Hastelloy C-276 Research Articles

Optimization of parameters to attain higher tensile strength in pulsed Nd: YAG laser welded Hastelloy C-276–Monel 400 sheets

In this study, an empirical relationship is developed to predict the tensile strength of pulsed Nd: YAG laser welded Hastelloy C-276–Monel 400 alloy sheets by optimizing the process parameters viz., welding speed, pulse energy and pulse duration. Experiments were conducted based on a three factor, three level, central composite face centered design with full desirability. Analysis of Variance (ANOVA) results indicate that the welding speed holds the greatest influence on tensile strength, followed by pulse energy and pulse duration. Microstructural studies of the optimized condition reveal full penetration weld with finer dendritic grains and a narrow heat affected zone (HAZ). Tensile fracture surface of the optimized weld exhibits a ductile mode of fracture with high tensile strength. XRD analysis of weld zone exposed the formation of various Chromium-rich carbide and Nickel-rich oxides precipitates.

Staggered spinning of thin-walled Hastelloy C-276 cylindrical parts: Numerical simulation and experimental investigation

Staggered spinning is a cost-effective method to manufacture axisymmetric components, especially for the ultrathin cylindrical parts. However, due to the complex material flow behavior during staggered spinning of Ni-based thin-walled cylindrical parts, the accurate control of geometric precision is still a great challenge. In this work, a three-dimensional (3D) finite element model (FEM) is developed to investigate the effects of staggered spinning parameters on the dimensional accuracy of a thin-walled Hastelloy C-276 cylindrical part. It is found that the deviations of wall thickness and inner diameter are sensitive to spinning parameters. Based on the results from the finite element analysis, the optimized spinning parameters are obtained for the studied thin-walled cylindrical part, i.e., an appropriate wall thickness reduction range is 30%–40% during the single pass spinning. Meanwhile, the effects of feed ratio on the uniformities of wall thickness and inner diameter are significant, and a suitable feed ratio is 0.8 mm/r. Finally, the industrial three-roller staggered spinning experiments are carried out to verify a fact that the developed FEM, as well as the optimized spinning parameters, can be effectively used for the staggered spinning of thin-walled Hastelloy C-276 cylindrical parts.

Effect of MIG welding process parameters on microstructure and tensile behavior of hastelloy C276 using response surface methodology

The present study aims to construct a new empirical relationship for forecasting the tensile strength of Hastelloy C276 welded joints using Robotic Metal Inert Gas (MIG) welding process. The filler wire employed for this present investigation is hastelloy C276 wire. A logical approach was employed to reveal the result of MIG welding for the process parameters viz., welding current (90–110 amps), welding voltage (14.5–16.5 volts) and welding travel speed (18–22 cm min−1) on weld strength using central composite rotatable design matrix. The adequacy of developed model was checked using Analysis of variance (ANOVA) and interaction effect of parameters were studied using response surface methodology. From the experimental results, the sound joints yielded maximum tensile strength of 741 MPa, at welding current of 102 A, welding voltage of 15.5 V and welding speed of 19.8 cm min−1. It may be attributed to the density distribution of precipitates in the weld region. From the ANOVA, it is observed that welding current is the most significant parameter on establishing the ultimate tensile strength followed by welding voltage and welding travel speed. Bend test was carried out in 90° three point bending machine for both root and face of the welded joints and no defects like cracks or fracture are observed. Erichsen cupping test was executed on the welded joint to examine the formability and observed that the joint has good formability and ductility. Macrograghic examination have been executed to examine the weld joint quality. Microstructure have been explored with field emission scanning electron microscope to study the fusion zone, Heat Affected Zone and fractured surface. The presence of columnar dendrites at the weld zone evidences the plastic fracture during tensile testing owed to its ductile nature.

