Spring Wire Heat Treatment

Spring wire that gets coiled has to have the bending stress relieved. Stress relieving is the most common heat treating operation. It relieves the stresses that occur as a result of the spring forming operation. It also returns the material to the strength levels prior to the forming operation and can actually increase the strength to levels greater than originally supplied.

When the spring is under the stress relieve treatment, it may change its dimensions. Stainless steel coils will generally expand slightly when heated: music wire coils will generally contract slightly.

For compression springs:

• If the spring will set solid (compress all the way, so that all the coils touch each other) at the limit of its travel, the diameter of the wire times the number of coils cannot be greater than the space allowed, unless the spring itself that is being design will act as a mechanical stop to the motion.
• Springs that operate in a high-temperature environment will need to be made slightly longer to compensate for the fact that the heat may have an effect on the length of the spring.
• As a compression spring assumes a load and shortens, the diameter of the active coils will increase. This could represent a problem when the spring has to work in a confined space.

For extension springs:

• There should be some mechanical limit on how far the spring will extend, or the spring will lose its shape and not return to its initial condition with all coils closed.
• Extension springs operating in a high-temperature environment may have to be coiled extra-tight, as the heat will tend to weaken the spring.

Heat Treating Chart for Spring Wire

Different wire materials require diverse lengths of time for stress relieving.