Origin of the enhanced hardness of a tempered high-nitrogen martensitic steel

The tempering process of a high-nitrogen martensitic stainless steel has been studied using small-angle neutron and X-ray scattering. The formation of an extremely fine nitrogen-enriched region has been confirmed for the first time in the tempering stage where the hardness starts to increase. After reaching peak hardness, the size of the N-enriched regions increases and their shape is anisotropic, which is typical for coherent precipitates.