Master of Science, The Ohio State University, 2016, Welding Engineering

Pipes of solid solution strengthened Ni-based alloys, as Alloy 826 and Alloy 800H, have been used for high temperature service in once through steam generators (OSTGs) on off-shore platforms. The oil and gas industry is seeking to increase service temperature, improve service reliability, and extend service life to 40 years of such installations. Alloy 230 has better-high temperature stability and mechanical properties, and higher service temperature than Alloys 825 and 800H, and is therefore considered as a potential replacement of these alloys in newly built OTSGs. However, the weldability and the high temperature service behavior in welds of Alloy 230 have not been thoroughly investigated yet. This study is a comprehensive comparative research focused on susceptibility to solidification cracking and stress relief cracking in Alloys 800H, 825, and 230. To evaluate the solidification behavior and solidification cracking susceptibility in these alloys, the Cast Pin Tear Test (CPTT), thermodynamic simulations with Thermo-Calc, and the technique of Single-Sensor Differential Analysis (SS-DTA) were used. The results revealed that Alloy 230 and Alloy 825 were more resistant to solidification cracking than Alloy 800H, due to narrower solidification temperature range and crack back filling with eutectic constituents. The OSU Stress Relief Cracking (SRC) Test was applied to evaluate the susceptibility to stress relief cracking in autogenous gas tungsten arc welds of the investigated alloys. None of the three alloys failed by stress relief cracking mechanism while loaded at stress equal to 90% of the high temperature yield strength at 650 oC for 8 hours.. Alloys 825 and 800H showed significant amount of stress relief, while Alloy 230 sustained the applied load at 650C with almost no stress relief. Tensile testing at 650 oC after the 8 hours SRC test showed that the autogenous weld in Alloy 230 had significantly higher yield and tensile strength and slightly lower el (open full item for complete abstract)

Committee: Boian Alexandrov (Advisor); Avraham Benatar (Advisor) Subjects: Materials Science; Metallurgy

Doctor of Philosophy, The Ohio State University, 2016, Welding Engineering

Wide-spread implementation of 7xxx series aluminum alloys (AAs) in the mass production of automotive vehicles can have a broad impact on vehicle structural light-weighting and fuel efficiency improvement, while maintaining or improving structural integrity. However, there are two significant technical barriers that limit the implementation of fusion welded 7xxx series AAs, which are solidification cracking and stress corrosion cracking (SCC). The present research addresses both technical barriers through a combination of experimental testing, microstructure characterization, and computational thermodynamics simulation. First, with respect to AA 7003 base metal (BM) welded with AA 5356 filler metal (FM), cracking of the weld joint was exhibited during testing in a saline fog, where fractography confirmed the cracking type as SCC. The present research established a mechanistic understanding of the aggravated and accelerated SCC that occurs in fusion welded 7xxx series AAs, when compared to un-welded parent material. Second, a preliminary investigation into a novel solution for solidification cracking was conducted for Cu-rich AA 7075 BM. A novel discovery in the present research is the phenomenon of a fused-overlap zone (FOZ) existing as a fusion zone layer that overlaps and fuses to the BM. FOZ may, and typically does, become enriched with solute elements that are constituents of the BM and/or FM. Moreover, large precipitates form in the solute-enriched FOZ. For instance, for AA 7003 BM welded with AA 5356 FM, a transmission electron microscopy (TEM) investigation identified the FOZ enriched with Mg and Zn and the precipitates there as T phase [(Al, Zn)49Mg32]. The FOZ was found to be a prevalent phenomenon in AA weldments, occurring regardless of joint geometry, welding heat input, welding process, or BM and FM investigated in the present research. The corrosion response of the FOZ was dependent on BM and FM compositions, which was likely a result of different (open full item for complete abstract)

Committee: Wei Zhang (Advisor); Antonio Ramirez (Committee Member); David Phillips (Committee Member); Arthur Burghes (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2016, Welding Engineering

