Study on the parameters affecting the gear properties of sinter hardening

This research categorized sinter alloyed steels four different types based on their hardenability, alloying method and content. The parts were pressed to a green density of 6.85g/cm3. The gears were sintered for 30 minutes at 1120℃ in endothermic atmosphere and cooling rates of 24℃/min and 48℃/min were applied to control the phase transformation during the cooling process. After that, the sintered alloy steel gears were tempered at 200℃ for 1 to 4 hours. Finally, the hardness, gear accuracy, tooth crush load and metallographic observation of the alloy steel gears were determined. Research results show that the hardness of the sintered alloy steel increases with increasing hardenability and the gear accuracy decreases with increasing the content of martensite. The cooling rate is also a crucial parameter affecting the gear properties. Therefore, when developing a sinter alloyed steel gear with a gear accuracy higher than JIS 5, the multiplying factor should be lower than 25. If it is sinter hardening alloy steel, the multiplying factor should be between 15 and 25 with a cooling rate of 48℃/min to ensure the hardness of the gear to be above 30HRC. Furthermore, it requires more than 1 hour's tempering process to obtain the optimal gear accuracy and mechanical properties.