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Introduction to Metallurgy...a Metallurgical Tutorial

Welding - Carbon Steels - Stainless Steels - Cast Iron - Super Alloys - Steel - Heat Treating - Corrosion - Galvanic corrosion - Ceramics - Refractories

Heat Treating (Heat Treatment)

This is a combination of heating the cooling of steels to obtain a specific outcome or metallurgical property. Forging and the like is not considered heat treating.

There are three-common forms of heat treating processes and they are:

  • Normalizing - This is used on ferrous metals to condition the part for grain refinement or grain uniformity. To achieve this requires the part or metal to be heated such that the building blocks (crystal lattices) reorientate themselves or make like new. This choice of language is meant to be figuratively, but not literally.

  • Annealing - This heat treating process is the most versatile or has the most wide spread applications. For instance this can be used to soften the metal to altering the electrical properties and to stress relief annealing. Unlike normalizing there is no transformation temperature specified although the procedure may call for this temperature. Annealing is a term used to describe a heating, holding and cooling process to achieve desired metallurgical results.

  • Stress Relieving - Always done below the transformation temperature of the metal to minimize the welds residual stress. The temperature is held for a certain amount of time (could be 1-hour) until the residual stresses are minimized, then cooled very slowly to prevent new stresses from setting up in the metal. This can also be done on non-ferrous metals.

Heat treating can be accomplished by in a factory or shop or in the field at a remote location. The types of furnaces can be large gas fired furnaces that can hold many tons or portable electric wraps around piping but not limited to electric. Torch or a flame can be used in the field to achieve heat treating.

Heat treating can be confusing to follow because the same equipment maybe interchangeable and the technique can be the same, but the objectives are different as are the procedures.

 

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