure.

incoloy 800ht serpentine coil - Nickel-based super alloy: Incoloy 800HT (UNS N08811/W.Nr. 1.4959)

Incoloy 800HT serpentine coils for the heat exchanger.

Characteristics of nickel-based alloy incoloy 800ht (UNS N08811):

  • (1) It has excellent corrosion resistance in extremely high temperature aqueous media up to 500°C.
  • (2) Good resistance to stress corrosion.
  • (3) Good processability.

Chemical Composition Requirements of Incoloy 800HT

The Chemical Composition of Incoloy 800, %
Nickel 30.0-35.0
Cromium 19.0-23.0
Iron ≥39.5
Carbon 0.06-0.10
Aluminum 0.15-0.60
Titanium 0.15-0.60
Manganese ≤1.50
Sulfur ≤0.015
Silicon ≤1.00
Copper ≤0.75
Al+Ti 0.30-1.20

Physical Properties of Incoloy 800HT

Density Melting Range Specific Heat Electrical Resistivity
g/cm3 °C °F J/kg. k Btu/lb.°F µΩ·m
7.94 1357-1385 2475-2525 460 0.110 989

Temperature ℃ Specific heat capacity J/Kg K Thermal conductivity W/mK Resistivity μΩcm Elastic modulus KN/mm 2 Coefficient of thermal expansion 10-6 /K
20 440 10.8 112 195  
100 462 12.4 114 190 14.1
200 488 14.1 118 185 14.9
300 514 15.6 120 179 15.2
400 540 16.9 124 174 15.6
500 565 18.3 126 168 15.8
600 590 19.6 126 161 16.0
700 615 21.0 127 154 16.7
800 655 23.2 128 142 17.2
900 680 25.7 129 130 17.6
1000 710 28.1 130 119 17.9

Mechanical Properties of Incoloy 800HT

Tensile Strength, min. Yield Strength, min. Elongation, min. Hardness, min.
Mpa ksi Mpa ksi % HB
600 87 295 43 44 138

The properties listed in the following table apply to the soft annealing (stabilizing annealing) of the specified specifications of Incoloy800HT alloy. The special properties of non-standard size materials can be provided according to the requirements of specific applications. 

Mechanical properties at room temperature (minimum) (Test the minimum value of mechanical properties at 20℃).:

Product Specification
Yield strength 

P0.2  N/mm2

Yield strength

P1.0  N/mm2

Tensile strength 

m N/mm 2


50 %

Brinell hardness 


Sheet and strip/cold rolled 

plate/hot rolled

0.5-6.4 240 265 585 30 <=200
5-100 135-165


processing and hot processing of bars
>100-240 220 250 550 35


processing and hot processing of pipes
64-240 180 530 30
5-100 240 265 585 30
Condensation and heat exchanger 16-76

High temperature mechanical properties (minimum)

product Yield strength R P0.2  N/mm 2 Yield strength R P1.0  N/mm 2
Temperature ℃ 100 200 300 400 450 100 200 300 400 450
Plate, strip, tube 205 180 170 160 155 235 205 195 185 180
Baton 190 165 155 145 140 220 190 180 170 165

ISOV type notched impact test of Incoloy 800HT (UNS N08811):

Room temperature average value:

  • Axial>=150J/cm 2
  • Radial>=100J/cm 2

Time-temperature-sensitization curve:
1 1F11Q22931331 - Nickel-based super alloy: Incoloy 800HT (UNS N08811/W.Nr. 1.4959)

Conditional stress value of Incoloy 800HT (UNS N08811):

The high-condition stress value that reaches 90% of the yield strength can be used in applications where a slightly larger amount of deformation is allowed. The permanent stresses caused by these stresses can cause dimensional changes, so it is not recommended for flange and gasket connections. 

Metallographic structure of Incoloy 800HT (UNS N08811):

Incoloy800HT alloy has a stable face-centered cubic structure. The chemical composition and proper heat treatment ensure that the corrosion resistance is not impaired by sensitization. 

Corrosion resistance of Incoloy 800HT (N08811) alloy:

Incoloy 800HT is a general engineering alloy, which is resistant to acid and alkali metal corrosion in both oxidation and reduction environments. The high nickel content makes the alloy have effective resistance to stress corrosion cracking. It has good corrosion resistance in various media, such as sulfuric acid, phosphoric acid, nitric acid and organic acids, and alkali metals such as sodium hydroxide, potassium hydroxide and hydrochloric acid solutions. The high comprehensive performance of Incoloy800HT is manifested in nuclear combustion dissolvers with various corrosive media, such as sulfuric acid, nitric acid and sodium hydroxide, which are all processed in the same equipment.

