TIG welding phenomena and properties of welds made in atmospheres with various oxygen and nitrogen partial pressures (Part 2) Study of welding of zirconium alloy tubing

摘要

The purpose of this study is to investigate the effects of extremely low oxygen and nitrogen partial pressures, P_(O_2) and P_(N_2), in pressurised 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 P_(O_2) and P_(N_2), at a total pressure (P_T) of 0.32 MPa (to some extent 0.55 MPa), the arc voltages were measured, and the properties of the welds (surface discoloration, oxygen and nitrogen contents) were examined. Although no definite arc voltage change is found at P_(O_2) ≤ 12.9 Pa and P_((O_2)+(N_2)) = 15.6-67.2 Pa (P_(O_2)/P_(N_2) = 1/4), a significant arc voltage drop occurs with an increasing P_(N_2) ring welding at P_(N_2) = 13.1-53.0 Pa (P_(O_2) = 0.3 Pa). The weld metal surface and heat affected zone (HAZ) in the P_(O_2) = 0.3 Pa and P_(N_2) = 1.3 Pa welding atmospheres remain bright. Some surface discoloration is found on the weld metal and HAZ in the P_(O_2) = 3.4 Pa welding atmosphere, the initial straw colour darkening to a partially blue colour with an increasing P_(O_2). No surface discoloration is found on the weld metal and HAZ in the P_(N_2) ≤ 53.0 Pa with P_(O_2) = 0.3 Pa welding atmosphere. The nitrogen content [N] in the weld metal linearly increases with an increasing (P_(N_2))~(1/2), with the increasing amount of [N] in the inner part of the weld metal being lower than that in the outer part. The oxygen content [O] in the weld metal linearly increases with an increasing (P_(O_2))~(1/2), showing the same relationship as [N], although the [O] value in the weld metal fluctuates more than the [N] value. The increasing contents of [N] and [O] in the weld metal at P_T = 0.32 MPa are lower than those of [N] and [O] in the weld metal at P_T = 0.10 MPa as noted in the 3rd Report.