Metal vapors in gas tungsten arcs: part i. spectroscopy and monochromatic photography
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I.
INTRODUCTION
A longstanding problem in GTA welding is the variation in weldability between different heats of the same metal. With increasing automation, it is desirable to obtain consistent weld quality with a single set of weld parameters. It is believed by many investigators I-" that these variations in weldability are a result of varying concentrations of minor elements in the material. These elements may vaporize and enter the arc, thus affecting its characteristics. To develop an understanding of such phenomena, it is first necessary to experimentally measure vapor concentrations in welding arcs, and to correlate these concentrations with observed weld behavior. In this study, emission spectroscopy was used to determine which metallic vapor spectra are dominant in the welding arc. Monochromatic photography was used to determine the distribution of these vapors in the arc. In Part II of this report, theoretical calculations of the effects of these elements on arc transport properties will be discussed.
Oyler, et al. 5 cited a preferred composition of Si and Mn in 304L stainless steel for increased penetration. Savitskii and Leskov 6 found that "smaller depths of penetration and greater weld widths always corresponded to reduced amounts of sulfur and oxygen in the steel, and increased amounts of calcium." Bennett and Mills 7 argue that an increased amount of aluminum in the weld metal seems to "interact with manganese to produce increased Mn in the arc." This in turn was believed to be the cause of decreased penetration. Patterson8 found that poor penetration in high Mn austenitic stainless steels blamed on aluminum content could be improved by titanium additions. Republic Steel9 has correlated improved weld penetration in AOD refined stainless steels with increased carbon and sulfur content and decreased silicon content. Of these, sulfur had by far the greatest effect. Savage, et al. 10,it investigated the effects of 64 possible combinations of sulfur, phosphorus, silicon, manganese, titanium, and aluminum powder inserts in INCONEL 600.* *INCONEL is a trademark of the INCO family of companies.
II.
PREVIOUS WORK
The effects of minor elements on the weldability of various basemetals have been reviewed up to 1976 by Glickstein and Yeniscavich. 1 In 1968 Ludwig2reported finding variable penetration and skewed welds between two different heats of 304 stainless steel. He attributed this to the concentration of easily ionized impurities in the basemetal, in particular the alkali and alkaline-earth elements "of which calcium is strongly suspected." Moisio and Leinonen3 reported similar results with heats of 304 and 316 stainless steels, and noted that, in a butt weld between two steels of different weldability, the arc was strongly attracted to the side of the steel which exhibited a lower depth-to-width ratio. Metcalfe and Quigley 4 explained this type of phenomenon in their studies on stainless steel as a propensity of the arc to move toward the material with a higher concentration of A1 and Mn.
G.J. DUNN
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