Processing of rolling technologies for Alloy 718

Abstract

The need of thermomechanical processing of Alloy 718 for tighter properties is well known and published mainly for forged products. Less information are published for rolled products, while the today's requirements for increased productivity lead to the replacement from forging trough rolling steps, wherever it is possible. At Böhler-Edelstahl GmbH several rolling technologies for alloy 718 products were developed. Cogging of 20inch ingots, two-heat-rolling from ingot to bar for AMS 5662/3 and 3 heat rolling to flat 2×0.5 inch for extended properties show the range of different rolling processes following the TMP demands of alloy 718. The aim was to establish the needed combination of temperature- and deformation windows in the relevant steps over the cross section of the real format. The evaluated aggregates varied from reverse roughing to continuous precision mills with flat and grooved rolls. The main challenge was the transmission of the thermomechanical demands to the technical possibilities of the aggregates. The method was a combination of simplified calculation model based on 2D FDM and systematic trials with an intense metallurgical evaluation. While the behavior of alloy 718 in single or several step deformation is predictable with FEM and attached micro structural models, in multi pass rolling a save prediction is not possible. The main reason is that the reaction movements of the rolls have to be predictable too. This would include a complete simulation of the hole rolling aggregate in reaction with a material, which is impossible for complete mills.