Mathematical modeling of the hot-deformation behavior of superalloy IN718

Isothermal constant-displacement-rate compression tests of superalloy IN718 were conducted using a computer-controlled MTS machine, at temperatures fr om 960 degrees C to 1040 degrees C, initial strain rates from 0.001 to 1.0 s(-1), and true strains from 0.105 to 1.204 (corresponding to a relative he ight reduction from 10 to 70 pct). The flow stress was obtained directly fr om compression tests using the controlling computer. The grain size was obt ained by the intercept method and by comparing microstructures to the ASTM standard grain chart. Based on the results of these tests, a mathematical m odel showing the hot-deformation behavior of superalloy IN718 was developed in the form of a constitutive equation and a Hall-Fetch relationship. Both the flow stress and the grain size calculated from the model were compared to the experimental results. Meanwhile, the effect of hot-deformation para meters such as strain, strain rate, and temperature on the flow stress and on the grain size was analyzed according to the model. It was found that th ese parameters influenced the flow stress and the grain size. The model dev eloped in this work can be used to explain such effects.