Metallurgical and Materials Transactions A

, Volume 40, Issue 3, pp 625–636 | Cite as

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
Article

Abstract

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 Cr5B3 formed through the reaction between the increased boron and nitrogen and the matrix during FS welding (FSW).

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Copyright information

© The Minerals, Metals & Materials Society and ASM International 2009

Authors and Affiliations

  • Seung Hwan C. Park
    • 1
    • 2
  • Yutaka S. Sato
    • 1
  • Hiroyuki Kokawa
    • 1
  • Kazutaka Okamoto
    • 2
  • Satoshi Hirano
    • 2
  • Masahisa Inagaki
    • 2
  1. 1.Department of Materials Processing, Graduate School of EngineeringTohoku UniversitySendaiJapan
  2. 2.Hitachi Research LaboratoryHitachi Ltd.HitachiJapan

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