The Effect of Nb on High Temperature Properties of Austenitic Steels.

Abstract

This report concerned the effect of Nb and C on mechanical properties such as creeprupture strength; tensile strength, impact value and deformation resistance at high temperature, aging hardness and microstructure of austenitic stainless steels.
Specimens used in the experiments were 18 Cr-12 Ni austenitic stainless stees. The C content of the steels were of three kinds (0.03, 0.06, 0.12%).
The Nb content were n times as much as C for each C content (in this case n=0, 5, 8, 10, 12, 15). In these steels, Nb C and Cr₂₃C₆ precipitated during aging at 600, 650, 700 and 750°C. Precipitates were concentrated by electrolyzing specimens in ethyl alcohol containing 10% of HCl, and examined by X-ray diffraction method. Cr23C6 precipitated mainey on grain boundary but it had no effect on aging hardness.
Creep rupture strength increased with Nb content but it was almost invariable when Nb content exceeded about 11 times as much as C content. High-temperature tensile. strength was almost invariable with Nb content. There was no correlation between the effect of Nb on creep rupture strength and that on high-temperature tensile strength.
High-temperature deformation-resistance depended only upon the amount of Nb dissolved in matrix.