Name: Alloy 800H
Brand: Ever Nickel
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Alloy 800H

Alloy 800H/800HT^® are two individual solid solution strengthened, iron-nickel-chromium alloys. They are typically oﬀered as one, dual certiﬁed alloy, meeting the chemical composition requirements of both alloys. The principle diﬀerence between alloys 800H and 800HT^® is the restricted aluminum and titanium content in 800HT^®, which results in higher creep and stress rupture properties. Both alloy 800H and 800HT^® are generally considered to be superior to the base alloy 800 (UNS N08800) because of greater creep and stress rupture properties and a more restrictive C wt% range. Alloy 800H limits the C wt% from just 0.1% max in base alloy 800 to a 0.5% to 0.1% range. Alloy 800HT^® further controls this by limiting the C wt% to 0.6% to 0.1%. There are also limitations on the grain size for alloy 800 H/HT^® that are not in place for alloy 800.

Alloy 800H

800HT®

UNS N08810 & N08811

W.Nr. 1.4958 & 1.4959

Data Sheet

Industries and Applications

Alloy 800H/800HT^® is frequently used in applications that involve long-term exposure to elevated temperatures where resistance to oxidation, carburization and other types of elevated temperature corrosion is required. Heat treatment and power generation are two common industries where alloy 800 H/HT^® is used. Typical applications include superheater and reheater tubing, headers, pigtails, outlet manifolds and sheathing for heating elements. Pressure vessels and vessel components constructed from 800H and 800HT^® are approved under the ASME Boiler and Pressure Vessel Code, Section VIII, Division 1.

Resistance to Corrosion

The high nickel and chromium contents in alloy 800H/800HT^® results in excellent resistance to oxidation, carburization and sulﬁdation. The high nickel content also increases the resistance to nitriding, although resistance could be lower than other alloys containing a higher percentage of nickel, such as alloy 600. Alloy 800H/800HT^® has excellent resistance to nitric acid at concentrations up to 70% largely due to the chromium content. The alloy has good resistance to organic media like formic, acetic and propionic acids.

Fabrication and Heat Treatment

Hot-working temperatures should be between 1600°F and 2200°F with heavy forming to be performed at temperatures above 1850°F. No forming should be performed between 1200°F and 1600°F and preheating of tools and dies to 500°F is suggested to avoid chill. Cooling after hot working should be as quick as possible, avoiding extensive time at temperatures between 1000°F and 1400°F. Cold working should be performed on material in the annealed condition. Depending on the amount of strain induced by cold work during fabrication, an additional stress relieving or annealing heat treatment may be necessary. Because excessive grain growth can negatively aﬀect mechanical properties, care must be taken in selecting an annealing temperature and time at temperature for the process. If material is to be deformed more than 20% and a ﬁnal anneal is desired, ﬁne-grain material should be considered for the starting stock. Stress relief is performed between 1000°F and 1600°F and should be at temperature for 1 hour per inch of material or for a minimum of 1½ hours at 1600°F, whichever is greater. Recrystallization anneal is achieved at temperatures between 2100°F and 2200°F.

Chemical Composition

Chemical Composition Limits
Weight %	Ni	Cr	Fe	C	Al	Ti	Al+Ti
Alloy 800	30-35	19-23	39.5 min	0.10 max	0.15-0.60	0.15-0.60	0.30-1.20
Alloy 800H	30-35	19-23	39.5	0.05-0.10	0.15-0.60	0.15-0.60	0.30-1.20
Alloy 800HT	30-35	19-23	39.5	0.06-0.10	0.25-0.60	0.25-0.60	0.85-1.20
ASTM Grain Size - Alloy 800 is not specified, Alloy 800H is 5 or coarser, Alloy 800HT is 5 or coarser.

Mechanical Properties

Temper	800		800H/HT
Tensile Rm	77.8	ksi (min)	65	ksi (min)
Tensile Rm	536	MPa (min)	448	MPa (min)
R.p. 0.2% Yield	22	ksi (min)	25	ksi (min)
R.p. 0.2% Yield	150	MPa (min)	172	MPa (min)
Elongation (2” or 4D gl)	20	% (min)	20	% (min)

Physical Properties (Room Temperature)

Specific Heat (0-100°C)	460	J.kg-1.°K-1
Thermal Conductivity	11.5	W.m -1.°K-1
Thermal Expansion	14.4	μm/μm/°C
Modulus Elasticity	208	GPa
Electrical Resistivity	9.89	Ohm-cm
Density	7.94	g/cm3

A brief history of Alloy 800/800H/800HT

Originally developed in the 1940s, Alloy 800 was introduced as a nickel-iron-chromium alloy specifically designed for high-temperature applications requiring resistance to oxidation and carburization. Over time, Alloy 800 was further refined into two derivative grades, 800H and 800HT, which offered improved creep and stress rupture strength for use in even more demanding environments. These alloys have become essential materials in industries requiring long-term stability and corrosion resistance at elevated temperatures.

Common applications

Alloy 800 and its derivatives are widely used in high-temperature and corrosive environments. In the power generation and petrochemical industries, they are employed in components such as heat exchangers, steam generators, and superheater tubing. In the chemical processing industry, they are used in equipment exposed to acidic and high-temperature environments, such as process piping and reactor vessels. Additionally, Alloy 800H and 800HT are commonly found in furnace components, muffle tubes, and other heat-treating fixtures due to their enhanced strength and resistance to thermal fatigue.

Resistance to corrosion and heat

Alloy 800’s high nickel and chromium content provides excellent resistance to oxidation, carburization, and sulfidation in both oxidizing and reducing environments. The alloy maintains its strength and structural integrity over long periods of exposure to temperatures up to 1100°F. Alloy 800H and 800HT, with controlled carbon and grain size specifications, exhibit improved creep and stress rupture properties, making them suitable for prolonged use at temperatures up to 1500°F. These alloys also demonstrate excellent resistance to chloride-ion stress corrosion cracking and pitting, even in aggressive environments.

Modern Innovations

Advancements in processing and manufacturing technologies have expanded the applications of Alloy 800/800H/800HT. These alloys are now being used in newer energy systems, such as solar power plants and waste-to-energy facilities, where durability under high-temperature and corrosive conditions is critical. Additive manufacturing techniques have also made it possible to produce complex components with greater precision and reduced material waste. Today, Alloy 800 and its derivatives remain indispensable materials in industries requiring high-performance alloys for extreme conditions.