Many nuclear reactor components previously constructed with Ni-based alloys containing 20 wt% Cr have been found to be susceptible to stress corrosion cracking. The nuclear power industry now uses high chromium (~30wt%) Ni-based filler metals to mitigate stress corrosion cracking. Current alloys are plagued with weldability issues, either solidification cracking or ductility dip cracking (DDC). Solidification cracking is related to solidification temperature range and the DDC is related to the fraction eutectic present in the microstructure. It was determined that an optimal alloy should have a solidification temperature range less than 150°C and at least 2% volume fraction eutectic. Due to the nature of the Nb rich eutectic that forms, it is difficult to avoid both cracking types simultaneously. Through computational modeling, alternative eutectic forming elements, Hf and Ta, have been identified as replacements for Nb in such alloys. Compositions have been optimized through a combination of computational and experimental techniques combined with a design of experiment methodology. Small buttons were melted using commercially pure materials in a copper hearth to obtain the desired compositions. These buttons were then subjected to a gas tungsten arc spot weld. A type C thermocouple was used to acquire the cooling history during the solidification process. The cooling curves were processed using Single Sensor Differential Thermal Analysis to determine the solidification temperature range, and indicator of solidification cracking susceptibility. Metallography was performed to determine the fraction eutectic present, an indicator of DDC resistance. The optimal level of Hf to resist cracking was found to be 0.25 wt%. The optimal level of Ta was found to be 4 wt%. γ/MC type eutectics were found to form first in all Nb, Ta, and Hf-bearing compositions. Depending on Fe and Cr content, γ/Laves eutectic was sometimes found in Nb and Ta-bearing compositions, whil (open full item for complete abstract)

Committee: John Lippold (Advisor); Antonio Ramirez (Advisor); Boian Alexandrov (Committee Member) Subjects: Engineering; Materials Science

Doctor of Philosophy, The Ohio State University, 2009, Welding Engineering

Conventional welding consumables used to join stainless steels are alloyed with Cr to produce welds with adequate corrosion resistance by promoting a passive oxide surface layer. Vaporization of Cr results in the formation of hexavalent chromium compounds in stainless steel welding fume. Government regulations in the United States and abroad are decreasing allowable exposure levels of hexavalent chromium to welding related personnel. A 2006 OSHA ruling reduced the permissible exposure limit of airborne hexavalent chromium from 52 to 5 micrograms/cubic meter. Achieving the new level may not be practical from an engineering controls standpoint during the fabrication of tightly enclosed stainless steel components. One method of addressing this problem is to implement a chromium-free welding consumable that provides equivalent mechanical performance and corrosion characteristics to current stainless steel welding consumables. This project was aimed at developing such a consumable and evaluating its suitability for replacement of current stainless steel consumables such as E308L-16. A new shielded metal arc welding consumable based on the Ni-Cu-Ru system was developed for austenitic stainless steel welding. Mechanical properties of welds deposited with the new consumable were found to exceed minimum values of Type 304 stainless steel based on tensile testing. Hot ductility testing revealed a narrow crack susceptible region (33 to 54°C) indicating a low susceptibility to weld metal liquation cracking. A low ductility region was found at intermediate temperatures in the range of 800 to 1100°C. This ductility trough is believed to result in the weld cracking phenomenon known as ductility dip cracking (DDC). Threshold strain levels to initiate DDC were approximately 2 to 3% as determined by strain-to-fracture testing. Varestraint testing revealed that weld deposits have a higher solidification cracking susceptibility than stainless steel consumables used to join Type 304. Th (open full item for complete abstract)

Committee: John C. Lippold (Advisor); Gerald S. Frankel (Committee Member); S. Suresh Babu (Committee Member) Subjects: Engineering; Metallurgy

