Photon Factory Activity Report 2004 #22 Part B (2005)
Materials Science

16A1/2002S003

Stress imaging of welded steel by X-ray diffraction microscope
Mari MIZUSAWA and Kenji SAKURAI*
National Institute for Materials Science, Sengen, Tsukuba, Ibaraki 305-0047, Japan
Introduction
A projection-type X-ray microscope, which wasinitially developed for X-ray fluorescence, is a strong toolfor 2D X-ray diffraction imaging of polycrystalline
materials. Its recent extension to stress imaging [1] issignificant because it can provide a good gauge of thereliability of the mechanical strength of materials. This
report describes the preliminary results of an experimentto obtain the stress distribution of welded steel.
Experimental
The sample studied is a T-joint weldment of steel plates,
as shown in Fig.1. The powder diffraction pattern (seeFig.2) indicates that the main structure consists of the αFe type. The (200) reflection has been chosen for stressanalysis. Details of the instrumentation of the X-ray
diffraction microscope are described elsewhere [1]. The
experiment consists of repeated exposures during thewavelength scan of the incident X-ray photons for several
2θ angles, 78, 90, and 105 deg, in the present case.
Typical exposure time was 1 sec.

Figure 1 Top view of the sample. The size of theviewing area of the X-ray microscope is 8mm × 8mm.
The stress distribution of the welded part was studied.

Results and Discussion
In energy-dispersive X-ray diffraction experiments [2],the Bragg peaks are given as the X-ray wavelength. For
the (200) reflection, when 2θ is 78, 90, and 105 deg., thewavelength is 1.798, 2.023 and 2.263 Å, respectively.
The present technique can give a 2D map of the peakwavelength for each case. This corresponds to the strain
map for different Ψ angles, i.e., the orientation of thesample, which almost equal half of the 2θ angles in thepresent case. Therefore, one can calculate the slope ofthe sin2Ψ-λ/λ0 plot for each pixel from those three maps.
Figure 3 shows the stress image that was finallyobtained. In the present study, the viewing area waspreliminarily segmented as a 10 × 10 matrix, although theoriginal X-ray image had 1000 × 1000 pixels. This is acompromise to improve reliability in the determination ofthe slope. As the figure shows, one can see some clear
non-uniform distribution of the stress, in particulararound the welded part. Good agreement has been
confirmed by conventional X-ray stress analysis with asmall X-ray beam, although the measurements were only
for several points because such an experiment requires avery long measuring time. The advantage of the present
microscope is that stress imaging can be performed much
more quickly than with the conventional method. Theauthors would like to thank Drs. H. Sawa, Y.
Wakabayashi, Y. Uchida, for their assistance and advice
during the experiment..
References[1] K.Sakurai and M.Mizusawa, Photon Factory Activity
Report, this issue.
[2] Ch.Genzel, C.Stock and W.Reimers, Mater. Sci. &Eng. A372, 28 (2004); Y.Hosokawa et al., J. Soc. Mat.
Sci., Japan, 43, 766 (1994)*sakurai@yuhgiri.nims.go.jp

X (×100 pixels)
0020000

46810-0.3865-0.3852

10000

Fe3O4 Fe O
3 4(220) (222)
Fe3O4α-Fe (211)α-Fe (200)α-Fe (220) α-Fe (310)(204)

020406080100120

2θ[deg.]Figure 2 Powder diffraction pattern of the sample for
CuKα radiation. In the present study, the (200)reflection peak found at around 65 deg was chosen for
stress analysis.

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Users' Report

Y (×100 pixels)

Intensity[cps]α-Fe (110)-0.3840
4-0.3827-0.38156810Figure 3
The results of stress imaging, which2
represents the map of the slope of the sin Ψ-λ/λ0 plot.