Spring Wire Heat Treatment
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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.

Material Spring Outside Diameter Opens/Closes Temperature Time
Hard Drawn closes 550 F 20 mins
K Monel   1000 F 5 hours
Monel does not move 600 F 1 hours
Valve Oil Tempered closes 500 F - 600 F 30 mins or until blue on ends
Oil Tempered closes 500 F - 600 F 30 mins
Music Wire closes 500 F 30 mins
Stainless Steel 302 opens 600 F - 650 F 30 mins
Stainless Steel 316 does not move 700 F 1 hour
Stainless Steel 17-7PH or 17-4PH opens a little 900 F 1 hour
Inconel 718   1375 F 16 hours
Inconel   700 F - 900 F 1 hour
Inconel No. 1 Temper does not move 1375 F 16 hours then reduce to 700 F for 1 hour
Inconel X-750   1225 F 4 hours
Inconel 600   900 F 1 hour
Inconel X Spring Temper   1250 F 4 hours
Chrome Silicone closes 800 F 30 mins
Chrome Vanadium closes 800 F 30 mins
Bronze   350 F 15 mins
Beryllium Copper closes 1% 600 F 30 mins to 2 hours
Beryllium Copper 25 1/2 hard   600 F 30 mins
Elgiloy (open more in salt) opens 3% 900 F 5 hours
Aluminum   400 F 30 mins
Brass   just warm up just warm up
Basic   none none
Premier   600 F - 650 F 15 to 30 mins
Rene 41   1400 F 16 hours
Ni Span C (on big wire) opens some 1250 F 3 hours
Ni Span C Alloy 902 50% cold worked   900 F 5 hours
Titanium opens (like SS) 800 F 10 hours
Maraging Flat Stock does not move 950 F 4 hours NO LESS
Maraging Wire does not move 850 F 30 mins
MP35N   1200 F 4 hours
Hastelloy C-22   Stress Relief @ 750 F-840 F 30 mins
Rocket Wire Min. Tensile Strength 25 KS   525 F 2 hours
Are you ready to get started on your spring project?

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