Effect of electron beam accelerating voltage on the melt zone area, secondary-dendrite arm spacing and fusion line microstructure of bead-on-plate welded Hastelloy C-276 sheet

Effects of beam current and welding speed on weld morphology (e.g., bead geometry and microstructure) of electron beam welded joints for different types of alloys have been widely analyzed, however, the study of the role of accelerating voltage on weld morphology is limited. In the present investigation, bead-on-plate welding of 2.6-mm-thick Hastelloy C-276 sheet was carried out using the electron beam to study the effect of accelerating voltage on melt zone area and secondary-dendrite arm spacing. Real-time photographic images showing variation in the shape of the plasma plume (generated due to the interaction of electron beam with the substrate) with accelerating voltage were collected. Increase in interaction volume of the substrate with the electron beam at higher accelerating voltage might have increased the melt zone area. The possible phenomenon of increase in the secondary-dendrite arm spacing with accelerating voltage has been analyzed with the help of an index defined as the ratio of ‘segregation ratio of element’ to ‘segregation ratio of nickel’. The index showed that the increase in molybdenum segregation with accelerating voltage might have caused under-cooling and increased the secondary-dendrite arm spacing. The temperature gradient of the melt pool normal to the scanning direction of the electron beam was derived (from Rosenthal's equation for three-dimensional heat flow) to study the variation in microstructure at the fusion line. As the temperature gradient decreases with increase in accelerating voltage, the grain morphology was found to change from cellular structure to cellule-like structure at the fusion line of the weld bead.

High Temperature Isothermal Oxidation Behavior of Superheater Materials

Abstract During combustion of biomass, alkali chloride-rich ash deposits condense on the surface of superheater tubes, thereby induce corrosion. A well-developed protective oxide layer formed from pre-oxidation treatment is an environmental friendly and cost effective technique for corrosion protection of superheater materials at high temperature in alkali salt environment. The ability of the pre-oxidized layer to protect the alloys depend on the properties such as porosity, thickness, continuity and composition of the layer. The characteristics of the oxide layer could be controlled by proper understanding on the oxidation behaviour of the materials. The main objective of this work is to obtain information on the oxidation behaviour of Hastelloy C22 (C22) and 304 Stainless Steel (304SS) at high temperature environment, hence to justify the suitability of these alloys to be subjected for pre-oxidation treatment. Oxidation of C22 and 304SS was conducted at temperature 900 °C and 1000 °C for 24 hours by thermogravimetric analysis (TGA). The oxide morphology and elemental analysis were characterized using Field Emission Scanning Electron Microscope (FESEM) equipped with Energy Dispersive X-ray Spectroscopy (EDX). The phases of the oxidation products were determined using X-ray diffraction analysis (XRD). The weight change of 304SS is higher as compared to C22 which indicates higher oxidation rate for 304SS. However, the oxide layer formed on Hastelloy C22 is more protective compared to the oxidation products of 304SS. The finding justifies the high potential of C22 alloy to be subjected for pre-oxidation treatment before used as superheater materials for biomass industry.

Effect of post-weld heat treatment on the tensile strength of laser beam welded Hastelloy C-276 sheets at different heat inputs

Laser beam welding of 2.6-mm-thick Hastelloy C-276 sheets was carried out at two different values of linear heat input, i.e., 60 J/mm and 120 J/mm. Uni-axial tensile test of as-welded (AW) Hastelloy C-276 sheets showed failure (fracture) occurring mainly at the weld zone, irrespective of the linear heat input. Following that, AW Hastelloy C-276 sheets were subjected to post-weld solution heat treatment (PWSHT). After PWSHT, it was observed that the samples welded at 60 J/mm failed mainly at the weld zone, while all the samples welded at 120 J/mm failed at the base metal. X-ray diffraction (XRD) analysis carried out in the weld zone of PWSHT sample of 120 J/mm, fractured at the base metal, showed the presence of relatively higher density of chromium-rich carbide precipitate phases, especially Cr3C2 and Cr7C3. Scanning electron microscopic (SEM) analysis of the weld zone for samples welded at 120 J/mm, both AW condition and PWSHT condition, shows the presence of chromium-rich carbide precipitates. However, size and distribution density of the precipitates were found to be relatively more in PWSHT condition. Also, the amount of chromium-rich carbide precipitates in the base metal of PWSHT sample was found to be less than that of the weld zone. The hardness of the weld zone after PWSHT was increased significantly as compared that of the AW counterparts. Hence, it might be possible that cumulative effect of (a) higher number of grain boundaries, (b) increase in hardness, and (c) high density of chromium-rich carbide precipitates, the PWSHT sample of 120 kJ/mm could have resisted the failure at weld zone. Analysis of XRD patterns of the weld zone for different welded samples showed the formation of various stoichiometries of chromium-rich carbide precipitate (i.e., Cr23C6, Cr3C2 and Cr7C3) due to the variation in the heat input and treatment condition. Transmission electron microscopic (TEM) analysis showed the formation of Mo-rich p-type (phase) precipitates in the weld zone of PWSHT sample.

