【作者】 高岩；

【导师】 刘晨曦； 孙莉；

【作者基本信息】 天津大学 ， 材料工程， 2018， 硕士

【摘要】 9Cr铁素体/马氏体（9Cr Ferritic/Martensitic steel）钢因其卓越的热物理性能而被誉为是未来核反应堆中最有应用前景的结构材料。核反应堆第一壁/包层的结构复杂,在核反应堆部件中对于9Cr铁素体/马氏体钢的焊接要求较高,一般要求接头处的成分和微观组织均匀并具有良好的抗辐照脆性,残余应力尽可能小,因此,焊接技术和工艺的成熟对9Cr铁素体/马氏体钢在核反应堆中的实际应用至关重要。本文旨在探索适用于9Cr铁素体/马氏体钢的新型焊接工艺,从而为9Cr铁素体/马氏体钢的连接方法提供新的思路和实验依据,本文开展了9Cr铁素体/马氏体钢的线性摩擦焊以及采用电沉积镍做中间层的扩散连接实验。通过光镜、扫描电镜、透射电镜以及电子背散射衍射等现代材料分析测试方法,对9Cr铁素体/马氏体钢采用扩散连接和线性摩擦焊工艺的可焊接性以及连接界面的组织演变和力学性能进行了系统研究,研究结果表明:采用电沉积镍作为中间层进行9Cr铁素体/马氏体钢的扩散连接可以获得冶金结合良好的扩散连接接头,在9Cr铁素体/马氏体钢与镍中间层的连接界面处形成由富含镍的（γFe,Ni）固溶体组成的过渡区域,在室温下转变为残余奥氏体,有利于连接接头韧性的提高以及阻碍裂纹扩展。此外,本文还研究了回火处理对扩散连接后9Cr铁素体/马氏体钢连接接头的组织演变和力学性能的影响。在回火处理后,连接界面处的过渡区域由于固溶原子对位错的钉扎作用具有高密度位错,起到了固溶强化的作用。拉伸实验表明,回火处理可以提高接头的结合强度,经过回火处理后的连接试样在母材金属中断裂,而没有经过回火处理的试样在连接界面处断裂。线性摩擦焊可以实现9Cr铁素体/马氏体钢的有效连接,焊接接头区域无孔隙和裂纹等缺陷存在,在线性摩擦焊过程中的高温以及高剪切力和轴向应力的作用下,焊接区域发生高温塑性变形以及动态再结晶,焊缝附近的晶粒细小,起到细晶强化的作用,有助于提高焊接接头的强度,焊缝区的硬度最高。热输入随着离焊缝区的距离增加而逐渐降低,热力影响区仅发生小范围的动态再结晶,热影响区有大量弥散分布的M₂₃C₆碳化物析出。线性摩擦焊接头的抗拉强度为478MPa,试样均在母材处断裂,验证了9Cr铁素体/马氏体钢通过线性摩擦焊获得的焊接接头的可靠性。更多还原

【Abstract】 9Cr ferritic/martensitic steels are considered as the most promising structural material in the nuclear reactors for their outstanding thermal physical properties.Due to geometrical complex structure in test blanket module,the welding requirements for9Cr ferritic/martensitic steels are high in nuclear power components.Generally the composition and microstructure of the joints are required to be uniform and good to resist radiation brittleness,meanwhile,the residual stress is as small as possible.Therefore,the maturity of welding technology and process is crucial for the practical application of 9Cr ferritic/martensitic steels in the nuclear reactor.This paper explores new welding technology of 9Cr ferritic/martensitic steels to provide the experimental foundation and new idea for the welding method of 9Cr ferritic/martensitic steels.Diffusion bonding with an electro-deposited Ni interlayer and linear friction welding are employed to join 9Cr ferritic/martensitic steels.The weldability of 9Cr ferritic/martensitic steel using diffusion bonding and linear friction welding as well as the microstructure evolution and mechanical properties of bonded joints are systematically characterized by optical microscope（OM）,scanning electron microscope（SEM）and transmission electron microscope（TEM）,respectively.The main conclusions can be summarized as follows:The diffusion bonding of 9Cr ferritic/martensitic steels with an electro-deposited Ni interlayer was developed.For the steel/Ni interface,the inter-diffusion of elements formed Ni-rich solid solution at the transition region that would transform into retained austenite at room temperature.The retained austenite along the joint interface may release the local stress concentration and reduce the microcrack formation opportunities in the steel during deformation due to its greater plasticity.In addition,the effect of tempering treatment after diffusion bonding on the microstructure evolution and mechanical properties of the joint is also studied.After tempering treatment,the joint interface in steel still has high density of dislocations,due to the pinning effect of solute atoms.The tempering treatment can improve interface bonding at the joints according to the tensile tests.Since the joints prior to tempering treatment fractured at the interlayer,while the joints subjected to tempering treatment fractured in the base steel.No intermetallic compounds were observed at the bonding interface.9Cr ferritic/martensitic steels can be effectively joined by linear friction welding,the joints that are free of cracks and pores can be obtained under appropriate welding parameters.The high-temperature plastic deformation and the dynamic recrystallization are caused by high temperature and high stress during welding,resulting in the smaller grains near the weld zone.Due to the strengthening of fine grains,the strength of the joints has been improved and the weld zone exhibits the highest microhardness.The heat input gradually decreases with the increase of the distance from the weld zone,partial dynamic recrystallization occurs in the thermo-mechanically affected zone and massive M₂₃C₆ carbide particles precipitated along the prior austenite and martensite lath boundaries in the heat affected zone.The tensile strength of joints is about 478 MPa and the fracture of the joints takes place at the base metal.Tensile strength tests at room temperature verify the reliability of the joint attained by linear friction welding.更多还原