[논문]Low Heat Input Welding to Improve Impact Toughness of Multipass FCAW-S Weld Metal

Bang, Kook-soo; Park, Chan; Jeong, Ho-shin

doi:10.5574/ksoe.2014.28.6.540

Low Heat Input Welding to Improve Impact Toughness of Multipass FCAW-S Weld Metal 원문보기

韓國海洋工學會誌 = Journal of ocean engineering and technology, v.28 no.6 = no.121, 2014년, pp.540 - 545

Bang, Kook-soo (Department of Materials System Engineering, Pukyong National University) , Park, Chan (Department of Materials Science and Engineering, Pukyong National University) , Jeong, Ho-shin (Department of Materials Science and Engineering, Pukyong National University)

Abstract ▼ AI-Helper

Multipass self-shielded flux cored arc welding with different heat inputs (1.3–2.0 kJ/mm) was conducted to determine the effects of the heat input on the proportion of the reheated region, impact toughness, and diffusible hydrogen content in the weld metal. The reheated region showed twice the impact toughness of the as-deposited region because of its fine grained ferritic-pearlitic microstructure. With decreasing heat input, the proportion of the reheated region in the weld metal became higher, even if the depth of the region became shallower. Accordingly, the greatest impact toughness, 69 J at −40℃, was obtained for the lowest heat input welding, 1.3 kJ/mm. Irrespective of the heat input, little difference was observed in the hardness and diffusible hydrogen content in the weld metal. This result implies that low heat input welding with 1.3 kJ/mm can be performed to obtain a higher proportion of reheated region and thus greater impact toughness for the weld metal without the concern of hydrogen cracking.

주제어

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제안 방법

However, impact toughness of two regions have not been measured and compared yet because each region is too small in size to extract impact toughness specimens. In this study, thermally simulated specimens that have a duplicated microstructure for each region by thermal simulation were used to measure impact toughness of the two regions. Theoretically, a reheated microstructure should be obtained by reheating an as-deposited microstructure.
In this work, multipass FCAW-S weld metals were fabricated with different heat inputs. The improvement of impact toughness in the reheated region was ascertained first, and then the effects of heat input on the proportion of the reheated region, impact toughness, and hydrogen content of weld metal were investigated.

대상 데이터

3-86. The test specimens, which were composed of a center test piece and the starting and run-off tabs, were made from 600 MPa grade high tensile strength steel(JIS G 3103 SM570). For the removal of residual hydrogen before welding, the specimens were degassed at 400℃ for two hours in air.
Three FCAW-S multipass welds with different heat inputs, 1.3, 1.6, and 2.0 kJ/mm, were fabricated in a 29 mm thick plate using 2.0 mm diameter AWS E81T8-Ni1 wire. The weld beads were laid using the stringer bead technique in a Vee butt joint.

성능/효과

(1) Due to the fine grained ferritic-pearlitic microstructure, the reheated region in the weld metal had much higher impact toughness than the as-deposited region. The thermal simulation test showed that the reheated region has two times greater impact toughness than the as-deposited region.
(2) Even if shallower reheated regions are formed, a higher proportion of reheated region was obtained in lower heat input welding because of the larger number of reheated regions. Accordingly, the largest impact toughness, 69 J at -40℃, was obtained in the lowest heat input welding of 1.
(3) Because of little difference of cooling rate between the heat inputs, almost same hardness and diffusible hydrogen content are obtained in the weld metals. This suggests that low heat input welding with 1.
(2) Even if shallower reheated regions are formed, a higher proportion of reheated region was obtained in lower heat input welding because of the larger number of reheated regions. Accordingly, the largest impact toughness, 69 J at -40℃, was obtained in the lowest heat input welding of 1.3 kJ/mm.
Multipass self-shielded flux cored arc welding with different heat inputs, 1.3-2.0 kJ/mm, were conducted to determine the effects of heat input on the proportion of the reheated region, impact toughness, and diffusible hydrogen content of weld metal. Important findings are as follows.
(1) Due to the fine grained ferritic-pearlitic microstructure, the reheated region in the weld metal had much higher impact toughness than the as-deposited region. The thermal simulation test showed that the reheated region has two times greater impact toughness than the as-deposited region.
(3) Because of little difference of cooling rate between the heat inputs, almost same hardness and diffusible hydrogen content are obtained in the weld metals. This suggests that low heat input welding with 1.3 kJ/mm can be performed to get a high proportion of reheated regions and thus high impact toughness without the risk of hydrogen cracking in the weld metal.

후속연구

However, no attempt was made to investigate the stress relief effect in this experiment. The effect of stress relief on the weld metal toughness requires further investigations.

참고문헌 (12)

Boniszewski, T., 1992. Self-shielded Arc Welding. Abington Publishing, Cambridge, UK.
Dorling, D.V., Rodrigues, P.E.L.B., Rogerson, J.H., 1978. A Comparative Study of the Effect of Welding Conditions on the Microstructure and Toughness of Self-shielded Arc and Manual Metal Arc Weld Metals. Proceedings on Trends in Steels and Consumables for Welding. London, UK, 351-359.
Dorling, D.V., Rogerson, J.H., 1982. The Factors Which Control the Toughness of Self-shielded Flux Cored Arc Weld Deposits in Carbon-manganese Structural Steels. Proceedings on Fracture Toughness Testing, Cambridge, UK, 239-249
Easterling, K., 1992. Introduction to the Physical Metallurgy of Welding. 2nd Edition, Butterworth-Heinemann Ltd, Oxford, UK.
Eisenhuttenleute, V.D., 1992. Steel. Handbook for Materials Research and Engineering. Springer-Verlag, Berlin.
Evans, G.M., 1985. The Effects of Heat Treatment on the Microstructure and Properties of C-Mn All Weld Metal Deposits. Metal Construction, 17(10), 676-682.
Hesbrrok, W.G., 1993. Adopting Self-shielded Wire Welding for Shipbuilding. Welding & Metal Fabrication, 6, 223-224.
Keeler T., 1981. Innershield Welding. Part 1: Development and Application. Metal Construction, 13(11), 667-673.
Killing, R., 1980. Welding with Self-shielded Wires-The Mechanism of Shielding and Droplet Transfer. Metal Construction, 12(9), 433-436.
Kotecki, D.J., Narayanan, B., 2005. Welding Consumable Developments in the Aftermath of the Northridge Earthquake. Welding in the World, 49(1/2), 42-46.

상세보기
Pisarski, H.G., Jones, R.L., Harrison, P.L., 1987. Influence of Welding Procedure Variables on the Fracture Toughness of Welds made with Self-shielded Flux Cored Wire. Proceedings of 6th Intl Symposium on Offshore Mechanics & Arctic Eng. Houston, USA, 111-119.
Rodgers, K.J., Lochhead, J.C., 1987. Self-shielded Flux Cored Arc Welding-The Route to Good Fracture Toughness. Welding Journal, 66(7), 49-59.

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Low Heat Input Welding to Improve Impact Toughness of Multipass FCAW-S Weld Metal 원문보기

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Low Heat Input Welding to Improve Impact Toughness of Multipass FCAW-S Weld Metal 원문보기

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