Q&P钢在冷却过程中铁素体的相变规律

 为了研究冷却过程中Q&P钢(quenching and partition steel)铁素体的相变规律,在热膨胀仪上以846 ℃均热200 s为冷却的初始条件,检测了成分(质量分数)为0.2%C、1.25%Si、2.0%Mn的Q&P钢在不同冷却速率下铁素体的相变热膨胀数据,应用杠杆定律将数据处理为相变规律与温度的关系,通过光学显微镜检测热处理后金相中的铁素体相体积分数和铁素体晶粒尺寸,得出了饱和位置形核条件下铁素体的形核率,基于混合控制模型得出了铁素体相变的相界迁移速率。结合相变开始温度,利用混合控制模型计算了相变结束温度和铁素体晶粒尺寸在相变过程中的演变规律,铁素体晶粒尺寸计算值与实测值吻合程度较高,相变结束温度的计算值与实测值的误差在±15 ℃以内,所获得的铁素体相变规律可以用于控制Q&P钢在冷却过程中的铁素体相变体积分数。

Ferrite transformation law of Q&P steel during cooling process

In order to study the ferrite transformation of Q&P (quenching and partition steel) during cooling,the ferrite phase transformation thermal expansion data of different cooling rates of Q&P steel with chemical composition 0.2%C,1.25%Si,2.0%Mn was measured on the thermal dilatometer. The soaking hot treatment process was 846 ℃ soaking for 200 s. The thermal expansion data were treated as the relationship between the phase volume fraction and temperature by lever law. The ferrite phase volume fraction and ferrite grain size were measured by optical microscope. Based on the mixed model,the phase boundary migration rate of ferrite was obtained. Combined with the starting temperature of transformation,the end temperature of transformation was calculated by the mixed model. The evolution process of ferrite grain size in the process of transformation was discussed. The calculated value of ferrite grain size was in good agreement with the measured value. The error between the calculated value and the measured value of the end temperature of transformation was within ±15 ℃. The obtained ferrite transformation law can be used to control the ferrite volume fraction in the cooling process of Q&P steel.