Creep properties and design curves for nitrogen enhanced grade of 316LN stainless steel

Abstract

316L(N) stainless steel (SS) containing 0·02–0·03 wt-% carbon and 0·06–0·08 wt-% nitrogen is the principal material for the high temperature structural components of the prototype fast breeder reactor in India. In order to increase the economic competitiveness of sodium cooled fast reactors (SFRs), there is a strong desire to increase the design life from the current level of 40 years to at least 60 years for the future reactors. As a part of the efforts to develop materials with superior mechanical properties suitable for longer design life, the influence of nitrogen at concentrations higher than 0·07 wt-%, on the high temperature mechanical properties of type 316L(N) SS is being studied. Four heats of 316L(N) SS, containing 0·07, 0·11, 0·14 and 0·22 wt-% nitrogen have been evaluated extensively in terms of their tensile, creep, low cycle fatigue and creep fatigue interaction properties. Based on these studies, the nitrogen content has been optimised at 0·14 wt-%. This nitrogen enhanced grade of steel (NE316LN SS) was found to have significantly better tensile, creep, low cycle fatigue and creep-fatigue properties as compared to the PFBR grade of 316L(N) SS. This paper presents the influence of nitrogen on the creep deformation, damage and fracture behaviour of NE316LN SS. Design of high temperature SFR components is made on the basis of RCC-MR design code. The creep properties of NE316LN SS have been analysed in terms of the procedures for generation of the design code. Time–dependent design curves have been generated.     

Tribology of laser modified surface of stainless steel in physiological solution

The laser surface treatment of stainless steel (SS) 316L, an important alloy for biomedical applications, was used to improve its corrosion and wear-corrosion resistance in bio-environment. Microstructural and X-ray diffraction (XRD) pattern analysis showed presence of an austenitic phase in both untreated and laser-treated SS316L. Laser melting produced homogenized and refined microstructure on the surface with higher hardness (143–171 HV) compared to untreated SS316L (131 HV). Increase in intensity of γ (200) peaks in XRD pattern for laser-treated (>800 W) SS316L indicated possible crystallographic orientation along γ (200) plane. Passive currents were reduced to <2.8 μA/cm² and pitting potentials was increased to >+344 mV for samples laser surface treated at greater than 1200 W. The volume-loss and wear-rate of laser-treated SS316L were significantly reduced compared to untreated sample. Abrasive wear was the main wear mechanism for both untreated and laser surface treated SS316L. Wear particles/debris were found to be cold welded on the surface of SS316L and showed brittle cracking with further wear-straining.     

High temperature tensile properties of 316LN stainless steel investigated using automated ball indentation technique

Type 316LN stainless steel (SS) is the principal structural material for the components of sodium cooled fast reactors operating under elevated temperature conditions. In order to assess the degradation in strength of service exposed components using a small specimen testing technique such as automated ball indentation (ABI), it is necessary to carry out prior detailed ABI studies on the virgin material. In this investigation, the tensile behaviour of as-received 316LN SS were investigated at several temperatures in the range 298–973 K using ABI technique. The load-depth of indentation data measured from ABI tests was analyzed using semi-empirical relationships to obtain the tensile properties. The yield stress and the flow curves were determined by correlating ABI results with corresponding uniaxial tensile test results. Trend curve for tensile strength with temperature, as estimated from ABI tests, exhibited a plateau region in the temperature around 823 K, similar to uniaxial tensile tests. The variations of strength coefficient, strain hardening exponent, yield ratio, hardness and uniform ductility with temperature were evaluated from ABI tests. The ABI technique was found to estimate the influence of temperature on tensile properties sensitively.     

Impression creep deformation behaviour of 316LN stainless steel

The impression creep deformation behaviour of 316LN SS was investigated from microstructure, substructure, microhardness and profilometry studies of the creep deformed region. Impression creep tests were conducted on 316LN SS in the temperature range of 923–973?K, at different punching stresses in the range of 472–760?MPa. The impression creep deformation was characterised by a hemispherically shaped plastic zone which developed around the indentation. The study revealed the distinct regions under the punch undergoing deformation to different extents. The deformation was found to occur predominently on (111) planes. The dislocations in the highly deformed region were well dispersed in the matrix. The size of the plastic zone was estimated to be ～1·5 times the diameter of the indenter based on the microhardness and profilometry studies. The critical spacing to be maintained between the adjacent indentations was estimated to be >5 times the diameter of indenter.     

