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Neutral Hardening Process

The term “Neutral Hardening” is to have a component be heated above temperature Acɜ, in a protective atmosphere, to achieve a complete transformation to 100% austenite for the material being processed.

The atmosphere must be conditioned and the carbon potential setpoint is the carbon content of the material’s chemical composition.

Setting the carbon potential accurately is important.

  • Too low of a setpoint and decarburization of the part surface will occur.
    • If this occurs a carbon restoration cycle must be run to “correct” the surface carbon content.
  • Too high of a setpoint will cause carburization of the part surface.
    • Under this scenario the engineering group must analyze the hardness and mechanical properties of any mating part before accepting this carburized condition.

Heating the material above the Acɜ temperature and staying above this temperature for the assigned time period is critical to form 100% austenite then rapidly cool the component to transform the microstructure to 100% martensite.

  • There are alloy materials that do not 100% transform to 100% martensite. Meaning there is austenite that did not transform.
    • This microstructure is called having “retained austenite”.
      • Cryo treatment does help transform this remaining austenite however customer approval by their engineering group must be had.
    • The “retained austenite” can be viewed under microscopic evaluation.

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Anneal Process

Annealing should be used throughout the manufacturing process. Temperature and cooling rates are controlled differing from Normalizing process.

Annealing a component can:

  • Increase a part’s ductility
  • Improve a part’s “workability”
  • Increase a part’s toughness
  • Reducing the part’s hardness

Engineering groups need to be aware of all manufacturing processes required and the sequence of events they lay. Such workability processes include: bending, cold forming, welding or (deep) drawing. Various manufacturing steps (including welding stresses) make further manufacturing steps difficult or create fractures. Not annealing the parts may make further manufacturing impossible or result in fracturing.

By heating the material above the A temperature, it makes the part microstructure more ductile allowing further manufacturing possible and a uniform grain size to work with. Welding on the component creates stresses as cooling (solidification) begins.

Other materials such as aluminum, brass and copper are a few that also benefit from annealing.

Annealing temperatures of alloys are based on the alloy elements. The process cycle times will also vary by material alloy.

Controlled cooling can become lengthy in time. Anywhere from 10˚F/hr. – 30˚F/hr. cooling rates. Thicker cross sections can create concerns. This must be considered by the engineering groups of the manufacturer, for their quoting process to their customer.

Normalizing Process

It is said to achieve the best possible quality for your finished product begins with the pre-machining microstructure of your material. Steel (Bars and tubular products as CRS, HRS… etc., casting, forging)

With castings, it is important to understand the chemistry of the steel at hand. Variation of normalizing temperature may be necessary.

It is important to understand that while most ferrous material can be normalized, not all are or can be. The manufacturing team should identify all variables in the material of choice. Work closely with Thermal Process Holdings to share your journey to making a high end quality product. The material should be normalized processed at the appropriate temperature and time to meet the application demands.

A review of the manufacturing process will inform the supplier what the highest manufacturing temperature the component will be exposed to. The material will ultimately respond according to the highest manufacturing process temperature. A good manufacturing practice is to perform a normalize process 50˚F above the highest manufacturing process temperature.

What is Normalizing?

Heating your material to a predetermined, elevated, temperature and then allowing it to slowly, air cool to room temperature. The material will develop a uniform fine grain structure. Pearlite (Fe3C) and cementite is the make-up of this normalized homogeneous structure. As a result of proper normalizing, machining should become optimal.

For most materials, normalizing will reduce the material hardness and increase the ductility. However, this is not true for all ferrous materials so it is vital to check and understand before manufacturing begins.