【作者】 周峰；

【导师】 吴开明；

【作者基本信息】 武汉科技大学 ， 材料学， 2014， 博士

【摘要】 为适应管线工程经济性和安全性的要求，管线钢必须具有优秀的强度、韧性、焊接性、高抗氢致裂纹、抗应力腐蚀和抗CO2腐蚀能力。目前国内外已普遍将高钢级管线钢X80列为石油、天然气输送管线的首选钢级，X100、X120级别管线钢作为未来发展的重点。目前国内外主要采用微合金化及控轧控冷工艺生产高钢级管线钢，通过加入Mn、Mo、Cr、Ni、Nb、Ti、V、B等合金元素，起到析出强化、细晶强化、固溶强化、相变强化作用。控轧控冷工艺由于受到轧制条件及冷却速度的局限，在高钢级管线钢产品开发中不能充分发挥作用，而超快冷工艺能有效地解决以上问题。本课题通过采用超快冷技术研究开发生产高钢级管线钢，尽可能地发挥轧制、轧后冷却等环节对钢铁产品性能的调控作用，最大限度减少对合金元素消耗，达到提高产品性能、节约能源与资源的目的。本课题针对国家能源管线建设对高钢级管线钢的需求以及钢铁企业重点产品开发的急需，采用新型超快冷工艺研究开发了低成本X80、X100管线钢。本课题在实验室应用研究的基础上开展工业化试制，论文第一部分为国内外现状与研究进展分析（第1章）；第二部分为在实验室条件下进行应用研究，由第25章组成；第三部分为在工业化生产条件下进行试制及其主要性能研究，由第610章组成；第四部分为全文总结及展望（第11章）。本课题应用热模拟实验机、热膨胀仪、光学显微镜对高钢级管线钢的再结晶规律、高温变形抗力、连续冷却转变规律等进行了研究。利用高温热重分析仪、热模拟实验机等仪器研究超快冷条件下高钢级管线钢氧化铁皮的演变规律。利用光学显微镜、扫描电子显微镜、透射电子显微镜、X射线衍射仪、能谱分析仪、显微硬度仪、万能试验机、冲击试验机、落锤试验机等手段检测高钢级管线钢的微观组织与力学性能；利用NaCl、CH3COOH、H2S水溶液和高压釜等研究高钢级管线钢的耐腐蚀性能。通过研究得到了X80管线钢动态再结晶数学模型表达式z exp(356.59/RT)和Z=1.61012[sinh（0.012)]4.095p， X100管线钢动态再结晶数学模型表达式Z exp(399.23/RT)Z6.4247.014和p。X80管线钢静态再结晶激活能为QSRX＝393kJ/mol，X SRX1exp[0.693(t/t)0.95静态再结晶动力学方程为0.5]。X100管线钢静态再结晶激活能为QSRX＝365kJ/mol，静态再结晶动力学方程为X SRX1exp[0.693(t/t)0.950.5]。 X80管线钢高温变形抗力数学模型为σ=3327.758ε0.315ε0.0109exp （-0.002Τ-1.12ε），X100管线钢高温变形抗力数学模=3155.8080.48型为0.13exp（-0.002T-0.65）。通过实验室研究，得到了X80、X100管线钢的静态和动态连续冷却转变曲线，获得了不同化学成分、不同冷却速度条件下的微观组织结构，为超快速冷却控制提供了理论依据。通过实验室研究，采用超快冷工艺生产的X80管线钢氧化铁皮结构与传统工艺生产的Q235B差别较大，其氧化铁皮结构共有5层。超快冷工艺及合金元素是导致X80高温氧化铁皮结构存在差异的主要原因。采用新型超快冷工艺生产的低钼X80管线钢与采用传统加速冷却工艺生产的高钼X80管线钢有非常相似的显微组织和力学性能。实验室试验和工业试验验证了上述结果，这证明了通过超快速冷却工艺可以降低合金成本，获得良好的力学性能。晶粒细化是超快速冷却工艺获得良好综合力学性能的主要原因。该工艺提供了一种新的技术途径来生产低成本高强度低合金钢。本课题研发的X80、X100管线钢具有低屈强比和优良低温冲击韧性。这主要是由于超快冷却在相变前保持了硬化奥氏体，降低了相变温度，另外，Nb-Ti碳氮化物在超快速冷却过程中被抑制析出。超快速冷却工艺仍然坚持了传统TMCP的两个原则，即控制奥氏体的硬化及硬化奥氏体的相变，因此超快速冷却在晶粒细化方面扮演着重要的角色。虽然在高温完成热变形，但是在形变后的短时间内钢带依然处于未再结晶状态，含有大量的“缺陷”，处于高能状态，存在大量的相变形核点。由于采用超快速冷却，钢带很快通过了奥氏体相区，奥氏体硬化状态得以保持，有利于细化相变组织。超快速冷却与传统层流冷却相比降低了相变温度，相变温度越低，组织细化的驱动力越大，因此获得了更细的组织和更优的韧性。依据NACE标准研究了超快冷工艺生产的X80管线钢抗硫化物应力腐蚀开裂（SSCC）、抗氢致开裂（HIC)和抗CO2腐蚀的情况。SSCC腐蚀实验表明，产生开裂的临界应力值在65﹪s（390MPa）左右。超过此临界值，试样的腐蚀敏感性较高，抗腐蚀能力较差，在95﹪s加载水平下，应力敏感性极高。HIC腐蚀实验表明，裂纹敏感率、裂纹长度率和裂纹厚度率均为零。抗CO2腐蚀实验表明，在CO2压力为0.1MPa条件下，平均腐蚀速率为0.6843mm/a。因此采用新型超快冷工艺生产的X80管线钢具有优良的抗SSCC腐蚀性能、抗HIC腐蚀性能和抗CO2腐蚀性能。根据上述研究结果，制定了合理的工艺路线，采用超快冷工艺生产晶粒细小、力学性能优良的X80和X100高钢级管线钢，并对X80和X100高钢级管线钢制管后的性能及焊接性能进行了研究，优良的综合力学性能主要归因于晶粒细化。本课题的研究结果证明，超快速冷却工艺开辟了一种新的低成本生产低合金高强度高韧性钢的途径。更多还原

【Abstract】 In order to adapt to the requirement of the economy and safety of pipelineengineering, pipeline steels require high strength, toughness, weldability and highresistance to hydrogen induced cracking (HIC), sulfide stress corrosion cracking(SSCC)and CO2corrosion. The X80pipeline steel has been used as the first choice for the oiland gas pipeline steel grade at home and abroad. X100and X120steels are the focus ofthe future pipeline research and development. Microalloying and thermal-mechanicalcontrol processing (TMCP) are the main technique for the product of pipeline steels.The addition of alloying elements, such as Mn, Mo, Cr, Ni, Nb, Ti, V and B, has theeffects of precipitation strengthening, fine-grained strengthening, solid solutionstrengthening and phase transformation strengthening. Due to the limit of rollingcondition and cooling speed, thermal-mechanical controlled processing can not playfull role in the development of high grade pipeline