Doctor of Philosophy, The Ohio State University, 2008, Welding Engineering

The use of nickel-base alloys has increased in recent years as the demand for high-temperature corrosion resistant alloys increases. However, the introduction of new alloys can present challenges in materials joining. During fabrication involving welding, both solidification cracking and ductility-dip cracking (DDC) cracking may occur in these alloys if proper precautions are not followed. One such nickel-base alloy is Alloy C-22, which has limited weldability data to date. Alloy C-22 is one of the most corrosion resistant Ni-Cr-Mo alloys available today, and is particularly versatile. As a result, Alloy C-22 is being considered for use in the construction of storage canisters for permanent disposal of radioactive waste in the Yucca Mountain Project. However, in such a critical application, weld related defects (such as these two forms of cracking) are simply unacceptable. This investigation examined the solidification cracking and ductility-dip cracking susceptibility of Alloy C-22 in two phases. The first phase or the investigation determined the baseline susceptibility of two commercial heats of Alloy C-22 to these two forms of weld cracking. Solidification cracking was evaluated using the transvarestraint test, and ductility-dip cracking was evaluated using the strain-to-fracture and hot-ductility tests. The alloy was found to be highly resistant to solidification cracking, yet susceptible to ductility-dip cracking in the strain-to-fracture test. However, it is noted that Alloy C-22 has not been found to be susceptible to ductility-dip cracking within industry. The second phase of the investigation examined the effects of compositional variation (specifically the variation of Mo, W, and Fe) on solidification cracking and ductility-dip cracking. This was accomplished using a combination of thermodynamic simulations and button melting experiments. The button melting experiments were coupled with a new version of differential thermal analysis known as single-sensor (open full item for complete abstract)

Committee: John Lippold (Advisor) Subjects:

Master of Science, The Ohio State University, 2013, Welding Engineering

High-Cr Ni-base alloys have been used in the nuclear industry for weld overlay repair of dissimilar metal welds which have been affected by primary water stress corrosion cracking. During welding, defects may result from super-solidus and sub-solidus cracking phenomena. The ability to evaluate and quantify the degree to which a given alloy is susceptible to each cracking mechanism is of great importance in alloy selection, alloy development and weld design. The first aim of this project was to improve the reliability of the cast pin tear test (CPTT) as a tool for evaluation of solidification cracking susceptibility. The second aim was to evaluate the weldability of a new heat of Inconel alloy 52MSS (ERNiCrFe-13) with reduced iron content as well as a single heat of Kobelco 690NB (ERNiCrFe-7A) comparing these materials with other available alloys of the same type. The incorporation of levitation melting has enabled precise control of the casting process in the CPTT. Active temperature monitoring during melting enables control of the casting temperature with a standard deviation of 8.8 C. Gradual reduction in the power applied to the coil has enabled focused transfer of the charge into the mold. Thermocouple measurements indicated that the cooling rate during solidification in the CPTT was approximately twice that which is experienced in GTAW welding using parameters typical for use in weld overlay repairs. Finite element simulations indicated that a significant reduction in cooling rate of the casting could be obtained by altering the mold material, mold outer diameter or cast pin diameter. Prototype mold screening tests enabled design of a mold that provides a cooling rate of 160 C/s based on FEA modeling, compared with the previous cooling rate of 245 C/s, while maintaining feasibility of the CPTT. A longer pin length is required to cause cracking with the redesigned molds when compared with the previous molds. Also, significant crack healing wi (open full item for complete abstract)

Committee: Boian Alexandrov (Committee Member); John Lippold (Advisor); Suresh Babu (Committee Member) Subjects: Materials Science; Metallurgy

Master of Science, The Ohio State University, 2019, Welding Engineering

Ni-base alloys are widely implemented in the power generation industry for their corrosion resistant properties and high temperature strength. The weldability of Ni-base filler metals (FM) has been shown to be affected by variations in composition. With regards to solidification cracking, the effect of interstitial elements such as carbon (C) and nitrogen (N) along with nitride and carbide forming elements (Ti,Nb) is not well understood. The overall objective of this study was to achieve a better understanding of the single and interactive effects of these elements on solidification cracking in high Chromium Ni-base filler metals. Previous work showed that N additions have a detrimental effect on the solidification cracking resistance of mid-Chromium FM 82. This work analyzed the cracking response of higher Chromium Ni-base FMs 52M and 52MSS-C as a function of increasing N content. Low, medium and high levels of N weld metal content were established in arc-melted buttons to conduct weldability testing using the cast pin tear test (CPTT). Extensive solidification modeling and design of experiment (DoE) aimed to understand the single and interactive effects of different elements (N, C, Nb, Ti, Cr) on solidification behavior and cracking resistance in mid- and high Chromium Ni-base filler metals. Different criteria were explored that could be used to accurately reflect the cracking response in the CPTT as a function of weld metal N content. Results show that N additions do not have a detrimental effect on solidification cracking resistance in FMs 52M and 52MSS-C. The lower cracking threshold in the CPTT decreased by only one pin length upon increasing N content. For FM 82, Scheil solidification modeling indicated that the formation of mixed (Ti,Nb)(C,N) carbonitrides leads to a decrease in the NbC/γ eutectic start temperature by approximately 100 °C with more liquid available at the end of solidification and an increase in the effective solidification temperature ra (open full item for complete abstract)

