1993 Fiscal Year Final Research Report Summary
Electron Microscopic Investigation of M-a Constituent in Weld HAZ of Ultra High Tension Steel and Its Embrittlement
| Project/Area Number |
04452287
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
溶接工学
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| Research Institution | Osaka Univesity |
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Principal Investigator |
MATSUDA Fukuhisa Osaka University, Welding Research Institute, Professor, 溶接工学研究所, 教授 (90028994)
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| Co-Investigator(Kenkyū-buntansha) |
IKEUCHI Kenji Osaka University, Welding Research Institute, Associate Professor, 溶接工学研究所, 助教授 (10030058)
KIKUCHI Yasushi Osaka University, Welding Research Institute, Associate Professor, 溶接工学研究所, 助教授 (90005405)
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| Project Period (FY) |
1992 – 1993
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| Keywords | High tension steel / Weld heat affected zone / M-A constituent / Pressure-vessel steel / Toughness / Embrittlement / Post weld heat treatment / electron microscopy |
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| Research Abstract |
A metallographic investigation has been carried out of the M-A constituent that has been believed to cause the embrittlement of the weld HAZ of the HT(High Tension)steel, and the effects of PWHT(Post Weld Heat Treatment)for improving the toughness of the weld HAZ has been considered, in order to contribute to the development of the ultra HT steel applicable to the welding with high heat inputs. For this, thermal cycles simulating the HAZ of welding with high heat inputs and subsequent PWHT were applied to various HT steels of 80 and 100 kgf classes, and the formation and decomposition of the M-A constituent have been examined with particular reference to their influences on the toughness with electron microscope. With all the steels employed except for one with high Nicontent, the M-A constituent was formed as the weld heat input was increased, and was classified morphologically into the elongated and massive types. The toughness of the steels was lowered as the amount of the massive M-A constituent was increased, suggesting that the massive M-A constituent was a major factor causing the embrittlement. Observation with transmission electron microscope revealed that the M-A constituent involved two types of cementites in addition to martensite and retained austenite reported by several authors. To improve the toughness of the weld HAZ, PWHTs at 500-930 K were applied to the weld HAZ of the HT steels. A significant improvement in the toughness due to the decomposition of the M-A constituent into carbide and cementite was achieved by PWHT at 623 K.A steel for pressure vessel of higher C content than the HT steels was also employed for comparison. In the weld HAZ of the pressure-vessel steel, the formation of the M-A constituent and the decrease in the toughness were observed at lower heat inputs than those of the HT steels. The toughness of the pressure-vessel steel was decreased with the increase in the elongated M-A constituent and the massive, suggesting that the e
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