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Role of Chromium on Mechanical Properties of Fe - Mn - Ni - Mo - Ti Maraging Steels
HEO, Nam Hoe,LEE, Hu Chul 대한금속재료학회(대한금속학회) 1995 METALS AND MATERIALS International Vol.1 No.1
This experiment investigated the role of chromium in the mechanical properties of Fe-5Mn-9Ni-5Mo-1.5Ti maraging steels containing up to 3% chromium. Remarkable age-hardening responses were observed in the Fe-5Mn-9Ni-5Mo-1.5Ti and Cr-bearing alloys. A ductile-brittle-ductile transition occurred in the Cr-bearing alloys during isothermal aging below 510℃. This was due to the segregation of titanium and manganese to prior austenite grain boundaries and their subsequent desegregation into the matrix. The addition of chromium to the hale alloy considerably improved its ductility after aging at 520℃. From microstructure and AES analyses. it is suggested that chromium addition augments the volume fractions of (Fe,Mn)₂Mo and η-Ni₃Ti precipitates in the Fe-5Mn-9Ni-5Mo-Cr alloys. which act as sinks of manganese and titanium in the matrices. This resulted in the reduction of the alloying elements concentration in the matrix, which is followed by the reduction in the segregation level of the elements at prior austenite grain boundaries, and consequently enhanced intergranular fracture strength. The optimum combination of strength and ductility was obtained in the Fe-5Mn-9Ni-5Mo-3Cr-1.5Ti alloy aged at 520℃ for 2 hr. and was σ_(0.2)= 1721 ㎫, σ_(7.8)= 1756 ㎫, and ε_'= 10.2%.
Nam, Hoe HEO,LEE, Hu Chul,SEO, Dong Han 대한금속재료학회(대한금속학회) 1997 METALS AND MATERIALS International Vol.3 No.4
The effects of boron addition on the grain boundary segregation and fracture behavior of tempered Fe-Mn-Ni-Mo and Fe-Ni-Mn-W steels were investigated. High segregation of Mn to prior austenitie grain boundaries resulted in severe grain boundary embitterment in W-bearing alloys. Boron addition did not significantly affect the grain boundary segregation of other alloying elements. Nevertheless, improvement of tensile properties is observed in 16 ppm boron doped W-bearing steel. Segregation of boron itself to grain boundaries is believed to affect the grain boundary strength of this alloy. Lower Mn segregation in Mo containing steels resulted in the ductile fracture when tempered at 480℃.
Elevated temperature intergranular cracking of heat-resistant alloy under tensile stress
Heo, Nam-Hoe,Chang, Jung-Chel Cambridge University Press (Materials Research Soc 2011 Journal of materials research Vol.26 No.8
<▼1><B>Abstract</B><P/></▼1><▼2><P>In a 2.25Cr1.5W heat-resistant alloy, it is shown that the time to intergranular failure under tensile stress <I>t</I> can be expressed by $t_0 \sigma ^{ - n} \exp \left({Q/RT} \right)$, where <I>t</I>0 is the constant of proportionality, <I>n</I> is the stress exponent, and <I>Q</I> is the activation enthalpy. It is shown that the dimples observed at elevated-temperature intergranular fracture surfaces are not the micro-ductile fracture areas but the interfaces between the grain boundary carbides and the neighboring grains. It is also shown that the segregation concentration of solute atoms is much higher at the grain boundary carbide interfaces than at the carbide-free grain boundaries. Under tensile stress, the elevated-temperature intergranular cracking occurs through the decohesion of grain boundary carbide interfaces, which is followed by the eventual carbide-free grain boundary cracking.</P></▼2>
Heo, Kyung-Sun,Ryoo, Sung-Woo,Kim, Lila,Nam, Miyoung,Baek, Seung-Tae,Lee, Hyemi,Lee, Ah-Reum,Park, Song-Kyu,Park, Youngwoo,Myung, Chang-Seon,Kim, Dong-Uk,Hoe, Kwang-Lae Korean Society for Molecular Biology 2008 Molecules and cells Vol.26 No.5
<P>Low-density lipoprotein (LDL) induces cell proliferation in human aortic smooth muscle cells (hAoSMCs), which may be involved in atherogenesis and intimal hyperplasia. Recent studies have demonstrated that Cl- channels are related to vessel cell proliferation induced by a variety of stimuli. In this study, we investigated a potential role of Cl- channels in the signaling pathway of LDL effects on hAoSMC proliferation with a focus on the activation of Erk1/2-PI3K/Akt and the subsequent upregulation of Egr-1. Cl- channel blockers, DIDS, but neither NPPB nor Furosemide, completely abolished the LDL-induced DNA synthesis and cell proliferation. Moreover, DIDS, but not NPPB, significantly decreased LDL-stimulated Cl- concentration, as judged by flow cytometry analysis using MQAE as a Cl--detection dye. DIDS pretreatment completely abolished the activation of Erk1/2 and PI3K/Akt in a dose-dependent manner that is the hallmark of LDL activation, as judged by Western blot and proliferation assays. Moreover, pretreatment with DIDS (Cl- channel blockers) but not LY294002 (PI3K inhibitors) completely abolished the LDL-induced upregulation of Egr-1 to the same extent as PD98059 (MEK inhibitors to inhibit Erk), as judged by Western blot and luciferase reporter assays. This is the first report, to our knowledge, that DIDS-sensitive Cl--channels play a key role in the LDL-induced cell proliferation of hAoSMCs via the activation of Erk1/2 and PI3K/Akt and the upregulation of Egr-1.</P>
