日本神户制钢所发现了能使汽车启动齿轮的肃静性提高三倍的渗碳钢成分,确立了这种钢最佳热处理的两相淬火处理制度,目的是使齿轮实用化。 所开发齿轮的芯部为富有延性的铁素体相(体积比70～76％)和马氏体的混合组织,表面部分则是马氏体相。渗碳钢制的现行齿轮,芯部和表面都是马氏体相。由于减少芯部的马氏体相变,使伴随相变而产生的应力应变降低,这样就提高了齿轮尺寸精度而减小了使用的齿轮晃动,从而大幅度提高其肃静性。 Japan’s Kobe Steel discovered a carburizing steel that tripled the quietness of a car’s starting gear and established the two-phase quenching system for optimal heat treatment of the steel, aiming to make the gear practical. The core of the developed gear is a mixed structure of a ductile ferrite phase (70-76% by volume) and martensite, and the surface part is a martensite phase. The current gear made of carburized steel, the core and the surface are all martensitic phases. Due to the reduced martensite phase transformation of the core, the stress and strain associated with the phase transition are reduced, thus increasing the gear dimensional accuracy and reducing the gear rocking used, thereby substantially improving its quietness.