• Laser Solutions
• /
• v.1 no.1
• /
• pp.18-23
• /
• 1998

A Study on microstructural changes of sensitized Alloy 600 which was rapidly solidified by a $CO_2$ laser beam was conducted using microscopic equipments such as SEM and TEM. Dissolution of Cr-rich carbides and resultant Cr recovery on the grain boundaries occurred in the heat affected zone (HZA). The microstructure of the laser melted zone (LMZ) having epitaxially solidified from the HAZ was mainly celluar-dendritic with the 〈100〉 crystallographic direction of growth. The Cr concentration was observed to increase along the cell bondaries, and tiny particles were distributed along the cell walls with tangled dislocations around them. Cr-rich carbides had been completely melted by the high density of a laser beam, and were not re-precipitated during the matrix solidification due to a fast cooling rate in the LMZ.

• Journal of Power System Engineering
• /
• v.15 no.3
• /
• pp.52-57
• /
• 2011

440A martensitic stainless steels which were modified with reduced carbon content(~0.5wt.%) and addition of small amount of vanadium, tungsten and molybdenum 0.4wt.%, 0.4wt.% and 0.68wt.% respectively were manufactured. Effects of alloying elements and tempering temperatures on the intergranular corrosion were investigated through the method of DL-EPR(Double-electrochemical potentiodynamic reactivation). It was thought that the highest DOS(Degree of sensitization) of specimens was obtained at the tempering temperature of $450^{\circ}C$ regardless of types of alloy because of the precipitation of Cr7C3. Addition of vanadium lowered DOS a little above the tempering temperature of $550^{\circ}C$. It was considered to be effected by precipitation of VC carbides. Intergranular corrosion was influenced more by tempering temperature than by alloying elements of V, W and Mo.

• Journal of Advanced Marine Engineering and Technology
• /
• v.19 no.4
• /
• pp.42-50
• /
• 1995

To study the effect of welding methods on the Stress Corrosion Cracking (SCC) behavior of welded AISI type 316L and 304 austenitic stainless steel, the Slow Strain Rate Technique(SSRT) has been adopted in the boiling 45 wt% $MgCl_2$ solution. The results are as follows. 1) Welded sections are more susceptible than base metal in SCC, and the rank of SCC, and the rasistance in welding method is TIG, MIG, $CO_2$ and ARC. 2) The Ultimate tensile strength(UTS) and the strain of both base metal and welded joint are reduced as decreasing extension rate. 3) The SCC resistance of 316L base metal and welded sections are superior than that of 304. 4) The tendency of pitting and the SCC suseptibility are agreed well, and the SCC site is welded deposit section in 316L whereas HAZ in 304.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1995.05a
• /
• pp.790-795
• /
• 1995

합금 600의 대체 재료인 합금 690의 부식 저항성 향상을 위해 스테인리스강 등에서 내식성을 현저히 개선시켜 주는 합금 원소로 알려져 있는 Mo을 첨가하여 TT 열처리를 한 후 부식 특성과 TEM관찰을 행하여 미세 조직의 영향에 대하여 고찰하고자 하였다. TT 처리 시간이 길어짐에 따라 보다 많은 석출물들이 입계에 생성되었으며, Mo을 첨가함에 따라 입계에 탄화물 석출이 지연되었다. 양극 분극 시험, 침지시험, EPR 시험, Huey 시험 결과 소둔재에 비해 TT 처리재의 경우 내식성의 저하는 업었으며 오히려 개선되는 특성을 보였다. 또한 Mo의 함량이 증가함에 따라 탄화물 석출에 걸리는 시간이 길어져 3%의 Mo이 첨가된 합금 690 M2의 경우 예민화 현상은 15시간 TT 처리에서 관찰되었다. 응력 부식 균열 시험 결과 소둔재에 비해 TT 처리재의 응력 부식 균열 저항성이 증가하였으며 Mo의 함량이 증가함에 따라 대체적으로 응력 부식 균열 저항성도 개선되었다.

