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Evaluation of the $\sigma$-Phase Degradation for Cast Stainless Steel CF8M by the Electrochemical Method

전기화학적 방법에 의한 주조 스테인리스강 CF8M $\sigma$상 열화평가

  • Published : 1999.11.01

Abstract

The present investigation is concerned with the degradation characteristics of cast stainless steel(CF8M), exposed to the $\sigma$-phase degradation at $700^{\circ}C$. In the present paper, the degradation of CF8 M at $700^{\circ}C$ is evaluated by a non-destructive test, DL-EPR(double loop electrochemical potentiokinetic reactivation). The surface of specimens is observed by using scanning electron microscopy after DL-EPR test. Also. chromium contents of matrix, grain boundary and ferrite phase are analyzed by electron probe X-ray micro analyzer. Through the experiments, the following results are obtained 1) The degree of sensitization(DOS) of CF8M aged up to 15hr at $700^{\circ}C$ is increased with acing time while that is decreased with aging time from 15hr to 150hr. 2) The impact energy decreases with increase of $\sigma$-phase while DOS increases with $\sigma$-phase until aging time reaches to 15hr. After the aging time. 15hr, the $\sigma$-phase and the rate of impact energy with respect to aging time decreases. Therefore the degradation behavior of the CF8M can be evaluated by comparing SEM micrographs and the value of DOS.

Keywords

Cast Stainless Steel-CF8M;Degraded Material;Electrochemical Potentiokinetic Reactivation;Intergranular Corrosion;Chromium Depleted Zone;Degree of Sensitization

References

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