Boride formation induced by pcBN tool wear in friction-stir-welded stainless steels

Seung Hwan C. Park, Yutaka S. Sato, Hiroyuki Kokawa, Kazutaka Okamoto, Satoshi Hirano, Masahisa Inagaki

Research output: Contribution to journalArticlepeer-review

70 Citations (Scopus)


The wear of polycrystalline cubic boron nitride (pcBN) tool and its effect on second phase formation were investigated in stainless steel friction-stir (FS) welds. The nitrogen content and the flow stress were analyzed in these welds to examine pcBN tool wear. The nitrogen content in stir zone (SZ) was found to be higher in the austenitic stainless steel FS welds than in the ferritic and duplex stainless steel welds. The flow stress of austenitic stainless steels was almost 1.5 times larger than that of ferritic and duplex stainless steels. These results suggest that the higher flow stress causes the severe tool wear in austenitic stainless steels, which results in greater nitrogen pickup in austenitic stainless steel FS welds. From the microstructural observation, a possibility was suggested that Cr-rich borides with a crystallographic structure of Cr2B and Cr5 B3 formed through the reaction between the increased boron and nitrogen and the matrix during FS welding (FSW).

Original languageEnglish
Pages (from-to)625-636
Number of pages12
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Issue number3
Publication statusPublished - 2009


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