It is known in structural materials that metallurgical structural changes occur and creep or fatigue damage accumulates during long-term use at high temperatures.
In order to develop a non-destructive method to detect the creep damage for materials used at high temperatures, the changes in material properties caused by creep damage were observed by the test methods of electric resistance, hardness and sigma phase areas. The tested material was 17Cr-10Ni-0.4Ti (SUS321) austenitic stainless steel.
The results obtained are sumarized as follows;
(1) The ratio of electric resistivity decreased with increasing creep damage at first, and it becomes minimum at creep damage of 0.2. Then, the ratio of electric resistivity increased with increasing creep damage. The tertiary creep range started from creep damage of about 0.2.
(2) Vickers hardness increased with increasing creep damage.
(3) The percentage of sigma phase area increased in proportion to creep damage, and reached 5.6∼7.9% at creep damage of 1.0.
These results show that the creep damage in austenitic stainless steel can be detected nondestructively by measuring the ratio of electric resistivity, hardness and percentage of sigma phase area.