【作者】 李浩；

【导师】 严文；

【作者基本信息】 西北工业大学 ， 材料物理与化学， 2007， 硕士

【摘要】 本文采用LMC（Liquid Metal Cooling）高温度梯度定向凝固装置，研究了凝固速度及合金元素对高铬铸铁中初生碳化物和共晶碳化物析出行为的影响。在此基础上开展了以Fe-Cr-C系共晶合金和过共晶合金的研究，借助金相技术、电镜技术、图像处理技术等多种分析测试手段，考察了试样的界面形态、组织特征等凝固特性，建立了凝固过程控制与凝固组织的对应关系。 本文研究了过共晶高铬合金铸铁（3.51％C-30.8％Cr）碳化物的生长形态及力学性能。结果表明，本实验所用成分的相组成主要有（Fe-Cr）α相，M₇C₃相和少量奥氏体γ相；经过定向凝固后，碳化物纤维有明显的取向性，碳化物沿[150]方向生长，基体相沿[110]方向生长；初生碳化物为M₇C₃型碳化物；初生碳化物以包抄方式生长，逐渐形成闭合六边形环状；初生碳化物横截面的显微硬度为HV2000左右，纵截面为HV1450左右；随着凝固速的增加，抗拉强度呈马鞍型变化，当凝固速度为15μm／s时，抗拉强度最大，可达1913MPa。 过共晶高铬合金铸铁（3.51％C-30.8％Cr-1.03％V）和共晶高铬合金铸铁（2.85％C-30.80％Cr-0.40％Re）的主要相组成仍为（Fe-Cr）α相，M₇C₃相和少量奥氏体γ相；通过EDS分析，V主要存在于M₇C₃碳化物当中，可作为初生碳化物的形核质点，进而细化初生碳化物，RE主要存在于基体组织中，可细化共晶碳化物纤维，使其均匀的分布在基体组织中；Fe-Cr-C-V合金初生碳化物横截面的显微硬度为HV2200左右，纵截面为HV1550左右；随着凝固速的增加，其抗拉强度先增加后减小，平均抗拉强度为2029MPa，当凝固速度为15μm／s时，抗拉强度最大，可达2163MPa；Fe-Cr-C-RE合金共晶碳化物横截面的显微硬度为HV1850左右，纵截面为HV1360左右；随着凝固速的增加，抗拉强度逐渐增加，平均抗拉强度为2291MPa，当凝固速度为15μm／s时，抗拉强度最大，可达2486MPa。 在研究了碳化物生长形态的基础上，本文进一步探讨了Fe-Cr-C自生复合材料的组织和性能。结果表明，以1μm／s的速度凝固时固液界面比较平直，以2μm／s的速度凝固时固液界面虽然仍然保持平直，但局部已经开始失稳，当凝固速度为5μm／s时，固液界面已严重失稳，变得参差不齐；随着凝固速度R的增加，初生碳化物的大小S和体积分数B均减小，具有有S=0.0036R^-0.8078和B=9.1956R^-0.4882的关系式；共晶碳化物大体上比较规则，但在其精细结构的形貌上出现许多分叉，而且随凝固速度的增加，碳化物分叉现象越显著；随着凝固速度R的增加，共晶碳化物的间距λ减小，具有λ=11.95R^-0.6724的关系式；Fe-Cr-C自生复合材料的抗拉强度随着凝固速度的增大先增加，在凝固速度为15μm／s时达更多还原

【Abstract】 In the present paper, the high temperature gradient directional solidification apparatus with liquid metal cooling （LMC） has been used to study the influence on the precipitation behavior of both primary and eutectic carbides with different solidification rate and alloying elements. Longitudinal and transverse metallographic specimens for microscopic observation have been prepared using conventional techniques. The morphology evolution was observed with NikonEPIPHOT300 metal scope and KYKY-AMRAY1000B SEM. The size, volume fraction and spacing of M7C3 fibers have been measured with SISC-LAS instrument. JEM-2010F TEM is used to observe M7C3 phase. On these bases, the effect of solidification rate on the solidified microstructures such as size of primary M7C3 phase, volume fraction of primary M₇C₃ phase and average spacing of eutectic M₇C₃ phase are systematically investigated in the present paper. The relationship between solidification processing factors and solidification microstructures have been discussed and established.Morphology and mechanical property of directional solidified Fe-Cr-C hypereutectic alloy （3.51%C-30.8%Cr） have been studied. The results show that the alloy consists of Fe-Cr matrix, M7C3 and trace amounts of γ; After directional solidification, carbide fibers are regularly aligned in one direction; The carbides grow along with the direction of [150] and the matrix grows along with the direction of [110]; Primary carbides and eutectic carbides are M₇C₃-type carbides; Primary carbides grow in the manner of outflanking and the transverse section of primary carbides is hexagonal; With the increase of solidification rate, the size and volume fraction of primary carbides will be decreased; The microhardness of transverse section of primary carbides is about HV2000, while that of longitudinal section of primary carbides is about HV1450. With the increase of solidification rate, the tensile strength of Fe-Cr-C hypereutectic alloy decreases first, then increases and finally drops sharply. The maximum tensile strength is 1913MPa with the solidification rate of 15μm/s.Fe-Cr-C-V hypereutectic alloy （3.51%C-30.8%C-1.03%V） and Fe-Cr-C-RE eutectic alloy also consist of Fe-Cr matrix, M7C3 and trace amounts of γ ; According to EDS analysis, Element V which exists mainly in the M7C3 carbides can refine primary carbides as the nucleation particles; RE which exists mainly in the matrix can refine更多还原