Mathematical Simulation of Microstructural Phase Transformations in the Course of Welding Heating for the Case of Cladding of Protective Layer in the WWER-1000 Reactor Vessel

Abstract

By using the developed finite-element models, we perform the numerical investigation of nonstationary temperature fields and the kinetics of microstructural phase transformations in the base material of the WWER -1000 reactor vessel (15Kh2NMFА steel) under the conditions of submerged-arc cladding of protective anticorrosion layers of austenitic materials. We perform the comparative analysis of the results of simulation of microstructural phase transformations obtained by using two methods of prediction of the decomposition of austenite in the process of cooling. The first method is based on the application of regression equations and the characteristic cooling time Δ t8/5. The second method is based on the diagrams of isothermal decomposition of austenite, the Avrami equation, and the Koistinen–Marburger equation. As a result of simulation of microstructural transformations under cladding, we obtain the bainite-martensite composition in the heat-affected zone of the base material of reactor vessel, which is confirmed by results of the dilatometric analysis and metallography.