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利用光学显微镜(OM)、扫描电镜(SEM)等研究了Ti含量对700 MPa级汽车大梁钢奥氏体晶粒长大和析出相的影响。结果表明,添加Ti后的实验钢中主要析出相由单一Nb C转变为(Nb,Ti)C和Ti(C,N),随着Ti含量的增加,奥氏体晶粒得到有效细化。Thermo-calc热力学计算表明,钢中的(Nb,Ti)(C,N)和Ti(C,N)析出相析出温度比Nb C明显提高,因而能够在更高温度下稳定存在并对晶界迁移起到抑制作用。用Beck方程对奥氏体晶粒的长大行为进行了描述,并给出了晶粒长大的数学模型。随着Ti含量的增加,Beck方程的时间指数n呈现降低趋势,但晶界生长的扩散激活能反而升高。Ti的碳氮化物对晶界的钉扎和拖曳效应是晶界迁移扩散激活能升高的主要原因。
The effects of Ti content on the austenite grain growth and precipitates of 700 MPa automotive beam steel were studied by optical microscope (OM) and scanning electron microscope (SEM). The results show that the main precipitates in the experimental steel after addition of Ti are transformed from single Nb to (Nb, Ti) C and Ti (C, N), and the austenite grains are effectively refined with the increase of Ti content. The thermodynamic calculation of Thermo-calc shows that the precipitation temperature of precipitates of (Nb, Ti) (C, N) and Ti (C, N) in steel is obviously higher than that of Nb C, and thus can exist stably at higher temperature Migration has an inhibitory effect. The growth behavior of austenite grains is described by Beck equation and the mathematical model of grain growth is given. With the increase of Ti content, the time index n of Beck equation shows a decreasing trend, but the diffusion activation energy of grain boundary growth increases instead. The pinning and dragging effect of Ti on the grain boundaries of carbonitride is the main reason for the increase of the activation energy of grain boundary migration and diffusion.