| The Three Gorges hydro-turbine is the biggest one among these having beenconstructed and being constructed in the world. The turbine runner is 10m indiameter, weighs 450t, and unit capacity is 700MW. The runners are made of410NiMo martensitic stainless steel (13%Cr, 4%Ni, and 0.5% Mo) castings. Forsuch giant construction, casting -welding fabrication is the best way tomanufacture these runners, this is the crown, the vanes and the band of eachrunner is separately cast and then joined by welding. The Max-thickness ofwelded joint is up to 300mm. The joint is characterized by super-thickness,high restraint intensity and high strength martensitic stainless steel.At present, the normal mechanical properties of runner material and weldedjoint are required in the welding and design of the runner, but fractureresistance properties that play an important role in servicing safety andreliability are little investigated. So more welding materialand impacttoughness for the three gorge hydro-turbine martensitic stainless wereinvestigated.The main results are as fallows:1. Gas content of oxygen and nitrogen have abvious effect to impacttoughness of deposited metal, in which oxygen content is mainlyfactor, overfull nitrogen content will lead to pore defect in depositedmaterial.2. Impact toughness of deposited material were improved largely in TIG. Itis a optimal method to improve impact toughness of deposited materialby using TIG in welding repair.3. The impact energy of deposited material after PWHT can be improved largely by using atmospheric HS13/5L hige-speed MAG and laser-MAG.4. Impact toughness of deposited material after PWHT or not can beimproved when vacuum HS13/5L was used in laser-MAG.5. Impact energy of deposited material is proportional to the content ofthe retained austenite transformed by temper, the higher the contentof austenite inverter, the higher the impact energy.
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