CONTROLL OF DISTRIBUTION OF MICROSTRUTURE FOR IMPROVEMENT OF QUALITY IN WELDED ZONE

Research Project

Project/Area Number	61550548
Research Category	Grant-in-Aid for General Scientific Research (C)
Allocation Type	Single-year Grants
Research Field	溶接工学
Research Institution	TSUYAMA NATONAL COLLEGE OF TECHNOLOGY
Principal Investigator	HIROAKI OSHIGE PROFESSOR OF TSUYAMA NATIONAL COLLEGE OF TECHNOLOGY, 教授 (90029158)
Co-Investigator(Kenkyū-buntansha)	SATOSHI FUJIWARA ASSISTANT PROFESSOR OF TSUYAMA NATIONAL COLLEGE OF TECHNOLOGY, 助教授 (90110767)
Project Period (FY)	1986 – 1988
Project Status	Completed (Fiscal Year 1988)
Budget Amount *help	¥2,000,000 (Direct Cost: ¥2,000,000) Fiscal Year 1988: ¥400,000 (Direct Cost: ¥400,000) Fiscal Year 1987: ¥400,000 (Direct Cost: ¥400,000) Fiscal Year 1986: ¥1,200,000 (Direct Cost: ¥1,200,000)
Keywords	WELD-HEAT AFFECTED ZONE / MULTI-PASS WELDING / HIGH STRENGTH STEEL / TOUGHNESS / ミクロ組織 / 高張力鋼 / 靭性 / 溶接熱量影響部 / 組織分布 / コンピュータシミュレーション / 高帳力鋼 / 計装化シャルピー試験
Research Abstract	Method of the controlling of the distribution of microstructures in weld-heat affected zone(HAZ) of high strength steel was investigated, in order to controll toughness of welded joints. Main results obtained are as follows. 1. Fatigue pre-crack length controlling apparatus and instrumented Charpy impact testing system were developed in order to examine the fracture initiation tendency from various microstructures distributed in HAZ. 2. There were three kinds of microstructure in coarse grain zone in HAZ. That is, the microstructure formed by re-herrite-austenite temperature zone(TYPE I), the microstructure formed by heated to relatively low austenitize temperature zone(TYPE II) and the microstructure formed by heated to high austenitize temperature zone(TYPE III). 3. It was confirmed that brittle fracture was most difficult to initiate from the TYPE II microstructure and easiest to initiate from the TYPE I microstructure. 4. Many specimens with fatigue pre-crack tip located at various region in coarse grain HAZ were tested and the relation between heat input and the distribution of crack initiation energy was obtained. As the results, specimens were separated into two groups with low and high energy. But, in the case that the bead with a large and a small heat input were built up alternately, this separation was not obsreved and crack initiation energy was distributed uniformly. This mean that the possibility of the initiation of britlle fracture is lowered. 5. From the analysys of the distribution of microstructure, it was estimated that the main cause for these results were the tempering effect by the following bead rather than the distribution of microstructures. 6. These results mean that tempering effect must be considered combining with the distribution of microstructures, in order to controll the toughness of welded zone.