1990 Fiscal Year Final Research Report Summary
A Metallographic Study of Steel Weldments
| Project/Area Number |
63550545
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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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 | Tohoku University |
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Principal Investigator |
SATO Yoshihiro Tohoku University, Department of Materials Ppocessing, Research Associate, 工学部, 助手 (00170796)
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| Co-Investigator(Kenkyū-buntansha) |
KIGUCHI Ryuji Tohoku University, Department of Materials Processing, Research Associate, 工学部, 助手 (60005410)
KOKAWA Hiroyuki Tohoku University, Department of Materials Processing, Associate Professor, 工学部, 助教授 (10133050)
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| Project Period (FY) |
1988 – 1990
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| Keywords | STEEL WELDMENT / MICROSTRUCTURE / MECHANICAL PROPERTY / STAINLESS STEEL / PRECIPIATES / TRANSFORMATION / INTERGRANULAR CORROSION / COHERENCY |
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| Research Abstract |
In order to make clear the relationships between metallographic structure and various properties of steel weldments, several steels were welded in different atmospheres and the microstructures were observed. Also mechanical and corrosion tests were performed for the weldments. The results are as follows.
(1) A mild steel was arc-welded in pressurized Ar-CO_2 gas mixture atmospheres. The microstructure of weld metal depended on the atmospheric pressure and gas composition, and affected strongly the mechanical properties. An oxygen content of weld metal showed an optimum toughness.
(2) Purified iron and iron alloys were arc-welded in various atmospheres containing oxygen to study the oxygen absorption and deoxidation mechanism during arc welding process. The oxide inclusions formed in the weld metal were observed to have fundamental informations, because they play very important roles in formation of the microstructure of steel welds.
(3) Delta-ferrite transformations and their crystallogra
… More
phic characteristics in a type 304L austenitic stainless steel weld metal at elevated temperatures were observed mainly by transmission electron microscopy. The morphology change and sigma precipitation strongly depended on the initial ferrite structure in the weld metal. Incoherent boundary between ferrite and austenite resulted easily in sigma precipitation. These facts suggested that the boundary coherency affects strongly on the transformation in the weld metal.
(4) Grain boundary carbide precipitation and intergranular corrosion in the weld heat affected zone of a type 304 stainless steel were investigated using optical, scanning and transmission electron microscopy to discuss effects of grain boundary atomic structure on precipitation and corrosion from a crystallographic viewpoint. The results suggested that grain boundary carbide precipitation and corrosion in stainless steel weld HAZ depend sensitively on the crystallographic character of grain boundaries, and that weld decay in austenitic stainless steel can be prevented by increasing the percentage of ordered boundaries in the material. Less
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