大型LNG低温储罐用9Ni钢服役过程中组织性能变化研究

Investigation on Microstructure and Mechanical Properties of 9Ni Steel for LNG Storage Tank during Service

研究了9Ni钢在室温(25℃)低温(-196℃)多次保温循环后其组织性能的变化。借助金相显微镜、扫描电子显微镜等实验仪器表征材料显微组织的同时,用低温冲击试验机、万能电子拉伸试验机和洛氏硬度计分别测试材料的低温冲击功、拉伸性能及硬度,并用X射线衍射仪对9Ni钢中奥氏体的含量加以分析。研究结果表明经不同次数的高低温保温循环后,9Ni钢的强度和低温韧性均有所提高,并稳定在比原始材料性能较好的水平。在保温循环过程中,部分逆转奥氏体转变为孪晶马氏体形成的强化相,以及组织应力和宏观应力的松弛都是9Ni钢性能提高的重要因素。

In this paper, the change of microstructure and mechanical properties of 9Ni steel was studied after multiple Room temperature （25 ℃ ）←→deep cryogenics（- 196 ℃ ） insulation cycle treatment. OM and SEM were used to characterrizate the microstructure of materials;Low-tem- perature impact testing machine, universal electronic tensile testing machine and Rockwell hard- ness meter were used to test the low impact energy,tensile properties and hardness of the materi- als~ And X-ray diffraction was used to calculate retained austenite content in 9Ni steel. The results show that the strength and low temperature toughness of 9Ni steel after insulation cycle treatment were improved to a higher level than those of untreated material. During the insulation cycle treatment, there were two factors for the improvement of mechanical properties of 9Ni steel： the transtormation of reversed austenite into twinned martensite, which became the strengthing phase, and the relaxation of organizational stress and macroscopic stress.