What material should be used for springs in low ambient temperatures?

There are a wide range of views on what material should be used for springs in low ambient temperatures. Springs manufactured from the materials which are normally used to make coil springs (silico-manganese or low alloy spring steels) will have quite low impact toughness (circa 5J) but the pertinent question is “does this matter?” We have been given the following advice from the Institute of Spring Technology in UK. “For a failure to occur from impact loading, it is necessary for the material to be loaded suddenly and for some plastic deformation to be initiated. A spring is only loaded elastically and so the impact toughness does not matter.” Because a spring is inherently elastic, impact loading is absorbed by elastic deformation of the spring and the shock loading which is necessary to cause brittle failure is not likely to occur. 735A51 (Chromium-Vanadium) steel gives higher impact toughness (typically 12J) than other spring steels, though this is still not particularly tough. We have used this material on some contracts where the springs are being used in low ambient temperatures. There is a cost penalty in using this material, and there may also be some delivery implications depending on the scope of supply.

Spring coils can also be made from stainless steel grades which have much higher toughness, but these materials have a lower allowable stress so the spring will be made from a larger bar diameter and will be to generally larger dimensions at very much higher cost. With regard to experience of failures of springs in low ambient temperatures, we had one instance of a spring coil failure on a support in Siberia, but our investigation into the failure found that it was due to a quench crack which had not been spotted during our spring coil supplier’s crack detection, so this failure would still have occurred if the plant had been in the tropics – the failure was not due to temperature. We would offer spring coils plastic coated for corrosion protection, not galvanized as this process can cause hydrogen embrittlement in high strength steels.