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李德洛 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.6
The effect of prior austenite grain size on mechanical properties in a medium carbon ferrite-pearlite steel was investigated to find the optimum condition to minimize the deviation of mechanical properties. It is shown that the variation of hardness of a medium carbon steel containing ferrite and pearlite with cooling rate becomes smaller as prior austenite grain size becomes finer. The hardness of specimen with fine prior austenite grain increases less sharply than that of specimen with coarse one for the change of same amount of pearlite volume fraction in as-rolled state. It is concluded that the deviation of mechanical properties of medium ferrite-pearlite carbon steels can be reduced effectively by making prior austenite grain size finer.
Surface wrinkle defect of carbon steel in the hot bar rolling process
Kwon, Hyuck-Cheol,Lee, Ho-Won,Kim, Hak-Young,Im, Yong-Taek,Park, Hae-Doo,Lee, Duk-Lak Elsevier 2009 Journal of materials processing technology Vol.209 No.9
<P><B>Abstract</B></P><P>It is well known that surface defect is a common problem encountered in the multi-stage hot bar rolling process of carbon steel. In this study, the phenomenon was investigated by simulating the process by the finite element technique to identify the location where the surface defect might occur and checking the surface qualities obtained from the compression tests at various temperatures and strain rates to clarify the important parameter governing the possible surface defect formation. Also, the surface temperature was measured by employing pyrometer to support the experimental observation. The levels of temperature and specific deformation energy obtained from finite element simulations depending on the roll groove geometry were compared with the experimental observation to better understand the formation of the surface defect in the hot rolled bar. Based on this study, the surface defect might be formed by dissipating the excessive deformation energy accumulated by generating the new surface at the lower level of temperature where recrystallization cannot occur. According to this work, the comparison of the specific deformation energy level for determining the instability of the hot working process might be interesting for further investigation.</P>
주웅용,이덕락,Yue, Steve 대한금속재료학회(대한금속학회) 2001 대한금속·재료학회지 Vol.39 No.6
Inferior drawability of AISI4135 steel rod is sometimes due to the presence of hard constituents such as bainite and martensite in the microstructure of as-hot rolled state. The amount of hard phases can be minimized by controlled rolling, thus refining the austenite grains, which, in turn, shift the CCT diagram towards shorter times. For the same cooling rate, the austenite to ferrite-plus-pearlite transformation is accordingly enhanced. In conducting numerous hot torsion tests, equations describing the recrystallization behavior of AISI4135 steel during hot deformation were developed in order to find the best condition for grain refinement. Austenite grain sizes predicted by the equations are in good agreement with data from commercial rod rolling.
Kim, Ji Soo,Lee, You Hwan,Lee, Duk Lak,Park, Kyung-Tae,Lee, Chong Soo The Iron and Steel Institute of Japan 2007 ISIJ international Vol.47 No.6
<P>The effect of intergranular ferrite (IGF) on hydrogen delayed fracture of an ultrahigh strength boron added steel with yield strength over 1 GPa was investigated. For this purpose, a series of constant loading tests and thermal desorption analyses was conducted on the hydrogen precharged steel having different volume fractions of IGF, 0%, 6%, and 10%. Tensile strength of unnotched and notched specimens slightly decreased only by 4% with increasing the volume fraction of IGF up to 10%. Time to failure of the steel in the constant loading tests became prolonged with increasing the volume fraction of IGF. Microstructural observation informed that the presence of IGF at prior austenite grain boundaries suppressed the precipitation of film-like carbides, which act as the susceptible crack nucleation sites, at these boundaries. In addition, IGF was very effective on retarding crack propagation. The thermal desorption analyses revealed that hydrogen was trapped mainly at grain boundaries and that the critical hydrogen content causing delayed fracture increased with increasing the volume fraction of IGF, resulting in better hydrogen delayed fracture resistance. The present results shed light on the fact that the presence of IGF is beneficial for improving hydrogen delayed fracture resistance of the steel with little degradation of strength.</P>
Rheumatoid Arthritis and HLA Class II Genotypes in Korean
Kim, Jung-Man,Lee, Hee-Dai,Han, Chang-Whan,Kim, Jin-Young,Kim, Weon-Yoo,Sung, Jin-Hyung,Ryu, Jae Duk,Ko, Lak-Hyun 가톨릭대학교 2000 Bulletin of The Catholic Research Institutes of Me Vol.28 No.-
