Super304H奥氏体耐热钢的时效析出与强化机理

发布时间：2018-05-04 10:40

本文选题：Super304H奥氏体耐热钢 + 富Cu相　；参考：《上海交通大学》2015年博士论文

【摘要】：随着火力发电机组的迅速发展,机组运行的蒸汽压力和温度参数不断提高,对机组用耐热钢的性能要求也越来越高。Super304H奥氏体耐热钢是在18/8Cr-Ni不锈钢基础上添加约3 wt%的Cu以及少量的Nb而开发的一种新型奥氏体钢。由于Super304H奥氏体钢具有良好的高温强度和抗氧化性能,因此当前被广泛应用于国内外超超临界(UltraSupercritical-USC)机组中的过热器和再热器管。Super304H奥氏体钢良好的高温强度主要来源于其在高温服役过程中析出的纳米级富Cu相和MX相(Nb(C,N))的沉淀强化作用。此外,M23C6和Z相(NbCrN)在Super304H奥氏体钢高温服役过程也起到了辅助的强化作用。然而,到目前为止对于这些析出相在Super304H奥氏体钢中的析出行为和强化机理还不甚清楚。对Super304H奥氏体钢析出行为和强化机理的研究将会进一步完善人们对于Super304H钢中析出相的认识,从而为该钢种的高温服役性能评估提供实验依据。本文以Super304H奥氏体钢为研究对象,利用扫描和透射电子显微镜对其显微结构进行深入观察和分析,研究了Super304H奥氏体钢的时效析出行为,并把时效析出行为和宏观力学性能结合起来分析,探讨了Super304H奥氏体钢的沉淀强化机理。本文的主要研究结论如下:1.固溶态Super304H奥氏体钢原始组织的奥氏体基体中存在有少量大块状的富Nb MX相和圆形夹杂物。经650°C长时时效5000 h后的研究结果表明:Super304H奥氏体钢在时效过程析出的析出相包括富Nb MX相、M23C6碳化物以及富Cu相。其中,纳米尺寸的富Nb MX相与基体存在立方取向关系和非共格界面关系;M23C6可以在奥氏体晶粒内以富Nb MX相为核心析出形成双层结构,偶尔在基体内单独析出,M23C6与奥氏体基体存在立方取向关系;在奥氏体晶界析出不连续的链状M23C6也与基体存在立方取向关系;奥氏体晶粒内析出大量纳米尺寸的富Cu相与基体存在立方取向关系和共格界面关系。2.富cu相的粗化行为研究结果表明:super304h奥氏体钢在650~750°c温度范围内时效后析出的富cu相在长大过程中始终与奥氏体基体保持立方取向关系和共格界面关系,富cu相颗粒的粗化行为遵循lifshitz-slyozov-wagner(lsw)理论;富cu相的长大激活能约为212±3kj/mol,其粗化长大主要由cu原子在奥氏体基体中的体扩散所控制。3.super304h奥氏体钢在室温~650°c温度范围内的拉伸屈服行为研究结果表明:富cu相的沉淀强化作用对super304h奥氏体钢屈服强度增量的贡献约为17~23%;时效态super304h奥氏体钢比固溶态具有更高的激活体积和激活能表明在拉伸变形过程中存在有位错和富cu相之间的交互作用。super304h奥氏体钢室温拉伸变形过程中富cu相的沉淀强化主要来源于共格应变强化以及部分来源于层错强化,理论计算获得的由于富cu相强化而引起的剪切应力增量与实验结果是一致的。super304h奥氏体钢在650~750°c温度范围内的时效硬化行为研究结果表明:在不同的时效温度下,析出相的沉淀强化作用对super304h奥氏体钢峰值硬度的贡献约为17~25%,富cu相的沉淀强化同样主要来源于共格应变强化和部分来源于层错强化。4.super304h奥氏体钢在650~700°c及190~210mpa应力水平条件下的蠕变行为研究结果表明:super304h奥氏体钢蠕变变形的平均表观应力指数和激活能分别为21.5和687.3kj/mol;高的平均表观应力指数和激活能表明在蠕变变形过程中存在有一个位错与富cu相的交互作用所引起的门槛应力。在此温度范围内,super304h奥氏体钢的蠕变变形机制为基体晶格扩散所控制的位错攀移过程,蠕变过程中的门槛应力主要来源于富cu相与奥氏体基体之间正的晶格常数错配引起的共格应变场,理论计算获得的由于富cu相强化而引起的门槛应力值与实验结果基本一致。super304h奥氏体钢在650°c及250mpa应力水平条件下蠕变447h后mx相的析出行为研究结果表明:在奥氏体晶粒内可以析出纳米尺寸立方形状的富nbmx相,富nbmx相与奥氏体基体的界面是非共格的;此外,纳米尺寸的富nbmx相更容易在富cu相与奥氏体基体的界面处以及沿着奥氏体基体的位错线析出。
[Abstract]:With the rapid development of thermal power generating sets, the steam pressure and temperature parameters of the unit are increasing, and the performance requirements for the heat resistant steel are getting higher and higher..Super304H austenitic heat-resistant steel is a new austenite steel which is opened by adding about 3 wt% Cu and a small amount of Nb on the base of 18/8Cr-Ni stainless steel. Due to Super304H austenite With good high temperature strength and antioxidant properties, the high temperature strength of the superheater and reheater tube.Super304H austenite steel in the super supersupercritical (UltraSupercritical-USC) unit at home and abroad is mainly derived from the nanoscale Cu phase and MX phase (Nb (C, N)) precipitated during the high temperature service. In addition, the M23C6 and Z phase (NbCrN) also plays an auxiliary strengthening role in the high temperature service of Super304H austenitic steel. However, the precipitation behavior and strengthening mechanism of these precipitates in Super304H austenite steel are not yet clear. Study on the precipitation behavior and strengthening mechanism of Super304H austenite steel The understanding of the precipitated phase in Super304H steel will be further improved, thus providing experimental basis for the evaluation of the high temperature service performance of the steel. In this paper, the microstructure of Super304H austenitic steel was investigated and analyzed by scanning and transmission electron microscopy, and the aging of Super304H austenite steel was studied. The precipitation behavior was analyzed and the precipitation strengthening mechanism of Super304H austenitic steel was discussed. The main conclusions of this paper are as follows: 1. the austenite matrix of Super304H austenite steel in solid solution state has a small amount of large Nb MX and circular inclusions in the austenite matrix. The results after 5000 h have shown that the precipitated phases precipitated in the aging process of Super304H austenitic steel include rich Nb MX phase, M23C6 carbide and Cu rich phase. Among them, there is a cubic orientation relationship and a non common interface relationship