Room-temperature stress relaxation of high-strength strip and wire spring steels-procedures and data. Discussion. Authors' closure

Stress relaxation of strip spring steels was investigated with the vibrating string technique. The modified AISI 301 austenitic stainless steel had the lowest relaxation rate up to 170 h followed by a standard AISI 301 stainless steel, a martensitic stainless chromium steel (Type 420), a texture rolled carbon steel (Type 1078), and a hardened and tempered carbon steel (Type 1074). A high elastic limit had a beneficial effect in lowering the stress relaxation rate. The stress relaxation rate for the carbon steels was accelerated after an initial period. The specimens that had an acceleration in stress relaxation also exhibited a simultaneous change in stress-strain behavior as proved by tension testing. Helical extension wire springs were tested at constant length in a test rig. The modified AISI 301 austenitic stainless steel had the best relaxation properties, followed by a 17-7 precipitation hardenable steel and a standard AISI 302 austenitic stainless steel. An increase in prestress level decreased the stress relaxation as measured at the same testing stress. Springs coiled from wire with the highest values of yield and tensile strength gave the lowest relaxation rate.