In-situ Observation of the Formation and Interaction Behaviour of the Oxide/Oxysulphide Inclusions on a Liquid Iron Surface

摘要

Characteristics of non-metallic inclusions, e.g. their number density, size and size distribution, morphology and chemistry, have important effects on steel properties1-6. For instance, inclusions with high number density and large size shorten the bearing and fatigue life of steel products1. Oxide inclusions with irregular, dendritic and clustered morphology may cause crack flaw during the rolling process. Coating these oxides (e.g. Al2O3) with a soft layer of sulphide (MnS) can reduce this detrimental effect of the oxides due to the lubricant function of MnS2.3. Furthermore, the MnS inclusions induce the intragranular ferrite (IGF) nucleation during the heat treatment, which refines the ferrite structure and consequently improves the mechanical properties of the steel product4. On the other hand, the sulphides can also act as the starting point of pitting corrosion and decrease the corrosion resistance of stainless steel5. Both the beneficial and detrimental effects of oxysulphide inclusions highly depend on the inclusion number density, size, morphology and chemistry. In general, inclusions with small size, low number density, spherical shape and proper coating of the oxides surface are preferred1. Therefore, to utilize the beneficial effect and minimize the detrimental effect of the oxysulphide inclusions, it is necessary to understand their formation, growth and interaction behaviour during the steelmaking process.