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Solidification Crack Performance and Optimization of EN82H

Filler metal EN82H, or Filler Metal 82,  is frequently used in the nuclear power industry for dissimilar metal weld groove welds in pressurized water reactor components. Although known to be relatively resistant to solidification cracking, BWXT has been observing such indications in this material during service.  More importantly, it has been observed that the material’s susceptibility to solidification cracking differs greatly from heat-to-heat despite only slight variations in chemical composition. The first phase of this project utilizes the CPTT to verify the solidification cracking thresholds and susceptibility rankings of three heats of EN82H exhibiting either superior or poor cracking behavior obtained in a former study.  Excellent correlation between the two studies shows evidence of reproducibility of the CPTT. Metallurgical characterization, scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) studies show evidence of solidification cracking but no notable feature distinction between “good” and “bad” heats. However, fractographic studies of crack surfaces show interesting distinctions in precipitate morphologies between opposing performing heats. The differences in precipitate morphologies point towards differing solidification paths of these secondary phases.

There is reason to suspect that nitrogen may be playing a role in the alloy’s susceptibility to solidification cracking. The second phase of this work is comprised of CPTT along with SEM and EDS analyses showing the differences between altering amounts of nitrogen additions in the gas mixture during welding. If solidification disparities can be resolved and verified, the cracking responses of a well-performing and poor-performing heat can be better understood. Lastly, computational thermodynamic software, ThermoCalc™, will be utilized in conjunction with standard composition ranges and actual bulk chemical compositions to determine solidification temperature ranges and terminal phase formation of the subject material. Using the correlation of solidification behaviors of each heat between computational and microscopy techniques, an optimized bulk chemistry “window” within the MIL-EN82H/ERNiCr-3 specification range will be resolved.

 

Industry Sponsor: BWX Technologies Inc

Faculty: John Lippold (OSU)

Graduate Student: Michael Orr

Industry Contact: Frank Argentine