湿式水中アーク溶接に関する研究(第3報)

高張力鋼のインプラント試験

抄録

The cold cracking sensitivity of high strength steel in wet underwater welding was experimentally investigated by means of the implant weldability test with coated electrodes.
The experiments were done with HT60 steel plates and D5003 covered electrodes, and the specimen
6 mm in diameter having 1 pitch 40 degree spiral V notch with 0.5 mm depth, and 0.1 mm tip radius.
The results are the following:
(1) In the implant two pass welding in comparison to single pass welding, the lower critical stress for the cold cracking (σ_cr)_imp increased by about 20 kgf/mm² to about 55 kgf/mm² in underwater welding and also by about 20 kgf/mm² to about 75 kgf/mm² in air welding: The lower critical stress ((σ_cr)_imp in underwater welding was about 65-75 percentage of that in air welding.
(2) By underwater two pass welding the columnar structure of the weld metal was transformed into a globular structure, and the martensitic structure of the heat-affected zone was transformed into the tempered structure. By air two pass welding the needle-like martensitic structure of the heat-affected zone was transformed into a bainite structure which was a fine pearlite.
(3) In underwater welding, the micrography of the implant fracture surface showed mainly the quasi-cleavage of hydrogen embrittlement and the intergranular pattern near the notch in case of single pass welding. In air welding, it showed mainly the dimple fracture, and the quasi-cleavage of hydrogen embrittlement at lower stress.