在珠光体转变的温度范围内,除下珠光体区域的停留促进上珠光体区的形核过程外,奥氏体在非连续冷却时,转变的形核过程具有相加性。在下珠光体区的形核过程中,可能先形成与奥氏体共格的核胚。 在贝菌体转变的温度范围内,较高温度的停留延缓较低温度时的形核过程,延缓作用随温度间隔及停留时间的增加而增大。较低温度的停留促进较高温度时的形核过程,促进作用随温度间隔的增加而增大,但随时间的延长而减小。建议贝茵体的核胚和马氏体的相同,即位错圈所包围的体心立方结构区域。 下珠光体区停留促进贝茵体的形核过程。
The nucleation process in the pearlite range is additive, except that holding in thelower pearlite range it tends to accelerate subsequent reaction at high temperature. Inthe bainite range, holding at a high temperature retards subsequent nucleation at a lowtemperature, while holding at a low temperature appears to accelerate subsequent nuclea-tion at a high temperature. The deviation from additivity depends upon difference be-tween the temperatures involved and the holding duration. It is suggested that the embryo of bainite is the same as that of martensite, i. e., ab. c. c. region surrounded by a dislocation loop. Holding in the lower pearlite range accelerates subsequent transformation to bainite.
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