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[en] The effects of volume fraction and stability of retained austenite on formability of a 0.1C-1.5Si-1.5Mn-0.5Cu (hereafter all in wt.%) TRIP-aided cold-rolled steel sheet was investigated after various heat treatments (intercritical annealing and isothermal treatment). Tensile tests and limiting dome height (LDH) tests were conducted on the heat-treated sheet specimens, and the changes of retained austenite volume fraction as a function of tensile strain were measured using an X-ray diffractometer. The results showed a plausible relationship between formability and retained austenite parameters such as stability and initial volume fraction. The formability was improved with increasing volume fraction of retained austenite. However, when the volume fraction of retained austenite was same, the better formability was obtained in the specimens with the higher stability of retained austenite. This indicated that the strain-induced transformation of retained austenite to martensite could be stably progressed, thereby leading to the improvement of formability. Thus, the heat-treatment conditions should be established in consideration of the maximum volume fraction and high stability of retained austenite, and the optimal conditions were found to be intercritical annealing in the temperature range at which the austenite volume fraction was about 50%, followed by isothermal treatment at Ms temperature
[en] This paper presents an approach to detect damage in composite laminates. The physical basis of the coin-tap method has been investigated in previous studies. The tap test has the ability to indicate damage such as delamination and disbond in a composite structure due to a localized change of stiffness. The changes in vibration signature may be detected by ears or more precisely by measurement instrumentation. It has been shown that the characteristics of sound radiating from a structure during a tap are changed by the presence of defects in the composite laminate. For structurally radiated sounds, the sound field is directly coupled to the structural motion. Therefore, impact response analysis should be performed. In this study, the radiated sound induced by tap was computed by solving the Rayleigh integral equation. Some damage models were also used to analyze the impact response and acoustic analysis of damaged composite laminates. The predicted impact force and sound pressure histories were compared with tap test data. The effects of in-plane load on the impact force and radiated sound were also investigated numerically.
[en] Precipitation mechanism of σ-phase in austenitic high-nitrogen steel (HNS) upon aging was investigated using electron microscopy and thermodynamic calculation. The precipitation sequence was found to be grain boundary Cr2N, cellular Cr2N and σ-phase with aging time. It was concluded that the nitrogen-depleted zone near Cr2N induces the nucleation of σ-phase
[en] In this study, core technologies has been developed for design and fabrication of the magnetostrictive strip transducers used in the LRUT field. They include the measurement technique for magnetic properties of the magnetostrictive strips and the prediction and evaluation techniques for the transducer performance. In addition, magnetic property effect of a magnetostrictive strip on the transducer performance has been analysed in detail. It is expected that the research results are useful to develop high performance transducers with enhanced inspection range and electrical instruments for operating the transducers
[en] Precipitation of various particles and their growth during rupture test have been investigated in TP347H austenitic stainless steels using a transmission electron microscopy. Various precipitates of MnS, Nb-rich MC, and MnS + MC and MnS + M_2P complexes are observed in the γ matrix after rupture test at 750 °C. The MnS particles formed independently in the γ matrix show a coherency or semi-coherency with the γ matrix. The Nb-rich MC carbides show also a coherency with the γ matrix. The Nb-rich MC carbides showing a semi-coherency with the MnS also form on the surface of the coherent or semi-coherent MnS particles, and they show a cube-cube orientation relationship with the MnS particles. The MnS + MC complex loses the initial coherency with the γ matrix, as the MC in the complex grows. The Nb-rich M_2P precipitates formed on the surface of the MnS particles do not show an orientation relationship with the MnS particles or the γ matrix. The MnS particles in the MnS + M_2P complex hold the initial coherency with the γ matrix. Effects of MnS precipitation followed by the formation of the complexes on rupture life of the TP347H austenitic stainless steels are discussed from the viewpoint of MnS precipitates acting as sinks of free sulfur segregating to the grain boundaries. - Highlights: • Coherent to incoherent transition of precipitates during rupture test in TP347H steels is clarified. • MnS precipitation actively retards the time to intergranular fracture. • Effect of the coherency of secondary precipitates on the coherency loss of the complex particle is compared.
[en] The effects of alloyed carbon on the pitting corrosion, the general corrosion, and the passivity behavior of Fe_18Cr_10Mn_0.4Nx_C (x=0 ⁓ 0.38 wt%) alloys were investigated by various electrochemical methods and XPS analysis. The alloyed carbon increased the general corrosion resistance of the FeCrMnN matrix. Carbon enhanced the corrosion potential, reduced the metal dissolution rate, and accelerated the hydrogen evolution reaction rate in various acidic solutions. In addition, carbon promoted the pitting corrosion resistance of the matrix in a chloride solution. The alloyed carbon in the matrix increased the chromium content in the passive film, and thus the passive film became more protective.
