The company is using the Alnor dew-point test unit. The Alnor unit has been in the heat-treatment industry since the mid-1920s. It is a tried-and-tested method. However, there are more up-to-date methods of carbon-potential control. An example is the oxygen probe, which offers a good analysis of the carbon potential of an atmosphere by measuring the electrical resistivity of the process gas on a real-time basis.

The dew-point meter is sensitive to:

  • Moisture content of the outside atmosphere
  • Process temperature
  • Interpretation of results and probable remedies
  • External influence within the furnace process chamber due to the humidity of the outside atmosphere


The Alnor has served the heat-treatment industry well during the past 85 years (or so), but it does have its limitations in terms of understanding and interpreting results.

As a result of the process, when the steel is austentitized and rapidly cooled (quenched) from the selected austenitization temperature, the martensitic transformation phase occurs (to martensite). The transformation is not an immediate occurrence. It will progress through its phases from austenite through the bainite range and down to martensite. During this transformation, in order for martensite to form, the temperature must past through Ms (martensite start), where the martensite phase will start to nucleate until Mf (martensite finish).