【作者】 陈小伟；

【导师】 廖波； 肖福仁；

【作者基本信息】 燕山大学 ， 材料学， 2013， 博士

【摘要】 西气东输二线管道是全球首条钢级最高、厚壁最厚、设计压力最高、距离最长的长输管线，主干线全部采用X80钢。而我国X80钢及钢管研究应用较少，尤其是针对低成本高Nb X80钢的应用可行性研究更少。因此，开展西气东输二线X80钢及钢管开发的基础研究，成功开发出项目所需的X80钢及焊管是保证管线顺利建设的前提。本文针对西气东输二线X80钢及直缝埋弧焊管开发面临的几个基础问题，采用热模拟技术、金相、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、理化性能测试分析等手段，系统研究了X80钢及焊管拉伸性能检测试验方法、高Nb钢制管过程拉伸性能变化规律、高Nb钢的可焊性，系统分析了钢管成分与性能之间的关系，深入研究了Nb、Cr、Mo等合金元素对钢管焊接热影响区强度和韧性影响规律。通过研究拉伸试样形式对试验结果影响规律表明：钢板矩形试样的屈服强度平均比圆棒试样高22MPa，而抗拉强度则比圆棒试样低10MPa；而对钢管，无论是屈强强度、抗拉强度还是屈强比，圆棒试样均高于矩形试样，屈服强度平均升高96MPa、抗拉强度升高17MPa、屈强比升高0.12。分析表明矩形试样能更好的反映钢板的拉伸性能，而圆棒试样能更好地反映钢管的拉伸性能。建议对钢板采用矩形试样、而钢管采用圆棒试样。对比研究了高Nb钢及传统Mn-Mo-Nb钢制管前后强度变化规律，结果发现无论高Nb钢还是低Nb钢均存在制管后屈服强度、屈强比显著升高的现象。研究发现钢板的显微组织是决定制管后屈服强度及屈强升高幅度的关键因素，获得少量块状铁素体及多边形铁素体可降低钢板制管后屈服强度和屈强比升高的幅度，降低钢管屈强比。根据钢管制管后屈服强度升高现象，可突破钢板屈服强度必须满足X80钢555MPa的限制，钢板的最低屈服强度可以降低至500~530Mpa，并要与组织相结合。热模拟研究结果表明，高Nb X80钢具有良好的焊缝及热影响区性能，在壁厚为22mm钢管焊接热输入达到4.5kJ/mm的多丝埋弧焊工艺条件下，焊接热影响粗晶区仍能保持较高的韧性。但焊接细晶区的强度明显降低，甚至低于标准规定555MPa。适当提高钢的合金含量有利于提高焊接粗晶区的韧性及细晶区的强度。对钢管的性能统计分析表明：管体及焊接接头的强度与钢的合金含量呈线性关系。随Ceq或Pcm的增加，管体抗拉强度及焊接接头抗拉强度均升高，但焊接接头强度升高幅度低于管体。然而，对管体和焊接热影响区韧性则表现为当Ceq或Pcm分别小于0.44%或0.17%时，冲击韧性保持在较高水平，且随Ceq或Pcm的增加，变化幅度不大；超过此值后，韧性降低明显。热影响区的韧性与管体相比有显著的降低，但管体的韧性越高则热影响区的韧性越高，提高钢板的韧性有利于保证钢管热影响区韧性。对比研究了Cr-Nb、Mo-Nb及Cr-Mo-Nb钢焊接热影响区连续冷却相变及组织与性能，结果表明：Nb对焊接过程中原奥氏体晶粒有显著的抑制作用，而对冷却过程中相变的抑制作用不大，对冷却后的组织和性能影响不大；Mo对高Nb钢相变的抑制作用大于Cr的作用，而Cr-Mo复合添加作用更大，更有利于焊接热影响区组织的细化和性能的提高。更多还原

