Thermodynamic analysis of the NaCl type of complex carbonitrides

本研究的目的是分析微合金钢中碳氮化物之间的相平衡，并建立一种计算复杂相关系的方法。1.对过渡金属碳化物和碳氮化物的混相间隙进行了实验研究。研究了（V，Nb）C、（Ti，V，Nb）C、（V，Nb）C、（V，Nb）（C，N）、（Ti，Nb）（C，N）和（Ti，V）（C，N）体系，并通过X射线衍射和能谱分析确定了体系的平衡组成。在实验结果的基础上，进行了热力学计算。碳氮化物的吉布斯自由能已被描述使用亚晶格模型和在伪二元系统的相互作用能估计从组分中的晶格常数的差异。计算了20种（X，Y，Z）C型碳化物、10种（X，Y，Z）N型氮化物和10种（X，Y）（C，N）型碳氮化物的可熔性间隙。2.建立了计算含Ti、V、Nb微合金钢中奥氏体和复合碳氮化物成分的热力学模型。应用热力学模型计算了奥氏体与（Ti，V，Nb）X、（M1，M2）（C，N）或（Ti，V，Nb）（C，N）型化合物之间的相平衡。通过计算，观察到合金中析出方式随合金含量和添加元素种类的不同而有所变化。单个元素的作用简要总结如下：（a）钛添加到微合金化钢中促进富钛氮化物的形成，主要是由于其在奥氏体中的极低溶解度。（B）元素的复合添加引起碳氮化物的相分离，在大多数情况下出现NbC与VC或NbC与TiN的分离。这一现象可以从二元化合物的相对稳定性的观点来解释。

The purpose of the present research is to analyze the phase equilibria between the carbonitrides in microalloyed steels and to develop a method to calculate the complicated phase relationship. 1.Miscibility gaps in some transition-metal carbide or carbonitride systems have been experimentally studied. The systems investigated were (V,Nb)C, (Ti,V,Nb)C, (V,Nb)C, (V,Nb)(C,N), (Ti,Nb)(C,N)and(Ti,V)(C,N),and the equilibrium compositions were determined by the X-ray measurements and EDX analysis. A thermodynamic calculation of the miscibility gaps was performed on the basis of the experimental results. The Gibbs energy of the carbonitrides has been described using a sublattice model and the interaction energies in the pseudobinary systems were estimated from the difference in lattice constants in components. The miscibility gaps in the 20 (X,Y,Z)C types of carbides,10 (X,Y,Z)N types of nitrides and 10 (X,Y)(C,N) types of carbonitrides were calculated. 2.A thermodynamic model was presented to calculate the composition of austenite as well as that of complex carbonitrides in the microalloyed steels containing Ti,V and Nb. The thermodynamic model was applied to the phase equilibrium calculation between the austenite and (Ti,V,Nb)X, (M1,M2)(C,N),or(Ti,V,Nb)(C,N) type of compounds. Some variations of precipitation mode were observed through the calculation according to the alloy contents and kinds of additional elements. The effect of individual element was briefly summarized as follow;(a) Ti addition to the microalloyed steels enhances the formation of Ti-rich nitrides mainly due to its extreme low solubility in austenite. (b)Complex addition of the elements brings the phase separation of the carbonitrides,and in almost cases the separation between NbC and VC or NbC and TiN is presented. This phenomena can be explained from the view points of the relative stability of binary compounds.