Evaluation of initial fatigue damage of SUS304 stainless steel at elevated temperature by a magnetic method

We investigated the relationship between magnetic properties and the accumulation of fatigue damage at elevated temperature for SUS304 stainless steel. The strain-controlled push-pull fatigue tests at 923 K under total strain range conditions of 0.4%, 0.5% and 0.7% were implemented. The leakage magnetic flux density was also measured before and after each fatigue test. As result, it was shown that the maximum differences in leakage magnetic flux density before and after the fatigue test subsequently increased proportionally with the loading cycles under all total strain range conditions, although its rate depended on the total strain range. Furthermore, we proposed that this difference was proportional to the estimated accumulation energy independent of the total strain range. This shows the possibility of a non-destructive evaluation of fatigue damage before crack formation. (author)