• Journal of Advanced Marine Engineering and Technology
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• v.35 no.4
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• pp.451-459
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• 2011

Austenitic stainless steels of 300 series are widely used as the structural material due to excellent their cryogenic mechanical properties at cryogenic temperature. There are 316 steel which molybdenum is added to improve the austenitic stability, 316L which carbon contents is reduced to decrease the grain boundary precipitation during welding process, and 316LN which nitrogen is added to improve the austenitic stability and the mechanical strength. But material researches for the welding conditions and mechanical properties at the cryogenic temperature were insufficient so far. In this paper, the characteristics of mechanical properties considering the effect of welding conditions and cryogenic temperature are studied.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.13 no.1
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• pp.92-100
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• 2017

Due to the presence of ferrite phase in the finished welds, austenitic stainless steel welds (ASSWs) are considered susceptible to the thermal aging embrittlement during long-term service in light water reactor environment. In this study, the thermal aging embrittlement of typical ASSWs, E308 and ER316L welds, were evaluated after the long-term exposure up to 20,000 h at $400^{\circ}C$, which is considered as an accelerated thermal aging condition. After thermal aging, the decrease of tensile ductility and fracture toughness was observed. The microstructure observation with high resolution transmission electron microscopy revealed that spinodal decomposition in ferrite phase of both E308 and ER316L welds would be the main cause of the degradation of mechanical properties. Also, it was shown that the difference of thermal ageing embrittlement between ER316L and E308 welds was significant, such that the reduction of fracture resistance for ER316L weld was much larger than that of E308 weld.

• Journal of the Korean Vacuum Society
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• v.19 no.6
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• pp.460-466
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• 2010

We measured the magnetic properties of stainless steels type 304 and 316L to see if those materials can be used for the applications where non-magnetic materials are required. The results show that the relative permeability of samples was greatly increased during manufacturing processes. After full solution annealing, however the permeability could be reduced to less than 1.02. Thus, the materials may be employed in the low-permeability applications.

• 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.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.39.1-39.1
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• 2011

가압경수로의 압력경계기기는 약 $300^{\circ}C$, 150기압의 고온고압수환경에서 가동되고 있다. 특히 가압기 밀림관은 고온수와, 저온수가 교차하는 부분으로 열성층 형성으로 열적, 기계적 피로 및 수화학환경이 더해진 부식피로 등에 의하여 손상을 받는다. PWR 원전에서 수화학환경은 대표적으로 용존산소(DO) 5ppb, pH 6~8, 용존수소(DH) <30 cc/kg, 온도 $316^{\circ}C$의 환경을 유지하게 된다. 가압기 밀림관에는 오스테나이트계 스테인리스강이 사용되는데, 오스테나이트계 스테인리스강은 고온 수화학환경에 민감한 것으로 알려져 있다. 따라서 오스테나이트계 스테인리강을 공기중에서의 기계적특성 및 피로특성을 향상시키기 위하여 질소를 첨가한 스테인리스강을 제조하여 PWR 원전환경에서의 피로균열성장특성을 평가하였다. 실험에 사용된 재료는 PWR 원전 가압기 밀림관 소재인 Type 347 스테인리스강에 0.0005 wt%가 첨가된 상용재와 0.11 wt% 질소가 첨가된 재료이다. 사용된 시편형상은 두께 5 mm, 폭 25.4 mm의 CT 시편이다. 수화학환경은 150기압, 온도 $316^{\circ}C$, 용존산소(DO) 5ppb, 용존수소(DH) 30 cc/Kg, pH는 약 7로 유지 하였으며, 응력비 0.1, 하중 반복속도 10Hz의 기계적 조건에서 하중제어로 시험을 진행하였다. 균열길이는 직류전위차법(Direct Current Potential Drop: DCPD)을 이용하여 측정하였다. 질소함량이 증가할수록 동일 사이클에서 균열길이가 늦게 성장하였고, 피로균열성장속도도 약간 늦어지는 것으로 나타났다. 각 스테인리스강의 피로파면 관찰결과 상용재는 약 1 ${\mu}m$의 산화물들이 생성되는 반면 질소첨가 스테인리스강은 약 0.1 ${\mu}m$정도 산화물이 생성되었다. 산화막의 두께도 질소가 첨가됨으로써 상용재에 비해 얇게 생성되었다. 따라서 질소가 첨가됨으로써 부식환경에서 내산화성이 향상되었으며, 이는 피로균열성장특성에 영향을 미치는 것으로 판단된다.

