Effect of calcium treatment on inclusions in DZ2 high-speed railway axle steel
Calcium treatment is employed to enhance the castability of aluminum-deoxidized DZ2 high-speed railway axle steel during continuous casting.Through the introduction of varied Ca content into steel,scanning electron microscopy(SEM)and energy dispersive spectrometry(EDS)are employed to scrutinize and count the morpholo-gies,types,and sizes of inclusions in the smelting procedure and continuous casting billet.This endeavor aims to investigate the evolution patterns of inclusions and the effect of Ca content on the inclusions.Research indicates that the evolution patterns of inclusions during the smelting process exhibit a general similarity between low calcium feed-ing Steel A and high calcium feeding Steel B.From LF end to the tundish,the inclusions undergo a progressive transformation from Al2O3-CaO-MgO with diminished CaO content to compositions characterized by elevated CaO content,specifically CaO-Al2O3-MgO.Nonetheless,a notable emergence of CaO persists in the inclusions within the tundish of B.In the continuous casting billet of Steel A,the inclusions are mainly small-sized,low-CaO-content Al2O3-CaO-MgO formed during the cooling and solidification process of the molten steel.The large-sized(＞10 μm)CaO-Al2O3-MgO inclusions,characterized by elevated CaO content,are present in only modest quantities.In the continuous casting slab of Steel B,the prevailing inclusions primarily consist of CaO induced by calcium treatment,exhibiting a larger size.The difference in the type and size of inclusions in the continuous cast slabs of Steel A and Steel B is intricately tied to the Ca content in the steel.Only a rational Ca content has the capacity to modify Al2O3 inclusions into purely liquid states.Excessive Ca content,however,leads to the emergence of solid inclusions,such as CaO and CaS.The calculation results from FactSage thermodynamic software reveal that the optimal Ca content for DZ2 axle steel,following calcium treatment,falls within the range of 0.000 5％to 0.001 8％.Prudent applica-tion of calcium treatment is imperative to secure the castability of molten steel.Furthermore,it is essential to opti-mize the metallurgical processes to eliminate large-sized liquid CaO-Al2O3-MgO inclusions formed after calcium treatment and during other refining stages.
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