Journal of the Korean Society for Heat Treatment (열처리공학회지)

The Korean Society for Heat Treatment (한국열처리공학회)
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Phase Changes during High Temperature Gas Nitriding of Nb Alloyed STS 444 Ferritic Stainless steel

Nb이 첨가된 STS 444 페라이트계 스테인리스강의 고온질화 열처리시 조직변화

  • Kong, J.H. (Department of Materials Science and Engineering, Dong-A University) ;
  • Yoo, D.K. (Steel Making Department, Hyundai Steel Company) ;
  • Lee, H.W. (Department of Materials Science and Engineering, Dong-A University) ;
  • Kim, Y.H. (Department of Materials Science and Engineering, Dong-A University) ;
  • Sung, J.H. (Department of Materials Science and Engineering, Dong-A University)
  • Published : 2007.11.30
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Abstract

This study has been investigated the effect of high temperature gas nitriding (HTGN) heat treatment of STS 444 (18Cr-0.01Ni-0.01C-0.2Nb) ferritic stainless steel in an atmosphere of nitrogen gas at the temperature range between $1050^{\circ}C\;and\;1150^{\circ}C$. The surface layer was changed into martensite and austenite with the nitrides of NbCrN by HTGN treatment. Due to the precipitation of nitrides and matrensite formation, the hardness of the surface layer showed $400Hv{\sim}530Hv$. The nitrogen concentration of the surface layer appeared as 0.05%, 0.12% and 0.92%, respectively, at $1050^{\circ}C,\;1100^{\circ}C\;and\;1150^{\circ}C$. When the nitrogen is permeated from surface to interior, Nb and Cr, which have strong affinities with nitrogen, also move from interior to surface. Therefore it is considered that this counter-current of atoms promotes the formation of NbCrN at the surface layer.

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References

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