1987 Fiscal Year Final Research Report Summary
Bainite and isothermal martenste in high carbon steels
| Project/Area Number |
61550534
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
金属材料(含表面処理・腐食防食)
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| Research Institution | Tottori University |
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Principal Investigator |
OKA Muneo Tottori University, 工学部, 教授 (60029866)
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| Co-Investigator(Kenkyū-buntansha) |
HAYAKAWA Motozo Tottori University, 工学部, 助教授 (60093621)
OKAMOTO Hisaki Tottori University, 工学部, 助手 (30029889)
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| Project Period (FY) |
1986 – 1987
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| Keywords | High carbon steel / Isothermal Transformation / Lower Bainite / 等温マルテンサイト |
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| Research Abstract |
The present researchers examined the isothermal transformations in high carbon steels by means of dilatometry and microscopy and they obtained the results as follows.
1. It has been cleared that thin plate isothermal martensites (TIM) were formed at higher temperatures than Ms and they accelarated the rate of isothermal transformations near Ms.
2. It was found that lower bainites with midrib (LBm) were formed at the temperature range between 423 K and 473K. As the formation mechanism for LBm,the following two-stage process is proposed: at the first stage a TIM is solely formed at the above temperature range, which constitutes a midrib of LBm, and at the second stage the bainitic decomposition of austenite at the TIM/austenite interfaces takes place at the same temperature range. That is, an LBm is a composite of TIM and lower bainite.
3. The temperature/catbon-content/transformation diagram was constructed in the hypereutectoid range of steel (0.85 1.87%C) and it has contributed to the research for isothermal transformations of high carbon steels.
4. The following results were obtained from the comparison of the lower bainite crystallography with the martensite one: the lower bainite crystallography is in a good agreement with the theoretical prediction by the phenomenological theory of martensitic transformation which is used the (101)b lattice invariant shear instead of the (112)b one. The above conclusion has given a light to the arguments for the formation mechanism of lower bainite.
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