Arc Welding of Specific Steels and Cast Irons
Arc Welding of Specific Steels and Cast Irons
Arc Welding of Specific Steels and Cast Irons
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<strong>Arc</strong> <strong>Welding</strong> <strong>of</strong> High-Strength Steel<br />
3.1.3 Essential factors for quality control in welding<br />
(a) Redrying <strong>of</strong> covered electrodes<br />
The main sources <strong>of</strong> diffusible hydrogen in a weld metal are the moisture contained in the<br />
covering flux in the as-produced condition, the moisture absorbed by the covering flux during<br />
exposure to the atmosphere, <strong>and</strong> the moisture in the atmosphere. As the amount <strong>of</strong> moisture<br />
increases, the amount <strong>of</strong> diffusible hydrogen in the weld metal increases. Diffusible hydrogen<br />
in a weld metal can cause welding defects such as cracks <strong>and</strong> blowholes. Covered electrodes<br />
should, therefore, be kept dry in storage <strong>and</strong> h<strong>and</strong>ling in order to minimize the moisture<br />
pickup. In particular, low-hydrogen covered electrodes must be redried before use in a<br />
redrying oven to reduce the moisture content <strong>of</strong> the coverings to the as-produced levels for<br />
recovering their inherent usability <strong>and</strong> weldability. The other types <strong>of</strong> covered electrodes<br />
should be redried when they picked up moisture so much that the usability <strong>of</strong> the electrode is<br />
degraded causing much spatter, undercut, <strong>and</strong> blowholes.<br />
Proper redrying conditions for high-strength steel covered electrodes are shown in Table<br />
3.6. It is recommended to redry ordinary low-hydrogen electrodes for 50kgf/mm 2 -class<br />
high-strength steel at 300-350 ℃ for 0.5-1 hour, while extra-low-hydrogen <strong>and</strong><br />
ultra-low-hydrogen electrodes are required to redry at 350-400℃ for one hour. It should be<br />
noted, however, that redrying conditions depend on individual br<strong>and</strong> <strong>of</strong> covered electrode.<br />
Redrying should, therefore, be conducted according to the manufacturer’s specification <strong>of</strong> the<br />
electrode to be used. Absorbed moisture cannot sufficiently be removed, if the redrying<br />
temperature is not proper <strong>and</strong> the redrying time is not sufficient. Redried low-hydrogen<br />
electrodes should be stored in a storage oven kept at the storage temperature shown in Table<br />
3.6 in order to prevent moisture pickup until they are used.<br />
Table 3.6 — Recommended redrying <strong>and</strong> storage conditions for low-hydrogen covered electrodes<br />
for high-strength steels<br />
Type <strong>of</strong> electrode<br />
(AWS)<br />
E7016<br />
E7018<br />
E7048<br />
E9016-G<br />
E9018-G<br />
E10016-G<br />
E11016-G<br />
Temperature for redrying<br />
(℃)<br />
Time for redrying<br />
(min)<br />
Storage temperature<br />
after redrying (℃)<br />
300-350<br />
30-60<br />
or 350-400 (1) (1) 100-150<br />
or 60<br />
350-400 60 100-150<br />
Note:<br />
(1) For the proper redrying temperature <strong>and</strong> time for a particular br<strong>and</strong> <strong>of</strong> electrode,<br />
the manufacturer should be consulted.<br />
1-20
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