• Journal of Welding and Joining
• /
• v.31 no.2
• /
• pp.49-56
• /
• 2013

We have investigated traits of clad metals in hot-rolled clad steel plates, sensitization and mechanical properties of STS 316 steel plate and carbon steel(A516). Clad steel plates were butt-weld by SAW+SMAW, and with the time of heat treatment as the variable, heat treatment was conducted at $625^{\circ}C$, for 80, 160, 320, 640, 1280 minutes. As a way to evaluate it, sectioned weldments and external surfaces were investigated to reveal the degree of sensitization by mechanical property, etching and those of EPR test, results were compared with it. In short, the purpose of this study is suggesting some considerations in developing on-site techniques to evaluate the sensitization of stainless steels.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2017.05a
• /
• pp.179-182
• /
• 2017

Cerebral nervous system intervention procedures have been reported frequently due to radiation exposure such as skin baldness, hair loss, and redness due to prolonged procedures. Therefore, the bismuth shield designed to reduce the radiation exposure of the target organ located in the anterior part of the human body sensitive to skin and radiation sensitivity during CT (computed tomography) scan is applied to the cerebral vascular system intervention by ergonomic design, To reduce the radiation dose of sensitive scalp, we propose a study.

• Corrosion Science and Technology
• /
• v.9 no.6
• /
• pp.300-309
• /
• 2010

The influences of sensitization on localized corrosion resistance of 304 stainless steel, were investigated, using micro-dropletcell techniques. Micro-droplet cell allows one to align the micro-electrode to the desired spot of the working electrode and measure directly local current with the potentiodynamic polarization, linear polarization and a.c. impedance. Micro-electrochemical tests were carried out inside of the grain and on grain boundaries separately. It was found that sensitization decreased the pitting potential, increasing corrosion current density around grain boundaries. Galvanic current density was also measured between grain and grain boundaries.

• Journal of Welding and Joining
• /
• v.16 no.3
• /
• pp.121-128
• /
• 1998

The degradation of mechanical properties in the high nitrogen steel HN3 developed for nuclear fusion reactor has been evaluated quantitatively using the small punch(SP) test, X-ray diffraction (XRD) analysis has also been conducted to identify carbides or nitrides precipitated on grain boundaries of the heat treated samples. Mechanical properties of the steel HN3 significantly decreased with increasing heat treatment time and temperature or with decreasing testing temperature. Combination of XRD and metallurgical observation, revealed that the material degradation in the thermally aged steel was caused by precipitation of carbides on the grain boundaries. While the weld metal showed the lowest mechanical properties among various microstructures in GTA weldments. By combining SP test and XRD analysis, cryogenic fracture behaviors and aging degradation for high nitrogen steel could be successfully evaluated in nondestructive manner.

• Journal of Advanced Marine Engineering and Technology
• /
• v.35 no.6
• /
• pp.802-808
• /
• 2011

One of the important mechanical properties of cryogenic temperature structure material is fracture toughness. Research on normalization of fracture toughness test method is becoming very important issue with development of cryogenic structural elements. Specially, mechanical properties estimation by each micro-structure of welding department is important because it can cause unstable fracture when use under cryogenic environment in case of welding department. In this study, fracture toughness estimation test was carried out to unloading compliance method and sensitization heat-tread minimized test specimen at liquid nitrogen (77K), liquid helium (4K), 293K temperature to STS-316L base metal and weld metal.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.22 no.2
• /
• pp.343-351
• /
• 1998

This paper was investigated degradation of the fracture toughness caused by sensitizing heat-treatment of the cryogenic structural material JN1 base metal using unloading compliance method reported as useful a method in evaluating the elastic-plastic fracture toughness at cryogenic temperature. The specimens used in this paper were 20% side-grooved 0.5T-CT specimens which were machined in the JN1 base metal. Also, to investigate cryogenic fracture toughness of the fusion line region in the JN1 GTA weldments, it was also used 20% side-grooved 0.5T-CT specimens that was machined fusion line to located in the middle of the specimen. The cryogenic fracture toughness values of the JN1 base metal were significantly decreased with increasing the time and temperature of the heat treatment. The fracture toughness value obtained from the fusion line specimen was invalid, but it was lower value than that of the JN1 base metal. Especially, this value was approximately equal with that obtained from the JN1 650.deg. C-5h heat-treated material.