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Stress Relieving

Stress relieving, is commonly used to induce stresses in parts in Machining. If the part is bigger and more complex, the more the stresses existing. These stresses can cause distortions in the part long term. If the parts are clamped in service, then cracking could occur. Also locations of hole can change causing them to go out of tolerance. For these reasons, stress relieving is often necessary.

Typically, the parts that benefit from stress relieving are large and complex weldments, castings with a lot of machining, parts with tight dimensional tolerances and machined parts that have had a lot of stock removal performed.

Stress relieving is done by subjecting the parts to a temperature of about 75 oC (165 oF) below the transformation temperature, line A1 on the diagram, which is about 727 oC (1340 oF) of steel—thus stress relieving is done at about 650 oC (1202 oF) for about one hour or till the whole part reaches the temperature. This removes more than 90% of the internal stresses. Alloy steels are stress relieved at higher temperatures. After removing from the furnace, the parts are air cooled in still air.