Austenitic Nickel Research Articles

Effects of flux-cored arc welding technology on microstructure and wear resistance of Fe-Cr-C hardfacing alloy

This research presented the effects of flux-cored arc welding (FCAW) with and without preheating, gas-shielding and buffering conditions on the microstructure and wear resistance of Fe-Cr-C hardfacing alloy. The flux-cored wires based on austenitic nickel and Fe-Cr-C alloyed steel were used as buffer and hardfacing layers. The welding quality was inspected by visual test (VT) and penetrant test (PT). The structural characteristics were analyzed by optical microscope (OM), X-ray diffractometer (XRD), and scanning electron microscope with energy dispersive X-ray spectrometer (SEM-EDS). The results exhibited that the preheating, gas-shielding and buffering could improve the quality, dilution and weldability of the hardfacing weld. The structural phase of the hardfacing weld was found in the form of (Fe,Cr)7C3 mixed with martensite-austenite matrix (MA matrix). The buffering could combine the interphase of hardfacing to structural steel base resulting in the reduction of crack and carbide precipitation (Fe3C) at the fusion line from the effect of elemental dilution. The combination of buffer and hardfacing layers affected to crystallite size and fraction ratio of (Fe,Cr)7C3 to MA matrix increasing the elemental diffusions. According to the wear testing results (hardness, impact and abrasion), it was found that the preheating, gas-shielding and buffering FCAW provided an excellent wear resistance of Fe-Cr-C hardfacing alloy due to the present of (Fe,Cr)7C3 eutectic carbide in a high fraction of MA matrix resulting in good toughness-hardness balance properties. In addition, the suitable FCAW condition from the study could be applied for hardfacing of the tooth plate of crushing roller that was used in the biomass energy industry with better service life than traditional FCAW.

Nuclear Physical Properties of Austenitic Nickel and Manganese Steels under Neutron Irradiation in Nuclear Fission (Fast) and Fusion Reactors

Nuclear Physical Properties of Austenitic Nickel and Manganese Steels under Neutron Irradiation in Nuclear Fission (Fast) and Fusion Reactors

Acid Dissolution Behavior of Ferritic FeCrAl Tubes Candidates for Nuclear Fuel Cladding

The international materials community is engaged in finding safer alternatives to zirconium alloys for the cladding of fuel in light water reactors. One solution is to replace the zirconium cladding using ferritic iron-chromium-aluminum (FeCrAl) alloys, which offer extraordinary resistance to high-temperature reaction with air or steam due to the formation of a protective alumina layer on the external surface. It is important to characterize the behavior of FeCrAl not only during accident conditions but in the entire fuel cycle, which may include reprocessing of the used fuel after it is removed from the power reactors. The reprocessing may involve the dissolution of the fuel rods in mineral acids. Little or nothing is known on the dissolution of FeCrAl alloys in common mineral acids, therefore the objective of this research was to study the dissolution of typical cladding tubing having two compositions of FeCrAl (APMT and C26M) in three acids (H2SO4, HNO3, and HCl) as a function of the temperature using both standard ASTM immersion tests as well as electrochemical tests. The dissolution behavior of the FeCrAl alloys is compared to the dissolution capability of other traditional nuclear materials such as austenitic stainless steels (304SS and 316SS) and austenitic nickel alloys (Alloy 600 and Hastelloy C-276). Results show that both C26M and APMT have a higher dissolution capability in the studied mineral acids, which will be beneficial for reprocessing procedures.

Study on Microstructure and Mechanical Properties of Laser Welded Dissimilar Joint of P91 Steel and INCOLOY 800HT Nickel Alloy.

