Laser beam welded cooling structure components made of martensitic high-temperature steels

A hollow structure made of a three-layered sandwich material with a grid-like intermediate layer structure is produced from cover plates and the woven wire mesh by means of capacitor discharge welding. A manufacturing variation where bent structures are manufactured directly with a 2D electrode is, at present, in the test phase. During the research phase, the dimensions of the hollow structure segments are limited by the available capacitor-discharge welding machines and also by the forming press. Using laser welding, the segments are welded into larger system components. With regard to the future application, laser welding is suitable for welding cooling collar segments, weldingin of the cooling components into the turbine casing and for necessary repair welds. During welding tests with cold wire addition a gap width of up to 0.4 mm was bridged. In the single pass" process option the lower cover layer is welded with the residual beam energy of the upper process. No hardness cracks were found. Strong hardening was significantly reduced by preheating or tempering. Preheating may be dispensed with when the components are subject to tempering or quenching after welding - as long as the sheet thickness remains thin and hardness cracks are not to be expected. The tests were made on 1mm thick X20 CrMoV12-1 and Nf616/P92 sheets."