The d. c. component of welding current of a. c. arc welder in innert gas arc welding of aluminum using tungsten electrode is discussed and is shown in table 1 and 2 the calculated results assuming secondary open voltageE20, unbalanced arc voltage EA1, EA2 of rectangular wave form, resistance r and reactance X of secondary circuit.
Following the two previous papers, in this report, relations between welding speed and thickness of base metal (plate thickness), amount of penetration or penetration ratio of base metal to the austenitic stainless steel weld metal, hardness and microstructure of the austenitic weld metal, etc. in each single bead which was deposited on four kinds of carbon steel plates with the same commercial 18-8 austenitic stainless steel electrode containing about 5 percent of manganese in core wire of 4 mm in diameter that was used in the 2nd. report, were studied. In the present experiment, D.C. reverse polarity was adopted and its welding current was held constant, that is, at 125 amperes. Welding speed was changed in four stages of 65, 200, 290 and 500mm/min. And plate thickness was varied in four kinds of 5, 10, 15 and 20mm, too. The results obtained are as follows : (1) Both amount of austenitic weld metal and that of penetration decrease independently of the plate thickness or carbon content of base metal, as welding speed increases. In the above conditions, particularly, the former rapidly decreases up to the neighbourhood of welding speed of 200 mm/min (3.3mm/sec). (2) Penetration ratio rapidly increases up to the neighbourhood of welding speed of 200 mm/min, but gradually increases above the range of that welding speed, In this case, penetration ratio is dependent upon both the plate thickness and carbon content of base metal and it increases from abbut 10 percent when the welding speed of 65mm/min (1.1mm/sec) and plates thickness of 20mm are used, to 45 percent when the welding speed of 500 mm/min (8.3mm/sec) and plate thickness of 5mm are used. (3) It is recognized that both the amount of austenitic weld metal and that of penetration are a little larger for the' range of thinner plate thickness than for the range of thicker one, and also that they are a little smaller in low carbon base metal than in high carbon base metal: (4) Vickers hardness of austenitic stainless steel weld metal tends to make somewhat rapid increase from the neighbourhood of penetration ratio of 30 percent. But the above tendency is smaller in the austenitic weld metal containing high carbon base metal than in the one containing low carbon base metal. (5) Maximum Vickers hardness of the heat-affected zone in base metal has a tendency to increase as welding speed, plate thickness and carbon content of base metal increase, respectively.
After statistical treatment of test results on all the specimens, representative values of tensile strength, elongation and shock of commercial electrodes have been found. First, possible application of law of large numbers was examined by establishment of an equation for frequency probability curve. It was confirmed that, with a wide range of variance elongation values are delicately subject to the state of deposit metal ; and that among those tested. Class A core wire is found, to be highly sensitive to flux with a tendency to produce inferior results to Class B if the flux composition does not match.