Super steel bulks with nano-sized grains

本研究的主要目的是利用多相组织制备超细晶材料，并探讨超细晶材料的变形机制。首先，研究了铁素体-马氏体双相钢的晶粒长大行为，发现其晶粒长大速率比单相合金的晶粒长大速率要慢。超精细，我。例如，纳米尺寸的微结构已经通过重塑性成形如拉伸和模锻获得。一个典型的例子是高碳珠光体钢，其拉制的钢丝被称为钢琴丝。在此基础上，研究了获得细小组织的形变热处理工艺。在本研究中，我们提出了在不进行高合金化的情况下获得细晶组织的观点。其次，利用原位中子衍射技术研究了超细晶材料的变形机制。一个钢琴线被拉在一个逐步的方式和中子衍射分布在每一步获得。轮廓分析结果表明，铁素体基体中的晶格应变相对于外部应力变得大得多。这意味着铁素体基体本身被强化，这与退火钢的情况不同，在退火钢中，铁素体板或颗粒承受比基体更大的应力，即。例如，通常的分散硬化机制。

The objectives of the present study are to show the fabrication of ultra-fine grained materials by using multi-structure and to examine the deformation mechanism of such a fine grained material.First, the grain growth behavior in ferrite-martensite dual phase steels was studied and the growth rate was found extremely slow compared with that for single phase alloys. The ultra-fine, i. e., nano-sized, microstructures have been obtained by heavy plastic forming like drawing and swaging. One typical example is high carbon pearlite steels whose drawn wire is so called piano wire. Based on the above findings, thermo-mechanical process was studied to obtain fine microstructure for cast irons. It has been proposed throughout this study that the fine microstructure should be achieved without high alloying.Second, the deformation mechanism for ultra-fine grained materials was studied by means of in situ neutron diffraction. A piano wire was pulled in a step by step manner and neutron diffraction profiles were obtained at each step. The results of profile analysis have revealed that the lattice strain in the ferrite matrix becomes comparably larger with respect to the external stress. It means that the ferrite matrix itself is strengthened, which is different for the cases of annealed steels, in which cementite plates or particles bears larger stress than the matrix, i. e., usual dispersion hardening mechanism.