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Phase Changes during High Temperature Gas Nitriding of Nb Alloyed STS 444 Ferritic Stainless steel  

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)
Publication Information
Journal of the Korean Society for Heat Treatment / v.20, no.6, 2007 , pp. 323-328 More about this Journal
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.
Keywords
High temperature gas nitriding; Ferritic stainless steel; NbCrN; Nitride;
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Times Cited By KSCI : 1  (Citation Analysis)
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