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The surface nitrogen permeation of Al alloyed 0.14%C-13%Cr stainless steels was investigated after heat treating at 1050℃∼1150℃ in the nitrogen gas atmosphere. The strong affinity between Al and nitrogen permeates the nitrogen through the interior of the steels. Two precipitates of round type and needle type are observed at the surface layer. These precipitates mainly consist of AlN containing plenty of aluminum. The surface layer of 0.53%Al alloyed specimen shows ferrite phase, while the surface layers of 1.65%Al and 2.27%Al alloyed specimens appear γ plus α phases. The depth of nitrogen permeation depends upon the Al content and microstructure of the matrix. The 1.65%Al alloyed specimen representing α+γ matrix phases at the nitrogen permeation temperature shows the maximum case depth in this experiment. Although the surface hardness increases by raising the Al content of the specimen owing to the increase of nitride precipitation density, the nitride precipitation deteriorates the corrosion resistance in the solution of HCl, H₂SO₄, and FeCl₃.
Volume fraction and morphology of retained austenite, tensile peoperties of TRIP type high strength steel sheet with Fe-C-Si-Mn-Cu chemical composition have been investigated. The retained austenite of granular, bar and film type existing in specimen was obtained after intercritical annealing and austempering. The granular type retained austenite increased with increase of intercritical annealing and austempering temperature. With increase of intercritical annealing temperature, retained austenite and carbon contents increased. Maximum contents of retained austenite was obtained by austempering at 400℃. The maximum tensile strength was obtained by austempering at 450℃ and maximum elongation was obtained at 400℃. T.S×E.L value increased with increase of retained austenite contents due to the elongation strongly controlled by contents of retained austenite, but tensile strength was affected with various factors such as bainitic structure etc.
This present study were investigated effect of Ni contents on the microstructure and strength characteristic in 9Cr ferritic heat-resistant steel added 1.7%W in place of Mo in order to restrain laves phase formation. The result obtained from this study are as follow. Volume fraction, number of particles per unite area and particle size of carbide decreased with increase of Ni contents. Other side, carbides of M_(23)C_6 type was mainly precipitated in this steel, but laves phases could not precipitated in spite of increasing of aging time. With increase of tempering temperature, hardness was increased, and maximum value was showed around 873k by secondary hardening due to precipitation of W₂C type carbide and then, was decreased. Tensile and yield strength due to decrease precipitation amount of carbide and number of particles per unite area was decreased, but elongation and impact value was increased. In case of aged specimen after tempering than tempered specimen, strength was higher and elongation was lower due to increasing of precipitated amount of carbide and number of particles per unite area
A case of congenital agenesis of left lung of a 19-years-old female is presented in detail with some review of literature. She had been suffered from mild dyspnea on exertion since early childhood but she was been comfatable unti16 months ago, when frequent upper respiratory infection and dyspnea developed. From 10 days earlier, mild fever was associated and dyspnea on exertion was aggravated. Her past history and family history were not contributary. Physical examination revealed asymmetrical development of both thoracic cage and showed limited respiratory movement of left thorax. There were increased percussion dullness and absent breathing sounds over entire left lung field except left upper lung field. The cardiac dullness was shifted to the left and heart sunds were heard over the 4th ICS X MCL. A roentgenogram of the chest revealed shifting to the left of trachea and mediastinum, homosgenou increased density of left lung, hyperlucency of right lung, and T, hemivertebra, Bronchoscopy showed total absence of left main bronchus. Bronchogram revealed above findings too, but right main bronchus was intact. CT scan revealed agenesis of left lung and herniation of right lung to left hemithorax. Intravenous pyelography showed malrotation of kidney. Pulmonary angioram and cardiac catheterization showed unremarkable findings except total absence of left pulmonary artery.
This investigation has been carried out to make clear the effect of deformation temperature, strain rate and grain size on the tensile properties of 304L stainless steel. Tensile properties of the metastable austenitic 304L steel remarkably influenced by deformation temperature. Tensile strength increased with decreasing deformation temperature and the elongation showed maximum value near 40℃. In order to obtain the high elongation, a large amount of deformation is available in austenite before martensitic transformation and the martensite has to be induced gradually. Tensile strength and elongation increased with decreasing grain size. The temperature representing the maximum elongation shifted to low temperature and the peak width of elongation became broaden with decreasing austenite grain size. The volume fraction of strain induced martensite decreased with decreasing austenite grain size. As the strain rate increase, the temperature representing the maximum elongation value shifted to high temperature and volume fraction of strain induced martensite decreased.
