CALCULATION OF CARBON AND NITROGEN ACTIVITIES OF HEAT RESISTANT STEELS USED IN POWER PLANTS
| Authors | |
|---|---|
| Year of publication | 2006 |
| Type | Article in Proceedings |
| Conference | Junior-EUROMAT 2006 |
| MU Faculty or unit | |
| Citation | |
| Field | Physical chemistry and theoretical chemistry |
| Keywords | DICTRA CALPHAD DESIGN SIMULATION |
| Description | The demand for higher efficiency of energy production in fossil fired power stations goes to increasing of the working temperatures, which rich up to 625degC now. This limitation is given by creep properties of the materials used for steam turbines, boilers, over heaters, and the other parts under long high-temperature exploitation. The most widely used materials for this permanent services remain steels. From thermodynamic points of view, the steels can be thermodynamically treated as Fe-Me-N-C based closed systems where Me means metal elements (Cr, V, Mo, etc.), N is nitrogen and C is carbon. Phase diagrams and temperature dependent carbon and nitrogen activities of the steels can be calculated using CALPHAD approach, which is based on semiempirical thermodynamic model of the multicomponent/multiphase system and thermodynamic condition of phase equilibrium. The activities of the all elements can be obtained during mathematical solution. In this contribution, the CALPHAD method is applied for an investigation of the bainitic ferritic steels like P23, P24, P92, E911, VM12, etc. The results calculated carbon and nitrogen activity temperature dependences are very important for a design of dissimilar weld joints, because it enables to predict the carbon and nitrogen diffusion fluxes in the regions with heterogeneity of chemical composition. This information is essential, for example, for time-life estimations of the heterogeneous welds under high temperature creep. |
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