Study on the effects of cold working on the mechanical behavior an‎d shape memory properties of Fe-10Ni-10Mn (wt.%) steel

10/22/2025 12:00:00 AM

Abstract Fe-Ni-Mn alloys represent a class of shape memory alloys in which the occurrence of the austenite (γ) to epsilon-martensite (ε) transformation during straining an‎d its reverse upon heating constitute the fundamental mechanism of the shape memory effect. In addition, these alloys exhibit pseudoelasticity behavior, which is also based on the reversible γ↔ε transformation. In this study, the effect of cold rolling with 20%, 40%, 60%, an‎d 80% thickness reduction on the microstructure, mechanical behavior an‎d shape memory properties of a dual-phase (austenite + α′-martensite) Fe-10Ni-10Mn (wt.%) alloy was investigated. The initial microstructure in the solution-annealed condition consisted of 58% γ-austenite an‎d 42% α′-martensite. X-ray diffraction (XRD) analysis an‎d microscopic observations revealed that increasing the degree of cold rolling led to a progressive increase in the martensite volume fraction an‎d a corresponding decrease in austenite content. Specifically, at 80% thickness reduction, the austenite fraction decreased to 37%, while the martensite fraction increased to 63%. Mechanical testing showed that the 80% cold-rolled specimen exhibited a significant enhancement in hardness an‎d strength, with the Vickers hardness increasing from 128 Hv in the solution-annealed sample to 393 Hv, an ultimate tensile strength (UTS) of 1110 MPa, an‎d elongation to fracture of 14.7%, indicating an optimal balance between strength an‎d ductility. Optical microscopy (OM) an‎d scanning electron microscopy (SEM) analyses confirmed an increase in dislocation density, grain elongation an‎d refinement, an‎d the occurrence of strain-induced γ→α′ martensitic transformation. Functional testing of shape memory an‎d pseudoelasticity demonstrated that cold rolling improved these properties in the studied alloy. Among all conditions, the 80% cold-rolled specimen exhibited the highest shape recovery ratio (~65%) an‎d maximum pseudoelasticity (~60%). This enhancement was attributed to the relative strengthening of the austenite phase, the increased dislocation density, an‎d the facilitated γ→ε transformation during deformation.

آلياژ حافظه دار پايه آهن Fe-10Ni-10Mn , نورد سرد , بررسي ريزساختار , خواص مكانيكي , اثر حافظه داري شكلي , سودوالاستيسيته

Iron-based shape memory alloy (Fe-10Ni-10Mn) , Cold rolling , Microstructural analysis , Mechanical properties , Shape memory effect , Pseudoelasticity

Majid Nourmohammadi

Hamidreza Koohdar