Growth and Distribution of Microcracks at the Surface of Smooth Specimen of 304 Stainless Steel in Creep and Effect of High Temperature Oxidation

Abstract

It is expected from the previous researches that the growth of many distributed cracks from the initiation to the size of several grains is the main process of creep fracture in heat-resisting alloys. Such a study on intergranular microcrack growth behaviors is important to clarify the characteristics of creep fracture.
In this study, a continuous observation of intergranular microcrack growth at the surface of smooth specimens of 304 stainless steel was made during creep tests at 650°C in air and in vacuum. It was found that the effect of environment was different depending upon the stress value. That is, at high stress, the rupture time was shortened by intergranular oxidation, and on the contrary at low stress, it was lengthened by the formed oxide film which has protective and restorative actions. Also it was shown that the microcrack growth behaviors in creep were explainable on the basis of Weibull distribution of crack length.