This investigation attempts to explore the weld characteristics of a laser welded dissimilar joint of ferritic/martensitic 9Cr-1Mo-V-Nb (P91) steel and Incoloy 800HT austenitic nickel alloy. This dissimilar joint is essential in power generating nuclear and thermal plants operating at 600–650 °C. In such critical operating conditions, it is essential for a dissimilar joint to preserve its characteristics and be free from any kind of defect. The difference between the physical properties of P91 and Incoloy 800HT makes their weldability challenging. Thus, the need for detailed characterization of this dissimilar weld arises. The present work intends to explore the usage of an unconventional welding process (i.e., laser beam welding) and its effect on the joint’s characteristics. The single-pass laser welding technique was employed to obtain maximum penetration through the keyhole mode. The welded joint morphology and mechanical properties were studied in as-welded (AW) and post-weld heat treatment (PWHT) conditions. The macro-optical examination shows the complete penetrations with no inclusion and porosities in the weld. The microstructural study was done in order to observe the precipitation and segregation of elements in dendritic and interface regions. Solidification cracks were observed in the weld fusion zone, confirming the susceptibility of Incoloy 800HT to such cracks due to a mismatch between the melting point and thermal conductivity of the base metals. Failure from base metal was observed in tensile test results of standard AW specimen with a yield stress of 265 MPa, and after PWHT, the value increased to 297 MPa. The peak hardness of 391 HV was observed in the P91 coarse grain heat-affected zone (CGHAZ), and PWHT confirmed the reduction in hardness. The impact toughness results that were obtained were inadequate, as the maximum value of impact toughness was obtained for AW P91 heat-affected zone (HAZ) 108 J and the minimum for PWHT Incoloy 800HT HAZ 45 J. Thus, difficulty in obtaining a dissimilar joint with Incoloy 800HT using the laser beam welding technique was observed due to its susceptibility to solidification cracking.

Effective hydrogen diffusivities of AISI 304 stainless steel with Ni or Au coating

AbstractMetallic coatings which provide a hydrogen diffusion barrier are thought to reduce hydrogen assisted cracking on stainless steel. The influence of a metallic layer on the hydrogen migration of AISI 304 stainless steel was investigated using a commercial electroplating layer of Ni and Au on a thin stainless steel coupon. Phase identification was performed using an X-ray diffractometer to determine the average thicknesses, measured from back-scattered scanning electron images. Regarding the ASTM G148-97 practice, the effective hydrogen diffusivities of AISI 304 austenitic stainless steel, nickel and gold were measured as 7.07 × 10-13, 2.72 × 10-14 and 9.64 × 10-16 m2 × s-1, respectively. In this work, a gold layer was found to be most effective for the prevention of hydrogen diffusion when compared with untreated and Ni-plated 304 stainless steel.

TWIP and Fracture Behavior in the Superalloy 625 at Room and Cryogenic Temperatures

In this study an austenitic nickel base alloy (Alloy 625) with medium to high stacking fault energy was tensile tested at room temperature and at cryogenic temperature, -196°C, to investigate if twinning was involved in the fracture process. Fracture surfaces and microstructure were characterized using scanning electron microscopy and texture was evaluated with scanning electron microscopy-electron backscatter diffraction at three positions along the tensile test specimens. Features where investigated with electron channelling contrast imaging. At room temperature the predominant deformation mechanism is slip and at cryogenic temperature slip is followed by deformation twinning. At room temperature deformation twinning will make an extra deformation contribution in the localized necking region compared to the cryogenic temperature case where deformation twins already are distributed in the microstructure and in this case will hinder the dislocations to move freely and instead cause stress field build up at the twin boundaries and subsequent microcrack and void formation.

Laser-treated austenitic steel and nickel alloy for human implants

ABSTRACTThe recent research in biocompatible materials has been useful in replacing and supporting the fractured natural human bones/joints. Under some condition, negative reaction like release of ions from the bare metal toward the human body fluid leads to corrosion. In this proposed research paper, the biocompatibility of the laser surface-modified austenitic stainless steel (SS316L) and nickel-based superalloy (Inconel 718) was studied. The investigation on laser-modified surfaces is evaluated through electrochemical polarization analysis using simulated body fluid (SBF). The samples subjected to electrochemical polarization analysis were characterized by optical image analysis, SEM, EDS, and XRD analysis. It was inferred that laser surface-modified materials provided enhanced corrosion resistance and bare nickel alloy is more susceptible to corrosion by SBF.

SUMITOMO SMC276-110

Abstract Sumitomo SMC276-110 (minimum yield strength of 110 ksi, or 758 MPa) is an austenitic high-strength nickel alloy for use in oil country tubular goods as a material suitable for severe sour service. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming and heat treating. Filing Code: Ni-730. Producer or source: Nippon Steel and Sumitomo Metal Corporation.

SUMITOMO SM2550-110

Abstract Sumitomo SM2550 is a high strength austenitic nickel alloy for use in oil country tubular goods as a material suitable for severe sour service. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming and heat treating. Filing Code: SS-1262. Producer or source: Nippon Steel and Sumitomo Metal Corporation.

