Evolution Of Precipitate Structure in the heat-affected zone of a 9 wt. % Cr Martensitic Steel during welding and post-weld heat treatment

Martensitic 9–12 wt. % Cr steels have been favoured grades for high temperature components in thermal power generation industry. The excellent creep properties of these steel grades can be related to their optimized martensitic microstructure containing finely dispersed precipitates. In the present work, the influence of weld thermal cycle and subsequent post-weld heat treatment on precipitate evolution of a martensitic 9 wt. % Cr steel is investigated. The microstructure at different stages of the thermal cycle is characterized by optical microscopy, scanning electron microscopy and transmission electron microscopy. The precipitates are identified by analytical transmission microscopy, namely energy-filtered TEM, energy dispersive X-ray diffraction and electron energy loss spectroscopy. The experimental findings are compared to kinetic simulations of the precipitate evolution during the complete thermal cycle using the software MatCalc. Results of kinetic simulations are in good agreement with experimental data. Optimization of heat treatment procedure as well as further application of microstructure modelling is discussed.