Effect of solution treatment temperature upon the microstructure and mechanical properties of hot rolled Inconel 625 alloy

The influence of solution treatment temperature on the microstructure and mechanical properties of hot rolled Inconel 625 alloy was investigated. The results show that the microstructure of the hot rolled alloy is mainly composed of austenite equiaxed grains, with the secondary phase being dominated by MC carbide rich in Nb and Ti. The alloy possesses a high strength of 959 MPa with a hardness of 262 HV, but modest plasticity with a tensile elongation of 48%. The effects of grain refinement and dislocation entanglement are considered to be the main mechanisms responsible for the excellent strength in the alloy. For the solution treatment temperature set in the range of 950–1050 °C, the average grain size of the treated alloy did not change significantly, and the carbide phase was dissolved slowly. As such, the temperature has little effect on the mechanical properties of the alloy. At the temperature higher than 1150 °C, the carbide was dissolved near the grain boundaries and, at the same time, the grains grew rapidly. Consequently, the tensile strength and hardness of the treated alloy decreased considerably, whereas the elongation to fracture increased from about 47% to more than 60%. The strength-ductility trade-off is attributable to a synergy of grain coarsening, dislocation annihilation and the dissolution of precipitate phase during solid solution treatment. Moreover, the recrystallization texture was observed after solution treatment at higher temperatures.