Long-Term Mortality in Patients With Stroke of Undetermined Etiology
Nam, Hyo Suk,Kim, Hyeon Chang,Kim, Young Dae,Lee, Hye Sun,Kim, Jinkwon,Lee, Dong Hyun,Heo, Ji Hoe Ovid Technologies Wolters Kluwer -American Heart A 2012 Stroke Vol.43 No.11
<P>The determination of stroke etiology is essential for planning treatment for stroke prevention. However, the etiology of stroke is undetermined in many patients.</P>
A Computerized In-Hospital Alert System for Thrombolysis in Acute Stroke
Heo, Ji Hoe,Kim, Young Dae,Nam, Hyo Suk,Hong, Keun-sik,Ahn, Seong Hwan,Cho, Hyun Ji,Choi, Hye-Yeon,Han, Sang Won,Cha, Myoung-Jin,Hong, Ji Man,Kim, Gyeong-Moon,Kim, Gyu Sik,Kim, Hye Jin,Kim, Seo Hyun,K Ovid Technologies Wolters Kluwer -American Heart A 2010 Stroke Vol.41 No.9
<P>Background and Purpose-An effective stroke code system that can expedite rapid thrombolytic treatment requires effective notification/communication and an organized team approach. We developed a stroke code program based on the computerized physician order entry (CPOE) system and investigated whether implementation of this CPOE-based program is useful for reducing the time from arrival at emergency departments (ED) to evaluation steps and the initiation of thrombolytic treatment in various hospital settings. Methods-The CPOE-based program was implemented by 10 hospitals. Time intervals from arrival at the ED to blood tests, computed tomography scanning, and thrombolytic treatment during the 1-year period before and the 1-year period after the program implementation were compared. Results-Time intervals from ED arrival to evaluation steps were significantly reduced after implementation of the CPOE-based program. Times from ED arrival to CT scan, complete blood counts, and prothrombin time testing were reduced by 7.7 minutes, 5.6 minutes, and 26.8 minutes, respectively (P<0.001). The time from ED arrival to intravenous thrombolysis was reduced from 71.7 +/- 33.6 minutes to 56.6 +/- 26.9 minutes (P<0.001). The number of patients who were treated with thrombolysis increased from 3.4% (199/5798 patients) before the CPOE-based program to 5.8% (312/5405 patients) afterward (P<0.001). The CPOE implementation also improved the inverse relationship between onset-to-door time and door-to-needle time. Conclusions-The CPOE-based stroke code could be successfully implemented to reduce in-hospital time delay in thrombolytic therapy in various hospital settings. CPOE may be used as an efficient tool to facilitate in-hospital notification/communication and an organized team approach. (Stroke. 2010; 41:1978-1983.)</P>
Nam, Hyo Suk,Han, Sang Won,Ahn, Seong Hwan,Lee, Jong Yun,Choi, Hye-Yeon,Park, In Cheol,Heo, Ji Hoe S. Karger AG 2007 Cerebrovascular diseases Vol.23 No.4
<P><I>Background:</I> The need for rapid evaluation and treatment of acute stroke patients has been well documented. A computerized physician order entry (CPOE) system can improve communication and provide immediate access to information, which may be useful for an effective team approach program targeted to reduce in-hospital time delays. <I>Methods:</I> To reduce the time from a patient’s arrival at the emergency department to thrombolysis, a team approach program using CPOE was developed, and its efficacy was investigated by comparing time intervals from arrival to evaluation and intravenous tissue-type plasminogen activator (tPA) treatment before and after the implementation of the program. <I>Results:</I> Among 379 consecutive patients who were screened as potential candidates for thrombolysis, 25 patients (6.6%) received tPA during a 1-year period after initiation of the program. Fourteen patients were treated with tPA in the previous year. After program implementation, time from arrival to computed tomography scan was reduced from 34 to 19 min (p = 0.01). Time to report of complete blood count was also shortened from 52 to 33 min (p < 0.01). Finally, time from arrival to tPA treatment was reduced by 23 min (from 79 to 56 min; p < 0.01). Onset-to-door time tended to be longer after the program implementation (from 41 to 60 min; p = 0.14). <I>Conclusions:</I> Implementation of the CPOE-based team approach program significantly reduced time from emergency department arrival to evaluations and treatment.</P><P>Copyright © 2007 S. Karger AG, Basel</P>