Development of Ni-free austenitic and duplex ductile irons

铸铁通常被称为含有石墨颗粒的金属基复合材料，分布在基体内作为嵌入结构。由于其相对较低的生产成本，优异的导热性和良好的摩擦学性能，被广泛应用于部件暴露于磨损和热的应用中。良好摩擦学性能的首要原因是石墨作为固体相自润滑剂存在于基体中。通过在铸铁中加入奥氏体基体，可以进一步改善铸铁的摩擦学性能。奥氏体铸铁是一系列被称为抗镍铸铁的材料，通常具有18 - 36%的高镍含量。本提案的主要目的是引入一种新的合金化概念，用于生产不含镍的奥氏体和双相（奥氏体-铁素体）组织的球墨铸铁。在这个提议中，稳定奥氏体的概念主要依赖于通过施加高温奥氏体化来使其饱和，使其具有最大可能的碳含量，然后淬火到室温（RT）。此外，加入适量的Mn可以进一步抑制Ms低于RT，从而在RT处获得奥氏体基体。另一种变体，也打算生产具有双相基体结构的球墨铸铁。在这种变体中，Si水平增加，使“铁素体+奥氏体”临界间区向高温转移，从而获得具有高碳水平的饱和“临界间奥氏体”。通过淬火，可以产生一种新的奥氏体和铁素体基体。在这个提议中，在预测的硅基相图中，定义了获得具有足够稳定的奥氏体（双相窗口）的双相结构所必需的成分温度范围。在双相基体的机械载荷作用下，亚稳奥氏体逐渐转变为马氏体，从而提高了高应变水平下的加工硬化速率（TRIP效应）。这种优良的应变硬化特性对双相球墨铸铁的机械性能和摩擦学性能都是有利的。在本项目框架内，确定奥氏体和双相球墨铸铁经济合金化的合金成分和工艺参数。此外，还研究了锰、硅含量和加工路线对材料微观组织发育和力学行为的影响。

Cast iron is commonly known as a metal matrix composite containing graphite particles distributed as an embedded constitute within the matrix. Due to its relatively low production cost, excellent thermal conductivity and good tribological performance, it is widely used in applications where the component is exposed to wear and heat. The foremost reason for good tribological properties is attributed to the presence of graphite as a solid phase self-lubricating agent in the matrix. Additional improvement of the tribological properties of cast iron is being achieved by obtaining an austenitic matrix in it. The austenitic cast iron is a series of materials known as Ni-Resist cast irons, which typically have a high nickel content of 18 to 36%. The primary aim of this proposal is to introduce a new alloying-concept for producing ductile irons with austenitic as well as with duplex (austenitic-ferritic) structure without alloying with Ni. The concept of stabilizing the austenite in this proposal relies principally on saturating it with the maximum possible carbon content by applying a high temperature austenitization, which is followed by quenching to room temperature (RT). Additionally, an adequate amount of Mn is to be added for further suppressing of Ms to be below RT and hence obtaining austenite matrix at RT. Another variant, in which production of ductile iron with duplex matrix structure is also intended. In this variant the Si level is increased to shift the “ferrite + austenite” intercritical region to high temperature and hence a saturated “intercritical austenite” with high carbon level is obtainable. By quenching, a novel matrix of austenite and ferrite can be produced. In this proposal the composition-temperature ranges within the predicted Si-based phase diagrams that are necessary to obtain the duplex structure with sufficiently stabilized austenite (Duplex Window) are defined. Upon mechanical loading of the duplex matrix, the metastable austenite fraction progressively transforms into martensite, thereby increasing the work hardening rate at higher strain levels (TRIP Effect). This expectedly superior strain hardening characteristics would be beneficial for both mechanical and tribological behavior of the duplex ductile iron. In the framework of the proposed project, the alloy compositions and processing parameters for economic alloying of the austenitic and duplex ductile irons are to be defined. Additionally, the effects of Mn and Si contents and the processing routes on the microstructural development and the mechanical behavior of the developed materials are to be investigated.