Influence of initial heat treatment on the fatigue life of austenitic Fe-Ni alloy

Purpose: The paper addresses the problem of determining the dependence between initial heat treatment of an austenitic Fe–Ni alloy and its mechanical properties and fatigue life at room temperature. Design/methodology/approach: For the investigated Fe–Ni alloy after solution heat treatment, two variants of specimen ageing were applied for comparison, i.e. typical single-stage ageing and novel two-stage ageing. Specimens that underwent heat treatment were subjected to a static tensile test and low-cycle fatigue tests (LCF), carried out at room temperature. Findings: It has been found that, the specimens of Fe–Ni alloy after two-stage ageing are distinguished by higher strength properties with a little lower plastic properties. In a case of low-cycle fatigue tests, specimens after singlestage ageing were characterized by higher fatigue life. Lower fatigue life of the alloy after two-stage ageing can be explained by increased brittleness of material in boundary areas. Practical implications: The fatigue life results obtained in LCF conditions can be used in predicting the duration of operation of products made out of Fe–Ni alloy at room temperature. Originality/value: The significance of the applied ageing variants’ effect on the mechanical properties and fatigue life of the tested austenitic Fe–Ni alloy is shown in the paper.