steels. However, the ultra fastcooling process provides an approach to solve the problems above. In the present work,in order to make full use of rolling and cooling on the control of mechanical propertiesas much as possible, and minimize the consumption of alloy elements, and thus saveenergy and resources, the high grade pipeline steels have been developed applyingultra fast cooling technology.In this paper, according to the requirements of high grade pipeline steels for nationalenergy pipeline construction and the important product development for steel corporation,low cost X80and X100pipeline steels have been investigated by a novel ultra fastcooling technology. The industrial trial production has been carried out on the basis oflaboratory and pilot plant tests. The literature review and current status at home andabroad is presented in the first part of thesis (Chapter1). The second part consists oflaboratory research works (Chapters2–5). The third part is trial production on anindustrial scale (Chapters6–10). The fourth part is the summary and outlook (Chapter11). The recrystallization behavior, high temperature deformation resistance andcontinuous cooling transformation were investigated by means of thermal simulator,thermal dilatometer and optical microscope. The evolution behavior of the oxide scalewas analyzed by high temperature thermogravimetric analyzer, hot simulationexperiment machine and other equipments, The microstructures and mechanicalproperties of high grade pipeline steels were investigated using optical microscope,scanning electron microscope, transmission electron microscope, X-ray diffraction andenergy dispersive system, microhardness tester, universal testing machine, impacttesting machine and drop hammer test machine. The corrosion resistance propertieswere investigated by mans of NaCl, CH3COOH, H2S aqueous solution and autoclave.The dynamic recrystallization mathematical model of X80pipeline steel isexpressed asz exp(356.59/RT)Z=1.61012[sinh （0.012)]4.095andp. Thedynamic recrystallization mathematical model of X100pipeline steel is expressed asZ exp(399.23/RT)Z6.4247.014andp. The static recrystallization activation forX80pipeline steel is QSRX＝393kJ mol-1and the static recrystallization kineticsX SRX1exp[0.693(t/t)0.95equation is0.5]. The static recrystallization activation forX100pipeline steel is QSRX＝365kJ mol-1and the static recrystallization kineticsX SRX1exp[0.693(t/t)0.95equation is0.5]. The high temperature deformationresistance model for X80pipeline steel are0.0σ=3327.758ε0.315109ε exp （-0.002Τ-1.12ε）and for X100pipeline steel is=3155.8080.480.13exp（-0.002T-0.65）. The static and dynamic continuous coolingtransformation curves for X80and X100pipeline steels have been carried out underdifferent cooling rates, which provides theoretical base for the control of ultra fastcooling modes.The low-Mo X80pipeline steel treated by a novel ultra fast cooling process has very similar microstructure and mechanical properties as those of the high-Mo pipelinesteel treated by the conventional accelerated continuous cooling process. The aboveresults have been verified by pilot plant test and industrial trial. It shows that the ultrafast cooling process can obtain superior mechanical properties by