The Morphological Classification of Precipitates at Elevated Temperature in 18-8 Stainless Steel Stabilized by Titanium and Their Precipitating Situation

Abstract

Phase changes at elevated temperature in 18-8 stainless steel stabilized by titanium were observed through their precipitates. The extracted carbides were analysed under an electron microscope. The precipitates were morphologically classifed and their constituents were analysed by selected-area electron-diffraction. The mode of their precipitation in steel was certified and the relation between heat treatment and the precipitates was studied. The test pieces were heat-treated under the conditions covering the temperature range from 650 to 1200°C and the heating time range from 30 second to 567 hours after solution treatment at 1300°C for one hour. As the results, three courses of precipitation were concluded, that is, the one was on the grain boundary; the second was in the grain and the third was on the twin boundary. It was shown that since a particular carbide was observed after each heat treatment, the metallographical characteristics of 321 type stainless steel were specified by the kinds of carbides.