The effects of cooling methods and Mg content on the inclusions and microstructures of 16Mn steel were observed, and the mechanism of intragranular ferrite nucleation induced by Mg containing inclusions is discussed. The results show that trace amounts of Mg in steel can induce intragranular ferrite nucleation. With increasing Mg content, the percentage of intragranular ferrite increases, while the optimum Mg content is y0?0048 wt-%. The appropriate cooling methods are furnace cooling to 1473 plus water cooling and water cooling. The lattice disregistry among MgAl 2 O 4 , MgO and ferrite-Fe phase is very small, and there is a Si enriched zone on the inclusions, which both contribute to the nucleation of intragranular ferrite.

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The change of inclusions and microstructure of 16Mn steel treated by Ce were observed, and the effect of austenitizing temperature on the microstructure was also examined. The results show that the inclusions are transformed from Si-Mn-Al composite oxide and MnS into AlCeO 3 , Ce 2 O 2 S, and MnS composite inclusions after being treated by Ce. Plenty of intragranular ferrites are formed in 16Mn steel containing ~0.017wt% Ce. A large amount of intragranular acicular ferrites are formed after being austenitized for 20 min at 1473 K. The prior austenite grain size fit for the formation of intragranular acicular ferrites is about 120 μm.

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