STS 316L Research Articles

Microstructures and intergranular corrosion resistances of hot-rolled austenitic stainless steel clad plates

In this study, two stainless steel clad plates (STS 316L/A516-70N and STS 304L/A516-70N) were fabricated without Ni interlayers by hot rolling and normalizing under the same conditions, and their microstructures and intergranular corrosion resistances were comparatively evaluated. Although a similar amount of C diffused from carbon steel to stainless steel during clad fabrication, the thickness of the grain-boundary carburized layer was thinner in STS 316L due to Mo atoms segregated at the grain boundaries. The stainless steel parts of both clad plates had carbides even at their free surfaces and STS 304L also had some amount of δ ferrite. Nevertheless, the corrosion resistance of the free surfaces of both stainless steels was not undermined.

Evaluation of Microstructures and Mechanical Properties in Functionally Graded Materials (STS 316L and Low Alloy Steel) Produced by DED Processes

Evaluation of Microstructures and Mechanical Properties in Functionally Graded Materials (STS 316L and Low Alloy Steel) Produced by DED Processes

Comparison of Welding Deformation Characteristics by Circumferential Welding for Austenitic and Duplex Stainless Steel Pipe : Experimental Study

During welding of structure, non-uniform thermal distribution is occurred by local heating and conduction in copula. This process causes non-uniform thermal deformation and that occurs thermal stress. Especially, pipe is used in shipbuilding and laying pipe is essential. As well pipe material is applied with STS 316L (Stainless Steel) and STS Duplex(Stainless Steel Duplex) in LNG carrier ship. So welding property of that material is studied in order to predict welding deformation and thermal stress. First of all each material is made a experiment to know thermal distribution and shrinkage deformation. Through this experiment, it was possible to obtain differences in welding shrinkage due to the mechanical and thermal properties of the two materials. As a result, basic data on welding shrinkage for each material were obtained, and it will be used to develop a prediction equation through additional research in the future.

Chemical Cleaning of Magnetite Deposits on the Flow Mini-Channels of a Printed Circuit Heat Exchanger in an EDTA-Based Solution.

The dissolution behavior of magnetite deposited on flow mini-channel surfaces within a printed circuit heat exchanger (PCHE) and the corrosion behavior of a STS 316L PCHE material were investigated in an ethylendiaminetetraacetic acid (EDTA)-based chemical cleaning solution at 93 °C. The fouling in the PCHE was simulated using a water-steam circulation loop system. Most of the magnetite deposits were rapidly dissolved in the early stage of the circulation chemical cleaning. An empirical equation for estimating the dissolution percentage was derived as a function of cleaning time. The PCHE material showed excellent corrosion resistance during the chemical cleaning tests. These results indicate the fouling layers in the PCHEs can be removed efficiently by the chemical cleaning process without concern about base metal corrosion.

Correlation Between Microstructure and Tensile Properties of STS 316L and Inconel 718 Fabricated by Selective Laser Melting (SLM).

The correlation between microstructure and tensile properties of selective laser melting (SLM) processed STS 316L and Inconel 718 were investigated at various heights (top, middle and bottom) and planes (YZ, ZX and XY). Columnar grains and dendrites were formed by directional growth during solidification. The average melt pool width and depth, and scan track width were similar in both specimens due to fixed processing parameters. SLM Inconel 718 has moderate tensile strength (1165 MPa) and tensile elongation (11.5%), whereas SLM STS 316L has outstanding tensile strength (656 MPa) and tensile elongation (75%) compared to other SLM processed STS 316L. Fine columnar diameter (0.5 μm) and dense microstructures (porosity: 0.35%) in SLM STS 316L promoted the enhancement of tensile elongation by suitable processing condition. Fractographic analysis suggested that the lack of fusion pore with unmelted powder should be avoided to increase tensile properties by controlling processing parameters.

Numerical and Experimental Investigations of Laser Metal Deposition (LMD) Using STS 316L

This study aimed to understand the effect of heat accumulation on microstructure formation on STS 316L during multilayer deposition by a laser metal deposition (LMD) process and to predict the microstructure morphology. A comprehensive experimental and numerical study was conducted to quantify the solidification parameters (temperature gradient (G) and growth rate (R)) in the LMD multilayer deposition process. During deposition, the temperature profile at a fixed point in the deposit was measured to validate the numerical model, and then the solidification parameters were quantified using the model. Simultaneously, the microstructure of the deposit was investigated to confirm the microstructure morphology. Then, a relationship between the microstructure morphology and the G/R was proposed using a solidification map. The findings of this study can guide the design of scanning paths to produce deposits with a uniform structure.

