Investigation On Horizontal Position Welding Technology Of Narrow Gap TIG Welding For Large Rotor In Steam Turbine

In recent years, the problem of the supply of large-scale whole rotor forging has restricted the the development of large steam turbine technology. Currently,feasible technical means is weld rotor structure to achieve.But in terms of manufacturing technology, the foreign companies consider it as Know-How and the development of manufacturing technology in weld rotor has been greatly limited. In this thesis, large steam turbine rotor steel 20Cr2 Ni Mo,was used to carry out the back welding of horizontal narrow gap TIG, sidewall fusion behavior of filler welding, weld configuration,microstructure and conventional mechanical properties of welded joint, finally the rotor model was welded.P-TIG parameters effect on one side welding with back free formation for horizontal position welding technology of narrow gap TIG, that is investigated.The optimum parameters of one-side welding with back free formation of horizontal narrow gap TIG of 4.5mm blunt edge was got, the following were the conclusions:the welding current and arc voltage has a vital important influence on penetration resistance; wire feed speed can play a decisive role in the back weld forming; pulse frequency for positive impact is relatively large, and can effectively inhibit the tendency to drip.For the problem of sidewall fusion stability in horizontal narrow gap TIG welding, up and down sidewall fusion behavior of narrow gap groove was separately studied, and the optimum window is obtained. The results show that:the position of Tungsten electrode and the arc voltage effects on sidewall fusion behavior obviously.When the position of Tungsten electrode is-1.5mm and-2.5mm,down sidewall weld is relatively stable, when arc voltage is between 14 V and 15 V, up sidewall weld is relatively stable. When the base current is between 150 A and 250 A,there is a good fusion. The wire feed speed and pulse frequency have a greater influence on the weld surface.The Tungsten position has an important influence on weld shape quality of filler weld in horizontal position of multi-pass welding narrow the gap TIG, and the parameters of "one layer four weld" is obtained. Using developed welding technology of complete sets, the cylindrical rotor models(25Cr2Ni4Mo V) with the diameter of 1100 mm, wall thickness of 25 mm was welded and finally a good positive and back weld. The weld pass the X-ray inspection one time.The microstructure and conventional mechanical properties of joints in horizontal position welding technology of narrow gap TIG for a typical low pressure rotor forging 20Cr2 NiMo in steam turbine is investigated.The results show that: The arc shape of horizontal position welding technology of narrow gap TIG has little influerence on the microstructure and conventional mechanical properties of up sidewall and down sidewall. The microstructure and properties of root weld is worth with concerning. The microstructure of filler weld in HAZ is tempered martensite, and the impact toughness is higher, reached about 190 J.