Nondestructive Evaluation of Temper Embrittlement in Cr-Mo-V Rotor Steel

概要

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Temper embrittlement in low-alloy steels, one type of typical material degradation, occurs during service, and it is important to detect this embrittlement by means of a nondestructive technique. In order to develop a nondestructive method of evaluating embrittlement for Cr-Mo-V rotors, a study was conducted using lab-charged P-doped and Sn-doped steels. P-doped steels showed evident embrittlement by segregation of P at grain boundaries. On the other hand, Sn-doped steels showed little embrittlement when compared with P-doped steels. Various testing methods were investigated and compared in terms of their sensitivity and factors were detected, using these steels. The chemical etching test was found to be a very good measure of embrittlement. That is, it was found that there is good correlation between the width W of the etched grain boundary measured by the penetration of replicas and FATT. The correlation between W and FATT was also recognized for samples taken from long-term-serviced rotors. The relation had the same slope as that found for lab-charged steels. From this, multiple regression analysis was conducted in order to express FATT using W and variables which are known or are nondestructively measurable. As a result, a regression equation which gives an estimate of the actual FATT with the scatter of ±20℃ was obtained.
一般社団法人日本機械学会の論文
1992-04-15