What is Heat Treat Stress Relieving?

What is Heat Treat Stress Relieving?

Stress relieving is a heat treatment process used to reduce internal stresses in parts that have been heavily formed, machined, cut, or fabricated by welding. These processes can introduce high levels of internal stresses that may cause distortion or even cracking during subsequent machining, forming, or service.

The stress relieving process involves heating the component to a temperature below the transformation temperature, typically around 75°F below that point. The part is held at this temperature for a specific duration, typically one hour per inch of thickness, to allow the entire part to reach the desired temperature. During this time, thermal relaxation occurs, and the internal stresses are gradually relieved.

By subjecting the part to stress relieving, up to 90% of the internal stresses can be alleviated. This helps to minimize the potential for warping or dimensional changes during further processing or use of the part. Stress relieving is particularly beneficial for large and complex weldments, castings that have undergone significant machining, parts with tight dimensional tolerances, and machined parts that have had substantial stock removal.

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In most cases, stress relieving is conducted in an air atmosphere since the parts are often subsequently machined. However, for complex aerospace weldments or when a protective atmosphere is required, stress relieving can be performed using such an environment. Additionally, Metlab offers the capability to stress relieve shafts and bars in a vertical position, resulting in a stress-free product that is relatively straight.

Overall, stress relieving is a valuable heat treatment method to ensure the dimensional stability and structural integrity of parts that have undergone extensive forming, machining, cutting, or welding processes. By effectively reducing internal stresses, the parts are less likely to distort or experience failures during subsequent operations or in service.

Heat Treat Stress Relieving temperature

The temperature for stress relieving during heat treatment typically ranges from 500°F to 1,300°F (260°C to 700°C). The specific temperature chosen depends on factors such as the material type, the level of internal stresses, and the desired results.

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The stress relieving temperature is usually determined by considering the transformation temperature of the material. The transformation temperature is the temperature at which the internal structure of the material undergoes a change, such as recrystallization or phase transformation, that helps relieve the internal stresses.

For common carbon steels, a typical stress relieving temperature is around 1,100°F to 1,300°F (590°C to 700°C). However, it is important to consult the material’s specifications or consult with a heat treatment expert to determine the specific stress relieving temperature for a particular material.

The duration of the stress relieving process is also important. As mentioned earlier, a general guideline is to hold the part at the stress relieving temperature for about one hour per inch of thickness. This allows sufficient time for the stresses to be relieved throughout the part.