Study the machinability characteristics of Nicked based Hastelloy C-276 under cryogenic cooling

This paper describes the machinability characteristics of turning Hastelloy C-276 with PVD coated nano-multilayer TiAlN cutting tool using dry turning and liquid nitrogen cooling methods. The turning operations were performed at a constant feed rate (0.111 mm/rev); depth of cut (1 mm) and three different cutting velocities (0.72, 1.17 and 1.97 m/s). The effects of liquid nitrogen cooling on cutting zone temperature, force components (Fz & Fx), roughness parameters (Ra, Rz & Rt), chip morphology and tool wear have been compared with those of dry turning. Turning of Hastelloy C-276 with liquid nitrogen cooling, reduction in cutting zone temperature by about 61–68%, the decrease in cutting force components by about 8–33%, and reduction in surface roughness parameters by 8–33% over dry turning were observed. Cryogenic cooling provided reduced serrated tooth formation for chips which was more than what was observed in dry turning. Improvement of cutting tool performance was achieved under liquid nitrogen cooling by control of wear mechanisms which, in turn, reduced the wear rate. The experimental results indicated the provisions of better performance than dry cutting by the machinability characteristics of Hastelloy C-276 under cryogenic cooling.

Comparison of numerical and experimental macrostructure in Nd: YAG laser welding of Hastelloy C-276

In this study, an attempt is made to correlate the macrostructure of Nd: YAG laser butt welded Hastelloy C-276 joints obtained by numerical and experimental methods, and which were performed at varied process parameters viz., welding speed (350 mm/min-450 mm/min), pulse energy (10–14 J/mm) and pulse duration (6–8 ms). The numerical macrostructure of the weld zone is determined in SYSWELD 16 - a 3D finite element software package, while experimentation was performed in a 600 W Nd: YAG laser welding machine. Complete penetration is observed for the attempted conditions, though the morphology of the laser weld differs. The variation in the temperature distribution across the various regions of the weld zone and the hardness distribution is reported.

The microstructures and anti-corrosion behavior of the thermal sprayed Hastelloy C276 coating on substrate of Q235 steel

Hastelloy C276 coating was prepared on the substrate of Q235 steel by arc thermal spraying process. The microstructure, microhardness, thermal shock resistance and anti-corrosion of the coating were investigated. The coating exhibits a layered buildup structure with some pores and unmelted particles appearing. There is a distinct and rough interface between the coating and the substrate which increases the contact area between the coating and the substrate. The coating and the substrate were meshed to each other in the boundary, showing a strong bonding. The coating exhibited a strong thermal shock resistance with the substrate of Q235 steel at 600 °C. The microhardness of the surface of the coating is much higher than the microhardness of the surface of the substrate. Uniform corrosion method of laboratory semi-immersion test was used to test the corrosion resistance of C276 coating. The coating exhibited good corrosion resistance in concentrated HCl with a concentration of 36.5%.

