Primary Creep Processes in Supersaturated 20%Cr–25%Ni Titanium-Stabilized Austenitic Steels

Abstract

Seven 20%Cr, 25%Ni austenitic stainless steels have been studied, in which the ratio of Ti : C varied between 1·2 and 22·1. Specimens were tested in the solution-treated condition, so that precipitation of carbides occurred during primary creep, and the changes in microstructure have been correlated with the primary creep characteristics.

Specimens were crept in air at temperatures between 650 and 825° C, and the creep rates were consistent with the operation of a recovery mechanism, the form of the curves being well described by the Garofalo equation. A divergence from this form in the initial stages arises from an increase in the work-hardening coefficient and in the dislocation density.

In contrast to observations on pre-precipitated alloys, the ratio of the initial creep rate to the steady-stage creep rate was not constant, but the behaviour was consistent with the expected influence of the precipitate, which nucleated and grew during the tests.