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냉간가공에 따른 오스테나이트계 18Mn-18Cr 고질소강의 기계적 특성
황병철 ( Byoung Chul Hwang ),이태호 ( Tae Ho Lee ),신종호 ( Jong Ho Shin ),이종욱 ( Jong Wook Lee ) 대한금속재료학회(구 대한금속학회) 2014 대한금속·재료학회지 Vol.52 No.1
The effects of nitrogen content, cold working, and stress relief treatment on the mechanical properties of high-nitrogen 18Mn-18Cr austenitic steels with different nitrogen content are investigated with respect to the specimen direction and location. The yield and tensile strengths usually increased with increasing nitrogen content and cold working, and they additionally increased after stress relief treatment. Based on these results, we propose a semi-empirical equation to predict the yield and tensile strengths of high-nitrogen 18Mn-18Cr austenitic steels. On the other hand, we discuss the ductile-brittle transition behavior depending on cold working and stress relief treatment in terms of the temperature sensitivty of yield stress.
임신중기 원인불명의 융모성 성선자극호르몬 상승과 임신예후와의 연관성
송경철(Kyung Chul Song),이지성(Ji Sung Lee),임승욱(Seung Ug Lim),엄기남(Gi Nam Eom),강철규(Cheol Gyu Kang),최유덕(Yu Duk Choi),김석영(Sug Young Kim),황병철(Byoung Chul Hwang),김광준(Kwang Jun Kim),이의돈(Eui Don Lee),박찬용(Chan Yong 대한산부인과학회 2001 Obstetrics & Gynecology Science Vol.44 No.8
N/A Objective : The purpose of this study was to compare the neonatal and maternal infectious morbidity between single and multiple courses of antenatal betamethasone treatment in patients with preterm premature rupture of membranes. Methods : One hundred seventy patients who delivered neonates between 28 and 34 weeks' gestation after preterm premature rupture of membranes from January 1992 to July 2000 were reviewed retrospectively. Patients were divided into 3 groups on the basis of the following betamethasone exposures: (1) none (control subjects), (2) betamethasone 4 mg IM, IV simultaneously and then 4 mg IV q 8 hours for 24 hours (single course) and (3) weekly administration after initial single course (multiple courses). All included patients received prophylactic antibiotics for group B streptococci. The statistical analyses were done using χ2 test, Fisher's exact test and one way analysis of variance (ANOVA). Multiple logistic regression analysis was performed to determine the confounding effect of the multiple variables those were considered as risk factors for neonatal sepsis. Results : This study included 67 patients in the control group, 60 patients in the single course group, and 43 patients in the multiple courses group. The latency (p=.0001) was significantly longer in the patients exposed to multiple course than the patients in the control group and those in the single course group. No significant difference was demonstrated in the incidence of neonatal sepsis (p=.881) and postpartum endometritis (p=.619) among the three groups. Neonatal sepsis was significantly associated with clinical chorioamnionitis (p=.022). Conclusion : According to our data, multiple courses of antenatal betamethasone treatment in patients with preterm premature rupture of membranes was not associated with the increased incidence of neonatal sepsis and postpartum endometritis.
API X70 및 X80 라인파이프강의 DWTT 특성에 미치는 시편 두께와 노치 형태의 영향
신상용 ( Sang Yong Shin ),황병철 ( Byoung Chul Hwang ),이성학 ( Sung Hak Lee ),강기봉 ( Ki Bong Kang ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 대한금속·재료학회지 Vol.44 No.5
In the present study, effects of specimen thickness and notch shape on drop weight tear test (DWTT) properties of API X70 and X80 line-pipe steels fabricated by varying hot-rolling conditions were investigated. The DWTT was conducted on the rolled steels, and the results were discussed in comparison with the Charpy V-notch (CVN) impact test and crack tip opening angle (CTOA) test data. The DWTT results indicated that the steels rolled in the single phase region had the higher upper shelf energy (USE) than the steel rolled in the two phase region because their microstructures were composed of acicular ferrites, which was similar to the CVN test results. The DWTT energy transition temperature (ETT) increased with increasing specimen thickness due to the increase in constraint state, and the ETT of the Chevron notch DWTT was slightly higher than that of pressed notch DWTT. The measured CTOA showed better correlation with the DWTT propagation energy than with the CVN or DWTT total energy as it was related with the crack propagation speed. Since the value of sin(2CTOA) was linearly proportional to the DWTT energy, it could be used as a useful parameter to estimate the CTOA.
다중회귀분석을 이용한 페라이트-펄라이트 조직 아공석강의 충격인성에 미치는 미세조직적 인자의 민감도 해석
이승용 ( Seung-yong Lee ),이상인 ( Sang-in Lee ),황병철 ( Byoung Chul Hwang ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.9
In this study, the effect of microstructural factors on the impact toughness of hypoeutectoid steels with ferrite-pearlite structure was quantitatively investigated using multiple regression analysis. Microstructural analysis results showed that the pearlite fraction increased with increasing austenitizing temperature and decreasing transformation temperature which substantially decreased the pearlite interlamellar spacing and cementite thickness depending on carbon content. The impact toughness of hypoeutectoid steels usually increased as interlamellar spacing or cementite thickness decreased, although the impact toughness was largely associated with pearlite fraction. Based on these results, multiple regression analysis was performed to understand the individual effect of pearlite fraction, interlamellar spacing, and cementite thickness on the impact toughness. The regression analysis results revealed that pearlite fraction significantly affected impact toughness at room temperature, while cementite thickness did at low temperature.(Received March 2, 2016; Accepted April 8, 2016)
페라이트-펄라이트 조직 아공석강의 강도와 연성에 미치는 미세조직적 인자의 영향
이상인 ( Sang-in Lee ),강준영 ( Jun-young Kang ),이상윤 ( Sang-yoon Lee ),황병철 ( Byoung Chul Hwang ) 한국열처리공학회 2016 熱處理工學會誌 Vol.29 No.1
This article presents a study on the tensile properties of hypoeutectoid steels with different ferritepearlite microstructures. Nine kinds of hypoeutectoid steel specimens were fabricated by varying carbon content and isothermal transformation temperature. The microstructural factors such as ferrite & pearlite fraction, interlamellar spacing, and cementite thickness were quantitatively measured and then tensile tests were carried out on the specimens in order to investigate the correlation of the microstructural factors with strength and ductility. The pearlite volume fraction usually increased with decreasing transformation temperature, while the pearlite interlamellar spacing and cementite thickness decreased mostly with decreasing transformation temperature, irrespective of carbon content. The tensile test results showed that the yield and tensile strengths of all the steel specimens increased and their ductility was also improved as the transformation temperature decreased. For the steel specimens investigated, the difference in the transformation temperature dependence of strength and ductility could be explained by the fact that the variation in pearlite fraction with transformation temperature noticeably affected various microstructural factors such as pearlite interlamellar spacing and cementite thickness associated with pearlite fracture mechanism such as void initiation, cementite necking, and cracking. (Received December 17, 2015; Revised December 24, 2015; Accepted December 30, 2015)