전기화학적 재활성화 분극시험에 의한 터빈부재의 열화손상 평가

Abstract

The extent of materials deterioration can be evaluated accurately by mechanical test such as impact test or creep test. But it is almost impossible to extract a large test specimen from in-service components. Thus material degradation evaluation by non-destructive method is earnestly required. In this paper, the material degradation for virgin and several aged materials of a Cr-Mo-V steel, which is an candidated as structural material of the turbine casing components for electric power plant, is nondestructively evaluated by reactivation polarization testing method. And, the <br/> results obtained from the test are compared, with those in small punch(SP) tests recommended as a semi-nondestructive testing method using miniaturized specimen. In contrast to the aged materials up to I,000hrs which exhibit the drgradation behaviors with increased △[DBTT]_sp, the improvement of mechanical property can be observed on the 2,OOOhrs and 3,OOOhrs aged materials. This is because of the softening of material due to the carbide precipitation, the <br/> increase of ferritic structures and the recovery of dislocation microstructure by long-time heat treatment. The reactivation rates(I_R/l_cril, Q_R/Q_crid calculated by reactivation current density(I_R) and charge(Q_R) in the polarization curves exhibit a good correlation with △[DBTT]_sp behaviors.