【作者】 刘清梅；

【导师】 关绍康； 吴振卿；

【作者基本信息】 郑州大学 ， 材料加工工程， 2003， 硕士

【摘要】 随着工业的发展，对金属材料不同部位的性能需要逐渐提高，尤其是对材料的耐磨性能和耐蚀性能提出了特别的要求。但一种材料同时具有高韧性和高硬度这两种性能在实际生产中是非常难以达到的，为此采用复合铸造工艺进行生产。复合双金属材料通过表面材料与基材的合理组合能在零件不同部位提供不同性能。本文采用了复合铸造工艺制备了高铬铸铁／中碳钢复合锤头，测定了复合材料的界面结合性能，重点讨论了工艺参数对复合界面结合强度、显微组织及力学性能的影响情况。同时在对复合金属凝固过程中的传热行为进行全面分析的基础上，建立了合理的数学模型，采用有限单元法对复合金属凝固过程的温度场进行了数值模拟，提出了优化的工艺参数。 双金属复合锤头使用在容易磨损的工况，所以总希望外层材料表面抗磨能力强。选用的外材高铬铸铁具有高的硬度，抗磨性，良好的流动性，通过化学成分的选择和热处理工艺的控制来获得高耐磨性能，中碳钢是一种韧性好的材料，不同的热处理工艺对它性能的影响较小。选用这两种材料的复合加上优化的工艺条件可以实现两种金属冶金结合。高铬铸铁和中碳钢的体积比值是非常重要的因素，在给定了高铬铸铁的浇注温度和中碳钢的预热温度的前提下计算出两者冶金结合的最小体积比是非常重要的。浇注高铬铸铁前，要对中碳钢表面采用硼砂处理，同时预热到一定的温度。选择适当的体积比和预热中碳钢后进行高铬铸铁的浇注将会使复合界面结合力增强，复合材料的使用效果越好。但是高铬铸铁浇注温度过高，会造成生产成本的浪费，所以合适的高铬铸铁浇注温度是很重要的。高铬铸铁导热率低，凝固过程表面和内部会出现较陡峭的温度梯度，为了避免热应力产生，淬火过程包括加热、在奥氏体化温度下进行脱稳处理、冷却三个步骤。 对在不同工艺条件下两种材料复合情况的研究表明：高铬铸铁／中碳钢复合材料的界面性能取决于界面结合力与其基体力学性能，然而不同的工艺参数对界面结合力有很大的影响。这些影响可以体现在不同条件下观察到的金相组织和测试的界面剥离强度、剪切强度的数值上。 对试样的金相组织进行研究表明：高铬铸铁在冷却的过程中将过热热量带给了中碳钢，随着工艺参数的优化，界面原子通过相对迁移可以使界面由机械结合方式向冶金结合方式过渡，界面结合增强，复合层呈犬齿状为结合的最好。高铬铸铁主要是抗磨骨架相的M₇C₃型碳化物，呈不连续的条块状，基体为奥氏体、马氏郑州大学工学硕士论文体及合金碳化物。高铬铸铁凝固的方向性层可以分为两个部分:①位于离中碳钢较近的部分，由于其的激冷作用较强而导致了高铬铸铁随机取向晶粒的形成;②远离结合线的区域，由于中碳钢的影响较小，在此处就形成了稳定的温度梯度，导致了晶粒的生长表现出了方向性。 对试样的力学性能的分析表明:减少高铬铸铁和中碳钢的温度差可以更好的获得优良的界面结合。适当的提高高铬铸铁的浇注温度和中碳钢的预热温度以及增加高铬铸铁/中碳钢的体积比是增强界面结合力学性能的关键。但是也存在临界值，高铬铸铁的温度过高后会导致金属在凝固过程晶粒的粗大。显微硬度测试表明，机械结合的界面会有脆性相的生成;剪切强度测试表明，提高体积比可以明显提高界面结合强度，但也会明显降低复合材料的整体强韧性。增加高铬铸铁的浇注温度既可以提高界面结合强度，提高了原子扩散能力，又不会降低复合材料的整体强韧性;剥离强度测试表明，冶金结合的界面不容易形成空洞而影响界面的结合性能 界面结合与金属凝固过程温度场模拟综合考虑了双金属复合热流施加、材料传热、材料相变等多方面的特点，建立了对双金属复合过程界面温度和非稳态温度场的数学模型，并利用有限单元法对此进行了分析和推导。采用C什语言，编写了界面温度和复合过程温度场计算程序，同时模型的建立采用了OPENGL的技术，加上C什BUILDER友好的人机交互界面及计算数据后处理程序，利用图形直观的反应温度变化过程，同时实现了保存数据和图形的功能。 对高铬铸铁/中碳钢复合材料在不同工艺参数下的温度场进行了模拟，对优化后的工艺参数下得到的试样和一般工艺参数下得到的试样进行了对比实验，结果表明优化工艺参数前生产的复合锤头在使用一个月后出现了细小的裂纹，而优化工艺参数后生产的复合锤头在使用数月后只有表面有小的磨损，在界面结合部位没有发现裂纹，这证实了所写软件对双金属复合前工艺参数的优化有很好的指导作用，对工厂提高产品质量，减少废品率，增加经济效益有重要作用。更多还原

