The Effect of Nickel on the Precipitation of Chromium Carbide in Austenite

Abstract

The rate of precipitation of M₂₃C₆ on dislocations in austenitic steels containing 16 wt.-% chromium and 0.25 wt.-% carbon increases by a factor of ∼ 17 with increase in nickel content from 9 to 22 wt.-%. Metallographic observations show that raising the nickel content and lowering the ageing temperature both give easier dislocation nucleation, so that the climbing dislocations continue to nucleate precipitate. This results in planar areas of fine precipitate extending from the original dislocation position and the continued nucleation contributes to an increase in the time exponent of the kinetics of precipitation. The greater ease of nucleation on adding nickel is not entirely responsible for the higher rate of precipitation and an increase in the growth rate of the particles is attributed to a rise in the metal ion diffusion rate by a factor of 2.5 on increasing the nickel content from 9 to 22 wt.-%.