Study of structural changes for STS 316L using the positron annihilation lifetime spectroscopy

The defects due to extrusion strengths and the temperature dependent deformities for low carbon stainless steel (STS 316L) were investigated using positron annihilation spectroscopy. The defects were restored after tempering at 700 °C. The gradients of the peak on the positron annihilation lifetime spectrum for a sample annealed at 700 °C is increased compared to the as extruded sample. In addition, we calculated the trapping rate and bulk lifetime based on the theoretical model. Both values are decreased, as the extrusion strengths are reduced. All annealed samples showed reduced trapping rate and bulk lifetime, comparing with as extruded samples.

Room Temperature Compressive Property and Deformation Behavior of Microporous STS 316L Stainless Steel Tube Manufactured with Powder Sintering Process.

This study investigated the room-temperature compressive property and deformation behavior of microporous STS 316L stainless steel tube for catalyst manufactured with powder sintering after two-way compression molding. The microporous tube was manufactured using STS 316L powder stocks with an outer diameter of 30 mm, inner diameter of 25 mm and length of 120 mm. In initial microstructure observed from different directions and locations, the porosity was measured as 32%, and the relative density obtained using micro-computed tomography was 0.54. Phase analysis did not identify phases other than γ-Fe. In a room temperature compression test, compressive yield strength measured 32 MPa. Observation of fractpgraphy after compression test revealed that dimples were formed at the powder-powder interface during the process where necks were disconnected. Based on the above findings, this study attempted to identify the deformation behavior of microporous STS 316L material manufactured with powder sintering after two-way compression molding and powder sintering process.

Experimental and Simulation Analysis of Hot Isostatic Pressing of Gas Atomized Stainless Steel 316L Powder Compacts

In this work, both experimental and numerical studies were conducted to investigate the densification behavior of stainless steel 316L (STS 316L) powders during hot isostatic pressing (HIP), and to characterize the mechanical properties of HIPed specimens. The HIP experiments were conducted with gas atomized STS 316L powders with spherical particle shaped under controlled pressure and temperature conditions. The mechanical properties of HIPed samples were determined on a series of tensile tests, and the results were compared to a reference STS 316L sample prepared by the conventional process, i.e., extrusion and annealing process. Corresponding microstructures before and after tensile tests were observed using scanning electron microscopy and their relationships to the mechanical properties were addressed. Furthermore, a finite element simulation based on the power-law creep model was carried out to predict the density distribution and overall shape change of the STS316L power compact during HIP process, which agreed well with the experimental results.

A Direct Methodology for Small Punch Creep Test

Small punch creep test (SPCT) has strong advantages in practice compared with traditional uniaxial creep test because a small sheet specimen (10 × 10 × 0.5 mm) can be obtained from in-service facilities or mechanical components without damage. In this paper, a novel investigation is proposed to directly interpret SPCT results in consideration of Chakrabarty’s membrane stretching theory, which features strain analysis on thin sheet material forced by large punch ball, and it is applied to derive equivalent strain and strain rate from SPCT results. Also, the Monkman-Grant model for evaluation of creep life is investigated by using equivalent strain and strain rate data obtained from the Chakrabarty’s membrane stretching theory. To validate this methodology, both uniaxial creep test and SPCT have been performed for STS 316L stainless steel at 650 °C. Displacement and time data in SPCT were converted into equivalent strain and strain rate. The Monkman-Grant models derived from two different creep tests show a great potential such that SPCT with the proposed methodology can be substituted for uniaxial creep test.

스테인리스강 STS 316L과 탄소강 A516-70의 이종금속 GTA 용접부 특성에 대한 연구

Abstract Characteristics of dissimilar metal welds between STS 316L and carbon steel ASTM A516 Gr.70 made with GTAW have been evaluated in terms of microstructure, ferrite content, chemical analysis, hardness and corrosion resistance. Three heat inputs of 9.00, 11.25, 13.00kJ/cm were employed to make joints of dissimilar metals with ER309 wire. Based on microstructural examination, the amount of vermicular type of δ-ferrite was increased with increasing heat input due to the increase of Creq /Nieq in the second layer of welds. Based on the EDX analysis of weld metals, Cr and Ni content in the 2nd layer increased while those content in the first layer of welds decreased with heat inputs. Cellular solidification mode in the 1st layer and dendritic solidification mode in the 2nd layer due to different cooling rates were prevailed, respectively. Heat affected zone which formed hard microstructure showed higher hardness than the weld metal. The salt spray test of dissimilar metals weld joints showed that the carbon steel surfaces only corroded. The weight loss rate due to corrosion increased up to 100hours but it decreased above 100 hours. There was little difference in the weight loss caused by corrosion regardless of heat inputs.Key Words : Dissimilar metals welding, GTAW, δ-ferrite, Vermicular ferrite, Corrosion, Heat input

Influence of Phase Evolution and Texture on the Corrosion Resistance of Nitrogen Ion Implanted STS 316L Stainless Steel