[en] The crystallographic features of sigma phase precipitation in super austenitic Fe-22Cr-21Ni-6Mo-(0.3N) stainless steels during isothermal aging were investigated utilizing transmission electron microscopy. The sigma phase precipitated along the austenite grain boundaries even after solution treatment due to higher Mo contents and remained stable throughout aging at 900 .deg. C up to 168 hours. The sigma phase observed in this study was found to be ternary Fe-Cr-Mo sigma phase and had tetragonal structure with lattice parameters of a=9.17A and c=4.74A. The orientation relationships between the sigma phase and austenite were determined from the analyses of selected area diffraction patterns taken by various zone axes and stereo graphic analyses. The orientation relationships between sigma and austenite phases obtained in this study were as follows; 1) (110)γ ll (110)σ, γ ll σ and (112)γ ll (110)σ, γ ll σ and 2) (110)γ ll (110)σ, γ ll σ and (111)γ ll (332)σ, γ ll σ. However, the former orientation relationship was predominant throughout aging and the latter orientation relationship was scarcely observed in very limited aging condition
[en] A mathematical approach u sign the phenomenological theory, originally developed by Kajiwara for Cu-based shape memory alloys, has been applied to the bcc-to-9R martensitic transformation in Fe-0.15C-1.5Mn-1.5Si-1.0Cu alloy. Analytical equations for the lattice invariant shear and habit plane were derived, and the calculated values of the lattice invariant shear and habit plane were g'=0.09669 and (0.34179, ± 0.80472, 0.48539)bcc, respectively. The orientation relationship between the ferrite matrix and 9R precipitate was calculated using the transformation matrix as follows: 9R//[1.00131, -1.00379, 1.00186]bcc and (114)9R//(0.07769, 1.07566, 1.00008)bcc. The deviation angles of orientation relationship between the calculated and the measured by HRTEM were found to be 0.06071 degree in direction and 3.67590 degree in plane, respectively. The present model successfully predicted the crystallographic features of bcc-to-9R martensitic transformation in ferritic steels
[en] At present, the most common substance used in radiation protection is lead. However, lead is a heavy metal that is harmful to the human body and causes environmental pollution. BaSO4 is an excellent material for X-Ray shielding because it has good X-Ray shielding ability and it is cheap. In this study, we fabricated Gypsum-BaSO4 (G-B) shields with gypsum and BaSO4 and Cement-BaSO4 (C-B) shields with cement and BaSO4 and conduct two tests (X-Ray shielding test, Strength test) to evaluate the performance of the shields. First of all, G-B, C-B Shields at 15 mm thickness were fabricated to evaluate X-Ray shielding performance, including 1.0, 1.5 mm thickness lead and IKEN Board. To achieve X-Ray shielding capability of 1.5 mm lead at 100 kV X-Ray tube voltage, BaSO4 content 66% G-B shield and 68% C-B shield were required. Secondly, flexural strength test was conducted for G-B and C-B shields. Test results show that at the same BaSO4 content, C-B shields were stronger than G-B shields. BaSO4 content 68% C-B shield was 3.5 times stronger than 66% G-B shield
[en] A hybrid-dynamic conformal arc therapy (HDCAT) technique consisting of a single half-rotated dynamic conformal arc beam and static field-in-field beams in two directions was designed and evaluated in terms of dosimetric benefits for radiotherapy of lung cancer. This planning study was performed in 20 lung cancer cases treated with the VERO system (BrainLAB AG, Feldkirchen, Germany). Dosimetric parameters of HDCAT plans were compared with those of three-dimensional conformal radiotherapy (3D-CRT) plans in terms of target volume coverage, dose conformity, and sparing of organs at risk. HDCAT showed better dose conformity compared with 3D-CRT (conformity index: 0.74 ± 0.06 vs. 0.62 ± 0.06, p < 0.001). HDCAT significantly reduced the lung volume receiving more than 20 Gy (V20: 21.4% ± 8.2% vs. 24.5% ± 8.8%, p < 0.001; V30: 14.2% ± 6.1% vs. 15.1% ± 6.4%, p = 0.02; V40: 8.8% ± 3.9% vs. 10.3% ± 4.5%, p < 0.001; and V50: 5.7% ± 2.7% vs. 7.1% ± 3.2%, p < 0.001), V40 and V50 of the heart (V40: 5.2 ± 3.9 Gy vs. 7.6 ± 5.5 Gy, p < 0.001; V50: 1.8 ± 1.6 Gy vs. 3.1 ± 2.8 Gy, p = 0.001), and the maximum spinal cord dose (34.8 ± 9.4 Gy vs. 42.5 ± 7.8 Gy, p < 0.001) compared with 3D-CRT. HDCAT could achieve highly conformal target coverage and reduce the doses to critical organs such as the lung, heart, and spinal cord compared to 3D-CRT for the treatment of lung cancer patients