Effect of cold-rolling on mechanical properties of Haynes 25 cobalt-based superalloy

Abstract

Effect of cold-rolling and annealing time on the microstructure, hardness and the tensile properties of Haynes 25 superalloy at room-temperature and 760 °C were investigated in this research. Hot-rolled and solutionized alloy of Haynes 25 was subjected to cold-rolling with different amounts of reductions, i.e. 5%, 10%, 20%, 30% and 35%. After that, all cold-rolled samples were annealed at 1230 °C for a period of time from 2 to 120 min. Microstructural analysis showed that for annealing time range from 30 to 120 min, the rate of grains coarsening remained approximately stable in all cold-rolled samples. On the other hand, the hardness results showed that expected decreasing trend of hardness did not occur after annealing of the cold-rolled samples at 1230 °C; on the contrary, hardness increased moderately in the range time from 10 to 120 min. Tensile properties after annealing of the cold-rolled samples at room temperature and 760 °C decreased. Loss of the tensile properties can be related to the high annealing temperature. According to the experimental results, decreasing trend of tensile properties and increasing trend of hardness is linked to the formation of hcp phase after annealing at 1230 °C for 30 min. Even though the hcp phase is a hard phase, the interface between fcc and hcp phases provides suitable sites for crack nucleation and propagation.