TIG welding phenomena and properties of welds made in atmospheres with various oxygen and nitrogen partial pressures (Part 1): Study of welding of zirconium alloy tubing (3rd report)

Abstract

Summary The purpose of this study is to investigate the effects of extremely low oxygen and nitrogen partial pressures, PO2 and PN2, in TIG welding atmospheres on the welding phenomena and properties of welds in zirconium alloy tubing. During TIG welding of Zircaloy‐2 tubing in welding atmospheres with various PO2 and PN2, the arc voltages were measured, and the properties of the welds (surface discoloration, oxygen and nitrogen contents) were examined. Although no definite arc change is found at PO2 < 4.1 Pa, a significant arc voltage drop occurs with an increasing PN2 during welding at PN2 = 0.4–16.9 Pa, so that oxygen appears to inhibit this arc voltage drop. The weld metal surface and heat affected zone (HAZ) in the PO2 = 0.1 Pa and PN2 = 0.4 Pa welding atmospheres remains bright. Some surface discoloration is found on the weld metal and HAZ in the Po2 = 1.1 Pa welding atmosphere, the initial straw colour becoming darker to a partially blue colour with an increasing PO2. No surface discoloration is fo...