【Abstract】 The Second West-east X80pipeline is one of the highest steel grade, highest designpressure, heaviest wall thickness, longest distance pipeline in the world. However, in ourcountry, studies and using of X80steel and pipe are very rare, especially for high Nbcontent X80steel. Therefore, to carry out fundamental research for developing X80steeland pipe, and to successfully produce the X80steel and pipe required for the SecondWest-east Pipeline is a prerequisite for the project construction.In the paper, X80steel and welded pipe tensile performance test methods, tensileproperties change rule of low cost and high Nb steel druing the pipe manufacture process,weldability of high Nb steel, the relationship between chemical composition and pipeproperties, and the effect of Nb, Cr, Mo and other alloying elements on steel HAZ strengthand toughness have been systematically studied using thermal simulation method,metallographic and scanning eletron microscope (SEM), transmision electron microscope(TEM), the physical and chemical properties test and analysis method.The results of tensile samples form influence law of the test results show that, forsteel plates, the average yield strength of rectangular sample is higer22MPa than roundbar sample, while the tensile strength is lower10MPa than round bar sample. For pipes,yield strength and tensile strength and yield strength ratio of round bar sample are all higerthan those of rectangular sample, the difference are96MPa,17MPa and0.12respectively.The results show that the rectangular sample can better reflects the tensile properties of thesteel plate, but the round bar specimen can better reflects the tensile properties of the steelpipe. So, the suggestion is rectangular sample for steel plate and round bar specimen forsteel pipe.The tensile properties change rule of high-Nb steel and Mn-Mo-Nb steel after pipemanufacturing shows, both yield strength and yield strength ratio of two steel increasedsignificantly. The microstructure of steel is the key factor that determines the variationrange. With the content of polygonal ferrite and/or massive ferrite in microstructureincreasing, the rising trend of yield strength and yield strength ratio reduce. Because theyield strength of X80steel rising significantly after pipe manufacture process, steel plate with low yield strength even lower than555MPa, which is the lowest technical standardvalue of the X80pipe, can be used to manufactrue X80pipe. The lowest required yieldstrength of X80steel plate can be500~530MPa, and microstructure must be considered.Thermal simulation research results show that higher Nb X80steel has goodweldability. For22mm thickness X80steel, when the heat input is4.5kJ/mm (simulatonof four wire submerged are welding process condition), the coarse grain heat affected zone(CGHAZ) remained high toughness. But in the fine grain heat affected zone (FGHAZ),strength weaken is very serious, even lower than555MPa. Appropriate increasing of alloycontent is benefit both for CGHAZ’s toughness and FGHAZ’s strength.Statistical analysis of X80pipes composition and mechanical properities show, thestrength of pipe body and welded joint has a linear relation with the steel alloy content.With the increase of Ceq and/or Pcm, the strength of pipe body and welded joint increase.But welded joint strength rise less tan the pipe body. For the toughness of pipe body andwelded joint, when the Ceq and Pcm less than0.44%,0.17%respectively, toughness ofpipe body and HAZ remained higher level. But with the Ceq and Pcm higher than0.44%,0.17%respectively, both toughness of pipe body and HAZ decrease rapidly. Compairedwith pipe body, the HAZ’s toughness decreased significantly. But the HAZ’s toughnessshows obviously relationship with pipe body’s toughness, higher toughness in body’s,higher toughness in HAZ.Comparative studied the continuous cooling transformation characteristics,microstructure and performance of Cr-Nb steel, Mo-Nb steel and Cr-Mo-Nb steel. Theresult shows that Nb can significantly inhibit austenite grain grew up in the process ofwelding, but has little effect on phase transion druing weld cooling process, and has littleeffect on microstructure and performance after cooling. Inhibitory effect of Mo on highNb steel phase transition during welding is greater than the effect of Cr, and the effect ofCr-Mo compound is even greater. Adding of Mo especially of Cr-Mo in high Nb X80steelis more advantageous to obain finer microstructure and better performance.更多还原