• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.5
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• pp.407-415
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• 2008

The tubes in heat exchanger are typically made from copper alloy, stainless steel, carbon steel, titanium alloy material. type-439 ferritic stainless steel is ferromagnetic material, and furnish higher heat transfer rates than austenitic stainless steels and higher resistance to corrosion-induced flaws. Ferritic stainless steel can typically be found in low-pressure(LP) feedwater heaters and moisture separator reheaters(MSRs). LP feedwater heaters generally utilize thin wall type-439 stainless steel tubing, whereas MSRs typically employ a heavier wall tubing with integral fins. Service-induced damage can occur on the OD(outside diameter) surface of type-439 ferritic stainless steel tubing which is employed for MSRs tubing, and the most typical damage mechanism is vibration-induced tube-to-TSP(tube support plate) wear and fatigue cracking. The wear has been reported that occurs mainly on the OD surface. Accordingly, in this study, we have evaluated the flaw sizing capability of magnetic saturation eddy current technique using magnetic saturation probe and flawed specimen.

• Journal of Welding and Joining
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• v.29 no.6
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• pp.40-44
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• 2011

Brazing of a stainless steel was described in this article. Brazing is a joining technology without melting a substrate and joining temperature is higher than $450^{\circ}C$. Brazing can be broadly applicable across industries. In particular, brazing of stainless steel is widely used in aircraft parts, car engines, heat exchangers, etc. due to its excellent strength, corrosion resistance and other suitable characteristics. Characteristics of the stainless steel depend on their classification like austenitic, ferritic and martensitic stainless steels. In addition, there are many processes in brazing and various parameters such as brazing heat source, filler metals, joint design, etc. Therefore, it is necessary to know basic knowledge about brazing to achieve good brazing joint. Accordingly, properties of stainless steel and design of brazing joint and related process were described in this article.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.123-124
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• 2006

This study aimed at exploiting low heat input characteristic of laser welding to effectively control grain coarsening in the fusion zone(FZ) and heat affected zone(HAZ) of 1.5mm thick 18wt% Cr ferritic stainless steel weld. The study demonstrated that as compared with gas tungsten arc welding(GTAW), laser welding brought about significant grain refinement in the FZ and HAZ. However, the impact absorbed energy of GTA weld was superior than that of laser weld because the strengthening effect during welding and cooling stage was higher In laser weld than that in GTA weld. The coarser grains in each weld than base metal resulted in an inferior toughness.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.179-182
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• 2000

The dynamic softening behavior of type 430 ferritic stainless steel could be characterized by the hot torsion test in the temperature range of 900-110$0^{\circ}C$ and the strain rate range of 0.05-5/sec. It is found that the continuous dynamic recrystallization (CDRX) was a major dynamic softening mechanism. The effects of process variables strain ($\varepsilon$) stain rate($\varepsilon$)and temperature (T) on CDRX could be individually established from the analysis of flow stress curves and microstructure. The effect of CDRX individually established from the analysis of flow stress curves and microstructure. The effect of CDRX increased with increasing strain rate and decreasing temperature in continuous deformation. The multipass deformation processes were performed with 10 pass deformations. The CDRX effect occurred in multipass deformatioon. The grain refinement could be achieved from multipass deformation The grain refinement increased with increasing strain rate and decreasing temperature. Also the CDRX in multipass deformation was affected by interpass time and pass strain. The total strain was to be found key parameter to occur CDRX.

• Proceedings of the KWS Conference
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• 2007.11a
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• pp.138-140
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• 2007

This study aimed to evaluate the low temperature properties of the 18Cr ferritic stainless steel weld. Applied welding methods were LB(Laser Beam) and GTA(Gas Tungsten Arc) welding to compare the different low temperature properties of the welds. Low temperature properties were evaluated by the Charpy impact, Erichsen and Expansion test at low temperature. LB weld showed superior low temperature properties in the cases of the Charpy impact test and expansion test at low temperature, while GTA weld showed a superior low temperature property in the case of Erichsen test at low temperature. The different low temperature properties with test methods are still under analysis and may be due to different crack path depending on the microstructure, test speed and stress concentration during test.

• Proceedings of the KWS Conference
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• 2002.05a
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• pp.89-91
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• 2002

• Proceedings of the KWS Conference
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• 2001.05a
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• pp.217-219
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• 2001

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1998.05a
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• pp.103-103
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• 1998

• Journal of Welding and Joining
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• v.29 no.4
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• pp.85-92
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• 2011

Microstructures and tensile properties in arc brazed joints of ferritic stainless steel, 429EM using Cu-8.6%Al insert metal was investigated as function of brazing current. The brazing speed was fixed at 800mm/min and brazing current varied in the range of 80A to 120A. The initial phase of filler metal was Cu single phase. However, the insert metal structures of brazed joints was composed of Cu matrix and intermetallic compound such as ${\gamma}_1(Al_4Cu_9)$, and flower-shape Fe-Cr. The fraction of ${\gamma}_1(Al_4Cu_9)$ phase was similar with 80A and 100A brazing currents while that of brazed with 120A was decreased. On the other hand, the fraction of Fe-Cr phase increased with increasing of the brazing current. A reaction layer at the base metal/insert metal interface was observed and this reaction layer was thickened with increasing of the brazing current. In the brazed joints with the current lower than 100A, crack was grew up along the interface which was perpendicular to the tensile stress, and then, passed through the insert metal in the final stage of fracture. As the brazing current increased to 120A, fracture occurred at the base metal.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.230-233
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• 2008

Stainless steels are alloy steels with iron as the primary constituent and chromium, nickel, and manganese as principal alloying elements. In addition to automotive, construction, and transportation industries, stainless steels have a variety of applications in the food, chemical, and pharmaceutical industries. Some common products made from stainless steel are sinks, wash basins, kitchen vessels, and cutlery. Among ferritic stainless steels, type 409 can be cold-formed easily and are used for deep-drawn parts such as vessels for the chemical and food industries. In this study, forming analyses and experiments to prevent the occurrence of inferiority such as wrinkles, crack, and neck for automotive muffler part are carried out to save the optimal conditions during forming by modifying the blank size and shape, blank holding force etc.