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Introduction

Alloy 800, 800H, and 800HT are nickel­iron­chromium alloys having high resistance to carburization and oxidation in high­temperature exposure and with good strength. These nickel steel alloys are identical except for the higher level of carbon in alloy 800H, and the addition of up to 1.20 % aluminum and titanium in alloy 800HT

Alloy 800 was the first of these alloys and it was slightly modified into Alloy 800H. The modification made was to control carbon (.05­.10%) and grain size to optimize stress rupture properties. Alloy 800HT has more modifications to the combined aluminum and titanium levels (.85­1.20%) to ensure optimum high temperature properties.

The nickel alloy is dual certified (800H/HT) and combines the properties of both forms. Alloy 800H/HT alloy was actually meant for high­temperature structural applications. These alloys are resistant to embrittlement from precipitation of sigma phase and chloride stress­corrosion cracking due to the nickel content. The corrosion resistance is quite high.

In the solution annealed condition, alloys 800H and 800HT have excellent creep and stress rupture properties. The dual certified 800H/HT alloy is commonly available also with Mega Mex.

Alloy 800 is mainly used in applications with temperatures up to 1100° F, where alloys 800H and 800HT are normally used in temperatures above 1100° F where resistance to creep and rupture is required. The chemical balance allows the nickel steel alloy to exhibit excellent resistance to carburization, oxidation and nitriding atmospheres.

Alloy 800HT will not become embrittled even after long periods of usage in the 1200­ 1600° F range where many stainless steels become brittle.

Superior cold forming properties associated with the nickel­chromium alloys are exhibited with 800HT. When cold forms extensively, the grain size produces a visibly undulated surface called “orange peel”. Alloy 800HT can be welded by the common techniques used on stainless steels.

Chemical Composition

Element 800 800 H 800HT
 Nickel 30.0-35.0 30.0-35.0 30.0-35.0
 Chromium 19.0-23.0 19.0-23.0 19.0-23.0
 Iron 39.5 min 39.5 min 39.5 min
 Carbon 0.1 max 0.05-0.10 0.06-0.10
 Aluminium 0.15-0.60 0.15-0.60 0.25-0.60
 Titanium 0.15-0.60 0.15-0.60 0.25-0.60
 Al + Ti 0.3-1.2 0.3-1.2 0.85-1.2

Physical Properties

  Metric Imperial
Density 8.05 g/cm3 0.291Metric lb/in3

Mechanical Properties

Property  
Tensile strength* 75-100 ksi
2% Yield* 30-60 ksi
Elongation* 60-30%

 *Annealed

Properties

The following are the list of main advantages of Alloy 800/H/HT:

  • High temperature strength
  • Good resistance to many sulfur­containing atmospheres
  • High creep rupture strength
  • Resistant to carburization and oxidation in high temperature environments
  • Good corrosion resistance in many acidic environments.

Applications of Alloy 800/800H/800HT

Alloys 800H/HT is used in a range of applications that involve exposure to corrosive environments and high temperatures such as heat treating equipment, chemical and petrochemical processing, nuclear power plants and the paper pulp industry.

Heat­treating equipment such as baskets, trays, and fixtures employ Incoloy 800H/HT. Petrochemical and chemical industries use the alloys for heat exchangers and other piping systems in nitric acid media especially where resistance to chloride stress­corrosion cracking is required. Power plants use them for super­heater and re­heater tubing.

The applications of Incoloy 800H/HT include:

  • Hydrocarbon cracking
  • Ethylene furnace quench boilers
  • Super­heater and re­heaters in power plants
  • Heat exchangers
  • Pressure vessels
  • Valves, fittings and other components exposed to corrosive attack from 1100­1800° F
  • Heat­treating equipment
  • Industrial furnaces
  • Chemical and petrochemical processing.

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