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JWJ > Volume 32(1); 2014 > Article
Journal of Welding and Joining 2014 February;32(1) :93-101.
Published online February 27, 2014.
Effect of Heat Input of Outside Weld on Low Temperature Toughness of Inside Weld for Multiple Electrode SA Welded API 5L X70 with Sour Gas Resistance
Hyun-Jun An*, Hee-Keun Lee**, Young-Gyu Park***, Seong-Su Eun***, Chung-Yun Kang*
*National Core Research Center(NCRC), Pusan National University, Busan 609-735, Korea
**Dept. of Material Science and Engineering, Pusan National University, Busan 609-735, Korea
***Technical Research Laboratories, SeAH steel, Pohang 790-240, Korea
Correspondence: Chung-Yun Kang  Email:
  Published online February 27, 2014
This study aims to investigate the effect of heat input of outside SAW weld on low temperature toughness(-20℃) of inside SAW weld for API 5L X70 with sour gas resistance. As increasing heat input of the outside weld, low temperature toughness of the inside weld was decreased. Especially, in spite of the same heat input, the value of low temperature toughness was fluctuated. On the basis of fracture and microstructure analysis, the low temperature toughness is correlated with the fracture area ratio of shear lips and four kinds of fracture sections. These sections were divided with size and shape of dimple correlated with grain boundary ferrite and cleavage correlated acicular and polygonal ferrite in grain. Therefore, it was seen that these sections were two of final solidification area in the inside weld and the outside weld, no reheated zone and reheated zone in the inside weld. In conclusion, it is thought that the difference of low temperature toughness at the same heat input is due to the fact that each of impact test specimens could have the different microstructure, even though the notch was machined under the error tolerance of 1mm. It is because the final solidification area of the inside weld is very narrow.
Keywords: API 5L X70 | Multiple electrode SAW | Low temperature toughness | Fractography | Microstructure.
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