In this study, nitrogen ions were implanted into STS 316L austenitic stainless steel by plasma immersion ion implantation (PIII) to improve the corrosion resistance. The implantation of nitrogen ions was performed with bias voltages of −5, −10, −15, and −20 kV. The implantation time was 240 min and the implantation temperature was kept at room temperature. With nitrogen implantation, the corrosion resistance of 316 L improved in comparison with that of the bare steel. The effects of nitrogen ion implantation on the electrochemical corrosion behavior of the specimen were investigated by the potentiodynamic polarization test, which was conducted in a 0.5 M H2SO4 solution at 70 oC. The phase evolution and texture caused by the nitrogen ion implantation were analyzed by an X-ray diffractometer. It was demonstrated that the samples implanted at lower bias voltages, i.e., 5 kV and 10 kV, showed an expanded austenite phase, γN, and strong (111) texture morphology. Those samples exhibited a better corrosion resistance.

금속사출성형을 이용한 STS 316L 밸브피팅 제작에 대한 연구

A net-shape forming of small and complex-shaped metal parts by metal injection molding (MIM) has economic advantages in mass production, especially for STS 316L valve fitting. STS 316L offers excellent corrosion resistance, but it has poor machinability, which is a limitation in using it for a cost-effective production where both forging and machining are employed. Simulation and experimental analysis were performed to develop a MIM STS 316L 90° elbow fitting minimizing trial and error. A Taguchi method was used to determine which input parameter was the most sensitive to possible defects (e.g. sink mark depth) during the injection molding. The final prototype was successfully built. The results indicate that the simulation tool can be used during the design process to minimize trial and error, but the final adjustment of parameters based on field experience is essential.

Electrochemical characteristics under cavitation-erosion for STS 316L in seawater

The offshore structure industry, which is emerging as a higher value-added business, has continued to evolve and expand. Much of this is contributed to development of new alloys with high corrosion resistance. Stainless steel, in particular, has significantly improved the corrosion characteristics of carbon steel. However, the protective film for corrosion protection of stainless steel is vulnerable to Cl− ions in seawater, leading to damages such as pitting corrosion and crevice corrosion. Especially, application of the material for underwater rotating body can cause physical erosion damage due to cavitation. This paper investigated the electrochemical characteristics of 316L stainless steel exposed to cavitation environment in seawater. The results revealed that the cavitation condition exhibited relatively high corrosion current density due to the breakdown of the protective film by either the impact pressure during bubble collapse or the micro-jet, suggesting that acceleration of corrosion damage was achieved compared to the static condition.

STS 316L 소결체의 대기중 고온산화 거동

In this study, analysis on the oxidation behavior was conducted by a series of high-temperature oxidation tests at both <TEX>$800^{\circ}C$</TEX>, <TEX>$900^{\circ}C$</TEX> and 1000 in the air with sintered STS 316L. The weight gain of each oxidized specimen was measured, the oxidized surface morphologies and composition of oxidation layer were analyzed with Scanning Electron Microscope-Energy Dispersive x-ray Spectroscopy (SEM-EDS), finally, the phase change and composition of the oxidized specimen were shown by X-Ray Diffraction (XRD). As a result, the weight gain increased sharply at <TEX>$1000^{\circ}C$</TEX> when oxidation test was conducted for 210 hours. Also, a plentiful of pores were observed in the surface oxidation layers at <TEX>$900^{\circ}C$</TEX> for 210 hours. In addition, the following conclusions on oxidation behavior of sintered STS 316L can be obtained: <TEX>$Cr_2O_3$</TEX> can be formed on pores by influxing oxygen through open-pores, <TEX>$(Fe_{0.6}Cr_{0.4})_2O_3$</TEX> can be generated on the inner oxidation layer, and <TEX>$Fe_2O_3$</TEX> was on the outer oxidation layer. Also, <TEX>$NiFe_2O_4$</TEX> could be precipitated if the oxidation time was kept longer.

A Study on the Galvanic Corrosion for Zirconium with Titanium and 316L Stainless Steel

The coastal area of Republic of Korea is very clean compared to other countries. In this reason, west coastal area of our country is a good place for breeding up a fish such as shrimp. In winter season, the heating system is required for preventing shrimp death caused by freezing in the farm. The heater in the heating system for fisherys farm is operated very severe combating corrosion due to high accumulation by feeding material and high temperature in heated sea water. Almost all manufactured heaters of STS 316L and Ti material are scrapped every year due to heavy corrosion such a general and crevice corrosion. For comparing the general and galvanic corrosion in new heater material, the test material of Zirconium (Zr), Titanium (Ti) and STS 316L are tested by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), current density-time methods and microscopic examination in a 3.5% NaCl solution. The corrosion potential (Ecor) measured by potentiodynamic polarization for Zr, Ti and STS 316L reveals -198, -250 and -450mV, corrosion current density 0.5, 2.5 and 6.5㎂/cm2 respectively. The film resistance measured by EIS are Zr 63,000, Ti 39,700 and 316L 3,150Ω, and the current of Zr-Ti couple is 0.03㎂, whereas Zr-316L SS is 0.1㎂. According to the result of this experiment in 3.5% NaCl solution, Zr is excellent corrosion resistance material than Ti and STS 316L.

