Grain refinement mechanism of Fe–32Ni alloys during multiaxial forging

Abstract

Warm deformation of Fe–32Ni alloy was studied in connection with microstructure developments in multiple axial forging at a temperature of 823 K (∼0·5T_m) and a strain rate of 10⁻³ s⁻¹. The microstructure evolution of the deformed alloys was investigated using EBSD and TEM. The structural changes are characterised by the evolution of many mutually crossing sub-boundaries at low to moderate strains, finally followed by the development of very fine grains with medium to large angle boundaries at large strains. These new grains are concluded to be evolved by a kind of continuous reaction, that is continuous dynamic recrystallisation; this process is that sub-boundaries crossing each other subdivide an austenite grain into several subgrains and these subgrains are gradually reoriented to new independent grains with their boundaries being transformed into large angle boundaries in subsequent deformation.