Long-term studies on the creep behaviour of the structural material 316 L (N) in the low-stress range at 550 and 600°C

Experiments were performed at 550degreesC in the stress range of 250-100 MPa. A further series of tests were run at 600degreesC in the range of 170-60 MPa. Continuous recording of the very small creep rate necessitated a special double-extensometer with an enlarged 200 mm gauge length in combination with a recorder of high resolution. When plotting the determined or estimated values for the minimum creep rate in the epsilon(pmin) versus sigma diagram, it was found that the experimentally determined creep rates in the low-stress range were much higher than the values that would have been obtained by extrapolation of the data observed at higher stress levels. The stress exponent decreased from 12.8-10.5 (550-600degreesC) to n approximate to 6.8 at low stress levels. The technically relevant time-strain limits t(epsilonf) also exhibited significantly changed dependencies in the upper and lower stress ranges.