2Cr12Ni4Mo3VNbN钢中析出相的热力学计算与试验分析

 利用Thermo-Calc热力学软件计算了2Cr12Ni4Mo3VNbN钢中各个元素在成分范围内均为中值时的平衡相图,同时计算了2Cr12Ni4Mo3VNbN钢中碳、铬、钼、铌、氮元素含量变化时的平衡相图,以此分析钢中主要平衡析出相和合金元素含量对析出相析出行为的影响。为验证热力学计算的可靠性,采用XRD、SEM及TEM等分析方法对热处理后的2Cr12Ni4Mo3VNbN钢中析出相类型进行了试验验证。结果表明,钢中的平衡析出相为MX相、M₂₃C₆、M₆C、Z相和Laves相。在热力学平衡条件下,MX相在850 ℃转化为Z相,M₆C在787 ℃转化为Laves相。但是在实际热处理过程,由于保温时间较短且冷却速度较快,上述转化过程不会发生,所以钢中主要析出相为MX相、M₂₃C₆和M₆C。平衡析出相种类与相分析的试验结果基本一致。MX相存在大尺寸的一次MX相和细小弥散的MX相,MX相主要受铌、氮元素影响,其析出量随氮含量升高而升高,析出温度随铌含量升高而升高;M₂₃C₆相的析出温度随碳含量增加而升高,析出量也随之升高;M₆C的析出温度随铬含量增加而降低,随钼含量增加而升高;在成分范围内,元素控制原则为增加碳含量以增加M₂₃C₆的析出强化作用,减少铬含量以避免热加工时进入δ-Fe相区,减少钼含量以降低Laves相析出倾向,减少铌含量以降低一次MX相的析出温度,氮含量需要采取中间量以减少一次MX相析出,增加低温阶段细小弥散的MX相析出。

Thermodynamic calculation and experimental analysis on equilibrium precipitation phase in 2Cr12Ni4Mo3VNbN steel

In order to analyze the influence of the main equilibrium precipitated phase and alloying element content in the 2Cr12Ni4Mo3VNbN steel on the precipitation behavior of the precipitated phase, the equilibrium phase diagram of 2Cr12Ni4Mo3VNbN steel was calculated by Thermo-Calc thermodynamic software when all elements in the composition range were median, and the equilibrium phase diagram of steel when the content of C, Cr, Mo, Nb, and N changed was calculated. To verify the reliability of thermodynamic calculations, XRD, SEM and TEM analysis methods were used to identify the types of precipitates in the heat-treated 2Cr12Ni4Mo3VNbN steel. The results show that the equilibrium precipitated phases in steel are MX phase, M₂₃C_6, M₆C, Z phase and Laves phase. Under thermodynamic equilibrium conditions, MX phase transforms into Z phase at 850 ℃, and M₆C transforms to Laves phase at 787 ℃. However, in the heat treatment process, due to the short holding time and the faster cooling rate, the above conversion process will not occur, so the main precipitated phases in the steel are MX phase, M₂₃C₆and M₆C. The types of equilibrium precipitates are basically consistent with the experimental results of microstructure observation and phase analysis. There are large-scale primary MX phases and nano-level MX phases in the MX phase. MX phase is mainly affected by Nb and N. The precipitation amount increases with the increase of N content, and the precipitation temperature increases with the increase of Nb content. The precipitation temperature of M₂₃C₆ phase increases with the increase of C content, and the precipitation amount increases with the increase of C content. The precipitation temperature of M₆C decreases with the increase of Cr content, and increases with the increase of Mo content. Within the composition range, the element control principle is to increase the C content to increase the precipitation strengthening effect of M₂₃C₆, reduce the Cr content to avoid entering the δ-Fe phase area during hot working, reduce the Mo content to reduce the precipitation tendency of the Laves phase, reduce the Nb content to Lower the precipitation temperature of the primary MX phase, the N content needs to take an intermediate amount to reduce the precipitation of the primary MX phase, and increase the precipitation of the dispersed fine MX phase in the low temperature stage.