On the direct aging of iron based superalloy hot rolled plates

In the present investigation, microstructure and mechanical properties of an iron based superalloy in different heat treatment conditions were evaluated using optical microscopy, transmission electron microscopy, hardness measurement and tensile testing. In the solution treated condition, the yield strength (YS) and ultimate tensile strength (UTS) was 437 MPa and 900 MPa, respectively with good ductility of 49%. An increase of 307 MPa and 278 MPa in YS and UTS with minor decrease in ductility was observed by aging at 775 °C for 16 h and air cooling. Combination of high strength with good ductility was achieved by direct aging of hot rolled samples: UTS: 1260 MPa, YS: 1020 MPa and elongation: 15.5%. The improvement in strength after solution treatment and aging is attributed to formation of nano-sized Ni3(Al,Ti) precipitates of 22±3 nm in austenite matrix. The superior strength observed in direct aged samples has been attributed to dislocation density and fine precipitates with the average size of 10±2 nm.