Creep Deformation Characteristics of Austenitic Stainless Steel Foils

Abstract

Creep deformation process of austenitic stainless steel foil with thickness 0.25 mm was investigated. The foil specimen was creep tested at 750oC, 54 MPa to establish baseline behavior for its extended use as primary surface recuperator in advanced microturbine. The creep curve of the foil shows that the primary creep stage is brief and creep life is dominated by tertiary creep deformation. The curve is well represented by the modified theta-projection concept model with hardening and softening terms. Morphology of fractured foil surface reveals intergranular fracture with shallow network of faceted voids. The formation of w-type creep cavities is significant, as revealed by microstructure of ruptured specimen. Composition analysis indicates the formation of carbides, namely, Cr23C6, NbC and Fe3Nb3C.

Design of a novel creep testing machine to investigate the creep life history of austenitic steel foil at elevated temperature

“…Table 3 expresses the creep rupture parameters in the oxidative and nonoxidative medium. The details of extraction for creep strain rate have been reported by Osman and Tamin 35 …”

“…This is possible due to the thermally activated voids nucleation and damages along the grain boundary and the simultaneous stretching of the grains by high localized tensile load, especially in severe loading conditions. These voids form at the triple‐point grain boundaries where the self‐diffusion rate is not high enough to relieve the stress concentrations 35 . The comparison between two plane surfaces of different samples can show that the oxidation effect on the outer surface is the main cause of microcrack growth.…”

“…These voids form at the triple-point grain boundaries where the self-diffusion rate is not high enough to relieve the stress concentrations. 35 The comparison between two plane surfaces of different samples can show that the oxidation effect on the outer surface is the main cause of microcrack growth. Figure 9A,B shows the microcrack growth on the surface of the test samples in the oxidative and protected mediums at 150 MPa stress.…”

“…Recuperators are a form of heat exchanger in which hot waste gases from a furnace are conducted continuously along with a system of flues where they impart heat to the incoming air or gaseous fuel 10 . The majority of them are developed with AISI 347 austenitic stainless steel, which exhibits complex high‐temperature creep cavitation processes with influences of creep strain and material softening 11 . In the meantime, limited reported experimental data on the long‐term creep response of AISI 347 stainless steel foils at high temperatures are available 12,13 .…”

“…31,32 Although several studies used existing models for predicting the creep life in the case of austenitic stainless steels, 7,14,33,34 there still seems to be a lack of a detailed investigation in the case of modeling the creep behavior of AISI 347 employing theta projection model. Moreover, it has been limited to 35 simulate the effect of oxidation on the creep life of material through a numerical study.…”