What is 1.4959 Stainless Steel?

1.4959 stainless steel, commonly known as Alloy 800HT or UNS N08811, is a high-temperature nickel-iron-chromium alloy specifically designed for applications requiring maximum creep and rupture strength at elevated temperatures. With its controlled grain size, higher carbon content, and optimized aluminum and titanium additions, it offers superior high-temperature performance compared to standard Alloy 800. It is the material of choice for demanding petrochemical, power generation, and heat treatment applications where long-term service at temperatures up to 1150°C is required.

 

This premium high-temperature alloy is standardized under key international systems.

Standard	Equivalent Grade
EN (Europe)	1.4959
ASTM/AISI (USA)	Alloy 800HT, UNS N08811
Common Name	Incoloy 800HT

Its composition is optimized with controlled carbon, aluminum, titanium, and grain size for maximum creep strength.

Element	C	Si	Mn	P	S	Cr	Ni	Fe	Al	Ti
Content (%)	0.06 - 0.10	≤ 1.0	≤ 1.5	≤ 0.03	≤ 0.015	19.0 - 23.0	30.0 - 35.0	≥ 39.5	0.25 - 0.60	0.25 - 0.60

It offers exceptional creep and rupture strength at elevated temperatures.

Property	Yield Strength (Rp0.2)	Tensile Strength (Rm)	Elongation (A)	Hardness (HB)
Typical Value (Room Temp)	≥ 240 MPa	550 - 750 MPa	≥ 35%	≤ 200
Typical Value (800°C)	~ 120 MPa	~ 250 MPa	~ 40%	-

 

Key Characteristics and Applications of 1.4959 / Alloy 800HT

Maximum Creep and Rupture Strength: Controlled grain size (ASTM 5 or coarser), higher carbon content, and optimized Al/Ti additions provide superior creep resistance for long-term high-temperature service.

Excellent High-Temperature Oxidation Resistance: Forms a stable, adherent chromium oxide layer that protects against scaling and oxidation in continuous service up to 1150°C (2100°F).

Exceptional Carburization Resistance: High nickel content provides superior resistance to carbon absorption, preventing embrittlement in carbon-rich atmospheres.

Good Sulfidation and Chlorination Resistance: Performs well in sulfur and chlorine-containing environments where conventional stainless steels would rapidly degrade.

 

Primary Applications:

Petrochemical Processing: Pyrolysis tubes, reformer tubes, cracking furnace components, and pigtails in ethylene production.

Power Generation: Superheater tubing, reheater tubing, and heat recovery steam generator components.

Heat Treatment: High-temperature furnace components, retorts, muffles, and radiant tubes.

Hydrogen Reformers: Tubes and manifolds in hydrogen production facilities.

Ammonia Production: Primary and secondary reformer tubes.

Heat Exchangers: High-temperature heat transfer equipment.

 

How does Alloy 800HT (1.4959) compare to Alloy 800 (1.4876) and 800H (1.4958)?
The three variants offer increasing levels of high-temperature performance:

Alloy 800 (1.4876): Standard grade with carbon ≤0.10%, suitable for general high-temperature applications up to 1000°C

800H (1.4958): High-carbon version (0.05-0.10%) with controlled grain size (ASTM 5 or coarser), designed for improved creep strength at elevated temperatures up to 1100°C

800HT (1.4959): Most advanced version with higher Al+Ti content (0.25-0.60% each), providing maximum creep and rupture strength for applications up to 1150°C

For applications requiring the highest creep strength above 650°C, 800HT is the preferred choice. For moderate temperatures or non-load-bearing applications, standard 800 may be sufficient.

 

What are the heat treatment requirements for Alloy 800HT?
Alloy 800HT requires specific heat treatment to achieve its optimal high-temperature properties:

Solution Annealing: Heat to 1150-1200°C, hold for sufficient time to achieve controlled grain size (ASTM 5 or coarser)

Rapid Cooling: Water quench or rapid air cool to prevent carbide precipitation

The controlled grain size is essential for optimum creep strength

No further aging or precipitation hardening is required

The material is supplied in the solution-annealed condition

Post-weld heat treatment is generally not required but may be specified for certain applications

 

What are the welding considerations for Alloy 800HT?
Alloy 800HT has good weldability using all common methods including TIG, MIG, and SMAW. Key considerations include:

Matching filler metals (ERNiCr-3, ERNiCrCoMo-1) are recommended

Low heat input techniques help maintain corrosion resistance and minimize grain growth

No preheating is generally required

Post-weld heat treatment (980-1010°C, 1 hour) may be beneficial for optimizing properties in heavy sections

For maximum creep strength, welding procedures should be qualified for the specific application

Post-weld cleaning is recommended to remove oxides

 

Looking for a Reliable Supplier of 1.4959 / Alloy 800HT Stainless Steel?
GNEE Steel supplies premium Alloy 800HT (1.4959) stainless steel in pipe, tube, plate, bar, and fitting forms for the most demanding high-temperature applications. We provide full material certification (EN 10204 3.1) and processing support including cutting, forming, and welding services. If you have any requirements, please feel free to contact us.