Effect of Rolling Reduction on Inclusions in a Sulfur-Containing Ti Microalloyed Gear Steel

The effect of rolling reduction on inclusions in a sulfur-containing 20CrMnTi gear steel is investigated. The characteristics, including composition, morphology, size, and amount of inclusions in continuous casting billets and hot-rolled rods, are investigated using an automated scanning electron microscope with an energy-dispersive spectrometer. Inclusions in the continuous casting billet are pure MnS, pure TiN, and complex TiN–MnS. Pure MnS inclusions are irregular and located along the grain boundaries, and pure TiN inclusions are distributed evenly in the billet. The shape of complex TiN–MnS inclusions is similar to pure MnS ones. After hot rolling, pure MnS inclusions are elongated, pure TiN is unchanged, and complex TiN–MnS undergo medium elongation. The maximum and average length of complex TiN–MnS inclusions are smaller than that of pure MnS. Pure MnS inclusions have largest deformation index during hot rolling, while pure TiN inclusions have the smallest deformation index. With increasing rolling reduction, the microstructure is refined. From the perspective of hot rolling performance, complex TiN–MnS inclusions are better for the industrial production of sulfur-containing 20CrMnTi gear steel. The work provides a new way to control the deformation of inclusions and microstructure of sulfur-containing 20CrMnTi gear steels, by adjusting the rolling reduction.