In the SADP for lower Mn sample is body-centred-cubic α phase with lattice
parameter 2.92 Å. The diffraction pattern confirms the ð1 11Þκ ==
ð110Þα and [011]κ// [001]α orientation relationships between κ-
carbide and α-matrix. The matrix in higher Mn sample is facecentred-cubic
γ phase with lattice parameter 3.66 Å. The orientation relationships
between κ-carbide and γ-matrix are (001)κ//(001)γ and
[001]κ//[001]γ. The lattice parameters for those phases are 3.61 Å for
γ, 2.86 Å for α and 3.78 Å for κ-carbide in literature [20–21]. This
gives the measurement errors in present work of 1.36% for γ, 2.05% for
α and 0.8% for κ, respectively. The lattice misfit around κ-α interface is
(3.75–2.92) / 3.75 = 22.1%, while that around κ-γ interface is (3.75–
3.66) / 3.75 = 2.40%. According to the previous results, α-matrix in
lower Mn steel contains 18% γ phase and 68% α phase [14]. κ-Carbides
are surrounded by α phase. The latter is embedded in γ phase [14].