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981.
Sang Chul Seo Hyun Jung Kim Byung Ho Park Kwang Suk Son Sung Keun Lee Sun Bae Kang Donggyu Kim 《Metals and Materials International》2006,12(3):273-277
In a continuous casting steelmaking operation, the surface of a slab is under a condition that can be characterized as high-temperature,
low-cycle fatigue in which the tensile and compressive stress is repeatedly developed. For this reason, for the evaluation
of the hot ductility of a slab, considering the fatigue deformation is more feasible before a tensile or compressive test.
In this study, the effects of low-cycle fatigue on the hot ductility of steels with a carbon content of 0.06–0.8 wt.% are
investigated at various temperatures. For a carbon content of 0.06%, there were no significant differences between the RA
values from a simple tensile test and those from a tensile test after fatigue deformation. The tendency of ductility deterioration
with fatigue deformation is evident in 0.1 %C steel, and is due to the deformation-induced ferrite film that forms around
the prior austenite grain. Conversely, high carbon steel containing 0.8 %C did not show a recovery of hot ductility in a low
temperature region, and the specimen on which the tensile was measured after fatigue showed a higher hot ductility in the
low temperature region, which is thought to result from the pearlite refinement effects. As the results obtained in this work
showed noticeable differences in the hot ductility of carbon steel through the test conditions, it is suggested that for more
accurate data, fatigue deformation be adopted in which the temperature range in an unbending operation is determined in the
steelmaking factory. 相似文献
982.
In the present study, the densification of Ti/TiB composites, the growth behavior ofin-situ formed TiB reinforcement, the effects of processing variables — such as reactant powder (TiB2, B4C), sintering temperature and time — on the microstructures and the mechanical properties ofin-situ processed Ti/TiB composites have been investigated. Mixtures of TiB2 or B4C powder with pure titanium powder were compacted and presintered at 700°C for 1 hr followed by sintering at 900, 1000, 1100,
1200, and 1300°C, respectively, for 3hrs. Some specimens were sintered at 1000°C for various times in order to study the formation
behavior of TiB reinforcementin-situ formed within the pure Ti matrix. TiB reinforcements were formed through different mechanisms, such as the formation of fine
TiB and the formation of coarse TiB by Ostwald ripening or the coalescence of fine TiB. There was no crystallographic relationship
between TiB reinforcement and the matrix. There were voids at the interface between the TiB reinforcement and the Ti matrix
due to the preferential growth of coarse TiB without a particular crystallographic relationship with pure Ti matrix and the
surface energy between the Ti matrix and TiB reinforcements. Therefore, the densification of Ti/TiB2 compacts was hindered by the preferential growth of coarse TiB reinforcements. The mechanical properties ofin-situ processed composites were evaluated by measuring the compressive yield strength at ambient and high temperatures. The compressive
yield strength of thein situ processed composites was higher than that of the Ti-6A1-4V alloy. It was also found that the compressive yield strength of
the composite made from TiB2 reactant powder was higher than that of the composite made from B4C at the same volume fraction of reinforcement. A crack path examination suggested that the bonding nature of interface between
matrix and reinforcement made from TiB2 reactant powder was better than that made from B4C. 相似文献
983.
Sung-Ik Shim Yong-Soo Park Soon-Tae Kim Chi-Bok Song 《Metals and Materials International》2002,8(3):301-307
Austenitic stainless steels such as AISI 316L have been used in equipment in which fluid flows at high speeds which can induce cavitation erosion on metallic surfaces due to the collapse of cavities, where the collapse is caused by the sudden change of local pressure within the liquid. Usually AISI 316L is susceptible to cavitation erosion. This research focuses on developing a better material to replace the AISI 316L used in equipment with high speed fluid flow, such as impellers. The effects of Rare Earth Metal (REM) additions on the cavitation erosion-corrosion resistance of duplex stainless steels were studied using metallographic examination, the potentiodynamic anodic polarization test, the tensile test, the X-ray diffraction test and the ultrasonic cavitation erosion test. The experimental alloys were found to have superior mechanical properties due to interstitial solid solution strengthening, by adding high nitrogen (0.4%), as well as by the refinement of phases and grains induced by fine REM oxides and oxy-sulfides. Corrosion resistance decreases in a gentle gradient as the REM content increases. However, REM containing alloys show superior corrosion resistance compared with that of other commercial alloys (SAF 2507, AISI 316L). Owing to their excellent mechanical properties and corrosion resistance, the alloys containing REM have high cavitation erosion-corrosion resistance. 相似文献
984.
