Welding of Zircaloy-2 in Controlled Atmosphere
1961 Volume 30 Issue 8 Pages 551-570
Details
1961 Volume 30 Issue 8 Pages 551-570
Mechanical and corrosion resistance properties were investigated of welded joints of Zircaloy-2 sheets, 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.
Characteristics of welded joints which welded in pure and impure argon atmospheres, namely, hardness, microstructure, tensile and bending properties and corrosion resistance against high temperature high pressure water were studied and the following conclusions were obtained ;
(1) Weld metal was the most hardened zone in welded joint because its microstructure consisted of α'+α structure. The heat-affected zone was more hardened than base metal.
(2) Tensile strength of weld metal was stronger than that of base metal at each temperature in the range of room temperature up to 500°C. Thus tensile fracture of welded joint occured in base metal.
(3) Rupture strengths at 1000 hr. of weld metal and base metal at 316°C were about 19 kg/mm2 and 16.5 kg/mm2, respectively.
(4) Corrosion resistance of welded joint against high temperature high pressure water was better than that of base metal when was pickled after welding.
(5) It is recommended for zircaloy-2 to pickle (HF 5%+HNO345%+H2O 50%, at room temperature for 30 sec) after welding for high temprature high pressure corrosion test.
(6) The effects of impurity gases in argon atmosphere on mechanical and corrosive properties of weld metal are as follows (shown in Table 2) :
(a) More than 5×102-103 ppm (vol.) of air, N2 gas and 103-5×103 ppm of O2 gas embrittled the mechanical properties, and hardness of the weld metal.
However, H2 did not change the hardness and tensile strength although more than 102-5×103 ppm it enbrittled the weld metal.
(b) More than 7 × 102 ppm of air and 102 ppm of N2, O2 and H2 gas if specimens would not be pickled after welding decreased greatly the corrosion resistance against high temperature high pressure water. On the contrary, if specimens would be pickled after welding, up to 104 ppm of air, 5 × 103 ppm of N2, 104-105 ppm of O2 and H2 gas did not decrease corrosion resistance.
(7) As far as the controlled atmosphere welding is concerned, it seems to be necessary for reactor purposes to use on initial vacuum less than 10-1 mmHg and filling with high pure grade (99.99% up) argon to one atmosphere and to pickle (HF 5%+HNO3 45%+H2O 50%) the specimens after welding.
