2004 Fiscal Year Final Research Report Summary
Microstructure control of ferrous martensite by defects inherited from austenite
| Project/Area Number |
14205104
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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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 | Kyoto University |
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Principal Investigator |
MAKI Tadashi Kyoto University, Department of Materials Science and Engineering, Professor, 工学研究科, 教授 (10026247)
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| Co-Investigator(Kenkyū-buntansha) |
FURUHARA Tadashi Kyoto University, Department of Materials Science and Engineering, Associate Professor, 工学研究科, 助教授 (50221560)
MORITO Shigekazu Kyoto University, Department of Materials Science and Engineering, Research Associate, 工学研究科, 助手 (00301242)
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| Project Period (FY) |
2002 – 2004
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| Keywords | steel / phase transformation / martensite / dislocation / precipitation / strength / shape memory alloy / thermomechanical processing |
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| Research Abstract |
(1)Inheritance of matrix dislocation and precipitate into martensite
In ausformed lath martensite in Fe-20%Ni-5.5%Mn, dislocations introduced in the austenite are inherited into martensite with the Bain correspondence. γ'-Ni3Al precipitated in the austenite of Fe-31%Ni-10Co-3Ti is inherited into thin-plate martensite. When γ', which has a finer size due to a short aging, changes its structure by transformation shear, thermally elastic martensite is formed in the cooling. When the γ' size gets larger by prolonged aging, no structure change occurs for γ' and athermal martensite is formed in the cooling.
(2)Refinement of lath martensite by precipitation
Lath martensite packets/blocks are refined by decreasing austenite grain size in Fe-(1.5,2)Mn-0.2C alloys. In the austenite of which grain size is about 2μm with pinning by alloy carbide, a block size of 1μm was obtained. The strength of the as-quenched martensite increases by following a Hall-Petch type relation against the block size. Finely dispersed V(C,N) particles are capable of refining the lath martensite structure.
(3)The change of martensite/bainite substructure with inherited dislocations
In lenticular martensite, substructure changes from twinning to dislocations. Near the martensite/austenite interface, the austenite contains tangled dislocations due to plastic accommodation of transformation strain. Similar tangled dislocations are also observed in the martensite, resulting in local lattice orientation near the interface. It is concluded that those dislocations are inherited from the surrounding austenite. It is observed that the deformation of austenite prior to transformation (ausforming) refines lath martensite structures but results in the coarsening of upper bainite structures in Fe-Ni alloys.
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Research Products
(18 results)