Young-Wook Kim Yong-Seong Chun Ji Yeon Park Woo Seog Ryu Dong-Soo Park 《Metals and Materials International》2007,13(3):197-200
A new process using SiC fiber fabrics and SiC tapes to produce dense 2D SiC fiber-SiC (SiC/SiC) composites is demonstrated.
The strategy for fabricating the SiC/SiC composites involves: (i) alternately stacking the SiC fiber fabrics and SiC tapes
at room temperature, (ii) pyrolyzing of the stacked composites, and (iii) hot-pressing the pyrolyzed composites. By controlling
the hot-pressing temperature, it is possible to obtain dense 2D SiC/SiC composites with relative densities of >98%. The 2D
SiC/SiC composites show no degradation of the SiC fibers and a higher mechanical strength. 相似文献
985.
This paper examines a new concept of corrosion surface damage analysis by using the digital image processing. Corrosion phenomena are analyzed using a digital value for morphological surface damages instead of electrochemical methods. Initial images are characterized by three categories: color, texture and shape features. To calculate corrosion surface damages color we use the interpretation of HIS model. For the texture attributes, the method of co-occurrence matrix is used. Five types of corrosion damage are examined. Multidimensional scaling procedure is used to define the classification plane. This study suggests a probabilistic method of decision-making. This analysis develops a method for automated identification system of corrosion damages and is supposed to be more advantageous than that of electrochemical techniques. 相似文献
986.
Il Song Park Tae Gyu Woo Min Ho Lee Seung Geun Ahn Myung Sik Park Tae Sung Bae Kyeong Won Seol 《Metals and Materials International》2006,12(6):505-511
Anodic oxidation is the process of creating a titanium oxide layer with various defects more dense and stable. In this study,
a dense, stable and porous oxide layer was formed using anodic spark oxidation on pure titanium surface and hydroxyapatite
crystals were formed on its surface via a hydrothermal treatment. A mixture of 0.02M−GP (Glycerolphosphate disodium salt)
and 0.2M-CA (Calcium acetate) was used as an electrolyte. By increasing the anodizing voltage to 220, 260, 300, and 360 V,
the effects of the anodizing voltage were examined by evaluating the film properties after anodization and a hydrothermal
treatment. Breakdown occurred around 230 V. As the voltage increased after breakdown, the pore size increased. After the hydrothermal
treatment, the amount of HA crystal precipitation was also increased as the voltage increased. The mean surface roughness
(Ra) of the anodizing surface was also increased as the voltage increased. The Ra value was larger in the hydrothermally treated
group compared with the group treated with anodization as a result of the HA crystals present on the surface after the hydrothermal
treatment. Corrosion resistance of the surface modified by anodization was significantly increased in a saline solution compared
to that for the non-treated group; this increased further after the hydrothermal treatment. These increases were most likely
due to a thick stable oxide layer formed through anodization. Thus, it is believed that titanium with its surface modified
through anodic spark oxidation would be a suitable biomaterial due to its corrosion resistance and biocompatibility. 相似文献
987.
