The "furnace atmosphere" means a gas to be filled and heated in the furnace by which the
product (workpiece) is indirectly heat-treated. The atmosphere gases include air,
inert gases, hydrogen (reducing gas), and others, which are heated up to 1000 - 2500℃
depending on the properties of the workpiece and purpose of the heat treatment.

What are the atmosphere gases?

A gas to be put into the furnace

How to fill the furnace with an atmosphere gas
 What kind of gas to be used?
 From where to put in the gas?
 How much gas to put in?
 How to provide the gas?

Why is it necessary to use an atmosphere gas?

To protect the workpiece
 −Protection against oxidation
  Heating in air causes the workpiece to react with oxygen which negatively affects the product's appearance
   and properties.
 −Protection against decarburization
  While a carbon-added iron shows excellent properties, they will return to ordinary irons once they lose
   the carbon from their surfaces (decarburization).

Use of atmosphere gases to improve product quality
  Conversely to the aforementioned decarburization, an addition of carbon to the surface (carburization)
   improves properties of the product.
  Provision of nitrogen to the surface of steel is called nitrization which improves surface properties of the

Type of atmosphere gases

Frequently used atmosphere gases
 −Exothermic generation gas
  DX gas
 −Endothermic generation gas
  RX gas
 −Inert gases
  Nitrogen, Argon
 −Hydrogen gas
  Hydrogen gas
 −Ammonia cracking gas (AX gas)
  Mixture of nitrogen and hydrogen obtained by dissociating ammonia
 −Methanol cracking gas
  Obtained by dissociating Methanol

Exothermic generation gas

This gas is called a DX gas
Produced from Propane or Butane

Endothermic generation gas

This gas is called an RX gas
Produced from Propane or Butane

Features of Generated gases

Generated from a variety of raw material gasses
Generated gasses are basically combustible mixtures of CO, CO2, H2, H2O, and N2.
Generated gas composition is determined by the mixing rate of the material gas and air.
Capable of reducing oxides of iron, steel, and copper, depending on the mixing rate and temperature.

Inert gases

Nitrogen and Argon for example.
It does not react with the product, as it name suggests.
 (While nitrogen may nitride some metals, it is generally considered inert.)
Neither oxidation nor reduction takes place on the product.
 (Trace amount of oxygen contained in commercially available inert gasses could slightly oxidize the product.)
Nitrogen is lighter than air, and argon is heavier than air.  

Hydrogen gas

Pure hydrogen
Reduces many kinds of metal oxides.
Mishandling of hydrogen may cause explosion accident.
Much lighter than air.  

Cracked (generation) gasses

AX gas
 −Produced by heat dissociation of ammonia in a designated generating furnace.
  Composed of hydrogen and nitrogen.
  Combustible and explosive due to hydrogen content.
  Efficient source of large amount of hydrogen, without needs of hydrogen tubes.
  Usable for sintering or brazing of iron based materials.

Methanol cracked gas
 −Produced by heat dissociation of methanol in a designated generating furnace.
  Composed mainly of CO and hydrogen.
  Capable of carburizing steels such as bearing steel.

Ellingham diagram

  • ●Visualization of atmosphere
    Conventional continuous furnaces would require experienced operators.
    Especially at the time of starting up a furnace, operators need to properly check and validate such important operating factors like atmosphere purge,furnace temperature, and operation of each instruments.
    KYK's unique Visualized Operation monitor panel can clearly and easily display real-time atmosphere of the furnace, which was only possible by the experienced operators before.
    This new technology enables even inexperienced operators to properly operate and manage equipment at foreign production facilities.

    Recommended equipment: Oxynon®Furnaces of all kinds.