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)

Summary

The purpose of this study is to investigate the effects of extremely low oxygen and nitrogen partial pressures, P_O2 and P_N2, 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 P_O2 and P_N2, 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 P_O2 < 4.1 Pa, a significant arc voltage drop occurs with an increasing P_N2 during welding at P_N2 = 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 P_O2 = 0.1 Pa and P_N2 = 0.4 Pa welding atmospheres remains bright.

Some surface discoloration is found on the weld metal and HAZ in the P_o2 = 1.1 Pa welding atmosphere, the initial straw colour becoming darker to a partially blue colour with an increasing P_O2.

No surface discoloration is found on the weld metal and HAZ in the P_N2 ≤ 16.9 Pa with P_o2 = 0.1 Pa welding atmosphere.

The nitrogen content [N] in the weld metal linearly increases with an increasing √P_n2’ 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 √Po_2, showing the same relationship as [N], although the [O] value in the weld metal fluctuates more than the [N] value.