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用热膨胀法和X射线衍射法研究了60Si2Cr VAT弹簧钢在Q-I-Q-T(Quenching-Isothermal-Quenching-Tempering)新工艺的Q-I阶段,即材料奥氏体化后短时淬火再等温这一过程中的亚稳态残留奥氏体的等温转变动力学。实验表明:随等温温度的升高,残留奥氏体含量先升后降。不同温度短时淬火等温冷却后均得到马氏体、贝氏体和残留奥氏体的复相组织。随等温温度的升高,发生完全转变的时间明显缩短,转变量明显减少,转变孕育期也从280℃的54 s减少到500℃的0.96 s。实验获得的亚稳奥氏体等温阶段的TTT曲线呈近C型特征。从亚稳奥氏体的转变量与等温时间的关系曲线可知曲线分为2个阶段,其中第Ⅰ阶段亚稳奥氏体的转变速率明显大于第Ⅱ阶段的转变速率,其等温转变动力学可以用对数曲线进行描述。
The thermal expansion and X-ray diffraction of 60Si2CrVal spring steel in the QI stage of QIQT (Quenching-Isothermal-Quenching-Tempering) new process, that is, the metastable Isothermal transformation kinetics of residual austenite. Experiments show that: with the increase of isothermal temperature, the content of retained austenite increases first and then decreases. Different temperature quenching after isothermal cooling are martensite, bainite and retained austenite complex phase organization. With the increase of isothermal temperature, the time of complete transformation obviously shortened and the amount of transformation significantly decreased. The transformation incubation period also decreased from 54 s at 280 ℃ to 0.96 s at 500 ℃. The TTT curve of the isothermal phase of metastable austenite obtained in experiment is near C type. According to the curve of metastable austenite transformation volume and isothermal time, the curve can be divided into two stages, of which the transformation rate of metastable austenite in stage Ⅰ is obviously higher than that of stage Ⅱ, and the isothermal transformation kinetics can be Use a logarithmic curve to describe it.