1992 Volume 41 Issue 467 Pages 1234-1240
There are two methods of evaluation of material degradation, that is, destructive and non-destructive. In this study, the degradation of Cr-Mo-V casting steel which has been used for about ten years as the internal casing of turbine was evaluated using a miniature Charpy impact specimen. The miniature specimen (thickness: 1.5mm, width: 1.5mm, length: 16mm) was taken from the Cr-Mo-V casting steel and the ductile-brittle transition curve was measured by the instrumented Charpy impact test. Moreover, the effects of specimen dimension on the ductile-brittle transition temperature (DBTT) and upper shelf energy and a relationship between the change of DBTT and micro-structural properties were investigated. The results of this study are summarized as follows:
(1) When the specimen dimension becomes smaller, the difference of DBTT due to the difference in degradation becomes smaller.
(2) The degradation of material can be successfully evaluated with a 1/6 size specimen.
(3) The change of DBTT can be predicted from the changes of hardness, innergranular hardness, diameter of precipitated carbide and depth of etched grain boundary groove.
