【作者】 沈卓；

【导师】 李玉海； 单以银；

【作者基本信息】 沈阳理工大学 ， 材料学， 2008， 硕士

【摘要】 人们对能源需求的迅猛增加,使得开发耐高压、长寿命、耐腐蚀管线钢势在必行。目前对管线钢研究和开发的重点放在成分设计和控制轧制工艺的优化上,以获得针状铁素体为主的管线钢的理想组织,从而提高管线钢的力学性能、抗H2S腐蚀性能等各项性能指标。但目前关于有害元素含量以及夹杂物形态对管线钢性能的影响报道很少,且观点也不尽相同。因此,有必要考察有害元素(特别是硫)含量以及夹杂物的形态对管线钢力学性能和抗H2S腐蚀性能的影响。本论文以不同硫含量的商业用管线钢为实验材料,首先进行了管线钢的连续冷却相变实验,研究了过冷奥氏体的相变规律。结果表明:冷却速度为7.5℃/s～20℃/s时能够获得以针状铁素体为主的组织。在上述工作的基础上,为实验用管线钢制定热机械控制加工工艺,讨论了化学成分、显微组织与力学性能之间的关系。结果表明:微合金化的管线钢更利于获得具有高密度位错的针状铁素体组织,具有优异的综合力学性能,而无微合金化元素管线钢得到多边形铁素体+珠光体组织,强韧性较好。当钢中含有高达100ppm的硫含量时,容易导致材料内部形成平行轧向的Ⅱ型MnS夹杂物,虽然并不显著影响材料的拉伸性能,但会导致材料的冲击韧性恶化。最后重点讨论了显微组织及硫含量对管线钢抗H2S性能的影响。结果表明:硫含量50ppm或者更低的管线钢具有良好的抗H2S性能,能够满足商业用管线钢抗H2S性能的评价标准。另外,含有高密度位错的针状铁素体管线钢具有较低的抗硫化氢应力腐蚀开裂性能,而位错密度较低的多边形铁素体+少量珠光体管线钢则具有相对较高的抗硫化氢应力腐蚀开裂性能。更多还原

【Abstract】 The demands for pipeline steels are being increased dramatically. It is necessary to develop high pressure resistant, long life and corrosion resistant pipeline steel. In order to obtain mechanical, H2S-resistant and some other excellent comprehensive properties, the ideal microstructure of pipeline steel should be acicular ferrite. Recently, most of the research and development of pipeline steels focus on component design and optimized Thermo-Mechanical Control Process (TMCP). However, the reports about the effects of detrimental element and inclusion shape on pipeline steels are very few, and the researchers held different views. It is necessary to research the effects of the detrimental element content and the inclusion shape on the mechanical property and H2S-resistant of pipeline steels.In the present work, the commercialized pipeline steels with different sulfur contents were adapted, and the transformation behaviors of super-cooling austenite in these steels were investigated by measuring continuous cooling transformation diagram (CCT). The results showed that acicular ferrite could be obtained under a cooling rate range of 7.5℃/s~20℃/s. Based on the above results, the TMCP schedule was applied to hot rolling process for the tested steels. The influences of compositions and microstructures on mechanical properties were discussed. The results indicated that pipeline steels with addition of micro-alloyed elements (Ni, V, Ti, Mo) are inclined to obtain acicular ferrite microstructure with high density dislocations, exhibiting excellent strength and toughness. Without micro-alloyed elements the microstructure are inclined to be polygonal ferrite plus pearlite. Especially, it is easy to form elongated MnS inclusions along the rolling direction once the sulfur content in pipeline steels reaches 100 ppm, which deteriorates the impact toughness.Finally, the influences of microstructures and sulfur content on the H2S-resistant behavior were analyzed. When the sulfur content in pipeline steels is 50ppm, the H2S-resistanit standard of pipeline steels can be satisfied. The pipeline steels of acicular ferrite with high density dislocation have poor sulfide stress corrosion cracking (SSC) resistance. However, the pipeline steels of polygonal ferrite+pearlite with low density dislocation have good SSC resistance.更多还原