A study on low magnetic permeability gas tungsten arc weldment of AISI 316LN stainless steel for application in electron accelerator

Low magnetic permeability is an important criterion in selection of the material of construction of beam pipes and vacuum chambers of electron accelerators for safeguarding against distortion of the magnetic field. In the modified design of new 20 MeV/30 mA Injector Microtron for the existing synchrotron radiation sources Indus-1 and Indus-2, AISI 316 LN stainless steel has been identified as the material of construction of its vacuum chamber. Welding of AISI 316LN stainless steel with conventional filler alloys like ER316L and ER317L of AWS A5.9 produces duplex weld metal with 3–8% ferro-magnetic delta ferrite to avoid solidification cracking. The results of the study has demonstrated that GTAW of AISI 316LN SS with high Mn adaptation of W 18 16 5 N L filler produced a crack free non-magnetic weld with acceptable mechanical properties. Moreover, AISI 316LN stainless steel is not required to be solution annealed after the final forming operation for obtaining a low magnetic permeability, thereby avoiding solution annealing of large vacuum chamber in vacuum/controlled atmosphere furnace and associated problems of distortion. Besides Injector Microtron, the study also provides useful input for design of future indigenous accelerators with vacuum chambers of austenitic stainless steel.     

Additive manufacturing of copper-stainless steel hybrid components using laser-aided directed energy deposition

Combining dissimilar materials in a single component is an effective solution to integrate diverse material properties into a single part.Copper-stainless steel hybrid components are attracting more and more attention since the high thermal conductivity of copper can greatly enhance the thermal performance of stainless steel,which benefits its applications in many industries.However,direct joining of copper and stainless steel such as SS316 L is challenging since they preserve significant dissimilarities in physical,chemical,and thermo-mechanical properties.This paper aims to fabricate well-bonded copper-SS316 L hybrid parts using a laser-aided directed energy deposition (DED) process.A nickel-based alloy Deloro 22 (D22) is introduced between copper and SS316 L to address the detrimental issues in copper-SS316 L direct joints.Using this technique,defect-free interfaces are achieved at both the D22-SS316 L and copper-D22 transition zones.Tensile testing of Cu-D22-SS316 L and D22-SS316 L hybrid parts shows the fracture occurs at pure copper and SS316 L region,respectively,indicating an excellent bonding at the interfaces.Ascending in the building direction,a transition of grain structure is observed.A significant diffusion zone is obtained at both the D22-SS316 L and the Cu-D22 interfaces.The large diffusion distance results in a smooth variation in microhardness over the dissimilar materials.The microhardness increases from SS316 L to D22 with the highest value of 240 HV and then decreases from D22 to Cu with the lowest value of 63 ± 4 HV.Testing of thermophysical properties of the Cu-D22-SS316 L system indicates there is a ～300 ％ increase in thermal diffusivity and a ～200 ％ increase in thermal conductivity when compared to pure SS316 L.The significant increase in thermal diffusivity and conductivity validates the enhanced thermal performance of SS316 L when it is joined with pure copper.     

Effect of a nanoparticle-filled lubricant in turning of AISI 316L stainless steel (SS)

Release of heat and generation of friction associated with machining operation ever posture a problem which not only reduce the tool life but also impair the quality of the product. Nano cutting fluids play a significant role in machining operations and impact tool life and quality of work. In the present work, tool flank wear is analyzed during turning AISI 316L Stainless steel (SS) under a nano cutting environment. Experiments are conducted by turning of AISI 316L SS under wet machining with and without multiwalled carbon nanotube (MWCNT) inclusions in the conventional lubricant. The second order quadratic models were developed to predict tool wear using response surface methodology (RSM) based D-optimal design. Machining parameters such as speed, feed rate, and depth of cut are chosen as numerical factors and the type of lubricant is considered as the categorical factor. The results show that the influence of the feed rate is more significant while machining the AISI 316L SS with a whisker reinforced ceramic insert. The addition of MWCNTs in SAE20W40 enhances the tool performance with their enhanced penetration. After turning experiment, a scanning electron microscope (SEM) with energy dispersive X-ray (EDS) was used to investigate the tool wear.     