reducing alloy cost.The excellent composite mechanical properties are attributed to grain refinement. Thisnovel process provides a new technique to manufacture low cost high strength lowalloy steels. The developed X80and X100pipeline steels have low yield ratio andsuperior low temperature impact toughness. The ultra-fast cooling results in workhardened austenite before phase transformation and also low dynamic transformationtemperature. Also, the precipitation of Nb-Ti carbonitrides is inhibited during ultra fastcooling.The two principles of ultra fast cooling still insist on the conventional TMCP,namely the control of austenitic hardening and the phase transformation of thehardened austenite. Therefore, ultra fast cooling plays an important role in grainrefinement. In the present work, complete thermal deformation occurs at hightemperature, but the steel is still in the state of non-recrystallization in a very shorttime after deformation, and is in a high-energy state which contained a large number of"defects". There are many nucleation sites for the phase transformation. Theimplementation of ultra fast cooling ensures passing through the austenite region in avery short time, resulting in work hardened austenite before phase transformation. Thework hardened state austenite is beneficial to refine the transformed product. The ultrafast cooling pushes transformation to lower temperature, compared with conventionallamellar cooling. The microstructure is transformed at lower temperature and refinedby a larger driving force. Therefore, more fine-grained microstructure and superiortoughness are obtained for ultra fast cooling.According to the NACE standard, the corrosion resistance of the X80pipeline steelproduced by the newly developed ultra fast cooling to sulfide stress corrosion cracking,hydrogen induced cracking and CO2have been investigated. SSCC corrosion results show that the critical stress value to produce cracking is about65﹪s(390MPa).Above the critical value, corrosion sensitivity of the test specimen is high, and thecorrosion resistance is poor. Below the95﹪sloading level, the stress sensitivity isextremely high. HIC corrosion results show that the crack sensitive ratio, the ratio ofcrack length and width are zero. CO2corrosion resistance results show that when thepressure of CO2is0.1MPa, the average corrosion rate is0.6843mm/a. It can be seenthat the X80pipeline steel produced by the ultra fast cooling process has superiorresistance to SSCC, HIC and CO2.The oxide scale of X80steel produced by ultra fast cooling process is differentfrom that of Q235B. The oxide scale structure of the X80has five layers. The ultra fastcooling process and alloying elements are the main reason for the difference of hightemperature oxide scale structure.On the basis of above research results, rational technological route has been made.Fine-grained microstructures and superior mechanical properties of X80and X100pipeline steels have been developed by the implementation of an ultra fast coolingprocess. The excellent composite mechanical properties attribute to grain refinement.This ultra fast cooling process provides a new technique to manufacturesuperior-strength high-toughness low-alloy steels with low cost alloy additions.更多还原