Chemical Analysis on Blowholes

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This study was carried out directly to detect the constituents of gas in blowholes of weld metal by microscopic micro-analysing and a mass spectrograph. Aluminum and its alloy, mild steel, high strength steel and austenitic stainless steel were used as base metals. And bead on plate was deposited by the gas shielded metal arc welding under various shielding gases for each base metal. The diameter of a collected gas bubble from blowholes was measured in various absorbents step by step by microscope through a thin glass. The composition of the gas bubble was determined by calculation from the difference of diameters of the bubble before and after absorption. The quantity of hydrogen was determined from the loss of explosion by using a special explosion pipet. The residual gas after microscopic micro-analyzing was determined by the mass spectrograph. According to the results of analysis on aluminum deposit metal, blowhole consists of the following gases ; hydrogen about 75 to 85%, oxygen and argon several % and nitrogen 10 to 20%. But with aluminum alloy deposit metal, oxygen could not be measured. Carbon dioxide, hydrogen sulphide, carbon monoxide and methane were not recognized in both cases. Blowhole in mild steel deposit metal consists of carbon monoxide, hydrogen and nitrogen. Under the carbon dioxide shielding gas with a wire of insufficient deoxydation elements or carbon dioxide shielding gas with excess oxygen, blowholes consist mainly of carbon monoxide over 55% and nitrogen. Blowholes which were formed in bead on rusted steel or on greased steel contained mainly 40 to 60% of hydrogen and 30 to 40% of carbon monoxide. In austenitic stainless steel deposit metal, the gases in blowhole are also carbon monoxide, hydrogen, nitrogen and argon in the case of argon of argon-nitrogen shielding.
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Chemical Analysis on Blowholes

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