Corrosion behavior in 10% H2C2O2·H2O solution of austenite stainless steel for double wall gas pipe of duel fuel engine for liquefied natural gas ship

In this study, to evaluate the corrosion resistance in the case of the identical welding by the gas metal arc welding with the STS 304 and STS 316L alloys, the double wall gas pipe materials, using the ER 308L electrode, the corrosion characteristics of the base metal and the welding zone were compared and evaluated by various electrochemical experiments in 10% oxalic acid solution, and the corrosion behavior was analyzed by observing the process of the corrosive damage. The STS 304 identical welding zone was a small cathode‐large anode cell where the base metal played the role of an anode and protected the welding zone. However, corrosion took place preferentially in the STS 316L welding zone because the welding zone played the role of an anode. Copyright © 2012 John Wiley &amp; Sons, Ltd.

STS 316L 교정시험편을 이용한 재가열기 튜브의 와전류신호와 초음파 IRIS 신호 특성

본 연구에서는 가공된 오스테나이트계 STS 316L ASME 표준 교정시험편을 이용하여 튜브 두께 감소율과 잔존두께에 대한 와전류 신호와 IRIS 신호특성을 비교하여 리보일러 튜브의 현장 적용성을 평가하였다. 그 결과 두께감소율의 경우 와전류탐상검사는 <TEX>$20%{\times}4$</TEX> 평저공, 10% 외면 그루브, IRIS는 80%홈, 10%외면 그루브에서 <TEX>${\pm}15%$</TEX> 이상의 편차가 발생하였다. 잔존두께의 경우 와전류탐상은 측정치가 모두 허용범위를 만족하였으나, IRIS는 80% 인공홈에서 <TEX>${\pm}15%$</TEX> 이상의 편차가 발생하였다. 따라서 와전류탐상검사 후 의사지시에 대한 해석, 두께감소율 측정을 위해 IRIS를 수행한다면 신뢰성이 향상될 것으로 판단된다. In this study, a field applicability of reboiler tube was evaluated by comparing ECT signal with IRIS signal about wall loss rate and remaining wall thickness using worked austenite STS 316L ASME standard calibration tube. In the case of wall-loss rate, as a result, tolerance about <TEX>$20%{\times}4$</TEX> flat bottom hole and 10% O D groove(ECT), 80% defect and 10% O D groove(IRIS) occurred up to <TEX>${\pm}15%$</TEX>. In the case of remaining wall thickness, ECT was satisfied with the both tolerance, but tolerance about 80% defect occurred up to <TEX>${\pm}15%$</TEX> in IRIS. Therefore, if the IRIS is performed for interpretation of non-relevant indication and measurement of wall-loss rate after ECT, reliability is supposed to be improved.

그래핀이 코팅된 스테인리스강의 고분자전해질 연료전지 분리판 적용을 위한 표면 특성

Graphene was coated on STS 316L by electro spray coating method to improve its properties of corrosion resistance and contact resistance. Exfoliated graphite (graphene) was made of the graphite by chemical treatment. Graphene is distributed using dispersing agent, and STS 316L was coated with diffuse graphene solution by electro spray coating method. The structure of the exfoliated graphite was analyzed using XRD and the coating layer of surface was analyzed by using SEM. Analysis showed that multi-layered graphite structure was destroyed and it was transformed into fine layers graphene structure. And the result of SEM analysis on the surface and the cross section, graphene layer was uniformly formed with 3~5 thickness on the surface of substrate. Corrosion resistance test was applied in the corrosive solution which is similar to the PEM fuel cell stack inside. And interfacial contact resistance test was measured to simulate the internal operating conditions of PEM fuel cell stack. The results of measurements show that stainless steel coated with graphene was improved in corrosion resistance and surface contact resistance than stainless steel without graphene coating layer.

분말붕소법을 이용한 오스테나이트계 스테인리스 316L강의 기계적 특성 향상을 위한 연구

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 <TEX>$900^{\circ}C$</TEX> and <TEX>$1000^{\circ}C$</TEX> 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, <TEX>$Fe_2B$</TEX>, CrB, <TEX>$Cr_2B$</TEX> and <TEX>$Ni_3B$</TEX>. Friction coefficient of boronized STS 316L was shown the low value at <TEX>$900^{\circ}C$</TEX> for 8 hours and <TEX>$1000^{\circ}C$</TEX> for 4 hours, respectively.