Committee: Carolin Fink (Advisor) Subjects: Engineering; Metallurgy

Doctor of Philosophy, The Ohio State University, 2018, Welding Engineering

This research seeks to understand eutectic backfilling and its utilization as a technique to combat solidification cracking in Ni-30Cr weld metal as function of Nb and Mo content. Initial research has suggested that levels of Nb greater than 4 wt.% in alloy 690 may increase the volume fraction eutectic enough to reduce solidification cracking susceptibility via a eutectic backfilling or crack healing mechanism. Mo additions appear to produce no substantial change in fraction eutectic but still result in a significant decrease in cracking susceptibility in some instances. Since Mo additions don't remarkably change the fraction eutectic, it is possible that the Mo may increase the “wettability” of this eutectic liquid, relative to the Nb-rich eutectic, with respect to grain boundaries, allowing it to backfill more quickly or efficiently. A reduction in cracking susceptibility would thereby result from the ability of a eutectic liquid to more completely backfill and heal cracks. Gleeble reheat tests produced qualitative confirmation that eutectic wettability at grain boundaries changed between the Nb- and NbMo- bearing alloys. Weldability test variations of the varestraint and strain-to-fracture tests have provided quantitative evidence of varied grain boundary wettability among varied eutectic compositions. Additional investigations suggest that interstitial nitrogen additions play a role in backfilling and that grain boundary orientations may produce slight preferences regarding boundaries that exhibit backfilling relative to those that do not. The objective of this study is to explore backfilling tendencies as a function of composition, specifically concentrating on the grain boundary wettability aspect. Gaining a fundamental understanding of the effect of Mo on grain boundary wetting of the Nb-rich eutectic liquid will impact a number of industries that rely on Ni-base filler metals, including power generation and petrochemical. Applying these princip (open full item for complete abstract)

Committee: John Lippold (Advisor) Subjects: Engineering; Metallurgy

Master of Science, The Ohio State University, 2017, Welding Engineering

Fusion welding is one of the joining processes industries prefer to use in order to produce high quality and safe joints for a desired manufactured product to meet customer needs. Unfortunately, sometimes fusion welding process is not applicable for some of the high strength materials and applying this type of join processes can lead to a solidification cracking due to material wide solidification temperature range. This issue pushes the designers to use different types of joining processes instead of fusion welding such as riveting or screws, which can be alternative solution for fusion welding. Using these processes instead of fusion welding can bring up even more problems for the joint such as material loss, increasing weight, corrosion, and high stress concentration. Therefore, improving the fusion welding process on one of the high strength and solidification crack susceptibility materials, like aluminum alloy 2024, will be the main goal of this study. Al alloy 2024 will be fusion welded autogenously, and material's solidification crack behavior and microstructure will be investigated in this work by four different GTAW processes and they will be compared with a new weld technique never used before this study called; tandem GTAW side by side process with alternating working electrodes.

Committee: Avraham Benatar (Advisor); David Phillips (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Materials Science; Metallurgy

Master of Science, The Ohio State University, 2016, Welding Engineering

High manganese steels are potential candidates for use in cryogenic applications as they exhibit desirable low temperature properties and are a cost-effective alternative to high-Ni steels (i.e. 9%Ni steel, Type 304L) and Invar alloys. Their cryogenic properties are derived from the austenite stabilizing ability of manganese. A potential use for these steels is in the fabrication of liquefied natural gas (LNG) storage tanks. The demand for natural gas is expected to increase 65% by the year 2040 and thus the need for cost-effective materials to replace conventionally used high-Ni alloys during construction of storage and transportation tanks is relevant. When fabricating these LNG tanks, welding is a critical procedure and thus the weldability of these high manganese steels must be evaluated. In this study, the effect of tungsten (W) and boron (B) additions on the microstructure and solidification cracking susceptibility of Fe-Mn-C filler metals was evaluated. Five compositions with tungsten additions up to 4.7 wt% and boron additions up to 27 ppm have been evaluated. Susceptibility to solidification cracking of these filler metals was determined using the Cast Pin Tear Test (CPTT). Solidification simulations were conducted using the Scheil approximation within Thermo-Calc™ and actual solidification temperature range measurements were conducted using the Single-Sensor Differential Thermal Analysis (SS-DTA™) technique. Metallurgical characterization was carried out using both optical microscopy, and scanning electron microscopy. The objective of this study was to determine the optimum range of tungsten and boron additions within the compositional range of interest that provides adequate resistance to weld solidification cracking. Results from Scheil simulations indicated only slight variations in the solidification temperature range (STR) among the alloys tested. The simulations showed that W additions lowered the liquidus temperature and subsequently the STR w (open full item for complete abstract)