Austenitic Nickel- and Manganese-Free Fe-15Cr-1Mo-0.4N-0.3C Steel: Tensile Behavior and Deformation-Induced Processes between 298 K and 503 K (25 °C and 230 °C)

The high-temperature austenite phase of a high-interstitial Mn- and Ni-free stainless steel was stabilized at room temperature by the full dissolution of precipitates after solution annealing at 1523 K (1250 °C). The austenitic steel was subsequently tensile-tested in the temperature range of 298 K to 503 K (25 °C to 230 °C). Tensile elongation progressively enhanced at higher tensile test temperatures and reached 79 pct at 503 K (230 °C). The enhancement at higher temperatures of tensile ductility was attributed to the increased mechanical stability of austenite and the delayed formation of deformation-induced martensite. Microstructural examinations after tensile deformation at 433 K (160 °C) and 503 K (230 °C) revealed the presence of a high density of planar glide features, most noticeably deformation twins. Furthermore, the deformation twin to deformation-induced martensite transformation was observed at these temperatures. The results confirm that the high tensile ductility of conventional Fe-Cr-Ni and Fe-Cr-Ni-Mn austenitic stainless steels may be similarly reproduced in Ni- and Mn-free high-interstitial stainless steels solution annealed at sufficiently high temperatures. The tensile ductility of the alloy was found to deteriorate with decarburization and denitriding processes during heat treatment which contributed to the formation of martensite in an outermost rim of tensile specimens.

Influence of correlation effects on radiation damage in solid solutions

The influence of correlation effects due to thermodynamic interaction of alloy components on segregation processes upon radiation treatment has been analyzed. The analysis has been performed for 53 metallic solid solutions. It has been shown that the short-range order in alloys causes a redistribution of flows of radiation defects and changes the mechanism of their annihilation, which in a certain temperature range is responsible for the high resistance of alloys to radiation swelling. The presence of two maxima in the curve of the temperature dependence of swelling for austenitic nickel–chromium alloys is associated with the existence therein of different types of short-range order at different temperatures.

Weldability and weld performance of candidate nickel base superalloys for advanced ultrasupercritical fossil power plants part I: fundamentals

Fossil fuel will continue to be the major source of energy for the foreseeable future. To meet the demand for clean and affordable energy, an increase in the operating efficiency of fossil fired power plants is necessary. There are several initiatives worldwide to achieve efficiencies >45% higher heating value (HHV) through an increase in steam temperature (700 to 760°C) and pressure (27.6 to 34.5 MPa). Realising this goal requires materials with excellent creep rupture properties and corrosion resistance at elevated temperatures. In order to accomplish this, three classes of materials have been identified: creep strength enhanced ferritic steels, austenitic stainless steels and nickel base superalloys. Although new alloys have been designed and developed to meet this need, welding can have a significant and often detrimental effect on the required mechanical and corrosion resistant properties. Two previous papers addressed the welding and weldability of ferritic and austenitic stainless steels. Welding and weldability of nickel base alloys will be discussed in a two part paper. In this paper, the primary focus will be on the fundamentals of welding and weldability of Ni base superalloys.

MATERIALS EVALUATION FOR GEOTHERMAL APPLICATIONS

In order to provide basic information on corrosion resistance to the designers and users of geothermal plants different metallic materials including duplex and austenitic stainless steels as well as a nickel alloy have been evaluated in artificial geothermal fluids simulating the conditions in some locations with geothermal potential in Germany as well as two sites in Indonesia. By electrochemical and long-term exposure tests at 100 °C and 150 °C the suitability of low alloyed steel UNS G41300, stainless steels UNS S31603 UNS S31803, UNS S32760, super austenitic steel UNS N08031 and nickel based alloy UNS N06059 was investigated in these geothermal fluids, using critical potentials and corrosion rates. In high-saline environments the crevice corrosion turned out to be the determining mechanism. The nickel based alloy shows excellent corrosion resistance against pitting corrosion. Excluding its high cost, it is very good to be used in the construction of geothermal facilities having highly saline brines. Stainless and duplex steels exhibit a limited corrosion resistance concerning pitting and crevice corrosion. Therefore they are not suitable for highly saline brines. The super austenite UNS N08031 showed a temperature depending behavior. In non-saline environments the low-alloyed steel UNS G41300 (beside of the higher alloyed materials) could be employed as a constructional material for the geothermal power plant, as long as a sufficient wall thickness of the material is considered.

