高碳铬轴承钢离异共析转变的热力学与动力学机理及可控性研究

High carbon chromium bearing steels are high-end variety in steel materials, which are mainly used for the bearings. The shape and distribution of carbides in the steels have great influence on the quality of bearing. Divorced eutectoid transformation has a special meaning for the spheroidizing of carbide, which is considered to be the basis for the most likely to achieve rapid spheeroidizing in high carbon chromium bearing steels. However, due to the understanding of divorced eutectoid transformation in high carbon chromium bearing steels is far from complete, the transformation is often neglected in the study of computational materials science. The key point of the calculation of the medium scale materials is the precision of thermodynamic information in the process. This project intends to study divorced eutectoid tansformation in GCr15 - representative of high carbon chromium bearing steel as starting point to research problems of thermodynamics and kinetics on the transformation of high carbon chromium bearing steels. Main contents include: 1. gathering of thermodynamic informations and clarifying their association on divorced eutectoid transformation of high carbon chromium bearing steels; 2. construction and evaluation of thermodynamics database on divorced eutectoid transformation in high carbon chromium bearing steels; 3. The exploration of complex kinetic factors and their controllability in divorced eutectoid transforming of high carbon chromium bearing steels. Our team has carried out some preliminary work, and achieved significant results. So we are with a certain basis of the work. The research of this project is of great significance to promote the development of high quality of bearings. And it also has contributed to enrich the knowledge of computational material science.

高碳铬轴承钢是钢铁材料体系中的高端品种，主要用于制作轴承。钢中碳化物形态与分布对轴承品质影响重大。离异共析转变对碳化物球化有特殊意义，被认为是最有可能实现碳化物高效球化处理的依据。然而，由于对高碳铬轴承钢离异共析转变的认识还远不够全面，在计算材料学介观尺度计算研究时，这一转变过程常常被忽视。介观尺度材料计算的关键是过程热力学信息的精准性。本项目拟以高碳铬轴承钢的代表性钢种—GCr15离异共析转变研究为切入点，对高碳铬轴承钢离异共析转变相关热力学和动力学基本问题开展研究，主要内容包括：1、高碳铬轴承钢离异共析转变的热力学信息及其关联性；2、高碳铬轴承钢离异共析转变热力学数据库的构建与评估；3、高碳铬轴承钢离异共析转变复杂的动力学因素和可控性原理。本课题组已开展了一些前期工作，取得了有意义的结果，具有一定的工作基础。本项目研究对推动高品质轴承研发意义重大，对丰富计算材料学知识亦有重要意义。

高碳铬轴承钢是钢铁材料体系中的高端品种。钢中碳化物形态与分布对制品质量影响重大。离异共析转变被认为是最有可能实现碳化物快速球化处理的依据。本课题基于上述观点开展了如下工作：. 1、测定了GCr15钢共析转变温度区间，研究了奥氏体化温度、时间和未溶碳化物量对离异共析转变的影响。. 2、开展了GCr15钢离异共析转变过程相变热力学研究，对比计算了两种不同形态碳化物（即片状和球状）形成的驱动力。. 3、开展了热变形对GCr15钢离异共析转变过程影响的研究。. 4、模拟分析了碳化物颗粒大小对深沟球轴承滚子疲劳损伤的影响。. 通过以上研究，得到如下认识：. 1、GCr15钢的共析珠光体转变是在一个温度区间完成的。离异共析转变发生在共析转变温度区间的较高温度范围，直接形成粒状珠光体，随温度下降，经过一个临界点后，逐渐变化到以片状珠光体转变为主导。GCr15钢中的碳化物主要为M3C型含铬碳化物。. 2、由于含铬碳化物属于正方结构，且因晶体的各向异性，导致其沿择优方向生长，因此，自然生长的碳化物形态为片状。但在共析转变较高的温度区间，驱动力相对较小，且原子扩散能力相对较强，相变阻力较低，碳化物可以直接形成球状。发生离异共析转变的相变驱动力是自由能，大大高于片状珠光体溶断进行球化的驱动力—界面能。. 3、热塑性变形的温度、变形量、变形道次和变形速率对离异共析转变的影响并不十分显著。但变形后的保温时间对离异共析转变的形成有明显的影响。过于粗大的球状碳化物会降低轴承的使用寿命。. 4、实验室条件下，推荐的GCr15钢球化工艺为：805℃保温30分钟奥氏体化，未溶碳化物含量为10.89%，平均尺寸为0.4987微米。随炉冷至715℃保温150分钟，再随炉冷却650℃取出空冷至室温。GCr15钢经上述球化处理后，试样平均硬度为181HBW。

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