9%Ni鋼溶接部の溶接割れについて

抄録

In recent years high strength steels for low temperature use have been developed for application and increased importance has come to be attached to their welding In this report special attention was paid to evaluation of weld cracking sensitivities of the 9 percent nickel steel electrodes (Table 1). Four kinds of electrode (10N, 20N, 40N, 70N, see Table 2) with different nickel contents were selected for the test. The RRC-test¹⁾ was adopted for the cracking test. Two series of experiment were made; series I was to evaluate weld cracking sensitivity except for crater cracks and series II was to evaluate crater cracking sensitivity.
In the test series I, weld cracks as shown in Fig. 4 were observed on the bead surface and inner weld metal of the ION, 20N and 70N electrodes under high restraint. The critical gauge length of restraint (l_cr) over which no weld cracks were observed was about 200 mm. Weld cracks as shown in Fig.4 were not observed in the 40N electrode weld metal even for 100 mm gauge length of restraint. Therefore l_cr for the 40N electrode will be less than 100 mm. Crack formation temperature was estimated higher than about 900°C and may be near the solidus temperature of weld metal.
In the test series II, crater cracks were observed even in specimens almost free from restraint or with l>3000 mm. Crater cracking seems to be almost independent of the magnitude of restraint It will be important, therefore, to take away the crater for avoiding weld cracking of the 9% Ni steel weldments.