Formation of diffusion interlayers in electron beam welded joints in diaphragms of steam turbines

摘要

The investigations were carried out into the formation of diffusion interlayers in electron beam welded joints in 12 KhM +12Khl3 steels in the process of thermal ageing at 450, 550 and 650 deg C for 100 h. The formation of the ferritic interlayers in the heat affected zone of 12KhM steel at 650 deg C starts after holding for five hours, and at 550 deg C after 60 hours. In this case, the grain size of ferrite in the root of the welded joint is considerably smaller in comparison with the size in the centre and top part of the welded joints. This is associated with special features of the thermal cycle of electron beam welding. With increase of the chromium content in the weld metal from 5 to 11 percent, the width of the ferritic interlayer in holding up to 100 h remains almost constant, and the width of the zone with a higher content of carbides decreases. The ferritic interlayer forms both in the heat affected zone of 12KhM steel and in the weld metal and the fusion line with 12Khl3 steel by means of thermal ageing at 650 deg C for 100 h at a chromium content of the welded metal smaller than 5 percent.