Role of molybdenum on the AISI 316L oxidation at 900 °C

In situ X-ray diffraction was used to study the oxide formation on AISI 316L stainless steel (SS) specimens during isothermal oxidation at 900 °C in air. Results were compared with those obtained on AISI 304 SS to determine the role of molybdenum on the oxidation process for the AISI 316L SS specimens. Our results show that molybdenum plays a major protective role during steel oxidation. This element is found in a NiMoO₄ phase at the internal oxide–metal interface. The high molybdenum content of the alloy hinders the outward diffusion of iron and leads to a lower growth rate and better scale adherence. The oxide scale is then composed of Cr₂O₃ with a small amount of Mn_1.5Cr_1.5O₄ at the external interface. The improved scale adherence appears to be due to a keying effect at the scale/alloy interface promoted by molybdenum.     

The influence of heat treatment on the microstructural,mechanical and corrosion behaviour of cold sprayed SS 316L coatings

The present study evaluates the response of cold sprayed SS 316L coatings on mild steel substrate to aqueous corrosion in a 0.1 N HNO₃ solution as determined using polarization tests. The corrosion behaviour of the SS 316L coating was studied not only in the as-coated condition, but also after heat treatment at 400, 800 and 1,100 °C. Heat treatment reduced the porosity, improved inter-splat bonding, increased the elastic modulus and more importantly increased the corrosion resistance of the cold sprayed SS 316L coating.     

Preliminary histological study of connective tissue response to Zinalco and stainless steel 316L implants after 120 days

Circular plates of Zinalco alloy (80 wt% Zn, 1.5 wt% Cu, 18.5 wt% Al) and stainless steel (SS) 316L were implanted in 12 female Wistar rats subcutaneously and intramuscularly to compare organism response, 120 days after implantation. The tissues surrounding the implants were analysed employing hematoxilin and eosin (H–E) and Gallegos trichromic techniques (GTT). Findings indicate that the reaction to Zinalco alloy was similar to the reaction to SS 316L. The Zn, Al and Cu concentrations in blood were measured, without evidence of any alteration due to implants. The presence and distribution of Zn, Al and Cu components of Zinalco alloy were detected in tissues by energy dispersive X-ray microanalysis. © 1998 Chapman & Hall.     

Reducing Staphylococcus aureus biofilm formation on stainless steel 316L using functionalized self-assembled monolayers

Stainless steel 316L (SS316L) is a common material used in orthopedic implants. Bacterial colonization of the surface and subsequent biofilm development can lead to refractory infection of the implant. Since the greatest risk of infection occurs perioperatively, strategies that reduce bacterial adhesion during this time are important. As a strategy to limit bacterial adhesion and biofilm formation on SS316L, self-assembled monolayers (SAMs) were used to modify the SS316L surface. SAMs with long alkyl chains terminated with hydrophobic (? CH₃) or hydrophilic (oligoethylene glycol) tail groups were used to form coatings and in an orthogonal approach, SAMs were used to immobilize gentamicin or vancomycin on SS316L for the first time to form an “active” antimicrobial coating to inhibit early biofilm development. Modified SS316L surfaces were characterized using surface infrared spectroscopy, contact angles, MALDI-TOF mass spectrometry and atomic force microscopy. The ability of SAM-modified SS316L to retard biofilm development by Staphylococcus aureus was functionally tested using confocal scanning laser microscopy with COMSTAT image analysis, scanning electron microscopy and colony forming unit analysis. Neither hydrophobic nor hydrophilic SAMs reduced biofilm development. However, gentamicin-linked and vancomycin-linked SAMs significantly reduced S. aureus biofilm formation for up to 24 and 48 h, respectively.     