Committee: John Lippold (Advisor); Antonio Ramirez (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

Master of Science, The Ohio State University, 2016, Welding Engineering

The main objective of this research is to investigate and eventually optimize the solidification cracking resistance of filler metal ERNiCr-3 (FM 82) in thick-section, highly-restrained, hot wire automatic gas tungsten-arc welding (AGTAW-HW) weld deposits used on reactor vessels in the nuclear energy industry. This investigation was achieved with experimental verification of cracking responses of three FM 82 heats using the Cast Pin Tear Test (CPTT), metallurgical/chemical analysis of each heat, and computational analysis. An intentional nitrogen addition study was conducted to observe the effect of increased weld metal N on solidification cracking susceptibility of FM 82. Experimentally, results were considered using the CPTT with varying heats of ERNiCr-3 exhibiting either superior or poor solidification cracking resistance behavior. A verification study was implemented using the CPTT and its designated procedure with three heats of FM 82 that were previously tested. Excellent correlation results showed accuracy and repeatability of the CPTT process. Quantitatively, zero-pin deviations were found at the lower cracking threshold (LCT) of each heat. The LCT is designated as the highest pin length to exhibit 0% and is the main ranking criterion of solidification cracking susceptibility. Qualitatively, the results proved to verify the same ranking of solidification cracking susceptibility as the previous study—this ranking also mimics what is observed in production mockups. Scanning electron microscope (SEM) imaging of fracture surfaces exhibited classic solidification fracture morphology to ensure failure mode. Additional work was completed using the CPTT for two dilution studies (10wt% and 25wt %) of a “resistant” heat by a “susceptible” heat. It was observed that 10% dilution of Heat B by Heat A reduced the LCT by one pin-length, whereas 25% dilution reduced it by three pin-lengths. Furthermore, computational thermodynamic software, Thermo-CalcTM, was utiliz (open full item for complete abstract)

Committee: John Lippold Dr. (Advisor); Antonio Ramirez Dr. (Committee Member) Subjects: Metallurgy

Master of Science, The Ohio State University, 2016, Welding Engineering

In the oil & gas industry, extraction of oil reserves from pre-salt subsea oil fields requires pipelines and risers to be joined with welds that overmatch the X65 pipe yield strength by 100 MPa, have high toughness, and do not utilize a PWHT. In typical oil extraction, these internally clad pipes are welded with fill passes of Alloy 625 that match the internal clad, however, the strength requirement for reeling is not met with this alloy. To meet the strength requirement, low alloy steel consumables were studied as fill passes to join X65 pipes that are internally clad with Alloy 625 with root passes welded using 625 filler metal. The problem with this metallurgical combination is that solidification cracking can occur in the low alloy steel weld passes that have been diluted by Alloy 625. Computational modeling was performed to screen potential consumables and welding trails were completed for consumables that demonstrated compatibility. Upon establishing welding parameters, bead-on-plate design of experiments were performed with low alloy steel (ER100S-G) welded over two different nickel-based alloys (Alloy 625 and Alloy 686). Buffer layer solutions were also tested using two other Ni-based alloys, UTP A 80 Ni and Alloy 625 LNb, to isolate the root pass material from the fill pass material. Solidification cracking was eliminated in bead-on-plate welds of ER100S-G over Alloy 625 using small weave amplitudes, however, Alloy 686 was determined to have better compatibility with the low alloy steel filler metal to avoid solidification cracking. Welding experiments in a narrow groove were performed for the compatible combination, ER100S-G fill passes over a root pass of Alloy 686, and solidification cracking was eliminated from the fill pass welds. During this study, a defect previously thought to occur only in castings has been identified in welds of low alloy steel filler metals over Ni-based alloy substrates. Referred to in this study as “shrinkage porosity”, (open full item for complete abstract)

