STRENGTHENING MECHANISM IN NITRIDED 18Cr2Ni4WA STEEL
ZHENG Jinghong;WANG Yufeng;SHEN Fufa;YU Degang Shanghai Jiaotong University;MAO Shukai China Mining Institute
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.
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.