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| STRENGTHENING MECHANISM IN NITRIDED 18Cr2Ni4WA STEEL |
| ZHENG Jinghong;WANG Yufeng;SHEN Fufa;YU Degang Shanghai Jiaotong University;MAO Shukai China Mining Institute |
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Cite this article:
ZHENG Jinghong;WANG Yufeng;SHEN Fufa;YU Degang Shanghai Jiaotong University;MAO Shukai China Mining Institute. STRENGTHENING MECHANISM IN NITRIDED 18Cr2Ni4WA STEEL. Acta Metall Sin, 1985, 21(5): 5-12.
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Abstract The microstructure and strengthening behaviour of the internal nitrided layerin 18Cr2Ni4WA steel after one-and two-step nitriding at various temperatureshave been studied by observation under TEM.Results showed that the formationof the internal nitrided layer proceeds as two stages:(1)a mixed clustering-order-ing zone of alloying elements and nitrogen atoms is formed on{100}_α basal planeof matrix;(2)the clustering zone transforms into equilibrium precipitate CrN.Theorientation relationship between the precipitate and parent phase accords withBaker-Nutting relation,i.e.,(001)_(CrN)∥(001)_α;[110]_(CrN)∥[100]_α.The CrN may alsobe formed from alloyed carbide at lower nitriding temperatures.The main causefor the very high hardness of internal nitrided layer is considered to be the for-mation of such mixed clustering-ordering zones within ferritic matrix.For one-step nitriding,the hardness of internal nitrided layer achieved maximum value at420—500℃ and decreased as the increase of nitriding temperature.For two-stepnitriding,owing to the mixed clustering-ordering zone which first formed at lowertemperature is remarkably stable,the nitrided layer remains its higher hardness tillhigh temperatures.Therfore,the two-step nitriding may provide a way to accele-rate the nitriding process and to shorten the nitriding time,but the hardness ofinternal nitriding layer keeps in high extent.
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Received: 18 May 1985
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1 Phillips,V.A.;Seybolt,A.U.,Trans.Metall.Soc.AIME.,242(1968) ,2415．
2 Pope,M.;Grieveson,P.;Jack,K.H.,Scand.J.Metall.,2(1973) ,29．
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4 Jack,K.H.,Heat Treatment '73,The Metals Society,London,1973,p.39．
5 Hirsch,M.A.;Howie,B.Sc.;Nicholson,M.A.;Pashley,B.Sc.;Whelan,M.A.,Electron Microscopy of Thin Crystals,Robert E.Krieger Publ.Comp.,Huntington,1977,p.320．
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