Quantitative study of microstructure evolution and the effect on mechanical properties of Super304H during aging

Abstract

ABSTRACTIn this paper, the evolution of microstructure and mechanical properties of Super304H during aging at 650 °C is investigated, and the effect between microstructure evolution and properties change are discussed. The results shows that the precipitated phases in the material during aging mainly include Cu-rich and MX particles with nano-size dispersed in matrix, M23C6 and σ particles with micron-size located at the grain boundary. These precipitates change significantly in quantity and size with the aging time, which affect the mechanical properties of the material. It helps to improve the tensile performance and hardness of the material, but it has an adverse effect on the impact energy. In addition, it is found that the degradation of impact energy is divided into two stages. Stage I witnesses the rapid drop in impact energy caused by Cr-depletion, which occurs between 0 to 1000 h during aging at 650°C. The content of Cr near the grain boundary rapidly drops from 21% to about 16% due to the precipitation of M23C6 particles on the grain boundary. Stage II is the stage of impact energy drop relatively smoothly, which occurs after aging for 1000 h. In this stage, although the Cr content increases from 16% to about 20% and remains stable due to intracrystalline diffusion, the impact energy decreased slowly, besides the M23C6 particles located at grain boundaries, the micron-sized brittle σ precipitated is another important reason.