The ω phase in a low alloy martensitic steel

The microstructure of a low alloy martensitic steel has been investigated using TEM. It was indicated that the as-quenched plate and lath martensites consist of ferrite matrix and high density of nanometer-scaled ultrafine particles embedded in the matrix. These particles were designated to be ω phase with a primitive hexagonal crystal structure. The ω particles exhibit an orientation relationship with the ferrite (α-Fe) matrix as follows: [1̄13]_α // [21̄1̄3̄]_ω, (110)_α//(11̄01)_ω and (2̄11̄)_α//(01̄10)_ω, with lattice parameters of a_ω=√2a_α, c_ω=√3/2a_α. The results of the present study suggested that the carbon atoms in the steel are not homogenously distributed in the martensites. The ferrite matrix possesses very low content of carbon, and most of the carbon atoms are concentrated in the ω phase.