To determine which HLA antigens are associated with rheumatoid arthritis in Korean, we studies the HLA class II genotypes in 40 patients with rheumatoid arthritis and 35 normal healthy persons by the two step polymerase chain reaction. At first we designed 20 pairs of group specific primers followed by the alleles which have the same nucleotide sequences in the exon 2 region. We performed amplification reaction with these 20 pairs of primers for 32 cycles. Recation products were electrophoresed and only specifically amplified products were reamplified for 15 cycles with total 76 pairs of allele specific primers. We typed the HLA class II genotypes with specific band patterns of each allele. The genotypes in patients were compared with those of normals. HLA-DR4 gave the highest relative risk for rheumatoid arthritis(RR=4), which was statistically significant(P<0.01). The frequency of HLA-DR4 was 75.0% in patient group and 42.9% in normal control group. Relative risk was also associated with HLA-DQw4 of DQB1 gene(RR=3.82), which was statistically significant(P<0.05). The frequency of HLA-DQw4 was 38.9% in patients group and 14.3% in normal control group. HLA-DR1 and DQw3 were not associated with rheumatoid arthritis(P>0.05), Among HLA-DR4 subtypes, the frequency of Dw14(0404) in patient group was relatively higher (19.2%) than that in normal control group(7.7%). The relative risk was high(2.85), although it was not statistically significant(P>0.05). From this study, HLA-DR4 was found to be highly associated while DRI was not associated with rheumatoid arthritis patients in Koreans. (The Journal of Korean Orthopaedic Research Society 2(1):61-67, 1999)
문취용(Chi Young Moon),이인상(In Sang Lee),박봉태(Bong Tae Park),강종득(Jong Duk Gang),김종한(Jong Han Kim),김민성(Min Sung Kim),이일수(Il Soo Lee),장도현(Do Heun Chang),박종호(Chong Ho park),조성락(Sung Lak Cho),이채원(Chae Won Lee 대한소화기학회 1995 대한소화기학회지 Vol.27 No.6
Primary multiple cancer means that more than two cancers occur independently in an individual. There have been many reports on primary multiple cancer since Billorth reported it for the first time in 1889. Owing to advancement of diagnostic procedures, reported cases of primary multiple cancers have been increased in number. The most frequent association in stomach cancer was followed by esophagus, larynx, liver, uterus. Here we report 1 case of primary multiple cancer who was a 60-year-old woman with epigastric pain. Endoscopy disclosed white patch and irregular base lesion on the antrum. A CT scan of the abdomen showed a lobulated soft tissue mass in the left kidney. The biopsy specimens showed adenocarcinoma on stomach and renal cell carcinoma on kidney. (Korean J Gastroenterol 1995;27:734 - 738)
Comparison of Cold Formability of Cold Drawn Non-heat-treated Steels Having Similar Strength
PARK, Kyong Su,PARK, Kyung-Tae,LEE, Duk Lak,LEE, Chong Soo Iron and Steel Institute of Japan 2005 ISIJ international Vol.45 No.9
<P>The cold formability of the drawn non-heat-treated steels, <I>i.e.</I> dual phase (DP) steel, low Si steel and ultra low carbon bainitic (ULCB) steel, was examined in terms of the deformation resistance and the forming limit. The present investigation was aimed at elucidating the effect of drawing on the cold formability of non-heat-treated steels which is directly affected by drawing since no heat treatment are involved during forming processes for them. A special care was taken for the present steels to exhibit the similar strength after drawing, so eliminating the strength effect. The present steels after drawing revealed the elastic-near perfect plastic behavior in compression. After drawing, the low Si steel exhibited the lowest deformation resistance estimated by the absorbed energy during deformation. In case of the forming limit in terms of the critical strain under which no cracking occurs during the upsetting test of the drawn steels, the low Si steel and the ULCB steel were better than the conventional heat-treated steel. Accordingly, among several non-heat-treated steels which can replace the conventional heat-treated steel as forging steels, the low Si steel seems to exhibit the best performance if they have the similar strength. The compressive deformation behavior of the present drawn non-heat-treated steels was discussed in association with the strain hardened state and the Bauschinger effect developed by drawing. In addition, their cold formability was explained by the plastic incompatibility between the constituent phases of each steel.</P>
Mechanisms of Tensile Improvement in Caliber-Rolled High-Carbon Steel
이태경,Chan Hee Park,Sang-Yoon Lee,Il-Heon Son,Duk-Lak Lee,이종수 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.3
The microstructural evolution and tensile characteristics of caliber-rolled plain carbon steels were quantita-tively investigated and compared with those of the as-received plain carbon steels. The caliber-rolled steels exhibited a similar microstructure consisting of an ultrafine-grained ferritic matrix and dispersed fine cementite particles. In contrast to the general trend of caliber-rolling processes showing significant reduc-tions in elongation while retaining a high strength, the present caliber-rolled high-carbon steel exhibited simultaneously improved strength and elongation. This distinctive tensile enhancement of the caliber-rolled high-carbon steel was attributed to the increased strain hardening rate caused by the high fraction of sub-micron cementite particles and to the transition of the fracture mode from a brittle state to a ductile state.