Predictions and measurements of residual stresses from forging and heat treatment

Controlled cooling is used after forging of many engineering components to introduce required microstructures, mechanical properties and residual stresses. However, there is uncertainty about the combined effect of forging and cooling on microstructures, mechanical properties and residual stresses. This paper describes finite element (FE) simulations and experimental studies of the manufacture and cooling of forged and machined S55C steel discs. Two cooling states, still air cooled and water quenched, were examined. Experimental results and numerical simulations show that air cooling of machined discs gives rise to ferrite–pearlite microstructures and negligible residual stresses. However, quenching in water (without mechanical agitation) generated large residual stresses and a fully martensitic microstructure. Good agreement between experiments and FE simulations for the machined discs was found. In contrast, experiments using forged and cooled discs revealed similar compressive residual stresses irrespective of whether they were air cooled or water quenched. The microstructures remained the same as for the machined samples. The FE results for the forged samples predicted different magnitudes for the aresidual stresses but similar trends.