• Journal of Powder Materials
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• v.16 no.2
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• pp.122-130
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• 2009

Austenitic oxide-dispersion-strengthened (ODS) stainless steel was fabricated using a wet mixing process without a mechanical milling in order to reduce contaminations of impurities during their fabrication process. Solution of yttrium nitrate was dried after a wet mixing with 316L stainless steel powder. Carbon and oxygen contents were effectively reduced by this wet processing. Microstructural analysis showed that coarse yttrium silicates of about 150 nm were formed in austenitic ODS steels with a silicon content of about 0.8 wt%. Wet-processed austenitic ODS steel without silicon showed higher yield strength by the presence of finer oxide of about 20 nm.

• Journal of Welding and Joining
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• v.16 no.3
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• pp.111-120
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• 1998

To predict and evaluate metallurgical and mechanical behavior of th welds, it is essential to understand solidification behavior and microstructural evolution experienced in the welds, neither of which follows the equilibrium phase diagram because of rapid heating and cooling conditions. Metallurgical phenomena in austenitic stainless steel fusion welds, types 304, 309S, 316L, 321 and 304N, were investigated in this study. Autogenous GTA welding was performed on weld coupons, and primary solidification mode and phase distribution were investigated from the welds. Varestraint test was employed to evaluate solidification cracking susceptibilities of the alloys. GTA weld fusion zones in type 304, 321 and 304N stainless steels experienced primary ferrite solidification while those in type 309S primary austenite solidification. Type 316L exhibited a mixed type of primary ferrite and primary austenite solidification. The primary solidification mode strongly depended on $Cr_{eq}/Ni_{eq}$ ratio. In terms of solidification cracking susceptibility, type 309S that solidified as primary austenite exhibited high cracking susceptibility while the alloys experienced primary ferrite solidification showed low cracking susceptibility. The relative ranking in solidification cracking susceptibility was type 304=type 304N < type 321 < type 316L < type 309S.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2326-2333
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• 2000

Creep tests for type 316L(N) stainless steel were carried out using constant-load creep machines at 55$0^{\circ}C$, 575$^{\circ}C$ and $600^{\circ}C$. Material constants necessary to predict creep rupture time were obtained from the experimental creep data. And the applicability of Monkman-Grant(M-G) and modified M-G relationships was discussed. The log-log plot of M-G relationship between the rupture time($t_r$,) and the minimum creep rate ($ $\varepsilon$ _m$) was dependent on test temperatures. The slope of m was 1,05 at 55$0^{\circ}C$ and m was 1.30 at $600^{\circ}C$. On the other hand, the log-log plot of modified M-G relationship between $t_r/$\varepsilon$_r$, and $ $\varepsilon$ _m$ was independent on stresses and temperatures. That is, the slope of m＇ was approximately 1.35 in all the data. Thus, modified M-G relationship for creep life prediction could be utilized more reasonably than that of M-G relationship for type 316L(N) stainless steel. It was analyzed that the constant slopes regardless of temperatures or applied stresses in the modified relationship were due to an intergranular fracture grown by wedge-type cavities.

• KEPCO Journal on Electric Power and Energy
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• v.7 no.1
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• pp.129-135
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• 2021

Recently, additive manufacturing (AM) technology such as powder bed fusion (PBF) and directed energy deposition (DED) are actively attempted as consumers' needs for parts with complex shapes and expensive materials. In the present work, the effect of processing parameters on the mechanical properties of 316L stainless steel coupons fabricated by PBF and DED AM technology was investigated. Three major mechanical tests, including tension, impact, and fatigue, were performed on coupons extracted from the standard components at angles of 0, 45, 90 degrees for the build layers, and compared with those of investment casting and commercial wrought products. Austenitic 316L stainless steel additively manufactured have been well known to be generally stronger but highly vulnerable to impact and lack in elongation compared to casting and wrought materials. The process-induced pore density has been proved the most critical factor in determining the mechanical properties of AM-built metal parts. Therefore, it was strongly recommended to reduce those lack of fusion defects as much as possible by carefully control the energy density of the laser. For example, under the high energy density conditions, PBF-built parts showed 46% higher tensile strength but more than 75% lower impact strength than the wrought products. However, by optimizing the energy density of the laser of the metal AM system, it has been confirmed that it is possible to manufacture metal parts that can satisfy both strength and ductility, and thus it is expected to be actively applied in the field of electric power section soon.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.451-465
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• 2021

