Inhomogeneity of impact properties of electroslag weld metal in constructional steels: Improvement of toughness properties of ESW weld metal in constructional steels (1st Report)

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Summary The purpose of this paper is to clarify welded joint performance, especially the impact properties of the weld metal produced by heavy‐current electroslag welding (ESW) and submerged‐arc welding (SAW), with special reference to the high heat input welding processes generally applied in the fabrication of four‐sided thick‐plate box columns. Two types of SM490A 40 mm thick plates were used in the tests. The results obtained may be summarised as follows: The impact properties of the high heat input weld metal produced under standard conditions (thickness of 40 mm) are generally such that ESW has a lower absorbed energy value (vE value) than SAW. The impact value of ESW high heat input weld metal is non‐uniform, and distinctive impact properties are found. That is to say, the vE value of the weld metal core is lower than that of the weld metal rim. ESW weld metal macrostructures have a non‐uniform morphology in both the core and rim. That is to say, a fine‐grained columnar zone is generated in the core and a coarse‐grained columnar zone in the rim. The results presented above in (1) and (2) suggest that the fine‐grained columnar zone in the ESW weld metal core has a low absorbed energy value (vE value) and that the coarse‐grained columnar zone in the rim conversely has a high one. This conflicts with what is conventionally stated about effects of grain size in otherwise identical microstructures, i.e. that the vE value decreases with an increasing grain size. The vE value of ESW weld metal tends to decrease in relation to the welding heat input Q. That is to say, it tends to have a low value at Q > 30.0 kJ/mm (up to around 80.0 kJ/mm). The analyses of the gas composition and five principal elements of the ESW weld metal at different Q values suggest that there is little change in relation to any heat input change. This suggests that the decrease in the vE value in relation to the welding heat input Q is not due to a change in the weld metal composition.