Processing and Heat Treatment of Incoloy 800HT (UNS N08811)

Incoloy800HT (N08811) alloy heating:

  • (1). Keep the workpiece clean before and during heat treatment.
  • (2). Do not touch sulfur, phosphorus, lead and other low melting point metals during the heat treatment process, otherwise it will damage the performance of the material. Care should be taken to remove dirt such as marking paint, temperature indicating paint, colored crayons, lubricating oil, fuel, etc.
  • (3). The lower the sulfur content in the fuel, the better. The sulfur content in natural gas should be less than 0.1%, and the sulfur content in heavy oil should be less than 0.5%.
  • (4). Considering the need for temperature control and keeping clean, it is best to conduct heat treatment in a vacuum furnace or a gas shielded furnace.
  • (5). It can also be heated in a box furnace or a gas furnace, but the furnace gas must be clean and neutral to slightly oxidizing. The furnace gas should be avoided from fluctuating between oxidizing and reducing properties. The heating flame cannot be directly heated. Burn to the workpiece.

Incoloy800HT (N08811) alloy thermal processing:

  • (1). The thermal processing temperature of Incoloy 800HT ranges from 1200°C to 900°C, and the cooling method is water quenching or cooling as quickly as possible between 760°C and 540°C. Thermal bending should be carried out between 1150℃-1000℃.
  • (2). In order to get the best corrosion resistance and creep resistance, annealing treatment should be carried out after hot working.
  • (3). The material can be directly fed into the furnace that has been heated to 1200°C, and the holding time of the material is 60 minutes per 100mm thickness. After being kept for a sufficient time, the furnace will be quickly released, and thermal processing will be carried out in the specified temperature range. When the material temperature drops below the thermal processing temperature, it needs to be reheated.

Cold processing of Incoloy800HT (N08811) alloy:

  • (1) The wor.k hardening rate of Incoloy 800HT is greater than that of austenitic stainless steel, so it is necessary to select processing equipment. The cold-worked material should be in an annealed heat-treated state, and intermediate annealing should be carried out during cold working.
  • (2). If the amount of cold working is greater than 10%, the workpiece needs to be softened and annealed before use.

Heat treatment of Incoloy 800HT (N08811) alloy:

  • (1). The soft annealing temperature range of Incoloy 800HT is 920℃~980℃, and the best treatment temperature is 950℃.
  • (2). In order to obtain the best corrosion resistance, the cooling method adopts water quenching, and the material with thickness less than 1.5mm can also adopt rapid air cooling.
  • (3). During the heat treatment process, the operation must be performed in accordance with the aforementioned items that must be kept clean during the heating process.

Incoloy 800HT (N08811) alloy descaling and pickling:

  • (1). Incoloy 800HT has stronger adhesion of surface oxides and weld slag around the weld than stainless steel. Both mechanical and chemical methods can be used. Choose mechanical The method should avoid the method that will produce metal pollution or produce surface deformation.
  • (2). Before pickling with HNO 3 /HF mixed acid, it must be carefully polished or salt bath pretreatment to break the oxide film.

Incoloy800HT (N08811) alloy machining:

Incoloy 800HT must be machined after annealing and heat treatment. Due to the work hardening of the material, it is advisable to use a lower cutting speed and re-entry tool than processing low-alloy standard austenitic stainless steel in order to be machined under the cold work hardened surface.

Welding of Incoloy 800HT (UNS N08811)

Incoloy800HT (N08811) alloy is suitable for welding by any traditional welding process.

Such as tungsten electrode inert gas arc welding, plasma arc welding, manual sub-arc welding, metal inert gas arc welding, melting electrode Inert gas shielded welding, shielded gas arc welding, etc. The welding of Incoloy 800HT must be carried out in an annealed state, and stains, dust and various marks must be cleaned up. With low heat input, the temperature between layers does not exceed 150°C. No pre- or post-weld heat treatment is required. 

Incoloy800HT (N08811) alloy cleaning:

remove oxide scale, oil stains and various marking marks, and use acetone to clean the base metal and filler alloys (such as welding rods) in the welding area. Note that trichloroethylene TRI and perchloroethylene PER cannot be used. And tetrachloride TETRA.  

