Effect of oxide inclusions on MnS precipitates and tensile mechanical property of high-strength low-alloy steel

The key role of oxide inclusions on the microstructure and mechanical property of a high-strength low-alloy steel was investigated. The field emission scanning electron microscope equipped with energy-dispersive spectrometry was used to characterize MnS precipitates. Oxide inclusions play an important role in the shape control of MnS precipitates. More oxides fovored to decrease the size and the aspect ratio of MnS precipitates. With less oxide inclusions in the steel, approximately over 16.7% MnS precipitates were with aspect ratio a > 5 and pure MnS precipitates accounted for 75.9% in number. However, with more oxide inclusions in the steel, only 7.4% MnS precipitates were with a > 5 and pure MnS precipitates accounted for 60.1% in number. Refinement of MnS by oxide inclusions improved the strength and inhibited the anisotropy. More oxide inclusions in the steel increased the yield strength and tensile strength of the steel in both longitudinal and transverse directions, and lowered the anisotropy of the mechanical property.