Microstructure-mechanical and chemical behavior relationships in passive thin films

The passive films play an important role in corrosion and stress corrosion cracking of austenitic stainless steels. The current research investigates the relationship between alloy chemistry, microstructure, and mechanical behavior of passive films formed on 316, 304, and 904L stainless steels (SS). X-ray photoelectron spectroscopy and transmission electron microscopy were used to investigate the effect of alloy chemistry and microstructure constituents on the thin film fracture properties determined by nanoindentation tests. The analyses showed that fracture loads are directly related to the crystallography of the thin films. It was found that decreasing the ratio of iron to other metallic elements in the film led to an increase in the load required to fracture the film. It was also found that films grown on 304, 316, and 904L stainless steels were the cubic polymorph of Cr₂O₃, rather than the lower energy rhombohedral form. In the case of 904L SS the film formed as an epitaxial layer. In the other two cases it consisted of small crystalline islands in an amorphous matrix. A dichromate treatment of 316 SS decreased the iron content in the oxide film and increased the hardness. It also resulted in an epitaxial film.     

Multiple heat isothermal stress rupture correlations for type 316L(N) stainless steel and their use Part 1 – Development of reference correlations

Abstract

A low carbon, nitrogen alloyed version of stainless steel type 316 (SS 316L(N)) is the current choice as structural material for fast breeder reactors, and there is a need to derive reliable stress rupture correlations for life extrapolation. The present paper demonstrates the success of the heat correlation proposed by Ray, Sasikala and Rodriguez in deriving multiple heat isothermal correlations for stress rupture data for a large number of heats of SS 316L(N) from the European Commission's Working Group. This method of using multiple heat data as the knowledge base allows reliable correlations and extrapolations also for individual heats, even when the available data are inadequate for meaningful single heat stress rupture correlations. It is also shown, concatenating data for SS 316L(N) heats with those for two groups of SS 316 grade material (from the National Research Institute of Metals), that as far as heat dependence of stress rupture life is concerned, it is possible to consider SS 316L(N) heats as belonging to the SS 316 group. The isothermal 'reference' correlations thus derived are robust because of the large number of heats and the volume of data in the concatenated database for SS 316 and SS 316L(N) grades.     

真空烧结制备316L不锈钢纤维/HA复合生物材料及其理化性能

用真空烧结成功制备了不同成分316L不锈钢纤维/HA复合生物材料和316L不锈钢纤维/HA-ZrO₂ (CaO) 复合生物材料,并通过金相显微镜、SEM、EDXA分析了材料的微观结构、断裂性能和微区元素含量。结果表明:不锈钢纤维和纳米ZrO₂ (CaO) 粒子对复合材料具有增强和增韧的作用。综合考虑认为,20% 316L不锈钢纤维/HA-ZrO₂ (CaO) 复合材料的性能最优,其抗弯强度和抗压强度分别为140.1MPa和348.9MPa。316L不锈钢纤维/HA-ZrO₂ (CaO) 复合材料抗弯强度随316L 不锈钢纤维直径和长度减小而增大,且纤维长度对抗弯强度的影响略大于纤维直径的影响。复合材料微观组织随HA粉末和316L不锈钢纤维成分变化呈规律性变化,没有出现明显的裂纹或孔隙,HA和316L不锈钢纤维结合紧密,界面平整,两相融合程度较高。5% 316L不锈钢纤维复合材料表现为脆性断裂,而10%、20%、40% 316L不锈钢纤维复合材料均表现为韧性断裂,且韧性程度随316L不锈钢纤维含量依次增加。基体与韧化相均相对独立,二者之间不发生任何化学反应,基体HA中发生微量的Fe元素扩散,但在316L不锈钢中不发生基体的扩散。      

Effect of dilution on GTAW Colmonoy 6 (AWS NiCr–C) hardface deposit made on 316LN stainless steel

