Publication details
Simulation of structural stability of weld joints of heat-resistant steels.
| Authors | |
|---|---|
| Year of publication | 2004 |
| Type | Article in Proceedings |
| Conference | Thermodynamics of Alloys TOFA 2004 |
| MU Faculty or unit | |
| Citation | |
| Field | Physical chemistry and theoretical chemistry |
| Keywords | DICTRA;phase;diffusion;CALPHAD |
| Description | Knowledge of microstructure stabilities is essential for reliable estimations of the lifetime limitations of materials and welded joints at higher temperatures. This information may be deduced from material phase diagrams and from heterogeneous weld joint simulations. The phase diagrams can be calculated using CALPHAD method [1]. This method complemented with appropriate diffusion approach [2], [3] can help us to simulate phase and element profile evolutions inside diffusion-affected zone of weld joint too. Thermodynamic database STEEL [4] and kinetic database DIF mentioned in [5] are used. The weld joints are simulated as heterogeneous diffusion couples. The results of the equilibrium calculations are presented as the phase diagram cross-sections of the selected materials: heat resistant steels and weld metals. The same equilibrium calculations offer element activities too. The carbon activity temperature dependences were calculated for individual materials. The observed difference between the carbon activities of two different materials (at given temperature) enabled us to predict diffusion flow direction, which can be in some cases opposite then deduced from carbon contents in some steel combinations (carbon up-hill diffusion). The simulations respect the coexistence of different carbide phases in the materials and they are conducted on the assumption that under the examined conditions the local phase equilibrium holds and that diffusion is the control process of phase transformation. The phase diagram calculations and diffusion couple simulations involving time-distance dependences for phase and element redistributions in diffusion-affected zones enabled us to obtain a basic information, which allow to estimate thermodynamic and diffusion stabilities of the studied materials and their weld joints and finally to deduce the weakest point(s) of the weld joins. |