| Budget Amount *help |
¥5,070,000 (Direct Cost: ¥3,900,000、Indirect Cost: ¥1,170,000)
Fiscal Year 2015: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000)
Fiscal Year 2014: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000)
Fiscal Year 2013: ¥2,470,000 (Direct Cost: ¥1,900,000、Indirect Cost: ¥570,000)
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| Outline of Final Research Achievements |
The increase in size and weight of recent structures has been demanding application of higher tensile strength steels. In such cases, difficulties have been encountered in obtaining adequate fracture toughness in arc weld metal and, therefore, a method to improve the toughness has been highly required. In this study, an attempt was made to improve the toughness by reducing oxide inclusions since the inclusions have been known to become initiation sites for fracture and so to deteriorate the toughness. In order to achieve this, it was necessary to establish a method to stabilize arc discharge in an atmosphere with less oxygen and to promote a fine acicular ferrite microstructure in weld metal. In contrast to the accepted understanding, it was found that stabilization of arc discharge was achieved by local oxidized gas addition together with pulsation of welding current and that a predominant fine acicular ferrite microstructure was obtained provided that adequate inclusions were formed.
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