1990 Fiscal Year Final Research Report Summary
Creep-Embrittlement and Creep-Cracking in Heat Affected Zone of Cr-Mo Steel
| Project/Area Number |
63420048
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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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 | Mie University |
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Principal Investigator |
TAMAKI Koreaki Mie University, Faculty of Engineering, Professor, 工学部, 教授 (30023047)
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| Co-Investigator(Kenkyū-buntansha) |
SUZUKI Jippei Mie University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (90111872)
KOJIMA Masatoshi Mie University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (90023275)
KATO Seizo Mie University, Faculty of Engineering, Professor, 工学部, 教授 (30023229)
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| Project Period (FY) |
1988 – 1990
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| Keywords | Cr-Mo steel / Heat-affected-zone(HAZ) / HAZ-creep-embrittlement / HAZ-creep-cracking / Simulation system / Transition temperature / Grain-boundary-cracking / Prior-austenite grain boundary |
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| Research Abstract |
Creep-embrittlement and creep-cracking have recently been inspected in certain welded constructions, such as boilers and reactors. They occur in the grain-coarsened-zone (GCZ) of heat-affected-zone (HAZ) when it is reheated in the temperature range of 500 to 600^OC. 11/Cr-1/Mo heat-resisting steel is very susceptible to them. These investigators have constructed an experimental system for simulating those phenomena ; it was composed of (1) a simulator of weld-thermal-cycle, (2) creep-loading test machines and (3) a Charpy-impact-test machine. The main results obtainedby using this experimental system are summarized as follows.
1. Nature of HAZ-creep-cracking : HAZ-creep-cracking can be defined as "the cracking which occurs along the prior-austenite grain boundary in GCZ, with a very small quantity of deformation at the time when the HAZ is reheated". This cracking occurs in an earlier time-period with an increasing stress and a raising temperature.
2. Nature of HAZ-creep-embrittlement : HAZ-creep-embrittlement can be defined as "the phenomenon of raising the transition temperature of GCZ after a prolonged reheating, such as 2000hr at 550^OC". This embrittlement occurs in an earlier time-period with an raising temperature.
3. Mechanism of causing these phenomena : HAZ-creep-cracking is produced by the following process. (1) Impurity elements segregate in the grain boundary of austenite during welding process, (2) their concentrations are enhanced by reheating process, (3) voids are produced in the grain boundary whereimpurity elements segregate. (4) stress connects the voids to form cracking.
The origin of brittle fracture in HAZ-creep-ement will be voids or micro-cracks which are formed by the processes of (1) to (4).
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