In order to research the effect of microalloying Nb, the microstructure and heat treatment distortion of case carburizing steels with and without Nb addition are compared. Results show that a uniform and fine prior austenite grain size was obtained for the steel with the addition of 0.03 wt.% Nb even after being carburized at 980 °C for 37 h, resulting in a very deep hardened layer of about 4 mm. Nb is an effective microalloying element to hinder austenite grain growth of gears during high-temperature carburizing. Theoretical calculation and experimental observation of NbC precipitates indicate that fine NbC precipitates have not evidently dissolved at 980 °C, and thus they can act as grain refiners due to pinning effect. Heat treatment distortion of Nb-added steel is much lower than that of the steel without Nb addition. It may be contributed to its fine and uniform grain size, which presumably influences stress during martensitic transformation.

为了研究微合金化Nb的效果，比较了添加和不添加Nb的渗碳钢的组织和热处理变形。结果表明，即使在980°C渗碳37 h后，添加0.03 wt。％Nb仍能获得均匀且细小的奥氏体晶粒尺寸，从而形成非常深的约4 mm的硬化层。Nb是一种有效的微合金元素，可防止齿轮在高温渗碳过程中奥氏体晶粒的生长。NbC沉淀物的理论计算和实验观察表明，细的NbC沉淀物在980°C时没有明显溶解，因此由于钉扎效应，它们可以充当晶粒细化剂。掺Nb的钢的热处理变形比不添加Nb的钢的热处理变形低得多。