Abstract

Nickel based Colmonoy 6 (conforming to AWS NiCr–C) hardfacing alloy finds application in hardfacing of various components made of austenitic stainless steel (SS) used in fast reactors. Owing to considerable difference in melting points of the SS and Colmonoy 6 alloys, significant dilution from substrate occurs during hardfacing using gas tungsten arc welding process. Dilution has a significant effect on microstructure, hardness and wear resistance of the deposit. To overcome the adverse effects of dilution on the hardness and, hence, the wear resistance of the deposit, often, the minimum thickness specified for the deposit on hardfaced components is high, which in turn increases the susceptibility of the deposit to cracking during deposition. In the present investigation, microstructure of different layers of multilayer Colmonoy 6 deposits on 316LN SS is characterised by optical and scanning electron microscopy, and the correlation between hardness and microstructure of the individual layers with dilution from the base metal has been established. The dilution from the base material is the highest in the first layer, and it progressively decreases in the subsequent layers. With progressive decrease in dilution, the precipitate fraction increases from about 16 to 20% from the first to the fifth deposit layers. This is accompanied by hardness increase from about 480 to 800 HV. The precipitates in the deposit consist of both borides and carbides, with the boride content varying more with dilution than the carbide content. The boride fraction increased from 5 to 8% with a decrease in dilution; however, layer to layer variation in carbide fraction was only marginal at about 11–12%. High dilution from the base material suppresses the formation of borides in the deposit and is responsible for low hardness of the deposit diluted with the austenitic SS compared to those of the undiluted deposit.     

核电材料在模拟反应堆环境中应力腐蚀破裂测试技术与性能评价

简要介绍了采用慢应变速率试验，Ｕ型弯曲和Ｃ形环试验等技术，分别对８００合金，３０４和３１６及３１６Ｔｉ不锈钢Ａ５３３Ｂ压力容器用多在模拟核反应堆环境中的应力腐蚀破裂敏感性性进行的试验研究的一些主要结果；并结合电化学测试和表面膜俄歇电子能谱分析结果进行了讨论。     

A parameter for power law creep

Experimental investigations on the creep rupture behaviour of type 304, 304£ and 316 stainless steels, a nickel-base superalloy SuperNi 600 and a turbine disc alloy (equivalent to MAR M 200) have been carried out. Stainless steels 304£ and 316 have been tested with and without weldment, and materials 304 SS and SuperNi 600 have been tested with and without corrosive coatings. MAR M 200 was tested in air. A parametric method is suggested for obtaining the master curves for these alloys under test conditions. The applicability of the parameter to 25-20 stainless steel and a modified nuclear grade 316 type stainless steel has been verified.     

Friction and wear behaviors of a gradient nano-grained AISI 316L stainless steel under dry and oil-lubricated conditions

A gradient nano-grained (GNG) surface layer was fabricated on an AISI 316L stainless steel (SS) by using the surface mechanical rolling treatment (SMRT). Reciprocating dry and oil-lubricated sliding tests of the GNG 316L SS in air at room temperature were conducted in comparison with the coarse-grained (CG) counterpart. Worn surface morphologies and subsurface microstructures were investigated for both 316L SS samples. 316L SS with a GNG surface layer shows a significantly improved wear resistance, especially under oil-lubricated condition. The notably wear resistance enhancement of the GNG 316L SS is attributed to the GNG surface layer with high strain accommodation ability and high hardness, which can reduce the wear volume in the running-in stage effectively.     

Fracture and strength properties of selected austenitic stainless steels at cryogenic temperatures

Austenitic stainless steels have an excellent combination of mechanical and physical properties for load-bearing structures of large superconducting magnets for plasma containment in magnetic fusion experiments. To assess their relative suitability fracture toughness, fatigue crack growth, and tensile properties data for five austenitic steels at 295, 76, and 4 K have been obtained. The steels were AISI 304, 316, 304LN, and 316LN, and an Fe-21cr-12Ni-5Mn alloy with a higher nitrogen content than the other four grades. The two principal findings were the systematic variation of yield strength with nitrogen content and a systematic inverse correlation between fracture toughness and yield strength. Data from previous studies are reviewed which confirm the trends of the present data.