Abstract
In this investigation, before and after of creep testing at 450°C to 720°C for 100 hours, the measurements of hardness, magnetic and micrographic testing of metal structures, and X-ray analysis of the specimens twisted up to 0.128π/cm and 0.256π/cm at some temperatures between-60°C and 800°C were taken. The present authors attempted to correlate the changes of the metallurgical properties with the creep testing results presented in the preceding report. The results obtained may be summarized as follows:
The reduction of hardness after creep testing is remarkable in the specimen worked at -60°C, but with increasing of the twisting temperature the value of reduction decrease and it becomes very little for the specimen twisted at 600°C. In the specimens worked at comparatively lower temperatures, a plenty of Cr-carbide (Cr23C6) precipitate in the slip planes during creep, and in the specimen worked at -60°C, the greater part of martensitic phase which had been produced at the working transformes into austenitic phase. On the contrary, in the specimen worked at higher temperature, these metal structural changes are very small. In our preceding investigation, it was found that the specimens twisted at higher temperature have higher creep strength than those twisted at lower temperature. Consequently, it may be concluded that the creep deformation of the worked 18-8 stainless steel is to be promoted by the reduction of hardness, precipitation of Cr-carbide (Cr23C6) and phase transformation during creep deformation.
