The Z-phase (CrVN) precipitation in a 9% Cr–3% Co martensitic steel during creep at 923 K and 948 K has been investigated with aim to establish the effect of temperature on the nucleation mechanism of these particles and their coarsening behavior. Ostwald ripening of VX carbonitrides strongly affects these processes. An increase in creep temperature significantly accelerates the transformation of the nanoscale MX carbonitrides into the Z-phase particles causing the Z-phase nucleation in a shorter time. Two different mechanisms of the Z-phase precipitation have been observed. Firstly, for creep tests at 923 K and 948 K with creep rupture time longer than 2000 h, the formation of the stable Z-phase particles with a tetragonal lattice occurs through in-situ transformation of a cubic lattice of the MX carbonitrides leading to a continuous flux of Cr atoms from the ferritic matrix into these particles. The coarsening Z-phase occurs at the expense of dissolution of VX carbonitrides. Secondly, for creep test at 948 K with duration of 773 h, the strain-induced metastable Z-phase with the cubic lattice nucleates on the V-rich MX/ferrite interfaces with following transformation into the stable Z-phase with the tetragonal lattice under creep testing with longer duration. Concurrently, extensive coarsening Cr-rich VX carbonitrides occurs independently. As a result, coarsening Z-phase leads to insignificant dissolution of VX carbonitrides. The creep strength breakdown appearance is not related to the formation and/or coarsening of the Z-phase at both temperatures.

研究了在923 K和948 K蠕变期间9％Cr-3％Co马氏体钢中的Z相（CrVN）析出，目的是确定温度对这些颗粒的成核机理及其粗化行为的影响。VX碳氮化物的奥斯特瓦尔德熟化强烈影响这些过程。蠕变温度的升高显着加速了纳米级MX碳氮化物向Z相颗粒的转化，从而在更短的时间内导致Z相成核。已经观察到Z相沉淀的两种不同机理。首先，对于在923 K和948 K上的蠕变试验，蠕变破裂时间超过2000 h，通过原位形成具有四方晶格的稳定Z相颗粒。MX碳氮化物的立方晶格的转变导致Cr原子从铁素体基体连续流入这些颗粒。Z相粗化的发生是以VX碳氮化物溶解为代价的。其次，对于在773 K下持续时间为948 h的蠕变试验，在立方晶格形核上，应变诱导的亚稳态Z相在富V的MX /铁氧体界面上成核，随后转变为在四方晶格下稳定的Z相。持续时间较长的蠕变测试。同时，大量富Cr的VX碳氮化物的粗化独立发生。结果，粗化Z相导致VX碳氮化物的微不足道的溶解。在两个温度下，蠕变强度击穿的外观与Z相的形成和/或粗化均无关。