THERMODYNAMIC AND KINETIC SIMULATIONS OF POST WELD HEAT TREATMENT APLICATED ON P91/P22 JOINT OF STEELS
| Authors | |
|---|---|
| Year of publication | 2005 |
| Type | Article in Proceedings |
| Conference | V. Pracovní setkání fyzikálních chemiků a elektrochemiků |
| MU Faculty or unit | |
| Citation | |
| Field | Physical chemistry and theoretical chemistry |
| Keywords | Equilibria;Calphad;DICTRA; weld;steel;heat-resistant |
| Description | Weld joints between dissimilar materials represent critical locations of structures operating at high temperatures. Among other industries, dissimilar joints are increasingly used in power generation & turbomachinery. The evaluation of diffusion-controlled processes is extremely valuable, since it allows estimating long-term mechanical and microstructural stability of dissimilar welds. Diffusion and phase transformation processes were studied theoretically for P91/P22 weld joint. Modified material P91 (0.14wt%C, 10.5%Cr, 1.5%Mo, 0.6%Ni, 0.2%V, 0.04%N 0.04%Nb) represents progressive chromium steel and material P22 (0.07%C, 2.3Cr, 0,9%Mo) can be used as weld alloy. CALPHAD approach1 and thermodynamic database STEEL2 were used for thermodynamic descriptions. It enables to predict phase diagrams and activity temperature dependences of the steels. The simulated weld joint was approximated as a diffusion couple after post weld heat treatment (PWHT). Diffusion-controlled processes were described using the same method as described. DICTRA program and kinetic database DIF5 were used for diffusion simulation. The calculated carbon activity difference shows that the carbon tends to diffuse from material P22 with low carbon content to material P91 with high carbon content (up-hill diffusion) as illustrated. The simulation of the diffusion process using described approach enabled to obtain results presented. The final carbon profile shows up-hill diffusion and carbon-depleted zone in material P22. The phase profiles indicate that complex phase transformations can be supposed inside diffusion-affected zone. These transformations produce for example LAVES phase inside carbon depleted zone and M23C6 carbide inside carbon enriched zone. The thermodynamic/kinetic simulation of post weld heat treatment of the P91/P22 joint shows how it is possible now to reduce time and money consuming experiments and optimise welding consumables used. |
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