松弛法研究含磷高强IF钢第二相粒子的应变诱导析出行为

I Research of Strain-Induced Precipitation Behavior of Second Phase Particles in a P-Bearing High Strength IF Steel By Stress Relaxation Method

在Gleeble3500型热模拟试验机上，利用应力松弛试验研究了含磷高强IF钢第二相粒子析出行为。试验结果表明，微合金元素析出钉扎住了位错与晶界，导致应力松弛曲线呈现出3个阶段的特征。试验用钢的PTT曲线呈现典型的“C”曲线形状，最快析出的鼻子点温度约为850℃，在此温度下，第二相粒子析出开始时间与结束时间分别为14，246s，随着弛豫时间的增加，第二相粒子析出数量逐渐增多，形貌逐渐粗化，析出粒子为Ti4C2S2和TiC，主要呈圆形颗粒形貌。由于试验钢种采用磷强化，在析出的第二相粒子中存在棒形和长条形FeTiP，同时由于磷的晶界偏聚，所以FeTiP同样存在晶界析出的规律。

The precipitation behavior of second phase particles in P-bearing high strength IF steel was studied by using stress relaxation method on Gleeble 3500 thermal-mechanical simulator. The results showed that the stress relaxation curve could be divided into three stages because of the pinning effect of precipitates of alloy elements on the dislocations and grain boundaries, and therefore the precipitation-time-temperature （PIT） curve showed a typical ＂C＂ shape. The precipitation temperature at the nose point was about 850 ~C, with precipitation-start time of 14s and precipitation-end time of 246 s respectively. With the extension of the isothermal relaxation time, the amount of second phase particles increased gradually, and grew during this process. The spherical shape Ti4CES2 and TiC precipitates were observed. The FeTiP precipitate, which presented as bar or rectangular shape, was found in the second phase particles because the focused steel was alloyed with P element. Caused by the segregation of P at the grain boundary, the FeTiP precipitate was mainly located along the grain boundary.