使用微机控制相变内耗仪测量了18CrNiWA钢连续冷却和等温淬火过程中的内耗.连续冷却测量表明,在400—430℃和320℃(M_s点附近)各出现一个内耗峰.试样经湿氢脱碳后内耗峰移向600℃。它们的峰温与频率无关,而峰高均随频率的降低而升高。等温淬火测量表明,无论试样脱碳与否,初期的内耗值总是最高,随着时间的延长逐渐降到背景值。实验结果显示,贝氏体与马氏体相变内耗峰有相同的频率效应;在贝氏体孕育期内存在预相变的实质是贝氏体自身的形核,而与碳的扩散与否无关,孕育期的最初阶段贝氏体即开始大量形核,通常测到过冷奥氏体的孕育期长短只不过是在特定实验条件下贝氏体长大到可以被察觉的时间。
By using of a new type low frequency internal friction instrument controlled through a microcomputer, the change in internal friction during the course of phase transformation under continuous cooling and isothermal holding in 18CrNiWA steel is measured. Under continuous cooling, two internal friction peaks are observed around 400—430 and 320℃ (M_s) respectively. In the specimen after decarbonized with wet-hydrogen, the peak temperature changes to 600℃. The peak temperature is independent with frequency and its height increases with the decrease of frequency. Under isothermal holding the value of internal friction is always the highest at the beginning of holding and gradually decreases to a base-value with holding time in specimen whether it is decarbonized or not. Experimental results shows that the effect of frequency on the internal friction peak in bainite transformation is the same as that in martensitic transformation; within the incubation period the prebainitic transformation occurs basically with the nucleation process rather than with the diffusion of carbon; and in the initial stage of the incubation period, there exists a great number of bainitic nucleus, so the incubation period usually measured in supercooled austenite only is the time at which the grown up bainite can be observed under a specified experimental conditions.
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