| 摘 要： | 4. Pro—eutectoid reactions In a steel not of eutectoid,composition the transformation at temperatures above about 550℃begins with the separation of pro—eutectoid ferrite or cementite, usually at the austenitic grainboundaries. The composition of the separating structure is now different from that of the parentaustenite so that[1]long—range migration of carbon is necessary to change the composition in thetwo regions of the decomposing grain. If the grain size is large the central region of a grain is so
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