What is the Difference Between Tempering and Annealing?

Tempering and annealing processes both apply heat to metal to modify its composition without altering its shape. Heat treating metal can make it more ductile, easier to work with, less brittle, and overall, more reliable for manufacturing and specialized applications. The key difference between the two heat treatments comes down to the cooling method. 

Tempering vs. Annealing

Both tempering and annealing processes use heat to change the physical characteristics of metal, and they’re particularly common in producing steel components. However, there are crucial differences between the two methods that manufacturers must keep in mind.

Every heat-treating process uses different maximum temperatures, heat exposure durations, and cooling processes. In the annealing process, the metal is heated in a large oven that allows for air circulation. The metal is heated to its recrystallization point, which allows the metal to reform and correct slight imperfections without fully melting. After this step, the metal cools slowly in a controlled process until it reaches room temperature.  The metal can simply be left in the oven to cool to room temperature or be immersed in a substance with low heat conductivity like sand or ash.  The slow cooling allows the newly formed metal grains to grow and makes the metal more ductile.

Annealing improves the ductility and electrical conductivity of metals and softens them in preparation for cold working. Cold working can cause metal to crack, but the annealing process mitigates that risk by releasing the mechanical stresses caused by working the metal. 

In tempering, the metal piece is heated in a vacuum, air, or an inert environment. Not only do manufacturers slowly heat the metal to prevent cracking and deformation, but they also control the final temperature, so it suits the type of metal and the desired characteristics. For example, tempering specialists can heat the metal to very high temperatures to make it extremely elastic, but much less strong. Alternatively, they can set a lower maximum temperature to reduce some hardness and brittleness without weakening the metal. Tempering is commonly used to increase toughness and decrease hardness.

As a general rule, annealing requires that metal be held at soak temperature for 1 hour per inch of thickness. This is a key difference between annealing and tempering — Annealing can require specific cooling rates, whereas tempered pieces are furnace cooled.

Annealing at TLC

At Thomson Lamination Company, Inc., we provided high-quality annealing services that can soften metals, optimize their electrical or magnetic properties, and make them easy to work with through machining and cold working processes. We follow a precise three-step process:

  • Recovery stage: We expose the metal to rising temperatures through a furnace until it reaches the point where the heat relieves internal stress.
  • Recrystallization stage: The metal temperature is raised until it starts to form new internal grains but does not begin to melt.
  • Grain growth stage: We carefully modulate the metal’s rate of cooling to encourage strong grain growth. This is critical to maximizing ductility. 

We offer batch processes, continuous processes of stress relief annealing for fully processed non-oriented electrical steel, specialized annealing processes for soft magnetic metals, and high-temperature processes for motor laminations

High-Temperature Annealing Expertise

We specialize in heat treating laminations at temperatures 1100-2150 F for use in specialty applications. We serve industries ranging from the military and aerospace to energy and medical. Contact us today to learn more about our capabilities or to request a quote.