Session: CS-07-04 The Warren H. Bamford Memorial Symposium on Recent Developments in ASME Codes and Standards-4

Paper Number: 155517

155517 - Approach for Qualifying Laser Powder Bed Fusion 316h in Section Iii, Division 5 

Abstract: 

Additive manufacturing techniques, such as laser powder bed fusion (LPBF) have the potential to allow for increased design flexibility through the ability to manufacture complex components. Efforts to include LPBF in Section III, Division 1 for use in light water nuclear reactors are well underway, however, there are a number of challenges with qualifying a new manufacturing technique for use in advanced nuclear reactors, where time dependent properties are critical. The Advanced Materials and Manufacturing Technologies (AMMT) Program, under the United States Department of Energy, Office of Nuclear Energy, is supporting efforts to develop a pathway towards qualifying LPBF 316H stainless steel. As a part of this effort, accelerated qualification strategies are being investigated and incorporated into the framework of the LPBF 316H qualification plan.

Division 5 working groups have identified a lack of relevant high temperature data as one of the primary obstacles towards developing a qualification approach for additively manufactured material. The AMMT Program has started an extensive testing program to provide tensile, fatigue, creep, and creep-fatigue data, which is required not only for the development of a code case, but also necessary for the development of the qualification approach itself. Important issues have been observed and qualification approaches developed to mitigate potential concerns. Methods for accelerating the qualification process, using modern techniques such as machine learning to supplement conventional analysis methods to extrapolate time-dependent material test data, are also being explored in conjunction with the collection of data and development of the qualification plan.

Variations in materials properties have been observed, and the AMMT Program has sought to understand these variations through variables such as the manufacturing equipment, location of manufacturing, processing parameters, specimen geometry, and powder chemistry. Microstructures and defects were characterized through electron and optical microscopy, as well as x-ray computed tomography. These studies provide a technical basis for understanding process-microstructure-property correlations and developing methods and limitations for the qualification approach. In addition to manufacturing parameters, post-build heat treatments were found to have a significant effect on the material performance. Examination and down-selection of heat treatments (as-built, stress-relieved, solution annealed, and hot isostatic pressed) has been a critical goal of the preliminary materials testing program. 

LPBF 316H tensile results have shown that the material has a higher yield strength than wrought 316H, even after being aged up to 10,000 hours. The ultimate tensile strength may fall below the average wrought properties, though it is within the scatter of the wrought data. Higher temperature heat treatments increased the ductility but reduced the strength. Anisotropy (build direction vs. transverse direction) was also found to be reduced with the more aggressive heat treatments. The creep results have shown that LPBF 316H steel has similar rupture times, but lower rupture strains compared to the wrought materials, particularly in the cases of the lower temperature heat treatments. Fatigue results were comparable to conventional fusion-welded 316H properties, although creep-fatigue results show a significant decrease in cyclic life, beyond what was expected based on wrought creep-fatigue design models. In some mechanical properties, batch variation was observed to be more impactful than heat treatment. Additional testing is still needed to qualify the material and manufacturing method.

Presenting Author: Michael McMurtrey Idaho National Laboratory

Presenting Author Biography: Dr. Michael McMurtrey (co-PI) is a staff scientist at INL in the Irradiated Fuels and Materials Department. Dr. McMurtrey is the Advanced Reactor Technologies High Temperature Metals Technical Lead and the Technical Area Lead for Technology Maturation in the AMMT Program. His work in these programs focuses on wrought and additively manufactured steels and nickel alloys, as well as high entropy alloys, for deployment in advanced nuclear reactors. He supports projects on novel methods for manufacturing compact heat exchangers, methods for increased throughput of creep testing, and pathways for qualifying dissimilar alloy welds. Dr. McMurtrey is a subject matter expert on high temperature structural alloys at INL and is a member of four ASME BPVC committees/groups: Allowable Stress Criteria, Creep-Fatigue and Negligible Creep, Division 5 Advanced Manufactured Components, and the Special Committee on Additive Manufacturing for Pressure Retaining Components.

Authors:

Michael McMurtrey Idaho National Laboratory
Caleb Massey Oak Ridge National Laboratory
Mark Messner Argonne National Laboratory
Robin Montoya Los Alamos National Laboratory
Malachi Nelson Idaho National Laboratory
Xuan Zhang Argonne National Laboratory