Incoloy800HT (N08811) alloy edge preparation:

It is best to use machining, such as turning, milling, planing, or plasma cutting. If the latter is used, the cutting edge (welding surface) must be ground clean and flat, allowing overheating fine grinding. The base material on both sides of the weld should be polished to expose the bright metal. 
1 1F11Q23236147 - Nickel-based super alloy: Incoloy 800HT (UNS N08811/W.Nr. 1.4959)

Incoloy800HT (N08811) alloy groove angle:

Compared with carbon steel, the physical properties of nickel-based alloy and special stainless steel are mainly low thermal conductivity and high coefficient of expansion. These characteristics must be prepared during welding groove preparation. It should be considered, including widening the bottom gap (1~3mm), and due to the viscosity of molten metal, a larger groove angle (60~70°) should be used in butt welding to offset material shrinkage. 

Incoloy800HT (N08811) alloy arc starting:

The arc cannot be started on the surface of the workpiece, and the arc should be started on the welding surface to prevent corrosion at the starting point. 

Welding process of Incoloy 800HT (UNS N08811):

  • (1) Incoloy800HT is suitable for welding with the same material or other metals using any traditional welding process, such as tungsten electrode inert gas shielded welding, plasma arc welding, manual sub-arc welding, and extremely inert metal Gas arc welding, MIG welding, pulse arc welding is the first choice. When using manual arc welding, it is recommended to use (Ar+He+H 2 +CO 2 ) shielding gas mixed with multiple components. 
  • (2) The welding of Incoloy800HT must be carried out in the annealed state, and a stainless steel wire brush should be used to clean up stains, dust and various marks. When welding the root of the weld, in order to obtain the best quality of the root weld, the operation must be very careful (argon 99.99), so that the weld does not produce oxides after the root is welded. The color generated in the welding heat-affected zone should be brushed off with a stainless steel brush when the weld area is not cooled. 
  • Recommended welding materials: welding rod: EniCrFe-3, welding wire: ERNiCr-3. 
  • (3) Incoloy800HT welding parameters and influence (heat input): The welding operation should be carried out under the low heat input specified in the heat input table, using stacked bead welding technology, the temperature between layers does not exceed 120 ℃, and welding specifications must be followed. The heat input Q is calculated according to the following formula: 

    1 1F11Q23311125 - Nickel-based super alloy: Incoloy 800HT (UNS N08811/W.Nr. 1.4959)

  • U = arc voltage, volt 
  • I = welding current, ampere 
  • V = welding speed, cm/min. 

Incoloy800HT (N08811) alloy post-weld treatment (pickling, brushing and heat treatment):

The stainless steel wire brush should be used to remove oxides immediately after welding, that is, when the metal has not yet produced a welding color, the ideal surface quality can be obtained without pickling. If there are no special requirements or regulations, pickling is usually the last process in welding. Please refer to the section on descaling and pickling. No heat treatment is required before and after welding.

Product Forms and Standards of Incoloy 800HT

Product From Standard
Rod and Bar ASTM B408, EN 10095
Plate, Sheet & Strip ASTM A240, A480, ASTM B409, B906
Seamless Pipe & Tube ASTM B829, B407
Welded Pipe & Tube ASTM B514, B515, B751, B775
Welded fittings ASTM B366
Forging ASTM B564, DIN 17460

Application areas of nickel-based alloy incoloy 800ht (N08811):

  • Heating pipes, containers, baskets and chains used in sulfuric acid pickling plants.
  • Sea water cooling heat exchanger, marine product pipeline system, acid gas environment pipeline.
  • Heat exchanger, evaporator, washing, dip tube, etc. in phosphoric acid production.
  • Air heat exchanger in petroleum refining.
  • Food engineering, chemical process.
  • Flame retardant alloy for high pressure oxygen application.
  • Heat exchange tubes
  • Pipe fittings
  • Flanges
  • Valves

Varieties, specifications and supply status of Incoloy 800ht (N08811) nickel-based alloys:

Variety classification:

Yaang Pipe Industry can produce Incoloy 800ht seamless pipes, Incoloy 800ht pipe fittings, Incoloy 800ht round bars, Incoloy 800ht forgings, Incoloy 800ht flanges of various specifications , Incoloy 800ht ring, Incoloy 800ht welded pipe, Incoloy 800ht steel strip, Incoloy 800ht wire and supporting welding materials. 

Delivery status:

  • Seamless pipe: solid solution + acid white, length can be set; plate: solid solution, pickling, trimming;
  • Welded pipe: solid solution acid white + RT% flaw detection, forging: annealing + car polish; 
  • Bars are forged and rolled, surface polished or car polished; strips are delivered after cold rolling, solid solution soft state, and deoxidized; 
  • Wire rods are finely ground in solid solution pickled disk or straight strips, solid solution straight strips Delivery in light state.

Source: China Incoloy 800HT Flanges Manufacturer – Yaang Pipe Industry (

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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