The Structure and Properties of Inconel 718 after Heat Treatment and Cooling in Various Media

Inconel is termed as superalloy because of its superior mechanical properties and corrosion resistance. It carries metal carbides in the metal solution which makes it highly strong. In addition, the availability of γ structure makes it tough and ductile. Inconel is a heat treatable alloy, and the microstructural changes were observed upon various heat treatment methods. The present work deals with analysis of tensile strength, bending strength, compressive strength, hardness, toughness, and microstructure of three different heat-treated Inconel 718 plates. These results of thermally treated plates were compared with those of ‘as received’ plate. The microstructural observation reveals an increment in needle-shaped δ phase upon sand, water, and furnace cooling. The alloying elements get precipitated toward the γ boundary. Therefore, both the tensile stress and yield stress have decreased for heat-treated samples. The similar reduction was also seen in the bending and compressive strength test. The heat-treated samples have shown a significant improvement in the elongation of the specimens till fracture in tensile test and till certain deflection in compressive and bending test. As a result, the highest toughness was recorded in the water quenched sample in which a high degree of δ phase has evolved on the γ grains. In contrary, the hardness (HRC) of the heat-treated samples got reduced as compared to ‘as received’ sample. According to the EDS mapping results, there was no significant variation in the alloying elements found after the heat treatment.