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 ε ̇ min , ε r , t r 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 ′ saturates to a value of 1.3 with dislocation-controlled deformation mechanisms operating. At low stress levels, λ ′ increases drastically ( λ ′ = 190 at 54 MPa) when slow diffusion-controlled creep is dominant.