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Effects of welding and post-weld heat treatments on nanoscale precipitation and mechanical properties of an ultra-high strength steel hardened by NiAl and Cu nanoparticles

Journal Article · · Acta Materialia

The effects of welding and post-weld heat treatment (PWHT) on nanoscale co-precipitation, grain structure, and mechanical properties of an ultra-high strength steel were studied through a combination of atom probe tomography (APT) and mechanical tests. Our results indicate that the welding process dissolves all pre-existing nanoparticles and causes grain coarsening in the fusion zone, resulting in a soft and ductile weld without any cracks in the as-welded condition. A 550 °C PWHT induces fine-scale re-precipitation of NiAl and Cu co-precipitates with high number densities and ultra-fine sizes, leading to a large recovery of strength but a loss of ductility with intergranular failure, whereas a 600 °C PWHT gives rise to coarse-scale re-precipitation of nanoparticles together with the formation of a small amount of reverted austenite, resulting in a great recovery in both strength and ductility. Our analysis indicates that the degree of strength recovery is dependent mainly upon the re-precipitation microstructure of nanoparticles, together with grain size and reversion of austenite, while the ductility recovery is sensitive to the grain-boundary structure. In conclusion, APT reveals that the grain-boundary segregation of Mn and P may be the main reason for the 550 °C embrittlement, and the enhanced ductility at 600 °C is ascribed to a possible reduction of the segregation and reversion of austenite.

Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
Sponsoring Organization:
USDOE Office of Science (SC)
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
1324206
Journal Information:
Acta Materialia, Journal Name: Acta Materialia Journal Issue: C Vol. 120; ISSN 1359-6454
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

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