Development of X-ray Imaging for Observing Solidification of Carbon Steels

Abstract

Time-resolved X-ray imaging of dendritic solidification for pure Fe and carbon steels with sufficient spatial and time resolutions has been developed for the first time by overcoming essential problems in low contrast between solid and liquid phases and in high melting temperatures. Static observation showed that the solid/liquid interface in pure Fe specimen was determined by the absorption contrast at photon energy ranging from 16 to 30 keV. In addition, the phase contrast was also observed in the vicinity of the interface. Dynamic observation showed that cellular growth in pure Fe specimen was observed at a growth velocity up to 400 mm/s. Feasibility observation was also performed for two different carbon steels (0.0025 mass% C and 0.45 mass% C). Growing dendrites were observed in-situ at a growth velocity up to 500 mm/s. This study proves that the developed imaging enabled to observe solidification phenomena in-situ for various kinds of steels.KEY WORDS: in-situ observation; radiography; synchrotron radiation; dendrite.of carbon steels by X-ray imaging will be concluded. Based on the requirements, the paper explains an X-ray imaging developed by this study and demonstrates in-situ observation of solidification for pure Fe. Feasibility observations for carbon steels were briefly presented. Preparation of X-ray Imaging Requirement for Transmission X-ray ImagingImportant parameters for developing X-ray imaging using the absorption contrast are intensity of transmission X-ray through a specimen and contrast between different phases. One estimates the intensities through Fe-C alloys and pure Fe for building X-ray optics and for choosing dimension of specimen. In general, intensity of transmission X-ray, I, is expressed by (m/r) and r are the mass X-ray absorption coefficient and the mass density, respectively. The suffix, i, indicates constituent element species. r¯is average density and w i is mass fraction of the constituent element, i. The mass X-ray absorption coefficient, (m/r), which is a function of photon energy, is uniquely defined by the element.The linear X-ray absorption coefficient of Fe-C alloys is given byThe mass X-ray absorption coefficient of C is 0.044 m 2 /kg at 20 keV while that of Fe is 2.57 m 2 /kg at 20 keV. 27) Since the mass fraction of C is mostly less than 0.01 in conventional carbon steels, the mass X-ray absorption coefficient and the density of Fe dominantly determine the linear X-ray absorption coefficient of the Fe-C specimen.Conventional carbon steels contain Mn as well. The mass X-ray absorption coefficient of Mn is 2.25 m 2 /kg at 20 keV. 27) Since the partition coefficient of Mn in Fe matrix is approximately 0.75, difference in Mn concentration between solid and liquid phases is estimated to be 0.1-0.3 mass% for a specimen with average Mn concentration of 0.3-0.9 mass%. Change in the linear X-ray absorption coefficient is evaluated by the same procedure as for Fe-C system. The solute redistribution gives only 0.01-0.03% change in the linear X-ray absorption coefficient. The ch...

Kinetics of the δ/γ interface in the massive-like transformation in Fe-0.3C-0.6Mn-0.3Si alloys

“…Figure 1 shows a setup for observing the massive-like transformation. Details of the setup were described in the previous work [6]. An ion chamber for measuring intensity of incident X-ray beam, vacuum chamber in which a specimen with a heating system is set, and an X-ray beam monitor are placed along X-ray beam stream.…”

“…Mother alloy with a composition of 0.3mass%C, 0.6mass%Mn and 0.3mass%Si was made by arc melting of electrolytic Fe, C, Mn and Si. A specimen cell made of Al 2 O 3 window plates 0.15mm) and BN retainer plates was used [6]. The specimen with a dimension of 10 mm x 10 mm x 0.1 mm was heated by graphite heaters.…”

“…For example, dendritic solidification of Sn and Al alloys has been reported [4][5]. Recently, the technique has been extended to observe solidification of Fe-C alloys [6][7][8] and deformation of semisolid [9]. Since the in situ observation allows us to know how the solidification and the phase transformation proceed, the technique provides direct and valuable information for modelling microstructural evolution and defect formation.…”

Dilatancy in semi-solid steels at high solid fraction

“…We study an equiaxed microstructure since this is a desired continuous casting microstructure that can be achieved industrially by, for example, electromagnetic stirring [11]. In order to directly image the microstructural response to load, we use synchrotron radiography building on the techniques developed for steel solidification by Yasuda et al [12]. We study deformation under conditions of fully-fed deformation and deformation with inadequate feeding with the following specific aims: (i) to identify and quantify the deformation mechanisms, (ii) to compare the observed mechanisms with those assumed in models of the continuous casting process and those measured in steels at lower solid fraction previously [13][14][15], and (iii) to develop an understanding of how shear deformation can generate macrosegregation and cracking during the final stages of solidification.…”

Comparative Study on Structural Variations during Containerless Solidification Processes of Fe-B and Fe-C Eutectic Alloys

“…Indeed, CNL is often used when performing x-ray diffraction experiments on high-temperature melts and solidification from the undercooled liquids. [13][14][15][16][17][18][19] While time-resolved x-ray diffraction (TRXRD) and imaging techniques for studying solidification of steels have been developed with utilizing high-flux x-rays from a synchrotron radiation source, 20,21) synchrotron TRXRD experiments combined with CNL have been also carried out by adopting a two-dimensional detector such as a charged coupled device (CCD) for investigations of structural variation during solidification from deeply undercooled melts. 18,19) In the present study, we conducted TRXRD experiments during containerless solidification of Fe-C and Fe-B binary alloys at the eutectic composition.…”