Investigation Of Cleaning Treatment Process And Mechanism Of Alloys For K465 And DZ40M

This thesis introduces the process and mechanism of cleaning treatment for the Ni-base alloy K465 and the recycled Co-base alloy DZ40M, analyses microstructures and the mechanical properties of the recycled Co-base alloy DZ40M after cleaning treatment.Contents of oxygen and nitrogen are examined by Oxygen-nitrogen analyzer and the content of sulfur are measured by Sulfur Determination Device; Microstructures of virgin alloy and cleaning treatment recycled alloy, the fracture morphology of alloys after broken were investigated and analyzed by Optical Microscope(OM), Scanning Electron Microscope(SEM) and Transmission Electron Microscope (TEM); Stress rupture and creep, room temperature tensile properties, high-temperature tensile properties of cleaning treatment recycled alloy DZ40M have been compared with the virgin alloy, the results are as follows:(1)Adding 0.02%C and 0.5%Al into Ni-base alloy K465 melting when it was refined at high temperature 1580℃, the content of O was decreased to 5ppm; When adding Al twice total 1%, each adding 0.5%, the content of N was reduced to 5ppm; When the CaO crucible were used to melt alloy, the effect of desulfurization was evident after adding a little Al into melting and it was decreased to 9ppm, adding Ca before tapping, as a result, the final content of S was 8ppm;(2)Melt superheating treatment and electromagnetic stirring made the melt composition uniformity, speed up the melt surface reaction, promoted denitrogenation; high temperature and longtime refining was beneficial to the reaction of carbon deoxidization reaction and denitrogenation reaction, meanwhile facilitating volatilization of toxic harmful trace elements; Shrinkage cavity and porosity, oxides, nitrides and sulfides have been reduced by use of stage cooling of melt , as a result, the microstructure of recycled alloy DZ40M is Cobalt-based Austenite distributed by Carbides M7C3 and other Carbides MC. M7C3 is rich in Cr, MC is made up of strong carbide forming elements, such as Ti, Zr, Ta, W and so on.(3)The mechanical properties of recycled alloy DZ40M have been analyzed in the following conditions: the stress rupture condition were 750～980℃/83～345MPa; the creep condition were 700～900℃/125MPa～360MPa,the overall properties of the cleaning treatment recycled alloy were higher than the properties of the virgin alloy, meanwhile, during the tensile deformation, some fine secondary precipitation phase M23C6 carbides released which strengthen the matrix; Tensile conditions were room temperature 20℃, intermediate temperature 700℃, high temperature 900℃and 1000℃; the result shows that the strength and the plasticity of cleaning treatment recycled alloy DZ40M have reached the level of virgin DZ40M's. It is concluded that properties of recycled alloy achieved the desired effect after cleaning treatment.