Atomistic computer simulation of the formation of Cu-precipitates in steels

Thermal ageing of Cu-alloyed steels is a result of Cu-precipitates which arise above 300 °C. Recently small angle neutron scattering was applied in order to analyse these precipitates in a defined initial state as well as in a thermally aged state. Atomistic computer simulations of the formation of precipitates can contribute to a deeper understanding of the mechanical behaviour of Cu-alloyed steels. A model is presented which is able to simulate the `diffusionʹ of atoms by vacancy jumps [12]. The underlying Monte Carlo method is presented and a binary system with components A and B is considered. Starting with a random distribution of atoms, the formation and growth of precipitates is simulated at a constant temperature of 600 °C. In a second simulation, an initial temperature of 700 °C is lowered to 400 °C. At 700 °C precipitates of radii between 1.1 and 1.7 nm are formed within seconds. At 400 °C a part of the still dissolved atoms forms smaller precipitates while other atoms increase the size of the larger precipitates. At longer simulation times a significant decrease of the number of small precipitates and an increase of the averaged precipitate radius is found. The Russel–Brown theory is applied on the simulation results in order to calculate the increase of the yield stress in the thermally aged state.