Improvement of Bragg-edge Neutron Transmission Imaging for Evaluating the Crystalline Phase Volume Fraction in Steel Composed of Ferrite and Austenite

Visualising Martensite Phase Fraction in Bulk Ferrite Steel by Superimposed Bragg-edge Profile Analysis of Wavelength-resolved Neutron Transmission Imaging

“…In the present study, U was 0.048 (4.8%). This value is comparable to the value of a ferrite/austenite phase fraction analysis using RITS, 18) although the sBE analysis method is easier in terms of data analysis handling, compared with RITS, which addresses a lot of microstructural parameters. Here, we discuss an estimated reason for the value of U.…”

“…A lot of crystalline microstructural information can be evaluated using this method, e.g., crystalline phase fraction, [15][16][17][18] crystallographic texture, 11,19,20) crystallite size, 11) macrostrain, [21][22][23][24] and microstrain/dislocation. 25) The Braggedge wavelength broadening effect has frequently been used for the analysis and imaging of the martensite phase in ferrite-martensite steel.…”

“…3,[5][6][7][26][27][28][29] The crystal structure of α'-martensite is close to that of α-ferrite, and the entire neutron transmission spectral patterns from these microstructures are almost the same. 26) Therefore, a traditional crystalline phase fraction analysis method identifying the spectral patterns [15][16][17][18] cannot be applied to the ferritemartensite phases. However, a single Bragg-edge profile caused by {110} and {101} diffractions of the α'-martensite phase is slightly broader than a single Bragg-edge profile caused by the {110} diffraction of the α-ferrite phase, which appears at the neutron wavelength of 0.405-0.415 nm.…”

“…where λ is the neutron wavelength, P is the index of crystalline phase, N is the total number of crystalline phases, σ P (λ) (cm 2 ) is wavelength-dependent neutron total cross-section of crystalline phase P, and t P (cm − 2 ) is the areal density of the atomic number of the crystalline phase P. Traditionally, the crystalline phase fraction is evaluated using t P 18,33) if there is a large difference in σ P (λ)s. However, in the case of the combination of the BCC-structured ferrite phase and BCT-structured martensite phase, the difference in σ P (λ)s between both phases is very small. 26) Figure 2 shows a schematic of the d-spacing distribution of the α-ferrite phase, α'-martensite phase, and their superimposed distribution.…”

“…11,19) Conventionally, it is important for crystalline phase fraction analysis that the Bragg-edge height and wavelength patterns of analysed crystalline phases such as ferrite (or martensite) and austenite differ, because the pattern decomposition is necessary for the quantification of each crystalline phase. [15][16][17][18] However, the pattern decomposition is not usable in the ferrite-martensite case because the spectral pattern between ferrite and martensite is almost the same. Therefore, in our present study, it is utilized that the Bragg-edge profile of martensite is broader than that of ferrite.…”