Or you can model what happens at a microscale when welding to determine what the microstructure might look like under a microscope. You can get a statistical model of each FEM element at a macro scale to determine the statistical nature of the microstructure such as grain size, particle density, etc. The results here could vary significantly depending on the specific parameters and how they change with time and with each other.Ģ) Yes and no. You would also need to know their compositions, temperature field, etc. You would need to know how austenite and ferrite behave in relation to what you are doing to them. It is postulated that this strain ratcheting exhausts the strength of the grain boundaries within the excessively reheated weld regions, which, when combined with the shear stress induced at the grain boundaries during the ratcheting events, promotes DDC.1) The answer to this question is difficult. Comparison of DDC occurrence to the model results suggests that multiple reheat cycles in the ductility-dip temperature range accumulate plastic strains during both the on-heating and on-cooling portions of the reheat cycles, resulting in a strain ratcheting effect. To assist with understanding the correlation between strain accumulation and the occurrence of DDC, computer modeling using SysWeld™, with validated weld parameter inputs, was used to simulate the narrow groove mockup weld. For the first phase of this work multi-pass narrow groove mockups using GTAW and filler metals 52 and 52M were made with precise heat input and bead placement controls to isolate the occurrence of DDC to a known region in the weld deposit. If successful, the data from this work will be used to assist in development of a simplified field deployable test which can effectively screen for DDC susceptibility. The primary aim is to design a weld mockup that replicates strain, strain-rates, stresses, and thermal cycles that occur in multi-pass field welds and which produces DDC in predicted weld regions. EPRI is working to devise a method to predict DDC susceptibility in multi-pass high-chromium nickel-base welds and to develop procedures and techniques that minimize the occurrence of DDC - a key issue in the nuclear welding industry that has yet to be fully resolved. Due to the complexities of welding, there are potentially significant differences in the applied strain, strain rates, stresses, and thermal cycles that occur with small scale test methods and actual multi-pass welding conditions. The research conducted to develop DDC theories has primarily been performed using test methods involving small-scale specimens that may not replicate all the welding conditions and factors that cause DDC. DDC is a solid-state cracking phenomenon and several theories have been proposed for the mechanism. Journal of Verification, Validation and Uncertainty Quantificationĭuctility-dip cracking (DDC) in high-chromium nickel-base weld metals has been an issue during fabrication and repair of nuclear power plant components for many years.Journal of Thermal Science and Engineering Applications.Journal of Offshore Mechanics and Arctic Engineering.Journal of Nuclear Engineering and Radiation Science.
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