Abstract
In testing for environmental induced cracking several types of specimens can be used. For instance, tensile specimens can be used with constant load technique or u-bends and c-rings with constant strain can be used. Naturally the decrease of load with time during testing is of great importance. For a constant strain type of corrosion specimen relaxation takes place and for a constant load specimen, low temperature creep occurs. In several documents the test load level for specimens is given. The load level in one document can be different whether constant load technique or constant strain specimens are used.
Low temperature creep and relaxation experiments at room temperature have been performed for stainless steels at 90% of the yield strength and at a load level corresponding to 2% strain. Four materials were included: the austenitic AISI 304L, 13Cr supermartensitic stainless steel and two duplex stainless grades UNS S32750 and UNS S32205. The creep experiments were performed with dead weight creep test equipment normally used for testing at high temperatures. For the same materials relaxation was also investigated with a tensile test machine. The experiments were performed at room temperature because this is the relevant temperature for HSIC-testing.
The results show that there is a difference in ranking of the alloys between the influence of low temperature creep and relaxation. Further the results indicate that the ranking at 2% strain and at 90% of the yield strength is not the same. The results illustrates that it is relevant to consider load level and corrosion test specimen type when designing an environmental induced cracking experiment.