Effect of chloride ions on corrosion behaviour of austenitic nickel and nickel free stainless steels in phosphoric acid solutions

The effect of chloride ions' presence (0·005–1·0M NaCl) in phosphoric acid solutions (5, 40 and 75%) on the corrosion behaviour of three austenitic stainless steels (an experimental steel Fe–18Cr–12Mn–0·6N and two trade grades, Fe–18Cr–9Ni and Fe–14Cr–15Mn–0·2N) has been studied by potentiodynamic polarisation measurements. The surface examinations of the samples tested involved X-ray photoelectron spectroscopy as well as optical and scanning electron microscopy. It was established that chlorides added to phosphoric acid solutions deteriorate the general corrosion resistance, and under anodic polarisation, they provoke pitting corrosion. The composition of the stainless steels significantly influences its corrosion behaviour in the phosphoric acid solutions containing chloride ions. The replacement of nickel with manganese and nitrogen on top of lower chromium content has a strong negative effect on the corrosion resistance.

Cyclic Plastic Response and Damage in Materials for High Temperature Applications*

The characteristic changes of the cyclic plastic stress-strain response of stainless steel and superalloys derived from the analysis of hysteresis loop at different temperatures are reported. The evolution of the surface relief in strain controlled cycling is documented using high resolution SEM and TEM. The mechanisms leading to cyclic strain localization, formation of surface relief, fatigue crack initiation and early crack growth are discussed. The study of the low cycle fatigue behavior of these materials was concentrated mostly to the analysis of the stress-strain response, internal structures, fatigue life and crack growth (1-3). In recent years, considerable attention has been attracted to the study of the early damage mechanisms in crystalline materials, starting with the cyclic slip localization and resulting finally in the initiation of fatigue cracks and their early growth (4, 5). In this contribution, the methods allowing to study the sources of cyclic stress and early fatigue damage at room and elevated temperatures are presented and used to reveal details of the mechanisms of cyclic plastic straining and fatigue damage evolution in austenitic steels and nickel superalloys. 1. Cyclic Plastic Stress-Strain Response. Cyclic plasticity of materials is usually studied in strain- controlled cycling with constant strain rate, since stress response of the material depends not only on temperature but also on the strain rate. In a standard low cycle fatigue experiment, several specimens are cycled in a symmetrical cycle with constant total or plastic strain amplitudes, and their stress response is recorded and evaluated. Hysteresis loops can be stored in computer memory, and stress, strain and plastic strain amplitudes are evaluated during the fatigue life. The plot of the stress amplitudes vs. number of loading cycles represents the fatigue hardening/softening curves. The plot of the saturated stress amplitude (or stress amplitude at half-life) vs. strain or plastic strain amplitude represents the cyclic stress-strain curve. In order to find the sources of the cyclic stress, more detailed analysis is necessary. Hysteresis loop and the analysis of its shape using the generalized statistical theory (6) can yield information on the sources of the cyclic

Corrosion resistance of nickel steel and nickel alloys in aggressive media

The corrosion resistance of austenitic steel and nickel alloys is studied in the most aggressive media within the chemical shops of coke plants: in the stock solutions of the sulfate department and in sulfuric-acid solutions used for the purification of crude benzene. In the study, the most dangerous ions, activating corrosion in 10X17H13M2T steel, are CNS− ions, which are capable of destroying the passive layers on chromium-nickel-molybdenum steel in the stock solutions of the sulfate department. Research shows that sulfuric-acid solutions used for the purification of crude benzene are very aggressive in relation to high-alloy steel, titanium, zirconium, and copper. Possible structural materials for use in contact with such solutions include the nickel alloys ХН63МБ, ХН65МВНУ, and Hastelloy C-276.

