Abstract
We investigate the effects of the annealing microstructure on the low-cycle fatigue (LCF) life (Nf), cyclic stress behaviour and fatigue microstructure of a Fe–15Mn–10Cr–8Ni–4Si alloy that exhibits a deformation-induced transformation of austenite (γ-phase) into ε-martensite (ε-phase). The alloy rolled at 800°C was annealed at 600°C, 700°C, 800°C and 900°C to vary the grain size, the fraction of recrystallised grains and the texture intensity. Fully reversed axial strain-controlled LCF tests were conducted at total strain amplitudes, Δεt/2, ranging from 0.007 to 0.02. The alloy showed a higher Nf than common steels and ferrous high-Mn alloys in this strain range. This type of annealing microstructure was found to impact the Nf, fatigue behaviour and deformation-induced ε-martensitic transformation (ε-MT) in the studied alloy. The fully recrystallised and weakly textured austenite formed at T ≥ 800°C facilitated the uniform development of ε-martensite under cyclic deformation and led to an increased Nf. The partially recrystallised and textured austenite-containing substructure with high dislocation density formed at T ≤ 700°C suppressed the ε-MT, retarded reversible dislocation motions in the un-recrystallised regions and moderately decreased Nf. Moreover, Nf and the deformation-induced ε-MT were observed to be less sensitive to variations in grain size.
