Volume 29, Issue 6 (November 2001)
Nondestructive Evaluation of Fatigue and Creep-Fatigue Damage in 12%Cr Stainless Steel by the Induced Current Focusing Potential Drop Technique
Steam turbine rotor material is subjected to damage by creep, fatigue, and creep-fatigue. It is important to develop nondestructive methods to measure the progress of crack initiation stage damage in materials. In this paper, for 12%Cr stainless steel, detection and evaluation of earlier stages of creep-fatigue damage by the potential drop method are described. Failure tests by fatigue, creep-fatigue, and creep at 600°C were carried out, and specimens intermittently damaged by fatigue, creep-fatigue, and creep at the same temperature were prepared. Morphologies of damage on the surface of damaged specimens were investigated, and quantitative measurements of damage were conducted using the induced current focusing potential drop (ICFPD) method. In creep-fatigue damaged specimens, slip traces were observed at an early damage stage, producing a large number of cracks. Fatigue generated little slip and the number of cracks was smaller. The potential drop data obtained by ICFPD indicate that creep-fatigue damage in 12%Cr stainless steel can be evaluated based on potential drop data obtained by using the ICFPD method.