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| PROCESS OF CARBIDE PORMATION DURING AUSTENITEPEARLITE TRANSFORMATION IN CHROMIUM STEELS |
| CHANG PEI-LIN;LIANG TZE-TEH Institute of Metal Research; Academia Sinica North-East Engineering College |
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Cite this article:
CHANG PEI-LIN;LIANG TZE-TEH Institute of Metal Research; Academia Sinica North-East Engineering College. PROCESS OF CARBIDE PORMATION DURING AUSTENITEPEARLITE TRANSFORMATION IN CHROMIUM STEELS. Acta Metall Sin, 1957, 2(4): 367-375.
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Abstract The process of carbide formation during isothermal decomposition of austeniteinto pearlite in four chromium steels has been investigated by X-ray method. Theexperimental results are analysed and compared with results obtained by otherauthors on chromium steels of various compositions, and unified conclusions aredrawn. 1) Depending upon the composition of steels, the initial carbide formed duringisothermal formation of pearlite may be cementite, (Cr, Fe)_7C_3 or (Cr, Fe)_(23)C_6.That is, special carbides can be formed directly from austenite, and they are notalways products of secondary process as some authors believe. 2) Type of carbides to be formed directly from austenite is not determined bythe requirements of equilibrium diagram, but depends upon Cr: C ratio in austenite.When the atom ratio Cr: C is smaller than 2, the initial carbide is cementite; whenthe ratio lies between 2 and 13, the initial carbide is (Cr, Fe)_7C_3; when the ratiois larger than 13, it is (Cr, Fe)_(23)C_6. It seems that the Cr:C ratio in austenite hasdecided influence on the kinetics of nucleation of different carbides. 3) When the type of carbides formed directly from austenite is not that re-quired by the equilibrium diagram, carbide transformation takes place as a secondaryprocess. 4) When the directly formed carbide is an alloy carbide, i. e. (Cr, Fe)_7C_3 or(Cr, Fe)_23C_6, diffusion of chromium in austenite immediately in front of the growingnodules of pearlite is a necessary process during transformation.
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Received: 18 April 1957
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