球墨铸铁热轧辊等离子合金涂层的织构化阻裂机理及其性能研究

The ductile cast iron hot rolls are widely used to roll the thick plate and profile steel. The intense wear and thermal fatigue during work remarkably reduce the lifetime and rolling quality of the hot rolls. Strengthening and repair of the rolls surface play an important role in the energy conservation and effect-raising of the metallurgy industry. Plasma alloying can be used to strengthen and repair the ductile cast iron hot rolls with low cost. However, its industrial application is restrained due to the crack of the alloying coating during preparation. In this project, the texture alloying coating on the ductile cast iron hot rolls is fabricated to solve the issue of the crack of the alloying coating. The influence factors of the interface morphology between the alloying coating and the ductile cast iron hot roll substrate will be researched. The interface morphology between the alloying coating and the ductile cast iron hot roll substrate will be discussed. The effect mechanism of the texture on the interface morphology of the alloying coating will be illuminated. The relationship between the residual stress and the crack of the coating during the plasma alloying process will be investigated, thereby reveals the influence rule of the texture on the crack of the ductile cast iron hot roll coating. The stress orientation of the alloying coating will be investigated, and the physical model about the stress orientation and temperature field will be built. A new method that can determine the plasma texture track will be proposed. The thermal fatigue, red hardness and wear resistance of the texture alloying coating will be measured to reveal the change rule of the properties of the texture alloying coating. The strengthening mechanism of the alloying coating will be clarified. According to the investigations of this project, the crack resistance mechanism of the texture alloying coating on the surface of the ductile cast iron hot rolls will be revealed. In addition, it will lay a theory foundation for the application of the texture alloying coating on the ductile cast iron hot rolls.

球墨铸铁热轧辊广泛用于厚板和型钢的轧制，工作时剧烈的磨损和热疲劳显著降低其寿命及轧制质量，轧辊表面的强化修复对冶金企业节能提效具有重要作用。等离子合金化可低成本强化修复球墨铸铁热轧辊，但合金涂层在制备时易开裂问题制约了其应用。本项目通过对球墨铸铁热轧辊合金涂层织构化来解决涂层制备时的开裂难题。将研究轧辊基材与合金涂层间界面形态的影响因素，分析轧辊基材与合金涂层结合的形态特征，阐明织构化对合金涂层界面形态的作用机理；研究织构化合金涂层残余应力与涂层开裂的关系，揭示织构化对球墨铸铁轧辊涂层开裂的影响；研究合金涂层的应力取向，构建涂层应力取向-温度场物理模型，提出科学确定等离子织构化纹理新方法；测定织构化合金涂层的耐磨性、红硬性和热疲劳，揭示织构化合金涂层性能变化规律，阐明织构化合金涂层的强化机制。本项目将揭示织构化对球墨铸铁热轧辊涂层阻裂机理，为织构化涂层在球墨铸铁热轧辊上的应用奠定理论基础。

球墨铸铁热轧辊广泛用于厚板和型钢的轧制，工作时剧烈的磨损和热疲劳显著降低其寿命及轧制质量，轧辊表面的强化修复对冶金企业节能提效具有重要作用。等离子束合金化可在球墨铸铁轧辊表面形成合金涂层，实现低成本强化修复，但合金涂层在制备时易开裂的问题制约了其工业应用。为了解决上述难题，本项目在M2高速钢合金涂料的基础上开发了两种新的涂料，即钴基高速钢和镍硬合金涂料，并提出了通过涂层表面点状和线状织构化处理的阻裂新方法，主要研究内容及结果如下：（1）添加Co元素制得的钴基高速钢合金涂层可提高修复涂层的抗氧化性，虽然对合金涂层的红硬性和高温耐磨性不利，但仍能够满足球墨铸铁热轧辊修复涂层的性能需要。（2）开发了新的NiCrMo镍硬合金化涂层并研究了多道次合金化处理对涂层厚度和质量的影响。研究发现，随着处理道次的增加，涂层厚度逐渐增大，但是当进行三道次处理时，因热输入较多而会在涂层中产生严重的皮下气孔，削弱了涂层的质量，因此，最佳的合金化处理道次为二道次。（3）利用EBSD/SEM研究了合金涂层与球墨铸铁轧辊基材（QT600-3和QT500-7）的界面组织和晶粒取向。因发生自淬火，界面组织由奥氏体转变为针状马氏体，且不具备明显的择优取向。（4）对比分析了点状织构化和线状织构化涂层的抗热疲劳性，点状织构化涂层抗热疲劳优于线状织构化涂层，其裂纹宽度仅为基体同频次淬火裂纹宽度的1/10左右。（5）模拟了点状织构化、线状织构化和线状搭接处理的三种合金涂层在等离子束修复时的温度场和应力场。温度场模拟结果表明点状织构化处理的合金涂层温度最低，约为1790℃，其次是线状织构化合金涂层，约为1820℃，线状搭接织构化处理的合金涂层温度最高，约为1993.68℃；应力场模拟结果表明点状织构化处理的合金涂层的残余应力最低，约为1080 MPa，而线状织构化和线状搭接合金涂层的残余应力最高，约为1120 MPa。本课题的研究拓展了球墨铸铁热轧辊修复途径，延长其使用寿命，提高轧制质量，对冶金企业节能提效具有重要意义。