【作者】 杜婷；

【导师】 卢正欣；

【作者基本信息】 西安理工大学 ， 材料科学与工程， 2009， 硕士

【摘要】 SUPER304H钢是一种新型18-8奥氏体不锈钢,由于它优异的综合性能被用于制造超超临界锅炉的过热器和再热器(SH/RH)。本文主要研究了时效、蠕变对未变形、15%、20%预变形SUPER304H奥氏体不锈钢析出行为及晶间腐蚀性能的影响,探索了表面喷丸对SUPER304H钢高温时效组织结构和晶间腐蚀敏感性的影响,分析测试了各种处理状态SUPER304H样品硬度变化。利用透射电镜(TEM)观察析出相的形状、大小、分布特征,利用X射线衍射技术分析析出相的晶体结构,结合能谱分析仪对析出相化学成分进行分析。通过双循环动电位再活化(DL-EPR)实验评价其晶间腐蚀性能。得到以下结论：未变形、15%、20%预变形SUPER304H钢经700℃下不同时间时效处理后,样品硬度随着变形量增加而增大。三种不同变形量样品晶界的析出物主要是M23C6型碳化物,晶粒内部及晶体缺陷处析出MC型碳化物。随着变形量和时效时间增加,沉淀相析出数量及大小均增加。随着变形量增加,SUPER304H钢再活化率降低,晶间腐蚀敏感性降低,抗晶间腐蚀性能得到改善。未变形、15%、20%预变形SUPER304H钢在700℃、180MPa下的蠕变过程中发生了强化和软化现象。与未变形样品相比,15%和20%预变形样品硬度有了较大提高。随着蠕变时间增加,预变形样品硬度降低缓慢。蠕变过程中SUPER304H钢在晶界处断续析出面心立方的(Cr,Fe)23C6颗粒,在晶粒内部和晶体缺陷处析出面心立方结构的MC型颗粒。随着变形量和蠕变时间增加,沉淀相析出数量及大小均增加。SUPER304H钢抗晶间腐蚀性随变形量增加而降低。对于未变形样品,抗晶间腐蚀性随蠕变时间延长而下降。预变形加速了SUPER304H不锈钢的敏化/脱敏过程。SUPER304H钢经不同喷丸工艺处理后表层硬度明显增大,提高到心部硬度的一倍以上,随着距表面距离增加,显微硬度逐渐下降。随着喷丸强度和喷丸时间增加,衍射峰逐渐宽化,表面结晶度逐渐下降,晶粒细化层变厚,表层硬度逐渐提高。表面喷丸强化处理的SUPER304H钢的抗晶间腐蚀性能比原始粗晶状态有了明显提高。喷丸强化明显加速了SUPER304H不锈钢的敏化/脱敏过程。更多还原

【Abstract】 SUPER304H is a new commercial 18-8 austenitic stainless steel. It is used to produce ultra-supercritical boiler super-heater and re-heater due to its excellent properties. In this research, experiments were done to investigate the precipitate behavior and intergranular corrosion property of 0%,15%,20% deformation SUPER304H stainless steel samples, which aged and crept at 700℃for different times, dealt with shot peening and aging treatment. The change in hardness of samples under different processing conditions was analyzed by hardness tester. The morphology, size and distribution of the precipitate were observed by transmission electron microscopy (TEM), and its crystal structure was characterized by X-Ray diffraction technology. The chemical composition of the precipitate was analyzed by means of the energy dispersive spectrum system (EDS). Degree of intergranular corrosion susceptibility was evaluated by DL-EPR. The conclusions show that:After 0%,15%,20% deformation SUPER304H stainless steel samples treated by aging at 700℃for different time, the hardness of strained sample is significantly greater than unstrained one, and the hardness increases as the deformation increasing. The precipitate of M23C6 carbide mainly composed of chromium occurs along the grain boundaries of unstrained SUPER304H stainless steel samples aged at 700℃. The MC-type carbide form of the stainless steel and a few disperse inside the grains or along the crystal defect like as dislocation. Both the number and size of precipitation increased with deformation and aging time growing. As deformation increased, the Ir/Ia of SUPER304H samples fell, degree of intergranular corrosion susceptibility reduces, and therefore intergranular corrosion resistance improves.The strengthening and softening of the SUPER304H stainless steel happened during the creep behavior at 700℃& 180MPa. The hardness of strained samples become significantly greater than unstrained one, and their hardness fell slowly as the creep went. During the creep tests, the discontinuous face-center cube (Cr,Fe)23C6 carbide precipitated at grain boundaries and fcc MC was found inside grains and along crystal defect. Precipitation grew both in number and size with an increase of deformation and creep time. The intergranular corrosion resistance of the samples reduced as deformation increasing, and that of unstrained samples reduces as the creep going. But the effect of creep time on intergranular corrosion property of strained samples is complex. The pre-deformation accelerates the sensitization/desensitization process.After shot peening process, the surface hardness of SUPER304H stainless steel increased significantly, to a degree greater than double of matrix hardness. Micro-hardness gradually declines from the surface to matrix. As the strength and time of shot peening grew, grain refinement layer became thicker, the diffraction peak was widening, the surface crystallinity decreasing and the surface hardness increasing. Compared with that in the original coarse-grained state, the intergranular corrosion resistance of SUPER304H stainless steel significantly improves after shot peening treatment. The strength of shot peening accelerates the sensitization/desensitization process.更多还原