Modified Monkman–Grant relationship for austenitic stainless steel foils

Characteristics of creep deformation for austenitic stainless steel foils are examined using the modified Monkman–Grant equation. A series of creep tests are conducted on AISI 347 steel foils at 700 °C and different stress levels ranging from 54 to 221 MPa. Results showed that at lower stress levels below 110 MPa, the creep life parameters ε̇min,εr,tr can be expressed using the modified Monkman–Grant equation with exponent m′= 0.513. This indicates significant deviation of the creep behavior from the first order reaction kinetics theory for creep (m′ = 1.0). The true tertiary creep damage in AISI 347 steel foil begins after 65.9% of the creep life of the foil has elapsed at stress levels above 150 MPa. At this high stress levels, Monkman–Grant ductility factor λ′λ′ saturates to a value of 1.3 with dislocation-controlled deformation mechanisms operating. At low stress levels, λ′λ′ increases drastically (λ′=190λ′=190 at 54 MPa) when slow diffusion-controlled creep is dominant.