Continuum creep damage mechanics modelling of creep has been combined with the recently developed Monte Carlo simulations of precipitation kinetics in power plant ferritic steels. The precipitation simulation has been validated by applying it to a 9 wt-%Cr ferritic steel, P92 and using the microstructural data published in the literature. The microstructural evolution results of precipitation kinetics simulation are used in the continuum creep damage mechanics model to calculate the damage evolution instead of the model equations developed for specific creep damage. This approach has been applied to P92 to study the effects of different creep damage mechanisms on the creep behaviour. Reasonable agreement with experimental creep rupture data and creep curves has been obtained. The new approach shows promise to provide a useful tool for both new alloy development and component life prediction.

No abstract

The microstructure evolution and precipitation kinetics of maraging steel C300 have been studied in the aging temperature range from 400 to 600°C. The relation between mechanical properties and precipitation hardening response is explained, and modelling is used to optimise the properties. Ultrafine needle shaped Ni3Ti phase is the main strengthening precipitate in maraging C300, and it shows very high resistance to coarsening. A spherically shaped Fe2Mo phase is formed at higher temperatures and in the overaged condition. Inter- and intralath reverted austenite nucleates at higher temperature (∼600°C). Rolling and aging treatment can produce the highest hardness by a combination of work hardening and precipitation strengthening. Microstructural evolution simulation using Monte Carlo modelling has been applied to this alloy, and the modelling has been validated by the experimental results.

No abstract

A new technique based on Monte Carlo random sampling has been proposed to simulate the precipitation kinetics in alloys. The new approach employs time dependent nucleation and diffusion laws, considers both intergranular and intra-granular precipitation, and also combines precipitation kinetics with intergranular segregation. The simulation can be used not only to predict the average size of precipitate phase particles, but also to predict particle size distributions, volume fraction, and interparticle spacing. The new approach overcomes the shortcomings of earlier model calculations where only the average size of the precipitate phase is considered. In addition, the proposed simulation overcomes the dif® culty of connecting Monte Carlo steps to real time using the Metropolis algorithm. The approach has been used to simulate M 23 C 6 precipitation kinetics in a creep resistant steel, P92: the results are in good agreement with published experimental measurements, and the model is believed to be applicable to other types of precipitates in different alloys.MST/5277