Recently, ultra high strength steel plate (in this study, over 780N/mm2 class steel is called 'ultra') such as 1000N/mm2 class strength is focused as material of various type of steel structure. 1000N/mm2 class steel has already applied in hydropower plant in order to enjoy its effect on cost reduction. However, in building construction field, high strength steel remains unfamiliar material. There are only a few example of application of 780N/mm2 class strength steel in building field. On the other hand, safety issue in a huge earthquake is more focused recently. Very large extent of elastic region of ultra high strength steel come to the front. Authors started the investigation of application of 1000N/mm2 class steel plate for buildings. When ultra high strength steel is investigated, welding always become an issue. However, authors think welding is absolutely necessary in assembling steel material for buildings because welding is the most common and economic way of joining the materials at the moment.In this report, welding material, which can match 1000N/mm2 class steel plate and can optimize the properties of welded joint, has been developed. Especially wide range of inter-pass temperature and heat input is tried to be available. By controlling carbon equivalent and oxygen content of deposit metal, finally new welding material of GMAW and SAW for building has been developed.
