Strain aging of martensite in austenitic stainless steel AISI 304, 25% pre-deformed at -5ºC, was studied to determine phenomenological aspects and mechanisms of strain aging. Under these conditions, the result was a martensite volume fraction of 60%. Ageing treatments were performed from 80 to 160ºC during 1 to 400 minutes. Yield strength increases with the increase of aging time and temperature, saturation being reached in about 20 minutes at 160ºC. A time exponent of ½ was found for the equation that describes the kinetics of the process. This value was associated to the formation of e precipitates. The value of the activation energy (65kJ/mol) was related to the diffusion of carbon in martensite.
Strain induced martensite; strain ageing; epsilon carbide
