Effect of nitrogen on microstructural evolution and mechanical properties of low carbon reduced activation ferritic/martensitic steel with boron microalloying

In this work, the microstructural evolution and mechanical properties of 0.01 wt% boron microalloying low carbon reduced activation ferritic/martensitic (RAFM) steel with various nitrogen content were studied. The results show that nitrogen could greatly reduce the dimension and volume fraction (f(V)) of M23C6 carbides and increase the f(V) of MX carbonitrides. Fine BN inclusions with the dimension of similar to 200 nm could form with the addition of 0.01 wt% nitrogen, while clustered BN inclusions with the dimension of similar to 6 mu m could be found by 0.02 wt% nitrogen added. The higher nitrogen could result in the higher f(V) and number density of MX carbonitrides, which contribute to the higher dislocation density and dislocation strengthening. However, the strength and toughness of RAFM steel deteriorated by clustered BN inclusions.