Investigation On Fracture Resistance Of MAG Deposited Metals And Welded Joints Of Three Gorges Hydro-turbine Runners

The Three Gorges hydro-turbine is the biggest one among these having been constructed and being constructed in the world. The turbine runner is 10m in diameter, weighs 450t, and unit capacity is 700 MW. The runners are made of 410NiMo martensitic stainless steel (13%Cr, 4%Ni, and 0. 5% Mo) castings. For such giant construction, casting -welding fabrication is the best way to manufacture these runners, this is the crown, the vanes and the band of each runner is separately cast and then joined by welding. The Max-thickness of welded 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 welded joint are required in the welding and design of the runner, but fracture resistance properties that play an important role in servicing safety and reliability are little investigated.In this thesis, the four kinds of gas shielded arc welding wires, that are now being used in the Three Gorges hydro-turbine runners is selected to make an investigation of welding technical performances and mechanical properties, especially the fracture resistance of deposited metal, weld metal and welded joint. Experimental wires are Stoody flux-cored wire, HS13/5L solid wire, PZ6166 metal powder-cored wire and Oerlikon solid wire. Main Experimental methods include instrumental Charpy impact test, CTOD, SEM and X~ray analysis. The results establish a technical basis to optimize we! ding consumables and technology, and supply a basis for the runner safetyoperation. The main results are as fallows:1. Within wide welding parameters, PZ6166 metal powder cored wire and Stoody flux-cored wire has welding usability, showing stable arc and good appearance of weld. Compared with cored wire, the solid wires have not so good welding usability showing oxidized and crinkled weld appearance as the welding parameters are greater.2. Experimental result of the normal mechanical properties of the deposited metal shows that HS13/5L and Oerlikon are better than other two wires, and the instrumental Charpy impact test, shows that HS13/5L is the best one.3. For the four kinds of wire, it is not suitable for weld metal to be used under as-welded condition because of the low value of CTOD. By PWHT, CTOD is obviously improved, showing good fracture resistance which is contributed to the retained austenite transformed by temper.4. On the whole, the fracture mechanism of the four kinds of deposited metal is the same, which is small and shallow dimple and cleavage fracture under as-welded, and dimple fracture by PWHT. For base metal and heat-affected zone it is big and deep dimple fracture.5. On the basis of comprehensive fracture resistance evaluation of four welding wires, HS13/5L excels other tested wires.