Microstructure and mechanical properties of S30432 heat-resistant steel aged at 650°C

Microstructure and mechanical properties of S30432 heat-resistant steel aged at 650°C for different time were investigated, and the effect of precipitates in the steel on its hardness and impact toughness was discussed. The results show that Ε-Cu and M23C6 precipitate quickly in the early stage of aging, and then both of them coarsen gradually. The size and the coarsening velocity of M23C6 is larger than that of Ε-Cu, while Ε-Cu particles grow slowly and keep fine in spite of aging for a long time. The precipitation of fine Ε-Cu plays a main role in the significant increase of hardness in the early stage, and fine Ε-Cu particles ensures higher hardness after aging for a long time. The sharp decrease of impact toughness in the early stage results from the precipitation of M23C6 particles, and then the impact toughness keeps on declining as a result of gradual coarsening of M23C6 carbide during aging.