with the matrix rich Nb MX phase and the matrix, and M23C6 can be precipitated at the core of the austenite grain at the core of the rich Nb MX phase. Double structure, occasionally precipitated in the matrix, there is a cubic orientation relationship between M23C6 and austenite matrix, and the discontinuous chain M23C6 precipitated from the austenite grain boundary also has a cubic orientation relationship with the matrix, and a large number of nanoscale Cu phases are precipitated in the austenite grain and there are vertical and common interface relations between the matrix and the matrix.2. rich Cu phase. The results of the coarsening study show that the rich Cu phase precipitated in the Super304H austenite steel after aging in the 650~750 C temperature range has always maintained the cubic orientation relationship and the common interface relationship with the austenite matrix during the growing process. The coarse-grained behavior of the rich Cu phase particles follows the lifshitz-slyozov-wagner (LSW) theory, and the activation energy of the rich Cu phase is about 212. The results of the tensile yield behavior of.3.super304h austenitic steel at room temperature ~650 degree C are mainly controlled by the Cu atom in the austenite matrix. The results show that the contribution of the precipitation strengthening of the rich Cu phase to the increment of the yield strength of the Super304H austenite steel is 17~23%; the aging state Super304H austenite. There is a higher activation volume and activation energy in the steel than the solid solution state. The interaction between the dislocation and the rich Cu phase exists in the tensile deformation process. The precipitation enhancement of the rich Cu phase in the tensile deformation process of the.Super304h austenite steel is mainly due to the common lattice strain strengthening and the part of the stacking fault hardening. The theoretical calculation obtained is due to the results. The results of the aging hardening behavior of the.Super304h austenitic steel in the 650~750 degree C temperature range are consistent with the experimental results. The results show that the contribution of precipitation strengthening to the peak hardness of the Super304H austenite steel is about 17~25% and the precipitate of rich Cu phase is strong at different aging temperatures. The results show that the creep behavior of.4.super304h austenite steel at 650~700 degree C and 190~210mpa stress level is mainly derived from the common lattice strain strengthening and partly from the stacking fault reinforcement. The results show that the average apparent stress index and the activation energy of the creep deformation of Super304H austenite steel are 21.5 and 687.3kj/mol; the high average apparent stress The force index and activation energy indicate that there is a threshold stress caused by the interaction of the dislocation and the rich Cu phase during the creep deformation process. In this temperature range, the creep deformation mechanism of Super304H austenite steel is the dislocation climbing process controlled by the matrix lattice diffusion, and the threshold stress in the creep process is mainly derived from the rich Cu phase and the Ordovician. The common lattice strain field caused by the mismatch of the positive lattice constant between the body matrix, the theoretical calculation of the threshold stress caused by the enrichment of the rich Cu phase is basically in agreement with the experimental results. The analysis of the.Super304h phase of the MX phase after the creep 447h under the conditions of 650 degree C and 250Mpa stress level shows that: in the austenite grain The interface between the rich nbmx phase and the austenite matrix is non common in order to precipitate the rich nbmx phase in the nanoscale cubic shape. In addition, the nanoscale rich nbmx phase is more easily precipitated in the interface between the rich Cu phase and the austenite matrix and along the dislocation lines along the austenite matrix.

【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG142.1

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