【Abstract】 With the development of industry, there are many increasing demands to different parts of metal materials, especially to wear resistance and corrosive resistance. However, it is difficult for a kind of material to have high toughness and hardness on actual condition, so compounding casting often is used. Bimetal supports various properties in every part through sound combination between outer-material and inner-material. This paper introduces to use compounding cast processes for making a kind of composite, which is make up of high chrome cast iron and mid-carbon steel, tests the capabilities of interfaces and emphasizes on discussing the compounding-strength, microstructures and mechanics performances. At the same time, with the base of the whole analysis of heat behaviors in the process of bimetal compounding, a reasonable mathematics model is built and used the FEM to calculate temperature field in the process.The chosen outer-material, high chrome casting iron, is of high hardness, wear-resistance and excellent fluidness, and middle carbon steel is a kind of material with good toughness, at the same time , different kinds of heat treats have a little effect on its properties. The volumes’ rates between high chrome casting iron and middle carbon steel is an important effect, so it is very necessary to calculate the critical volumes’ rates when the casting temperature of high chrome casting iron and middle carbon steel is known. Before casting high chrome casting iron, it is better to coat borax on the middle carbon steel and give middle carbon steel a predicting temperature. But if the high chrome casting iron’s casting temperature is too high, some beneficial elements will be damaged. In a result, there is an opportune range of casting temperature.From the research about different processes , we can conclude: the capability of high chrome cast iron and mid-carbon steel’s interface is decided by the interface binding strength. These effects can be displayed by the microstructure and values of interface’s combinative strengthen and cutting strengthen.From the research of microstructures , we can conclude: overheat which releases from high chrome casting iron is given middle carbon steel. With the optimal parameters, the binding method changes from mechanical binding to metallurgy binding, and it is best to gain a composite layer with the shape of dentation. The main strengthphase of high chrome casting iron is M7C3 carbide, which is discontinuous shape. Thesolidifying direction has two parts: tone is the nearest part of interface, which has random directions of grains because of sharp temperature gradient; another is part far from interface, which has stable temperature gradient.From the research of mechanical properties, we can conclude : decreasing the temperature difference between these two materials is good to gain an excellent interface compounding. The keys of adding interface mechanical properties are to increase high chrome casting iron and middle carbon steel’s temperature properly and the volume’s rate. But the value is a critical value ,otherwise the grain will grow sharply. Micro- hardness testing dedicates that interface of mechanical binding has brittle phase; cutting strength testing dedicates that increasing volumes’ rates will benefit the binding strength of interface, but at the same tine ,the whole tenacious performance will decrease; peeling strength testing dedicated that interface of metallurgy binding is not so easy to have cavities.About the calculation of interface and temperature field, this paper considers the add of heat during the period of bimetal binding .material heat transforming and material phase changing. A model of unstable temperature field and interface temperature is built, what’s more, used FEM to analyze and confer.Using C++, a program about calculating interface temperature and temperature field is developed, at the same time OpenGL is used in this program. With the friendly visual windows, this program can realize picture’s display.Through更多还原