摘要
采用电解相分析方法,结合X射线衍射分析和电感耦合等离子体原子发射光谱仪(ICP)、扫描电镜(SEM)、透射电镜(TEM)等对高铝铁素体基体中的析出相颗粒粉末和电解液进行定性定量分析.试验结果表明,试验钢中固态析出相主要为NbC以及少量的Al_2O_3和Al N夹杂.通过扫描电镜观察不同再加热温度下NbC分布状态,发现随着固溶温度的升高,铸态组织中存在的NbC析出逐渐回溶,数量随之减少且发生明显的粗化行为.当温度升高到1100℃,大部分NbC已经回溶到高温铁素体基体中.在利用Thermo-Calc热力学计算软件分析Nb及其碳化物的热力学性质基础上,计算得到Al与Nb的相互作用系数,表明Al能够降低Nb在铁素体基体中的活度,提高其在基体中的固溶度,进一步得到了Nb C在高铝铁素体钢中的固溶度积公式,发展了高温铁素体中的Nb微合金化理论,为进一步的应用提供了理论基础.
With the rapid development of the global economy,problems in energy production and environmental protection are becoming severe. To reduce fuel consumption and CO2 emissions,it is essential to reduce the weight of automobiles and other huge construction structures. Recently,a number of studies have been conducted on the use of low-density steels for automobile applications by incorporating aluminum in steel. The light elements can increase the lattice constant of steel while reducing the density of steel to achieve a lower atomic weight. Aluminum as a light element replaces the iron atoms in the unit cell,increasing the volume while reducing the weight,thereby reducing the density of steels. In this regard,ferritic Fe-8 % Al steels indicated a 10% reduction in density compared with the conventional steels. To clarify the solid solution and precipitation behavior of Nb in Al-bearing ferritic steels,heat treatment tests were carried out under a series of temperature. The precipitates of Nb C and the dissolved Nb solute in ferrite matrix with high Al content were studied using electrolytic dissolution technique,X-ray diffraction technique,and inductively coupled plasma-atomic emission spectrometry( ICP-AES). Scanning electron microscopy( SEM) and transmission electron microscopy( TEM) were also applied. The experimental results show that the precipitates are Nb C and also some Al2 O3 and Al N inclusions. It is also found that with increase in the solution temperatures,the Nb C in the as-cast samples becomes fewer and the coarsening behavior occurs. Moreover,when the temperature was over 1100 ℃,almost all the precipitates were dissolved. Furthermore,using Thermo-Calc software,the thermodynamic properties of Nb and relevant compounds were studied,and the interaction coefficient between Al an Nb was calculated.The results indicate that Al decreases the activity of Nb,and the solubility of Nb C increases. Finally,the solid solubility formula of Nb C was deduced,which can provide a basis for further application of ferritic steels with a high Al content.
引文
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