Ocena napraw regeneracyjnych staliwnych korpusów turbin parowych metodą metalograficzną

Na tle krótkiego uzasadnienia prowadzonych pra przedstawiono wyniki staliwa niskostopowego gatunku L450 II, z którego w 1953 roku wykonano korpus turbiny parowej. Ocena stanu korpusu przeprowadzono w roku 2002 spowodowała decyzję o jego regeneracji.Metodami mikroskopii świetlnej i skaningowej, pomiarami twardości i badaniami udarności (materiału korpusu i połączeń spawanych) wykazano przydatność metod spawalniczych i obróbki cieplnej do efektywnych zabiegów regeneracyjnych.Wykazano, że zastosowana obróbka cieplna powoduje wzrost własności mechanicznych materiału korpusu oraz korzystne zmiany jego mikrostruktury. Poprawnie wykonane metodami spawalniczymi naprawy uszkodzeń korpusu (pęknięcia i wady odlewu)powodują skuteczną eliminację zidentyfikowanych wad w toku obserwacji makroskopowych. Przeprowadzona po spawaniu obróbka cieplna powinna zapewniać wypełnienie funkcji przez korpus turbiny przez planowany po regeneracji 100.000 godzinny okres.

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Against a background of a short analysis of the problem the test results of unalloyed cast steel grade L450II of which a steam turbine casing was made in 1953 were presented in this paper. The estimation of the casing state made in 2002 caused the necessity of decision-making about its regeneration.With the help of light and scanning microscopy, hardness measurements and impact (of the casing material and welded joints)the usefulness of welding methods and heat treatment to the effective regenerative treatment was demonstrated. It was poved that the applied heat treatment results in the increase of mechanical properties of the casing material and in profitablechanges of its microstructure. The methods of welding repairs of casting damages (fractures and casting defects)executed correctly eliminate effectively defects identified during the macroscopis examinations. Research on casings made of cast steels L20HM and L20HMF conducted simultaneously allowed us to propose the procedure of regeneration. The estimation of casings' regeneration possibility should be preceded by macroscopic and penetrative examinations in order to identify the defects formed during the exploitation and resulting from the casting's production technology. These defects should be eliminated with the help of welding methods in order to receive joints without macroscopic defects and of possibility narrow heat-affected zones.Treatments executed in this way are the first stage of casings' regeneration process. The next stage is the application of heat treatment for whole casing. The heat treatment causes advantageous transformations of castings materials as well as welded joints, the decrease of internal stresses level and the increase of impact strength. Advantageous changes of structures lead to the presence of a structure of ferrite with small quantity of lamellar pearlite in a weld close to the equilibrium structure. In a fused zone only little intensity of the Widmanstetten structure features is observed. Whereas in a based of impact strength of welded joints (in relation to the state without heat treatment) is observed. Conducted research gives reasons to come to a conclusion that 100.000 hours turbine running period after the regeneration planned by Exploitators is possible to achieve.