连续缓慢冷却贝氏体转变特征及合金元素分布的影响

利用热膨胀仪对实验用预硬型塑料模具钢不同冷却速率进行热模拟,观察组织形貌,并用电子探针显微分析仪对不同组织区域进行定点分析,发现Mo,Si在抑制珠光体转变及粒状贝氏体转变过程中起重要作用.在冷速≤0.015℃/s 冷却条件下,组织转变较为复杂,转变过程中有珠光体出现.由于内部合金元素微观分布不均匀,贝氏体组织分为片状和...     

Characterization of Austempered Ductile Iron Through Barkhausen Noise Measurements

The outstanding mechanical properties of austempered ductile irons (ADI) are linked to the microstructure of the matrix obtained by subjecting a ductile iron with an appropriate composition to a heat treatment called austempering. Then the microstructure of the matrix consists of bainitic ferrite with different volume fractions of retained austenite. The aim of this work is to use the magnetic Barkhausen noise (MBN) as a nondestructive method for characterizing the microstructure of ADI. First, it is shown that the amplitude and position of the peak-shaped MBN response is quite sensitive to the microstructure of the matrix of ductile irons. Thus each type of constituent (equiaxial ferrite, pearlite, martensite or bainite) exhibits a typical response and, in turn, it can be identified from the MBN response. Furthermore, a good correlation is found between MBN signal parameters and ADI heat treatment parameters, indicating that MBN is also quite sensitive to fine evolutions of the microstructure of ADI. MBN peak position is especially sensitive to the type of bainite, whereas peak amplitude is linked to the progress of the bainite reaction. Hence MBN measurements appear to be a powerful tool to assess some important microstructural features of ADI castings.     

Ni对球墨铸铁热处理的影响

采用电子探针，图象分析仪、差质变分析仪和Ｘ射线衍仪定量研究了Ｎｉ在球铁中的分布和Ｎｉ铸态球铁组成相比例奥氏体中含碳量以及贝氏体转变ＴＴＴ曲线线的影响，结果表明，Ｎｉ在球铁中呈连续负偏析，其加入可以影响球铁组成上比例，并使粤氏体中含碳量和贝氏体转变孕育期期增加。     

A Dilatometry Study of the Austenitization and Cooling Behavior of Ductile Iron Meant for the Production of Austempered Ductile Iron (ADI)

An understanding of the kinetics of transformation during austenitization, cooling, and austempering of ductile iron is critical to achieving the desired microstructures and ultimately mechanical properties in austempered ductile iron (ADI). To this end, dilatometry experiments have been carried out to study the austenitization and cooling behavior of an unalloyed ductile iron. When a typical austenitization temperature of 900°C is used, unlike in steels, there is an initial expansion of the specimen, which levels off as the soaking time is increased. This occurs despite the fact that the temperature remains constant. This phenomenon, hitherto unreported, highlights the subtle differences between the austenitization of ductile irons and steels. The initial expansion is attributed to the increase in austenite lattice parameter, arising from the diffusion of carbon from the graphite nodules. The levelling off signals the saturation of austenite with carbon and can therefore be used as an indicator of the appropriate austenitization time. Studies of the cooling behavior of unalloyed ductile iron have also shown that the dilatometer can be used as a tool for determining the minimum cooling rates, which guarantee the formation of ausferrite during austempering. When ductile iron is appropriately heat-treated based on results from dilatometry studies, the mechanical properties obtained are typically superior and consistent.     

等温淬火对奥贝球铁上贝氏体转变动力学的影响

本文研究了等温淬火过程中奥氏体化温度和等温淬火温度对奥贝球铁上贝氏体第一阶段转变速度的影响及其机制；观察与测定了不同等温转变时奥贝球铁的组织与性能。结果表明，升高奥氏体化温度和等温淬火温度，使上贝氏体第一阶段转变速度减慢，在该转变结束时，奥贝球铁组织与性能最稳定。     

马氏体基体含碳量对马氏体球铁磨损性能的影响

针对马氏体球铁,研究了马氏体基体不同含碳量(不同奥氏体化温度)对两体磨损和冲击磨料磨损耐磨性的影响。结果表明:在软磨料作用下的高应力两体磨损中,马氏体球铁以疲劳机制破坏,硬磨料作用下以切削机制破坏;在有较大冲击载荷作用的动载磨料磨损中,马氏体球铁存在有抗冲击疲劳剥落的最佳马氏体含碳量;石墨球的存在对耐磨性有害。     

奥－贝球铁断裂与疲劳研究的新近进展

奥 -贝球铁具有很强的强度、塑性、韧性、疲劳强度和耐磨性等综合性能 ,应用日益广泛 ,已成为一种重要的工程材料。近年来对其断裂与疲劳的研究发展很快 ,得到不断的深入 ,本文详细介绍了其新近进展。     

奥贝球铁的现状与发展趋势

在综合大量文献资料的基础上，论述了奥贝球铁的研究和应用现状，阐述分析了存在的问题，指出了解决的途径和发展趋势。     

球墨铸铁机械性能的优化模型

通过对球墨铸铁机械性能影响因素的分析，指出在一定的生产条件下，球墨铸铁的机械性能主要取决于组织、成分。利用Matlab中的Neural Network Toolbox仿真环境和BP模型算法建立了球墨铸铁机械性能的优化模型，详细论述了模型结构的设计、数据处理、网络初始化、训练与仿真的过程。该方法对提高球墨铸铁的机械性能具有积极作用。     

电脉冲对铸态高韧性球墨铸铁凝固组织及性能的影响

对铸态高韧性球墨铸铁QT400-18的凝固过程进行电脉冲处理,电脉冲参数为电压2 600 V,频率0.88 Hz,电容200μF,处理时间15min。通过对比试验可知:电脉冲处理可使铸铁的过冷度相比未处理的升高12K,改善了石墨形核和生长的动力学条件,从而使球状石墨的粒径减小,石墨球数量增加。铸铁经过电脉冲处理,球化率由未处理的平均80%提高到平均91%,石墨球数由平均172/mm~2提高到209/mm~2,石墨不易变态生长,圆整度得到改善。同时,球墨铸铁的凝固组织得到了改善,铁素体数量增加,达到83%,相比未电脉冲处理的试样提高了26.6%,铁素体晶粒小于未处理试样,基体中分布的珠光体数量和片层间距减少,在抗拉强度符合要求的条件下,伸长率提高了4.89%,-233K的冲击功Akv提高了3.56J。