Chemical Analysis on Blowholes

Abstract

This study was carried out directly to detect the constituent of gas in blowholes of weld metal by a microscopic micro-analysing and a mass spectrometer. Aluminum and its alloy, mild steel, high strength steel and austenitic stainless steel were used as base metals. And a 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 by the microscope under a thin glass in absorbent step by step. The composition of the gas bubble was determined by calculation from the difference of diameters of the bubble before and after an absorbent solution. The quantity of hydrogen was determined from the loss of explosion by a special explosion pipet. The remainder gas after the microscopic micro-analysing was determined by the mass spectrometer (JMS-OISG).
According to the results of analysis for aluminum deposit metal, a blowhole consists of the following gases; hydrogen about 75-85%, oxygen and argon several % and nitrogen 10-20%. In aluminum alloy deposit metal, oxygen could not be measured. Carbon dioxide, hydrogen sulphide, carbon monoxide and metahne were not recognized in both cases. Blowhole in mild steel deposit metal is full 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 a bead on rusted steel or on greased steel contained mainly 40-60% of hydrogen and 30-40% of carbon monoxide. In austenitic stainless steel deposit metal, the gas in blowhole is also carbon monoxide, hydrogen, nitrogen and argon in the case of argon and argon-nitrogen shielding.