Computer simulation of the yield strength evolution in Cu-precipitation strengthened ferritic steel

During ageing of steel containing a few percent Cu, a maximum increase of hardness and strength can be observed after several hours of annealing at around 500–550 °C. This strength increase is caused by small coherent bcc-Cu-precipitates of 2–3 nm diameter. For consistent computer simulations of the early stages of precipitation, it is shown that variations in the equilibrium Fe-content of the bcc-Cu nuclei must be taken into account. The simulated precipitation parameters are compared to experimental data reported in literature. Good agreement between experiment and simulation can be achieved in terms of the evolution of phase fraction, number density and mean radius of the Cu-precipitates. Based on these results, different models for precipitation strengthening are assessed and their predictions compared to the experimentally observed strength evolution. We find that mainly the coherency strain and modulus strengthening effects contribute to the precipitation strengthening potential. Together with the intrinsic strength of the alloy and Cu solid-solution strengthening, a consistent description of the lower yield strength evolution during precipitation hardening of an Fe–1.4% Cu alloy is achieved.