EVALUATION OF THE EFFECT OF OXIDATION ON THE CREEP PROPERTIES OF STEELS

摘要

The paper presents and applies three simple models for the evaluation of oxidation on the creep properties of structural components and/or specimens operating and/or tested at high temperature. All the models are based on the hypothesis that the oxide layer has no load carrying capability and are proposed for the case of constant stress tests on cylindrical specimens in oxidizing environment causing parabolic oxidation. Two models were taken from literature and were here referred as Borggreen [3-4] and DDR [ 8] models. For a given applied stress (sigma_0) and a corresponding time to rupture (t_r) they compute the value of stress (sigma_(MODEL)) that, applied in inert environment, leads to failure at time t. In the Borggreen model such modelled stress (eq. 4) corresponds to the effective stress applied at time tr due to a metal loss of thickness x. The modelled stress in the DDR model (eq. 6) is the average between Borggreen and the initial stress. The third model (referred to as simplified model) inserts the reduction of cross section due to oxidation into the power-law equation describing the creep properties of the material (eq. 8).