The Effect of Size and Distribution of MnS Inclusions on the Austenite Grain Growth in a Low Cost Hot Forged Steel.

The size and thermal stability of Manganese Sulfide (MnS) inclusions in two low cost hot forged steels with no microalloying elements are carefully investigated. Based on the results, the austenite grain growth behavior of the two steels are studied and the effect of MnS inclusions on the austenite grain growth are discussed using an optical microscope, a scanning electron microscopy, and a confocal scanning laser microscopy. Results show that the MnS inclusions hold a favorable thermal stability and do not dissolve in the steel heated at 1250 °C for 30 min. Austenite grains of the steel with larger quantities of smaller size of MnS inclusions are significantly finer than that of the steel with less and larger size of MnS inclusions heated at a temperature above 1000 °C. The differences in grain size become greater, as the heating temperature increases. The pinning effect of MnS inclusions plays an important role during austenite grain growth, when the austenite grain size exceeds the average spacing of MnS inclusions. The results indicate that large quantities of small MnS inclusions can be used to inhibit austenite grain growth during heating process in a low cost hot forged steel, where expensive microalloying elements are removed. [ABSTRACT FROM AUTHOR]