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Effect of Interstitial Elements on the Weldability of Ni-base Alloys

Aguilar, Louie
http://orcid.org/0000-0002-3104-1556
http://rave.ohiolink.edu/etdc/view?acc_num=osu1563367451520424

Abstract Details

2019, Master of Science, Ohio State University, 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 range (STR). This correlates to the decrease in solidification cracking resistance with N additions seen in this filler metal. For FMs 52M and 52MSS-C, it is shown that the lower Ti mitigates the detrimental effects of N additions on solidification cracking resistance as seen in FM 82. In addition, the higher Cr content in FMs 52M and 52MSS-C plays a significant role in promoting the inherent lower cracking resistance as compared to FM 82. The (Ti,Nb)(C,N) composition in FMs 52M and 52MSS-C appears to contain very little C, indicating a change in C solubility in the mixed carbonitrides as N content is increased. Hence, C is available in the liquid phase to allow for the NbC/γ eutectic phase to form at higher temperatures from low N content at 1224 °C to 1300 °C at higher N content. This would lead to a decrease in the amount of liquid at the end of solidification and the effective solidification temperature range. The higher Cr content in FMs 52M and 52MSS-C increases the solubility of N in the liquid phase, while the lower Ti content directly limits the formation of carbonitrides. Ideally, having both lower Ti and Cr would act to mitigate the tie-up of C from the liquid phase during solidification, even upon increasing N content.
Carolin Fink (Advisor)
126 p.
Engineering; Metallurgy
Nickel Alloys; Solidification Cracking; Filler Metal 52M; Filler Metal 52MSS-C; Cast Pin Tear Test

Recommended Citations

Citations

  • Aguilar, L. (2019). Effect of Interstitial Elements on the Weldability of Ni-base Alloys [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1563367451520424

    APA Style (7th edition)

  • Aguilar, Louie. Effect of Interstitial Elements on the Weldability of Ni-base Alloys. 2019. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1563367451520424.

    MLA Style (8th edition)

  • Aguilar, Louie. "Effect of Interstitial Elements on the Weldability of Ni-base Alloys." Master's thesis, Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1563367451520424

    Chicago Manual of Style (17th edition)

osu1563367451520424
291
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This open access ETD is published by The Ohio State University and OhioLINK.