Nox emission of ternary nitrate molten salts in high-temperature heat storage and transfer process

NOx emission from the ternary eutectic molten salt (7 wt%NaNO3-40 wt%NaNO2-53 wt%KNO3, HITEC) has been investigated in thermal energy storage (TES) processes. The effect of different metal and exposure time on NOx emission is evaluated, including Incoloy 625 and Hastelloy C276® of nickel-based alloys, and AISI 310S (310S) and AISI 321 (321) of stainless steels. The mechanism of NOx emissions is analyzed by using thermodynamic calculation, scanning electron microscopy (SEM), energy dispersive X-Ray (EDX), X-ray diffractometer (XRD) and atomic absorption spectrophotometer (AAS). The experimental results indicate that HITEC can release less than 40 mg/m3 of NOx when exposing to In625 or HasC276 alloys below 500 °C, and more than 350 mg/m3 of NOx for 310S and 321 at 500 °C. It is found that oxide film is formed on metals surface for long exposure time in HITEC resulting in the decrease of NOx emission. The calculated Gibbs free energy change reveals that above 500 °C, Cr2O3 protective films on the metals are reduced, which contributes to rapid increase of NO2 and NO emissions. In625 or HasC276 alloys is recommend to be used in pipe line/container, and the NOx emissions of HITEC based TES system can be effectively decreased especially for long-term energy storage.

Optimization of Melt Zone Area for Electron Beam Welded Hastelloy C-276 Sheet and Study of Corrosion Resistance of the Optimized Melt Zone in 3.5 wt% NaCl Aqueous Solution

Hastelloy C-276 superalloy has a wide range of applications including petroleum and petrochemical industries. Since welding forms an essential fabrication method for joining different structures in these industries, selection of suitable welding parameters is a prime concern that is yet to be addressed for Hastelloy C-276. In the present study, optimization of process parameters for electron beam welding of 2.6-mm-thick Hastelloy C-276 sheet has been carried out to obtain weld bead having through-penetration and minimum weld (or melt) zone cross-sectional area. A simple optimization technique is employed in the present study to solve the multi-objective minimization problem. After carrying out the full factorial experiment using selected process parameters, various geometric elements of the weld bead are identified as the output responses. The regression equation is developed for each geometric element from the experimental data. The desired value of a geometric element is specified as a constraint for the corresponding regression equation. A number of regression equations (considering all the geometric elements) are solved in parallel to obtain an optimized set of process parameters, followed by a confirmation test. Further, the optimized melt zone is subjected to cyclic potentiodynamic polarization test to study its susceptibility to localized corrosion. It is observed that polarization curve characteristics of base metal and optimized melt zone are not significantly different; however, the repassivation potential of the melt zone is less than that of the base metal. A flowchart showing the layout of the employed optimization technique followed by corrosion test is attached.

Elemental micro-segregation characteristic of fiber laser welded Hastelloy C-276 sheet

Abstract The elemental micro-segregation characteristic within the weld zone for ytterbium fiber laser welded Hastelloy C-276 sheet was investigated. The analysis of segregation ratio and equilibrium distribution coefficient of elements, determined through EDS data, indicate the reduction in micro-segregation of elements compared with the previous reported literatures for laser welded Hastelloy C-276. High melting efficiency of ytterbium fiber laser, reduction in the amount of linear heat input, and high cooling rate of the mushy zone lead to the reduction in micro-segregation. The melting efficiency of ytterbium fiber laser for welding of Hastelloy C-276 of 64% is higher than that (48%) of conventional welding methods. High melting efficiency leads to the reduction in the linear heat input required for welding. Hence, in the present investigation, the same was found to substantially reduce as compared to the previous reported literature. The cooling rate from liquidus temperature to solidus temperature at the weld centerline was found to be in the order of 103 °C/s. Cellular dendritic substructure that constituted for lower micro-segregation was formed at the weld centerline.

