| Abstract |
| The welding characteristics and grooving corrosion resistance of electrical resistance welded steel pipes were studied. The macrostructures revealed that optimal width of bond layer for welding was 80-90 μm, while those formed with low heat input showed negligible bond layer. However, metal flow and heat affected zone did not show any appreaciable differences as long as welding bead were formed. The grooving corrosion, which is typical corrosion form in the steel pipes, is caused mainly by the different microstructures between the matrix and weld those are formed during the rapid heating and cooling cycle in welding. Even though the diminishing of sulfur content is most effective to decrease the susceptibility of grooving corrosion, it requires costly process. In this study, improvement of grooving corrosion resistance was pursued by post weld heat treatment in the temperature range between 650℃ and 950℃. By employing chromno-amperometry and potentiodynamic experiments, the corrosion rate and grooving corrosion index(α) were obtained. It was found that heat treatment could improve the grooving corrosion resistance. Among them, the heat treatment at 900℃ and 950℃ endowed excellent grooving corrosion resistance. The index of heat treated specimen at 900℃ and 950℃ were average 1.2, which are almost immune to the grooving corrosion according to KS. Potential differences between base and weld metal were decreased considerably after the heat treatment. While the as-welded one measured 61∼71mV, that of the 900℃ heat treated steel pipe measured only 10 mV. |
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| Key Words |
| Grooving corrosion, Electric resistance welding, Galvanic corrosion, Post-weld heat treatment |
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