In this investigation, electrochemical characteristics and damage behavior of 316L stainless steel polymer electrolyte membrane fuel cell(PEMFC) were analyzed by potentiodynamic and potentiostatic tests in cathode operating condition of PEMFC. As the result of potentiodynamic polarization test, range of passive region was larger than range of active region. In the result of potentiostatic test, damage depth and width, pit volume, and surface roughness were increased 1.57, 1.27, 2.48, and 1.34 times, respectively, at 1.2 V compared to 0.6 V at 24 hours. Also, as a result of linear regression analysis of damage depth and width graph, trend lines of damage depth and width according to applied potentials were 16.6 and 14.3 times larger, respectively. This demonstrated that applied potential had a greater effect on pitting damage depth of 316L stainless steel. The damage tendency values were 0.329 at 6 hours and 0.633 at 24 hours with applied potentials, representing rapid growth in depth direction according to the test times and applied potentials. Scanning electron microscopy images revealed that surface of specimen exhibited clear pitting damage with test times and applied potentials, which was thought to be because a stable oxide film was formed by Cr and Mo.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.574-575
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• 2006

Due to the increasing use that the stainless steel is getting recently in the nuclear industry, this document proposes the study of the stainless steel 316L with boron addition. With the final product, the properties of the stainless steel 316L (good mechanical properties and high corrosion resistance) with the boron neutron absorption properties are claimed to unify. The P/M technologies allow adding higher boron quantities than with the solidification conventional technologies, where segregation is produced.

• Journal of the Korean institute of surface engineering
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• v.44 no.2
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• pp.55-59
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• 2011

In this study, the mechanical properties of boronized 316L austenitic stainless steel have been investigated. Boronizing was carried out in solid medium consisting of Ekabor powder at $900^{\circ}C$ and $1000^{\circ}C$ for 2, 4 and 8 hours, respectively. The properties of sample were analyzed by field emission scanning electron microscope, X-ray diffractometer, Glow discharge spectrometer, micro-hardness tester and ball-on-disk wear tester. Increasing the boronizing time and temperature, the hardness of boronized samples were shown over Hv 2000 and the thickness of boride layers were also increased linearly. XRD patterns of samples were revealed the presence of borides such as FeB, $Fe_2B$, CrB, $Cr_2B$ and $Ni_3B$. Friction coefficient of boronized STS 316L was shown the low value at $900^{\circ}C$ for 8 hours and $1000^{\circ}C$ for 4 hours, respectively.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.6
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• pp.59-69
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• 2021

Directed energy deposition (DED) is an additive manufacturing technology involving a focused high-power laser or electron beam propagating over the substrate, resulting in melt pool formation while simultaneously supplying metal powder to the melt pool area to deposit the material. DED is performed to repair and strengthen parts in various applications, as it can be easily integrate local area cladding and cross-material deposition. In this study, we characterize stainless steel 316 L parts fabricated via DED based on various deposition conditions and geometries to widen the application of DED. The deposition characteristics are investigated by varying the laser power and powder feed rate. Multilayer deposition with a laser power of 362 W and a powder feed rate of 6.61 g/min indicate a height closest to the design value while affording high surface quality. The microhardness of the specimen increases from the top to the bottom of the deposited area. Tensile tests of specimens with two different deposition directions indicate that horizontally long specimens with respect to a substrate demonstrate a higher ultimate tensile strength and yield strength than vertically long specimens with lower elongation.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.435-450
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• 2021

The interest in eco-friendly energy is increasing, and polymer electrolyte membrane fuel cell (PEMFC) is attracting attention as alternative power sources. Research on metallic bipolar plates, a fuel cell component, is being actively conducted. However, since the operating conditions of PEMFC, in which sulfuric acid (H₂SO₄) and hydrofluoric acid (HF) are mixed, are strong acidity, the durability of the metallic bipolar plate is very important. In this research, the electrochemical characteristics and corrosion damage behavior of 316L stainless steel, a material for metallic bipolar plates, were analyzed through potentiostatic corrosion tests with test times and chloride concentrations. As the test times and chloride concentrations increased, the current density and corrosion damage increased. As a result of observation with scanning electron microscope(SEM) and 3D microscope, both the depth and width of pitting corrosion increased with increases in test times and chloride concentrations. In particular, the pitting corrosion damage depth at test conditions of 6 hours and 1000 ppm chloride increased the most. The growth of the pitting corrosion damage was not directly proportional to time and increased significantly after a certain period.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.11a
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• pp.159-160
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• 2007

저온 플라즈마 침탄 처리 후 연속적인 공정으로 저온 플라즈마 질화를 실시하여 내식성과 표면경도를 향상시키는 처리에서 질화처리 시 Ar 가스가 표면특성에 미치는 영향을 조사 하였다. 모든 시편의 경도가 미처리재 보다 약4배 증가하였으며, Ar가스의 양이 증가할수록 N의 침투깊이가 깊어졌다. 전체 경화증의 두께는 거의 일정하였고, 경화층은 모재보다 내식성이 증가되어 단면조직사진에서 밝게 나타났다.