1961 Volume 30 Issue 5 Pages 341-359
Mechanical and corrosion properties were investigated of welded joints of pure zirconium plates, 1 and 2 mm thick, which were welded in a controlled atmosphere welding chamber filled with either pure argon or impure argon mixed with an impurity gas of air, nitrogen, oxygen or hydrogen.
Effects of surface cleaning and impurity in argon atmosphere on mechanical properties and cor-rosion resistance against acids at room temperature and high temperature high pressure water were studied and the following conclusions were obtained :
(1) It is necessary to pickle (HF 5%+HNO3 45%+H2O 50%) the zirconium specimen prior to welding.
(2) Microstructure of weld metal shows α' (acicular α) and air, N2 and H2 in argon atmosphere increase the amount of α'.
(3) Tensile fracture of welded joint occurs at the most softened zone in base metal.
(4) The amount of absorbed nitrogen or oxygen in weld metal is proportional to its initial par-tial pressure in argon atmosphere.
(5) The effects of impurity gases in argon atmosphere on mechanical and chemical properties of weld metal are as follows :
(a) More than 200 ppm (vol.) of air or N2 decreases greatly the corrosion resistance against high temperature high pressure water.
(b) More than 700-1, 000 ppm of each gas (air, N2 or O2) embrittles the mechanical properties, and hardens the weld metal. However, H2 does not change the hardness and tensile strength although it embrittles the weld metal.
(c) More than 105 ppm of each gas decreases the corrosion resistance against HCl+Iron solution.
(d) Up to 104 ppm of each gas does not decrease the corrosion resistance against 81% H2SO4.
(6) It is necessary to pickle the weld zone after welding in order to improve high temperature high pressure corrosion resistance.
(7) As far as the controlled atmosphere welding is concerned, it seems to be necessary for reactor purposes to use an initial vacuum less than 10-2 mmHg and filling with high pure grade (99.99%) argon to one atm. For chemical industry purposes the chamber should be initially evacuated less than 0.5mmHg and filled with same high pure grade (99.99%) argon.
