Influence of Various Factors on the Elevated Temperature Ductility of 18Cr-12Ni Austenitic Stainless Steels

Abstract

Effects of chemical composition, cleanliness, grain size and morphology of grain boundary carbide on the tensile ductility of 18Cr-12Ni austenitic stainless steels have been studied in the temperature range of 500°1 000°C. Metallurgical factors which are concerned with the ductility drop in this temperature range have been discussed. The results obtained are as follows.
(1) The combined addition of carbon and nitrogen to 18Cr-12Ni steel causes a serious ductility drop resulted from the intergranular fracture in the temperature range of 600°900°C. Decreasing cleanliness and increasing grain size decrease the ductility in the temperature range.
(2) The ductility sensitively varies with distribution condition of carbides precipitated at grain boundaries. High dense precipitation of small carbides harms the ductility.
(3) Nitrogen retards the dynamic restoration process during deformation at the elevated temperatures. The deformed substructure in nitrogen bearing steel seems to have planar arrays of dislocations. The ductility drop may be concerned with the combined effect of the harmful precipitation condition and the nonhomogeneity of deformed substructure.