高マンガン鋼のガスシールドアーク溶接(第3報)

Abstract

A prototype gas shielded arc welding apparatus for continuous automatic welding of austenitic manganese steel rail was built. This apparatus consists of the main assembly including abed, copper blocks and a torch-moving mechanism, the special torch, the controller for controlling the torch movement, the operating panel and the ordinary gas shielded arc welder. It is provided with a device for water-cooling the heat affected zone (HAZ) of base metal.Using the above-mentioned apparatus, austenitic manganese steel rails were welded by gas shielded arc welding process. The materials and welding conditions adopted are as follows: Base metal; 50 kg/m PS type, Wire; 16 Mn-16 Cr, Dia.; 1.6 mm, Shielding gas; CO2-A (50-50%), Joint type; I-groove, Gap; about 16 mm, Arc voltage; 35V, Current; 475A (average), Procedure; automatic and continuous, Forced cooling of base metal; HAZ water-coiled during welding, the whole weld water-cooled after welding.The bending test results on welded rails show that the values of maximum load and deflection are fairly good-76-83 t and 61-103 mm with head up and 73-77 t and 71-77 mm with head down respectively (span 1 m, load applied at midspan). Fracture invariably propagates through the HAZ within 15 mm of fusion line. In certain areas of HAZ, the impact values. are considerably inferior to those of base metal, but except in the cases where casting defects are present, they exceed 10 kg-m/cm2 (2U, 20°C), with considerable toughness retained.Weld metal is almost free from such welding defects as cracks or blow-holes. Local high-temperature cracks may be observed in the HAZ.Presence of such cracks seems to be practically harmless in general use but they should be minimized in welded rail joint.Welding takes about 6 minutes, which is by far shorter than 4.5 hours needed for manual arc welding of Vee-groove joint.