高应力腐蚀磨损下含碳化物等温淬火球墨铸铁的组相调控机理研究

In order to improve grinding efficiency, the upsizing of ball mill is the development trend. Ordinary large diameter carbidic austempered ductile iron (CADI) grinding ball has large brittleness and higher crushing rate, and it is difficult to meet the requirements of large ball mill. This project mainly studies the control mechanism of carbide, matrix microstructure in CADI and the co-action mechanism of carbide and matrix under high stress corrosion wear. The number of carbides in CADI is controlled by the use of chromium element. The spheroidized treatment of cast iron uses copper-magnesium alloy nodulizer, and the microalloying of cast iron uses cerium, potassium, nitrogen, and titanium elements, which can control the morphology, scale and distribution of carbides and spherical graphite, and increase the strength and toughness of CADI. The number of austenite, austenitic carbon content and the scale of acicular ferrite in the matrix are controlled by using temperature control and cooling control on the study of isothermal transformation thermodynamics and kinetics, which can improve the wear and corrosion resistance of CADI. The failure law of CADI under the interaction of impact, corrosion and wear is studied by using the impact abrasive wear method in corrosive medium. The mechanism of matrix and carbide controls and the cooperative control mechanism under high stress corrosion wear are studied, which can increase the comprehensive performance of CADI. Above work can provide theoretical and technical support for the manufacture of CADI ball using in large wet grinding mill. The researching results can ultimately achieve the goal of improving the level of ore grinding in China.

为了提高磨矿效率，球磨机大型化是发展趋势。普通大直径含碳化物等温淬火球铁（Carbidic Austempered Ductile Iron，简称CADI）磨球脆性大、破碎率高，难以满足要求。本项目主要研究CADI碳化物、基体组织调控机理和高应力腐蚀磨损下组相协同控制：选用铬元素调控CADI碳化物数量，采用铜镁合金球化处理和铈、钾、氮、钛微合金化，调控石墨球和碳化物形态、尺度与分布，实现CADI强韧化；研究等温转变热、动力学，采用控温、控冷处理，调控基体组织中奥氏体数量、含碳量和针状铁素体尺度，提高CADI耐磨、耐蚀性；应用腐蚀介质中的冲击磨料磨损方法，研究CADI在冲击、腐蚀和磨损交互作用下的失效规律，探讨基体和碳化物调控机理及在高应力腐蚀磨损下的协同控制机制，实现CADI综合性能大幅度提高。为CADI用于制造矿山湿磨大型球磨机磨球提供理论和技术支撑，最终达到全面提升我国磨矿水平的目的。

含碳化物等温淬火球墨铸铁（Carbidic Austempered Ductile Iron，简称CADI）用做矿山湿磨中小型球磨机磨球，显现出磨耗少、破碎率低、节电和噪音小等优势。CADI晶界处粗大的网状碳化物严重破坏了基体连续性，组相性质对改善性能的机理尚不明确，腐蚀磨损和冲击疲劳失效机理缺乏深入研究，导致CADI难以直接用于生产大型湿磨机磨球。针对上述问题，本项目首先利用铬合金化调控了硬质相碳化物数量，分析了碳化物数量对 CADI 强度和韧性影响规律。基于第一性原理从原子尺度分析了微合金化元素对M3C型碳化物的异质形核机制和吸附机制，预测了微合金化处理调控CADI中共晶碳化物尺寸、形态、分布的可能性。然后结合实验对微合金化处理的效果进行验证。研究了铜合金化调控CADI耐蚀性和耐腐蚀磨损性，通过建模计算和实验相结合的方法。分析了含碳化物球墨铸铁热处理过程的热力学和动力学问题，并通过分级淬火方式调控了奥铁体基体中奥氏体数量和奥氏体含碳量及针状铁素体尺度。最后，揭示了CADI腐蚀磨损和冲击疲劳失效机理。研究表明，CADI中碳化物数量对Cr含量的变化非常敏感，铸态下随Cr含量增加，碳化物数量明显增加，并由条块状逐渐发展成为粗大的网状。微合金化元素Nb、Ti加入含碳化物球墨铸铁后，可以优先析出与M3C型共晶碳化物错配度低，界面稳定的NbC和TiC颗粒，作为M3C晶核核心，破坏了碳化物网状结构，提高了CADI的冲击韧性和耐磨性。Cu元素添加明显降低石墨与基体间的电位差，大幅度提高了CADI的耐蚀性和耐腐蚀磨损性。分级淬火工艺可以显著细化基体组织，轻微提高残余奥氏体体积分数及其含碳量，在不影响韧性的前提下，可以提高CADI耐磨性16%以上。CADI的腐蚀磨损失效机理是，基体率先腐蚀造成碳化物在裸露后出现断裂和剥落，最终引起了CADI腐蚀磨损失效。CADI的冲击疲劳失效机理是，石墨球变形和碳化物断裂产生了大量冲击疲劳裂纹，导致了CADI沿晶断裂。