Creep of Austenitic Stainless Steels at Room Temperature

摘要

A notable characteristic of the room-temperature mechanical behavior of austenitic stainless steels is creep even under moderate loads. The magnitude of this creep has been studied on three steels with 0.06% C, 18% Cr and nickel contents of about 13, 8 and 7%, showing decreasing stability of the austenite to structural transformations induced by cooling to low temperatures and/or deformation. The nature and extent of these transformations are detailed and several examples are given of the morphology of the resultant constituents. Creep tests on specimens solution treated at 1050 sup 0 C and air cooled were made at loads ranging from initial stresses below the conventional 0.2%-offset yield strength to initial stresses near the tensile strength. These tests showed that austenitic stainless steels generally follow a logarithmic creep law. The influence of structural transformations induced by deformation on this behavior is discussed. The occurrence of the austenite implies alpha ' martensite (bcc) transformation is accompanied by a significant retardation of creep but without a noteworthy change in the nature of the responsible mechanism. Finally, these tests indicated that plastic deformation of austenitic stainless steels always favors - either by simple work hardening or by partial destabilization of the austenite - the adaptation of the mechanical strength of the metal to the applied loads. This behavior guarantees the safety of installations from rupture and demonstrates why rational utilization of austenitic stainless steels can be obtained only if allowable design stresses are not established merely by reference to the 0.2%-offset yield strength of the solution-treated alloy. 42 figs., 5 tabs. (ERA citation 12:037256)