Microstructure and Properties of Nickel - Based Superalloy C-276 Pulse Laser Weld Joints Based on 0.381mm Thickness

Based on Hastelloy C-276 sheet materials, the microstructure, element segregation and mechanical properties of weld joints were studied using pulse laser welding technology. It is noted that there are three morphological grains in the weld zone, which is columnar dendrites, cellular crystals and equiaxed grains, respectively. Compared with the base metal, the microstructure of the weld zone is obviously refined. Element segregation exists in the weld zone where no secondary phases formed. In addition, the microhardness of the weld joints is greater than that of the base metal by 12%. Its yield strength is equivalent to the yield strength of the base metal, and the tensile strength is 93% of that of the base metal. There are plenty of dimples in the fracture of the weld joints and the base metal, and the fracture modes of both are all ductile fracture.

High-temperature corrosion behavior of selected thermally sprayed coatings in corrosive aggressive environment

The aim of this paper is to evaluate and compare the corrosion resistance of Hastelloy C-276 coating with Stellite 6 and Cr3C2%-25% NiCr coatings. The coatings were deposited using HP/HVOF (High Pressure/High Velocity Oxygen Fuel) thermal spraying technology. The corrosion test was conducted in the corrosive-aggressive environment of molten salts mixture in the composition of 40% Na2SO4–60% V2O5, simulating the corrosion environment of boilers for residual fuel oils. The corrosion test under cyclic conditions included 50 cycles at the temperature of 750 °C and subsequent cooling at the room temperature for 20 min. The corroded specimens were analyzed using scanning electron microscope (SEM) and elemental analysis (EDS). In comparison with Cr3C2-25% NiCr coating, both Stellite 6 and Hastelloy C-276 coatings provided the substrate material with sufficient protection against high-temperature corrosion. The corrosion mechanism of Hastelloy C-276 coating was based on the formation of protective oxide layer which prevented further penetration of corrosive media. Stellite 6 coating exhibited the corrosion attack along splat boundaries resulting in spat delaminating into the build-up. The corrosion mechanism of Cr3C2-25% NiCr coating included the attack on NiCr matrix resulting in gradual separation of carbide phases into the corrosive environment.

Cavitation erosion behavior of Hastelloy™ C-276 weld by laser welding

Ni-based Hastelloy C-276 was chosen as the material of the stator and rotor cans of a nuclear main pump for its excellent resistance to corrosive environments and superior mechanical properties. In the present work, the cavitation erosion (CE) behavior of the Hastelloy C-276 thin sheet weld joint was tested. The results indicate that both the CE damages of the weld metal and the base metal initiate at grain boundaries preferentially. The solidification grain boundaries (SGBs) of the weld metal and the twin boundaries (TBs) of the base metal are more susceptible to CE. For the weld metal, due to the microstructure inhomogeneity, regions that show the highest damage intensity are located near the central line of the weld surface where the columnar dendrites interact with the nearly equiaxed dendrites. For the base metal, grains with more TBs are damaged faster compare to other grains. The surface roughness of the eroded surfaces increases with exposure time, and the surface roughness of the base metal increases faster than that of the weld metal. Overall, the resistance to CE of the weld metal is better than that of the base metal.

Degradation of HVOF Sprayed Hastelloy C-276 Local Mechanical Properties after Exposure to High Temperature Corrosion

Hastelloy C-276 coating was deposited on stainless steel 1.4923 using HP/HVOF (High Pressure / High Velocity Oxygen Fuel) thermal spraying technology to increase high corrosion resistance. Possible influence of high temperature corrosion on local mechanical properties change of Hastelloy C-276 was also evaluated in this article. High temperature corrosion is corrosion in the molten salts environment. The salt mixture of 59 % Na2SO4with 34.5 % KCl and 6.5 % NaCl was used in this study. The selected exposure temperatures were 525 °C and 575 °C and the tests for both temperatures were conducted in autoclave for the time interval of 168 h. The coating and salt mixture layer was analyzed using scanning electron microscope (SEM), EDS analysis and nanoindentor (MTS Nanoindenter XP). High temperature resistance of Hastelloy C-276 coating was evaluated based on the changes in coating surface and according to the occurrence of various phases created on the coating surface during this test. It can be assumed that Hastelloy C-276 coating deposited by HVOF technology shows selective oxidation under the salt film.