Development of the active balancing device for high-speed spindle system using influence coefficients 总被引:10,自引:0,他引:10
Jong-Duk Moon Bong-Suk Kim Soo-Hun Lee 《International Journal of Machine Tools and Manufacture》2006,46(9):978-987
A high-speed spindle can be very sensitive to rotating mass unbalance which has harmful effect on many types of rotating machinery. Therefore, the balancing procedure is certainly needed to reduce vibration in all high-speed rotating systems. In this study, an active balancing program using influence coefficient method and an active balancing device of an electro-magnetic type with both simple and reliable structures were applied to the developed high-speed spindle system. A gain scheduling control using influence coefficients of the reference model was proved to be effective in balancing the spindle system although its characteristics were changed. The stability of reference influence coefficients was verified by experiments with frequency response functions. The active balancing experiment of the manufactured spindle system using an active balancing program and device was also performed efficiently during the operation. As a result, controlled unbalance responses after balancing work were below the vibration limit at all rotating speed ranges including critical speeds. 相似文献
988.
Yoon -Suk Choi Sung -Joon Kim Ik -Min Park Kwang -Woo Kwon In -Suk Yoo 《Metals and Materials International》1997,3(2):118-124
Boron distribution in a low-alloy steel (15B26:0.25C-0.29Cr-0.03Ti-0.028Al-0.0016B) has been characterized employing Fission
Track Etching (FTE) method. The characteristics of boron distribution with variation of cooling rate after austenitization
and through case-hardened depth after carburization were analyzed. Hardenability of 15B26 steel was also evaluated through
Jominy-end-quench test and the results are as follows: It was observed that, in austenitized 15B26 steel, boron was distributed
uniformly over the whole area of specimen with a little segregation along the austenite grain boundaries at higher cooling
rates and boron precipitates were formed in the intergranular as well as transgranular regions at lower cooling rates. Jominy
equivalents (HRC 35) of 15B26 steel were fairly increased between the Jominy temperatures of 820°C and 850°C, which might
result from the increase of the amount of soluble boron in austenite due to the dissolution of borocarbides between 820°C
and 850°C. In carburized 15B26 steel, the different through thickness features of boron distribution from the carburized surface
were found; coarse nodular boron precipitates up to the depth of 150 μm; uniform distribution of dissolved boron between 150~650
μm; and segregation of boron atoms along grain boundaries in the regions deeper than 650 μm. 相似文献
989.
Galvanic coupling effect on the corrosion of SiC-reinforced aluminum alloy-matrix composites was investigated in a sodium chloride solution. The potentiodynamic polarization measurement indicated that pitting potentials of metal matrix composites (MMCs) and AA2124 matrix alloy were similar, and pitting potential of MMCs was almost same as corrosion potential, while pitting susceptibility of MMCs was higher than that of AA2124 alloy. Galvanic current by formation of galvanic couple between SiCw and matrix reveals very low value because of large cathodic polarization of SiC. However, by increasing potential of matrix to pitting potential by this galvanic couple and thus, forming pits easily at the weak passive film near SiC reinforcing phase preferentially, it is concluded that pitting susceptibility of MMCs increases highly than AA2124 alloy of matrix composition. 相似文献
990.
Hwan-Cheol Kim In-Jin Shon J.E. Garay Z.A. Munir 《International Journal of Refractory Metals and Hard Materials》2004,22(6):257-264
The rapid sintering of nano-structured WC hard materials in a short time is introduced with a focus on the manufacturing potential of this spark plasma sintering process. The advantage of this process allows very quick densification to near theoretical density and prohibition of grain growth in nano-structured materials. A dense pure WC hard material with a relative density of up to 97.6% was produced with simultaneous application of 60 MPa pressure and electric current of 2800 A within 2 min. A larger current caused a higher rate of temperature increase and therefore a higher densification rate of the WC powder. The finer the initial WC powder size the higher is the density and the better are the mechanical properties. The fracture toughness and hardness values obtained were 6.6 MPa m1/2 and 2480 kg/mm2, respectively under 60 MPa pressure and 2800 A using 0.4 μm WC powder. 相似文献