Porosity of Weld Metal by Humid Low-Hydrogen Type Electrode

Influence of Absorbed Water of Coated Electrode on Porosity of Weld Metal (Report 2)

Abstract

All types of the humid coated electrode except low-hydrogen type produced sound weld metals in the experimental range of absorbed water contents, as described in the previous report. And in this study on the porosity by low-hydrogen type electrode were investigated with supply of complementary shielding gas, addition of deoxidizer in weld metal, rebaking of humid coated electrode and chemical analysis of blowhole gases in deposited metal.
The experimental results were as follows:
1) The porosity could not be prevented by CO₂ or Ar complementary shielding gas. Therefore, the cause of this porosity was not to be ascribed to nitrogen or oxygen by invasion of air.
2) The porosity could not be prevented by addition of various deoxidizing elements. Therefore, the cause of this porosity was not to be ascribed to carbon monoxide reaction in weld metal.
3) The sound weld metal was obtained by rebaking of the coated electrode at 150 or 400°C for 1 or 2 hours.
4) The gases in blowhole consisted mainly of hydrogen (ca. 80.0 %), some amount of nitrogen (ca. 3.0 %) and oxygen (ca. 1.1 %). But carbon monoxide was hardly determined.