Minimization of bead geometry by optimization of regression equations for laser-beam bead-on-plate welded Hastelloy C-276 sheet

The present study is aimed at selection of laser beam welding parameters that would produce through-penetrated weld zone with minimum cross-sectional area in 2.7-mm-thick Hastelloy C-276 sheet. Weld zone area was found to be comprised of geometrical features such as total throat, crown width, root width, neck width. A new, fast and relatively simple method of optimization has been proposed in the present study. Regression equation for each geometrical feature was generated from the full factorial experimental design data. Optimization of welding parameters to minimize weld zone area was carried out by solving regression equations using experimentally obtained values of geometrical features as the boundary condition. Once the optimized value of parametric combination was obtained, experiment was conducted to confirm the minimization of weld bead cross-sectional geometry.

Continuous electropolishing technique for long-length Hastelloy C-276 tape

Preparation of the second-generation high-temperature superconducting tape by ion beam-assisted deposition (IBAD) requires a flat metal substrate. In this work, the electrochemical polishing of long-length Hastelloy C-276 alloy was studied, and its process parameters, characterized roughness and other properties were investigated. A 10-meter-long Hastelloy C-276 alloy was prepared by electrochemical polishing. The following optimized processing parameters are obtained: temperature of 45 °C, current density of 0.439 A·cm−2 and polishing time of 60 s. The average roughness value (Ra) of the surface is less than 5 nm (5 μm × 5 μm), which was characterized by atomic force microscopy. This value satisfies the requirements for the further preparation of transition-layer pair by the IBAD technology route.

Relationships Between the Σ9 and Σ27 Boundaries and the Connectivity of Random Boundary in Hastelloy C-276 Alloy

Hastelloy C-276 was subjected to 10% deformation and annealed at 1100 °C for different time. The fractions of Σ3n (n=1, 2, 3) boundaries and the connectivity of random boundary networks were characterized by electron back-scatter diffraction (EBSD). The results show that the Σ3 boundary fraction is hardly increased during the annealing period. Instead, the fractions of Σ9 and Σ27 boundaries have a dramatic change with annealing time, whose peaks are arisen after annealing for 15 min. Meanwhile, the corresponding connectivity of random boundary network is effectively disrupted. This can be attributed to the incoherent Σ3 boundary producing more Σ9 and Σ27 boundaries and incorporating those boundaries into the random boundary networks. Actually, the connectivity of random boundary networks can be definitely identified by Σ(9+27)/Σ3 radio.

Corrosion Behaviour of Hastelloy C22 in Alkali Salt Environment

Chloride-induced corrosion at elevated temperature is the major drawback of commercialization of biomass fired power generation. The incapability of the biomass-fired boilers to increase the temperature has resulted in a lower efficiency of the power plant. Hastelloy C22 is one of the potential materials for superheater due to the high content of Ni-Cr which provides an excellent corrosion resistance. The aim of this work is to obtain more information on corrosion behaviour of Hastelloy C22 at high temperature in alkali salt environment with the influence of air humidity, hence to justify the suitability of this alloy as a superheater material for higher operating temperature. Corrosion tests were performed in the synthetic salt containing 80 wt% KCl and 20 wt% K2SO4 under normal and dry air conditions. The test was conducted at temperature 650°C for 218 hours. The surface morphology, elemental distribution and the corrosion products were characterized using Field Emission Scanning Electron Microscope (FESEM) equipped with Energy Dispersive X-ray (EDX). The phase identification was carried out using X-ray Diffraction (XRD) analysis. The results revealed a significant effect of humidity on the corrosion behaviour of the alloy where the presence of air moisture reduces the protective capability of the chromium oxide (Cr2O3) scale. A formation of unstable chromium (IV) hydroxide as well as the volatilization of Cr2O3 led to the oxide spallation, thus reducing the corrosion resistance of the superalloy.