Committee: Boian Alexandrov Dr. (Advisor); Avraham Benatar Dr. (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

Master of Science, The Ohio State University, 2015, Materials Science and Engineering

High chromium, nickel-base filler metals have been commonly used throughout the nuclear power industry for the weld overlay repair of dissimilar metal welds (DMW) affected by primary water stress corrosion cracking (PWSCC). These alloys provide optimum resistance to PWSCC in nuclear power plant cooling systems. However some of these nickel alloys present weldability challenges including susceptibility to solidification cracking and ductility dip cracking. There is a current need to incorporate the evaluation of weldability into the alloy development process. The Cast Pin Tear Test may provide a viable means for evaluating alloy susceptibility to solidification cracking in a timely and economical manner. The first objective of this study was to optimize the new generation CPTT procedure in order to improve the reproducibility and reliability of the test. The second objective was to generate solidification cracking susceptibility rankings using the CPTT in a series of high-Cr Ni-base filler metals: ERNiCrFe-7A (52M), ERNiCrFe-13 (52MSS), and ERNiCr-3 (82) filler metals, including two heats of 52M, two heats of 52MSS, and one heat of filler metal 82 and 690Nb. The effect of dilution with cast stainless steel substrate on solidification cracking was then investigated in alloys 52MSS-E and 52i-B at levels of 10% and 40% dilution. An optimized testing procedure was developed for the CPTT. Procedural improvements in mold and sample cleanliness, the purge procedure, and the casting procedure have resulted in improved testing reproducibility. A reproducibility study was conducted on the CPTT using alloy 52M (ERNiCrFe-7A). The new generation CPTT was capable of successfully casting 0.197 inch diameter pins ranging from 0.5-2.5 inches in length and 9.5-17.5 grams in mass. From the reproducibility study low standard deviation at pin lengths by which alloy susceptibility to solidification cracking are ranked (max. pin length with 0% cracking, min. pin length with 100% crack (open full item for complete abstract)

Committee: Boian Alexandrov (Advisor); John Lippold (Advisor) Subjects: Engineering; Materials Science

Master of Science, The Ohio State University, 2013, Welding Engineering

Recent attention has been given to developing austenitic high-Mn steels for cryogenic service conditions. Specifically, the austenite stabilizing capacities of Mn and C are being exploited to create lower cost alternatives to other cryogenic materials (9Ni steel, Invar, 304 SS, etc.) which are commonly used during the construction of liquefied natural gas (LNG) tanks. The proposed steel alloys contain Mn levels in the range of 20 to 28 wt% and C additions on the order of 0.4 wt%. Although austenite stability is beneficial from a low temperature mechanical property standpoint, the presence of such high concentrations of austenite stabilizing elements causes concern with regard to hot cracking during welding. The solidification cracking susceptibility of a wide range of high-Mn steel weld metal compositions was assessed through cast pin tear (CPT) testing. The tested compositions fell within the following ranges (wt%): Mn (14-34), C (0-0.7), and Al (0-3). Impurity elements were also present in the following ranges (wt%): S (0.005-0.011) and P (0.003-0.026). A total of 12 compositions were tested. It was found that C and P controlled the solidification cracking susceptibility of these alloys. In addition to solidification cracking testing, solidification temperature range (STR) analysis was performed on the test matrix using single-sensor differential thermal analysis (SS-DTA) and modified Scheil solidification simulations. STR analysis has previously been related to the weld solidification cracking tendencies of austenitic alloy systems, with large STR values relating to an increased susceptibility to solidification cracking. The measured and calculated STR values in this investigation exhibited a similar relationship. Results indicate that the tested alloys all exhibit primary austenite solidification. It was determined that C and P segregation were primarily responsible for STR expansion. Optical and scanning electron microscopy (OM and SEM) were used (open full item for complete abstract)

Committee: John Lippold (Advisor); Sudarsanam Babu (Committee Member) Subjects: Engineering; Materials Science; Metallurgy