0.2C-1.25Si-2.0Mn Q&P钢渗碳体的析出动力学分析

Precipitation Dynamics Analysis on Cementite in 0.2C-1.25Si-2.OMn Q&P Steel

为研究Q&P(淬火-分配)钢临界区均热工艺对配分过程中渗碳体析出的影响,通过Avrami动力学方程对Q&P钢渗碳体析出的PTT(沉淀量-温度-时间)曲线进行了计算。通过热膨胀仪对Q&P钢进行了单相区退火、临界区退火,退火后淬火,并通过透射电镜检测室温下马氏体的衍射斑,计算马氏体的碳含量,以此推测高温下奥氏体中的碳含量。通过连续退火模拟机模拟了不同临界区退火的Q&P工艺。在扫描电镜下检测了析出渗碳体的尺寸,结合热处理工艺和渗碳体的熟化率计算了析出开始时间。由此得出了渗碳体析出体积分数5%的PTT曲线绝对位置。846℃均热的条件下鼻子点温度为300℃。811℃均热条件下,鼻子点温度上升至325℃,764℃均热条件下,鼻子点温度上升至400℃。在746~846℃均热,配分时间≤450 s的情况下,可以避免渗碳体的析出。

In order to study the effect of soaking process in critical zone of Q&P(Queching and Partition) steel on the cementite precipitation during partitioning process,the PTT(precipitation amount-temperature-time) curves of the cementite precipitation of steel Q&P are calculated by Avrami dynamic equation.Q&P steel is annealed in single phase zone and critical zone,and quenched after annealing by thermal dilatometer,the carbon content of martensite is calculated by measuring the diffraction spot of room temperature martensite with transmission electron microscopy to predict the carbon content of high temperature austenite.Different critical annealing Q&P process conditions are simulated by continuous annealing simulate machine.The size of precipitated cementite is measured by scanning electron microscopy.Combining heat treatment process and maturity rate of cementite,the starting time of precipitation is calculated.The absolute position of the 5% cementite precipitated volume fraction PTT curve is obtained.At the soaking condition of 846 ℃,the nose temperature is300℃.At the condition of soaking at 811 ℃,the nose temperature rises to 325 ℃,and at the condition of soaking at764℃,the nose temperature rises to 400℃.The precipitation of cementite can be avoided when the partition time is ≤450 s at the condition of soaking al 746 ~846℃.