Microstructural evolution of CANDU spacer material Inconel X-750 under in situ ion irradiation

Work on Inconel®1Inconel® is a registered trademark of Special Metals Corporation that refers to a family of austenitic nickel–chromium-based superalloys.1 X-750 spacers removed from CANDU®2CANDU® is a registered trademark of Atomic Energy of Canada Limited standing for ‘‘CANada Deuterium Uranium’’.2 reactors has shown that they become embrittled and there is development of many small cavities within the metal matrix and along grain boundaries. In order to emulate the neutron irradiation induced microstructural changes, heavy ion irradiations (1MeV Kr2+ ions) were performed while observing the damage evolution using an intermediate voltage electron microscope (IVEM) operating at 200kV. The irradiations were carried out at various temperatures 60–400°C. The principal strengthening phase, γ′, was disordered at low doses (∼0.06dpa) during the irradiation. M23C6 carbides were found to be stable up to 5.4dpa. Lattice defects consisted mostly of stacking fault tetrahedras (SFTs), 1/2<110> perfect loops and small 1/3<111> faulted Frank loops. The ratio of SFT number density to loop number density for each irradiation condition was found to be neither temperature nor dose dependent. Under the operation of the ion beam the SFT production was very rapid, with no evidence for further growth once formed, indicating that they probably formed as a result of cascade collapse in a single cascade. The number density of the defects was found to saturate at low dose (∼0.68dpa). No cavities were observed regardless of the irradiation temperature between 60°C and 400°C for doses up to 5.4dpa. In contrast, cavities have been observed after neutron irradiation in the same material at similar doses and temperatures indicating that helium, produce during neutron irradiation, may be essential for the nucleation and growth of cavities.

Behaviour of Stress Corrosion Cracking of Austenitic Stainless Steels in Sodium Chloride Solutions

Click Stress Corrosion Cracking (SCC) is an environmentally well-known as a failure caused by exposure to a corroding while under a sustained tensile stress. SCC is most often rapid, unpredictable. Failure can occur in a short time as a few hours or take years and decades to happen. Most alloys are liable to SCC in one or more environments requiring careful consideration of alloy type in component design. In aqueous chloride environments austenitic stainless steels and many nickel based alloys are common to perform poorly. Stress corrosion cracking (SCC) of austenitic stainless steels of types 316 was investigated as a function of applied stress at room temperature in sodium chloride solutions using a constant load method. The experiment uses a spring loaded fixture type and is based on ASTM G49 for experiment method, and E292 for geometry of notched specimen. The stress dependence of fracture appearance and parameters of time to cracking, and cracking growth. The results are explained in terms of comparison between the two concentrations of sodium chloride solutions.

Intergranular pitting tendency of yttrium implanted Inconel 600 in acidic chloride media

Yttrium ions of energy 0.5MeV were implanted to modify the surface of Inconel 600 by using a Pelletron Accelerator. Microstructural and XRD studies reveal austenitic nickel solid solution (γ) and intergranular carbides. The surfaces were electrochemically investigated by potentiodynamic polarization, Electrochemical impedance spectroscopy and Mott–Schottky techniques in acidic saline solution. The results indicate that the yttrium ions implantation significantly reduces the intragranular pitting as compared to the intergranular pitting tendency of the alloy. The low passive current density, minor pseudo-capacitive behavior and high flat band potential with p-type nature of passive film limit the electrochemical dissolution of the yttrium implanted Inconel.

Improved oxidation resistance of ferritic – martensitic steels in water vapour containing environments via diffusion coatings

Ferritic – martensitic steels are of high interest as superheater materials or as materials for interconnectors in solid oxide fuel cells. In comparison to austenitic steels and nickel base alloys they offer much better heat transfer behaviour and a lower coefficient of thermal expansion, as well as lower costs. Modern 9% Cr-steels have sufficient creep strength however their corrosion resistance particularly in H2O containing oxidising environments (e.g. up to 25% H2O in the combustion of biomass or the oxyfuel process) needs further improvement.A large number of studies have shown that the corrosion resistance of 9% Cr-steels in water vapour containing combustion environments is inferior to that in dry atmospheres, due to the formation of a volatile Cr-species of the type CrO2(OH)2. This investigation starts from the idea of a shift of partial pressure of CrO2(OH)2 to lower values if the solid oxide phase on the alloy surface is a manganese –chromium – spinel scale, so that at 630°C the formation of volatile chromium species can be suppressed. Therefore, the metal subsurface region was enriched with manganese and chromium via a diffusion coating (pack cementation) to promote the formation of Cr –Mn– spinel during oxidation. In the course of the project it was observed that the diffusion treatment can lead to the formation of a chromium carbide surface layer. The surface treated alloys show extreme stability under oxidising water vapour containing environments, as illustrated by oxidation exposures in a simulated combustion environment (N2 + 1%O2 + 10%H2O) at 650°C for 800 h.