影响烧结硬化合金钢齿轮特性之参数探讨

Study on the parameters affecting the gear properties of sinter hardening

根据不同的合金钢合金化方式与合金添加种类,规画出四组不同硬化能力之烧结合金钢。将这四种硬化能力不同之烧结合金钢粉末分别压制成密度为6.58g/cm3的齿轮坯体,在RX型保护气氛下,1120℃烧结30min后,再以24℃/min与48℃/min的冷却速率来控制冷却过程中合金钢的相变行为,再将烧结态之合金钢齿轮施以200℃、1～4h之回火处理;最终对合金钢齿轮进行硬度、齿轮精度、齿破裂负载等量测与金相观测。研究结果显示,烧结合金钢的硬化程度随硬化能力的增加或烧结后淬冷速度的加快而提高,而齿轮精度则随其相变为马氏体含量的增加而降低。故在烧结硬化合金钢齿轮的开发制造过程中,烧结后淬冷区的冷却速度须达48℃/min,才能确保齿轮特性之硬度维持在30HRC以上,且硬化能力倍数宜调整在15～25之间,经1h以上的回火,即可获得具经济竞争力,又具优异力学性能与齿轮精度组合的烧结硬化合金钢齿轮。

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 6.85 g/cm3. The gears were sintered for 30minutes at 1120°C in endothermic atmosphere and cooling rates of 24°C/min and 48°C /min were applied to control the phase transformation during the cooling process. After that, the sintered alloy steel gears were tempered at 200°C 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°C/min to ensure the hardness of the gear to be above 30 HRC. Furthermore, it requires more than 1 hour's tempering process to obtain the optimal gear accuracy and mechanical properties.