Optimization of the hot forging parameters for 4340 steel by processing maps

The study presents an investigation of hot deformation behaviour of 4340 steel and optimization of its processing parameters. The isothermal compression tests were performed at the temperatures ranging from 800 to 1200 °C and at the strain rates in the range of 0.01–100 s−1. The changes in the microstructure of 4340 steel, resulting from processing, have also been studied. The workability parameters and processing windows were determined, and the processing maps were correlated with microstructural changes. The optimal parameters for the forging process were also determined and then the numerical modelling and also the industrial tests of closed-die forging with flash were performed. Thermomechanical processing parameters as well as their influence on the investigated steel microstructure evolution, mechanisms of plastic deformation and its formability were discussed.