Microstructure and Mechanical Properties of the 6 wt% Mn-Doped Martensitic Steel Strengthened by Cu/NiAl Nanoparticles

The microstructure and mechanical properties of 6 wt.% Mn-doped martensitic steel have been investigated through a combination of electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and small-angle neutron scattering (SANS). The 6 wt.% Mn-doped steel exhibits a yield strength of ~1.83 GPa and an elongation-to-failure of ~7% under peak aging, and the ~853 MPa of precipitation strengthening is much higher than that observed in the 1.5 wt.% and 3 wt.% Mn-doped steels. The steel is composed of α’-martensite and slightly equiaxed α-ferrite together with a high proportion (~62.3%) of low-angle grain boundaries, and 6 wt.% Mn doping and the aging treatment have an effect on the matrix’s microstructure. However, 6 wt.% Mn doping can obviously increase the mean size of the Cu/NiAl nanoparticles by enhancing the chemical driving force of the Mn partitioning on the NiAl nanoparticles, which differs from the refining effect on the nanoparticles in 3 wt.% Mn-doped steels. Furthermore, larger Cu/NiAl nanoparticles can significantly improve the yield strength of martensitic steel through precipitation-strengthening mechanisms.