Study on the weldability of ultra high strength steel for deep submersible research vehicle

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Study on the weldability of ultra high strength steel for deep submersible research vehicle

Takeda, T. / Yamada, S. / Fukunaga, I.

This paper describes the weldabilits and shielding characteristics of ultra high strength steel for Deep Submersible Research Vehicle (DSRV). 10Ni-8Co steel is selected for the pressure hull of DSRV to be operated under sea 6000 m in depth, that is a double quenched and tempered (aged) ultra high strength steel with proof stress above 120 kg/mm². Generally, TIG welding is employed for this steel to obtain high strength and notch toughness. Besides this, it has been said that this steel is very sensitive to the contamination of various gas elements, and so perfect welding is required. From this point of view, triple shielding type narrow groove TIG torch has been developed to satisfy that requirement, and performance test was carried out at various shielding conditions to investigate their basic properties and to confirm the effectiveness of that shielding equipment. The results obtained are summarized as follows: Mechanical properties of weld metal are related to nitrogen and oxygen content of weld metal. In the case of triple shielding method (Ar shielding gas), nitrogen and oxygen content of weld metal areas same as thorse of base metal. It is confirmed that triple shielding type TIG torch is very effective to prevent the contamination of weld joint. (Wassmann)