1994 Fiscal Year Final Research Report Summary
TRANSFORMATION OF STEEL AND SEGREGATION OF IMPURITY ELEMENTS INDUCED BY RAPID HEATING
| Project/Area Number |
05452294
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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 |
Material processing/treatments
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| Research Institution | MIE UNIVERSITY |
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Principal Investigator |
TAMAKI Koreaki Mie Univ.Faculty of Eng.Professor, 工学部, 教授 (30023047)
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| Co-Investigator(Kenkyū-buntansha) |
SUZUKI Jippei Mie Univ.Faculty of Eng.Associate Professor, 工学部, 助教授 (90111872)
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| Project Period (FY) |
1993 – 1994
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| Keywords | heat affected zone / ferrite / austenite transformation / rapid heating / segregation in grain boundary / Cr-Mo steels / austenite grain / grain boundary of prior-austenite / creep test / クリープ試験 |
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| Research Abstract |
A rapid transformation from fcrrite to austenite occurs in the heat affected zone (HAZ) of a steel when it is arc-welded. Several problems arising in HAZ would be brought about by this transformation. The process of transformation was examined systematically on HAZ of Cr-Mo steel and the following results were obtained.
(1) An experimental method, which used a simulated-HAZ specimen, was newly proposed. A special type of simulator for this experiment was developed in the laboratory, which could produce the heating rate as large as 2000ﾟC/sec.
(2) The temperature of ferrite/austenite transformation rose with an increasing heating rate. The A_1 temperature in the equilibrium state (740ﾟC for Cr-Mo steel) rose up to 1120ﾟC by the rapid heating with 2000ﾟC/sec.
(3) The following sequence of transforming process was observed in Cr-Mo steel. In the beginning of transformation, fine grains of austenite were produced along the prioraustenite grain boundary. Those grains joined in each other at higher temperature.They grew to a grobular form in the final stage of transformation.
(4) During the transformation, impurity elements, such as phosphorus were concentrated in the grain boundary of newly-produced austenite. The greater the heating rate, the larger the concentration of phosphorus in grain boundary.
(5) An intergranular fracture was observed in the specimen of creep-rupture test. This type of fracture will be brought about by the segregation of impurity elements in the grain boundary of austenite, which was induced by the rapid transformation.
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