The effect of deformation temperature and manganes contents on the tensile properties of duplex stainless steels with the structure of both ferrite and austenite were investigate. Far this investigation, Fe-19% Cr-5% Ni-4∼8% Mn alloys were prepared. The result obtained from this experiment are summerized as follows. With decreasing deformation temperature, tensile strengths of duplex stainless steel increased. Elongation showd to be increased and then decreased after representing the highest value at specific temperature. Tensile properties of duplex stainless steel were controlled by TRIP behavior in this experimental range of austenite contents. Tensile strengths decreased with increasing Mn contents. With increasing Mn contents, elongation decreased in the high temperature region, but increased in the low temperature region. The peak temperature representing the maximum elongation were changed to low temperature and the width of peak appeared to be broaden with increasing Mn contents.
A dual-channel automatic ac-do voltage transfer error measurement system in which the output voltages of two thermal voltage converters which are ac voltage standard are directly measured at the same time to reduce the output voltage drift is described. Forward-reverse measurement method by using a two-channel scanner is used to cancel the offset voltage of the voltmeters. The agreements of the 4-V TVC comparison results between other national standards institute and Korea Research Institute of Standards and Science were less than about ±2 ppm in the frequency range of 40 Hz∼100 kHz, and were less than about ±4 ppm at 200 kHz∼1 MHz. Measurement uncertainty is reduced significantly from ?5 ppm of manual system to ±3 ppm of new system(up to 100 kHz) typically and great increase in comparison efficiency has been achieved by this system.
In this study, microstructures of the heat affected zone (HAZ) of SA 508 steel were identified by Mo¨ssbauer spectroscopy in conjunction with microscopic observations, and were correlated with impact toughness. Specimens with the peak temperature risen up to 1350℃ showed mostly martensite, but the microstructures were not changed, much from the base metal because of the minor tempering effect when it was risen to 650℃ or 700℃. With the peak temperature risen to 900℃ over the A₃ temperature, the martensite fraction was reduced, while bainite or martensite island were formed because of the slow cooling from the lower austenite region. As the martensite fraction present inside the HAZ increased, hardness and strengths tended to increase, whereas impact toughness decreased. However, impact toughness of the subcritical HAZ with the peak temperature risen to 650℃-700℃ was seriously reduced after post-weld heat-treatment (PWHT) since carbide particles were of primary importance in initiating voids. Thus, the most important microstructural factors affecting impact toughness were the martensite fraction before PWHT and the carbide fraction after PWHT.
This study attempted to evaluate the effectiveness of parent training computer package for children with autism based on the analysis of profiles obtained with the child developmental areas and Autism Behavior Checklists(ABC). The computer package programs were provided for 20 autistic children ranging in CA from 3 to 7 for a period of six months by their own mothers. Subjects demonstrated significant treatment effects in the domains of developmental profiles and ABC. Statistically significant differences were noted. The proportional Change Index was 4.33.
Planar multi-junction thermal converters were fabricated for precise measurements of the ac voltage and current by an ac-do transfer method. A heater and a thermocouple array were fabricated onto a sandwiched membrane, Si₃N₄ (200 nm) / SiO₂(400 nm) / Si₃N₄(200 nm, a thickness of 0.8 ㎛ and a size of 2 x 4 ㎟, which is supported by a surrounding frame. The NiCr heater is located at the center of the membrane vertically. Hot junctions of 48 ∼ 156 pairs of thermocouples (Cu-CuNi44) are located near or onto the heater, and cold junctions are located onto the silicon frame. Output of the thermal converters for 10 mA do input was 76 mV ∼ 382 mV dependent on a model, and short term stability of the outputs was ±5 ∼ 15 ppm/ 10 min with 5 mA do input. Responsivity in air was in the range of 3.9 ∼ 14.5 V/W. Responsivity of the model BF48 in air which has 48 thermocouples was 2 times or greater than that of 3 dimensional multi-junction thermal converter in vacuum which has 56 thermocouples. AC-DC transfer differences with an input of 10 mA or less were less than ±1 ppm in the frequency range from 5 Hz to 2 kHz, and about 2 ∼ 3 ppm at 5 kHz and 10 kHz.