Environmentally assisted cracking behavior of a low-alloy steel under non-isothermal conditions

Abstract

The majority of experimental studies of environmentally assisted cracking (EAC) behavior of low-alloy steels in elevated temperature aqueous environments are conducted under isothermal conditions. However, some structural applications may involve cyclic stresses that occur under non-isothermal conditions. This study involved the testing of a high-sulfur EAC-susceptible ASTM A302-B steel under conditions where the temperature cycled continuously between 149 and 243°C. The temperature cycling was not in phase with the fatigue cycling. The testing commenced at conditions where the heat of A302-B exhibited EAC at 243°C, but not at 149°C. Crack growth rates were initially high, approximately equivalent to the EAC rates normally observed at 243°C, but over a 57-day period of non-steady-state behavior, the crack growth rates steadily dropped to the non-EAC rates normally expected at 149°C. For the duration of the testing, crack growth rates under the non-isothermal cycling behaved as if the test was being conducted at 149°C. This experiment illustrates the complex non-steady-state EAC behavior that may be observed under non-isothermal conditions.