| Abstract: | Special aspects of temperature control during heat treatment of high alloyed materials for the Chemical Industry High alloyed materials require a special control of the temperature during any annealing and fabrication procedure to assure the corrosion resistance, which was the main criterion for the selection of the material in the application proposed. Due to this requirement the time-temperature sensitization behaviour with respect to isothermal and polythermal heat treatments has been determined for alloy Cronifer 1925 hMo (1.4529), Nicrofer 3127 hMo (1.4562) as well as for the nickel base alloys Nicrofer 5716 hMoW (2.4819) and Nicrofer 5923 hMo (2.4605). The application of the standard corrosion test according to SEP 1877 II on alloys alloyed with at least 20% chromium shows no correlation between all second phase precipitation which can affect the corrosion resistance under practical conditions. For alloy Cronifer 1925 hMo and Nicrofer 3127 hMo the determination of the critical pitting temperature in the ferric chloride test has been shown to be an effective procedure to evaluate changes in the microstructure due to improper heat treatments during fabrication. The nickel based alloy Nicrofer 5716 hMoW, which is alloyed with only 16% chromium shows already high corrosion rates in the proper solution annealed and quenched condition, when tested according to the strong oxidizing test solution of ASTM G 28 A. Furthermore, the corrosion rate will increase rapidly after sensitization. Due to the fact that the alloy has not been developed for strong oxidizing media, the test media according to ASTM G 28 B should be applied, since it is more appropriate to this alloy. Although alloy Nicrofer 5923 hMo is alloyed with 23% chromium and 16% molybdenum the alloy exhibits a precipitation behaviour which allows easy fabrication of heavy components. Testing according to ASTM G 28 A allows the identification of improper heat treatments. |
