Sample preparation and test method for ferrous powder metallurgical gears

A gear tooth with fracture failure was randomly selected for fracture analysis. The fracture was cut off by wire cutting equipment, washed with alcohol in ultrasonic cleaning equipment, dried and then analyzed by ZEISS EVO MA 10/LS 10 scanning electron microscope (SEM), and analyzed by Oxford X-Max energy dispersive spectrometer (EDS).

Pre-alloyed powder Fe-1.8Ni-0.5Mo-1.5Cu-0.2C (mass fraction) in the same batch as the broken gear was used as the raw material for the validation test.Among them, carbon element is added in graphite state to form gap solid solution with iron element; copper element can produce solution strengthening effect to improve density and strength of material; nickel element can improve impact toughness of gear; nickel and copper elements can be alloyed at the same time to stabilize sintering size; molybdenum element can improve strength and hardenability of material and reduce tempering brittleness.

Powder metallurgy gear preparation process route is: pressing sintering heat treatment oil dipping packaging.Pressing process uses volume method to fill powder, scrape the upper surface of female die when filling powder box recedes to ensure the uniformity of powder loading, and press gear billet into gear billet by 630 t press; sintering process is completed in RCWJ-18 belt sintering furnace, using nitrogen and ammonia as protective atmosphere, sintering temperature 1120 C, sintering time 90 min; after sintering, gear is cooled to 830 C and kept warm for 30 min, the furnace oil is quenched immediately.Then temper at 180 C for 60 min to reduce quenching stress and brittleness.Up to now, pressing, sintering and heat treatment processes are completed, and then the products can be soaked and packed before being sent to the factory.

Metallographic samples were prepared in accordance with JB/T 2798-1999 Metallographic Standards for Iron-based Powder Metallurgical Sintered Products. Corrosives were prepared in 4% picric acid alcohol solution and 0.5% nitric acid alcohol solution; impact tests were carried out in accordance with GB/T 9096-2002 Impact Test Method for Sintered Metals (excluding Carbides).

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