1997 Fiscal Year Final Research Report Summary
Microstructural Control by Dynamic Recrystallization and Phase Transformation
| Project/Area Number |
08455332
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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 |
Material processing/treatments
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| Research Institution | The University of Electro-Communications (UEC) |
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Principal Investigator |
SAKAI Taku University of Electro-Communications, UEC,Faculty of EC,Professor, 電気通信学部, 教授 (40017364)
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| Co-Investigator(Kenkyū-buntansha) |
MIURA Hiromi University of Electro-Communications, UEC,Faculty of EC,Associate Professor, 電気通信学部, 助教授 (30219589)
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| Project Period (FY) |
1996 – 1997
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| Keywords | Dynamic phase transformation / Dynamic recrystallization / Static recrystallization / Austenitic grain / Ferritic grain / Iron and steels / Thermomechanical treatment / Grain refinement |
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| Research Abstract |
The effects of dynamic recrystallization (DRX) and dynamic phase transformation (DPT) on the grain refinement of iron and steels were studied by using interstitial free (IF) steels and a ferritic stainless steel. The main results are summarized as follows. The result of 1 and 2 are for IF steels, and those of 3 and 4 for the latter steel.
1. The DRX austenite shows multiple-step restoration processes and do not go to full softening for a long period of annealing time. Finer DRX austenite grains in IF steels lead to the evolution of finer ferrite grains compared with usual grains. Ferrite grains scarcely grow even after annealing of DRX austenite for a long period of time. These results from the stable existence of growing grains in DRX matrices.
2. Fine carbonenitrides precipitate on high density dislocation substructures developed in austenitic DRX grains. This can result in the stabilization of austenitic DRX grains, followed by the evolution of fine ferrite grains during repid cooling.
3. Stress-strain curves of a crominum ferritic steel in the metastable austenite phase show a sharp stress peak and a rapid work softening, followed by a steady state flow at hihg strains. The work softening results from austenite (gamma) to ferrite (alpha) phase transformation during deformation ; namely, this is termed dynamic phase transformation. This kind of gamma to alpha transformation, however, does not statically take place.
4. Ferritic grain sizes evolved by dynamic phase transformation decrease with increasing strain rate and temperature, leading to increase in room temperature hardness.
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