C含量对690合金M23C6相析出行为的影响

Effect of carbon content on precipitation behavior of M23C6 phase in alloy 690

为了研究0.011%~0.033%范围内C质量分数对690合金M23C6相析出行为的影响规律,采用SEM、TEM、物理化学相分析和热力学计算等手段,考察了不同C含量与M23C6相析出数量及析出位置关系。结果表明,随着C含量增加,M23C6析出相质量分数增加、完全固溶温度提高,前者与C质量分数呈线性关系变化,后者则符合抛物线关系。C含量升高,M23C6相的吉布斯自由能下降,从基体中析出M23C6相这一固态相变过程的驱动力增大,在相同的保温时间下,促进M23C6相在更多位置上的析出及其析出形貌的显著变化。对于较高C含量的690合金,除在晶界和孪晶端部外,还可在孪晶内部观察到M23C6相析出现象,其析出相颗粒发生粗化的同时,相质量分数也逐渐增加。

In order to study the influence of C content in the range of 0.011%-0.033%on the M23C6 precipitation behavior of alloy 690,SEM,TEM,physicochemical phase analysis and thermodynamic calculation were used to investigate the precipitation quantity and location of M23C6 phase with different C contents.The results showed that with the increase in C content,the content of precipitated M23C6 phase increased and the temperature of complete solid solution raised.The former has a linear relationship with C content,while the latter was conformed to have a parabolic relationship.With the increase in C content,the Gibbs free energy of M23C6 phase decreased,and the driving force of the solid phase transformation process of M23C6 phase precipitated from the matrix increased,which facilitated the precipitate of M23C6 phase at more positions and the significantly changed precipitate morphology under the same holding time.For the alloy 690 with high C content,the phenomenon of M23C6 phase precipitation can be observed not only at the grain boundary and the twin crystal end,but also inside the twins.At the same time of coarsening,the content of M23C6 phase also gradually increased.