Effect of aging on the impact toughness of 25Cr–20Ni–Nb–N steel

The impact toughness evolution of 25Cr–20Ni–Nb–N stainless steel during aging for different time at 973 K has been systematically investigated. It is found that the impact toughness of 25Cr–20Ni–Nb–N stainless steel declines sharply in the early stage of the aging (about 500 h). Thereafter, the impact toughness decreases slowly with the increase in aging time. The hardness on grain boundaries and within grains is analyzed by micro-indentation. The results of micro-indentation show that the hardness in grains during aging is higher than that on grain boundaries due to the precipitation of M23C6 and the decrease of the impact toughness of 25Cr–20Ni–Nb–N can be attributed to the reduction of the bonding interface strength when M23C6 precipitated on grain boundaries.