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

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.1
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• pp.11-16
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• 2014

The effects of environment and microstructure on low cycle fatigue (LCF) behaviors of CF8M stainless steels containing 11% of ferrites were investigated in a $310^{\circ}C$ deoxygenated water environment. The reduction of LCF life of CF8M in a $310^{\circ}C$ deoxygenated water was smaller than 316LN stainless steels. Based on the microstructure and fatigue surface analyses, it was confirmed that the hydrogen induced cracking contributed to the reduction in LCF life for CF8M as well as for 316LN. However, many secondary cracks were found on the boundaries of ferrite phases in CF8M, which effectively reduced the stress concentration at the crack tip. Because of the reduced stress concentration, the accelerated fatigue crack growth by hydrogen induced cracking was less significant, which resulted in the smaller environmental effects for CF8M than 316LN in a $310^{\circ}C$ deoxygenated water.

• Journal of the Korean Electrochemical Society
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• v.9 no.2
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• pp.70-76
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• 2006

Micro-droplet cell with free droplet as a micro-electrochemical technique has been limited to apply to electrochemical systems with high wetting properties such as an acidic solution and low grade stainless steels(Type 316L). By loading negative pressure to a droplet, control of droplet size, and use of hydrophobic gasket, the cell is modified to be allowed to use for electrochemical systems with high wetting properties. For giving the reliability of new cell, studies on local corrosion were conducted for three different systems-an acidic chloride solution and high chromium ferritic stainless steel, the other acidic chloride solution and type 316, and a neutral chloride solution and type 316. stainless steel. Firstly, the modified micro-droplet cell allows the anodic polarization curves in an acidic chloride solution to show the fact that the local corrosion of high chromium stainless steel near the $\alpha/\sigma$ interface is due to the Cr depleted zone. Secondly, the local anodic polarization test of type 316 L in the other acidic chloride solution can be successfully conducted in the cell. Furthermore, the local polarization curves help elucidating the corrosion of type 316 with $\delta-ferrite$ phase. Finally, the polarization curves of type 316 L in a neutral chloride solution indicates that the factor affecting the pitting corrosion resistance was inclusions rather than $\delta-ferrite$.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.16 no.1
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• pp.92-99
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• 2020

High-temperature mechanical behaviors of Type 316L stainless steel (SS), which is considered as one of the major structural materials of Generation-IV nuclear reactors, were investigated through the tension and creep tests at elevated temperatures. The tension tests were performed under the strain rate of 6.67×10^-4 (1/s) from room temperature to 650℃, and the creep tests were conducted under different applied stresses at 550℃, 600℃, 650℃, and 700℃. The tensile behavior was investigated, and the modeling equations for tensile strengths and elongation were proposed as a function of temperature. The creep behavior was analyzed in terms of various creep equations: Norton's power law, modified Monkman-Grant relation, damage tolerance factor(λ), and Z-parameter, and the creep constants were proposed. In addition, the tested tensile and creep strengths were compared with those of RCC-MRx. Results showed that creep exponent value decreased from n=13.55 to n=7.58 with increasing temperature, λ = 6.3, and Z-parameter obeyed well a power-law form of Z=5.79E52(σ/E)^9.12. RCC-MRx showed lower creep strength and marginally different in creep strain rate, compared to the tested results. Same creep deformation was operative for dislocation movement regardless of the temperatures.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.6
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• pp.709-715
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• 2006

The effects of thermal cycle condition and applied stress on the intergranular corrosion in austenitic 316 type stainless steels were investigated. Specimens were solution-treated at 1100$^{\circ}C$ for one hour and then sensitized in the temperature range of $500{\sim}800^{\circ}C$ by holding $2{\sim}300s$ with a various applied stresses of $0{\sim}8kg/mm^2$. Degree of sensitization. DOS %, was measured through polarization curve by electrochemical DL-EPR test. Microstructural observations were also conducted DOS % increased with an increase of sensitization temperature and/or holding time. Increase of applied stress resulted in increase of DOS % and more corroded surface because of acceleration of intergranular corrosion and fine grain size due to the stress. Cr depleted zone near grain boundary was observed. The amount of depletion was profounded with an increase of sensitization temperature, holding time and applied stress. $M_{23}C_6$ carbides were precipitated discontinuously at grain boundary. However, its amount was relatively small in the thermal cycle condition of 800$^{\circ}C$, 300sec and 4kg/mm$^2$.