1999 Fiscal Year Final Research Report Summary
Super steel bulks with nano-sized grains
| Project/Area Number |
10450253
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Structural/Functional materials
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| Research Institution | IBARAKI UNIVERSITY |
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Principal Investigator |
TOMOTA Yo IBARAKI Univ. Fuc. of Engineering, Professor, 工学部, 教授 (90007782)
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| Co-Investigator(Kenkyū-buntansha) |
SUZUKI Tetsuya IBARAKI Univ. Fuc. of Engineering, Research Associate, 工学部, 助手 (70261740)
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| Project Period (FY) |
1998 – 1999
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| Keywords | Ultra-fine grain / grain growth / heavy plastic forming / thermomechanical process / multi structure / neutron diffraction / 変形機構 |
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| Research Abstract |
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.
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