Study on Micro-Strain and Residual Stress of Austempered Ductile Iron

奥贝球铁（ADI）因其优异的强度和韧性近年来引起了人们的特别关注，并在一些工业中得到了实际应用。ADI的基体组织由贝氏体和残余奥氏体组成，这两种相在室温下不是普通球墨铸铁的平衡相，因此估计这两种相会受到较大的应变。通过分析铁素体和奥氏体的x射线反射，研究了ADI的微应变和残余应力；然后用x射线衍射分析了滚动疲劳过程和滑动磨损过程。所得结果总结如下：研制了一种利用普通x射线衍射仪和个人计算机对x射线反射进行测量和分析的系统。该系统能有效地进行x射线反射的数字测量，并能计算出Bragg角、半值宽度、积分宽度和积分强度、晶格常数、残余奥氏体的体积分数、微应变和残余应力等。在较低温度下处理的ADI，存在一个等温保持的时间范围，其中残余奥氏体的体积分数和溶解碳含量不随时间变化。在此时间范围内，子结构和微应变随保温时间的变化而变化。3 .通过跟踪铁素体和奥氏体在轧制表面的x射线残余应力、psi分裂和半值宽度或反射的综合宽度的变化，可以估计ADI在轧制接触中的疲劳过程和剩余疲劳寿命。ADI的轧制疲劳寿命和滑动耐磨性优于与ADI硬度相近的珠光体基体组织球墨铸铁。随着轧制和滑动，表面残余奥氏体的体积分数减小。这些优异的性能被认为是由于保留了大量体积分数的奥氏体。少

Austempered ductile iron (ADI) has recently attracted special interest for its excellent strength and toughness, and has received practical application in some industry. The matrix structure of ADI is composed of bainite and retained austenite, which are not equilibrium phases in normal ductile irons at room temperature, so that two phases are estimated to be subject to a large strain. In this work, the micro-strain and the residual stress of ADI were examined by analyzing X-ray reflections of ferrite and austenite ; then, the rolling fatigue process and the sliding wear one were investigated by X-ray diffraction.Results obtained were summarized as follows ;1. A system was developed to measure and analyze X-ray reflection by using a general X-ray diffractometer and a personal computer. This system effectively operated to digitally measure X-ray reflections and calculate the Bragg angle, the half-value breadth, the integrated breadth and the integral intensity, and the lattice constant, … More the volume fraction of retained austenite, the micro-strain and the residual stress could be exactly obtained from analysis of the reflections.2. As to ADI treated at relatively low temperature, there was a isothermally held time range where the volume fraction and the dissolved carbon content of retained austenite did not vary with time. In this time range, however, the sub-structure and the micro-strain varied with holding time.3. The fatigue process and the the remainder of the fatigue life in the rolling contact of ADI could be estimated by tracing variations of X-ray residual stress, the psi-split and the half-value breadth or the integrated breadth of reflections of ferrite and austenite on the rolling surface.4. The rolling fatigue life and the sliding wear resistance of ADI were superior to ductile irons with pearlitic matrix structure of which hardness were similar to ADI. The volume fraction of the retained austenite on the surface decreased with rolling and sliding. These excellent properties were considered to be due to large volume fraction of the retained austenite. Less