Reaserch On Optimization Of Smelting Craft And Quality Of Cold-heading Steel Containing Aluminum

To prevent the incident of tundish nozzle clogging in the process of developing aluminum-killed-cold-heading steel in Xuan Steel, an experimental and theoretical analytical research is introduced to investigate to causes of nozzle clogging incident on the basis of analyzing technique test and production process to ensure smooth going of cold-heading steel's production process. To improve cold-heading steel's quality and capability, with the analysis of inclusions'type, quantity and distribution in casting billet with the methods of field sampling and experimental measurement, a research on surface quality of cold-heading steel samples and wire rod samples as well as metallographical structures and inclusions is done.The result shows that the aggregation of Al2O3 on the upper side of tundish nozzle is the main cause of clogging. An analysis on bonding object on the residual steel sample surface in tundish nozzle and the inclusions in steel is carried out with the help of energy spectrum. The testing discovers that massive Al2O3 exists, the content of Ca and S are comparatively low. After experimenting the stoves through the LF refining and Calcium treatment, the Ca element in ladle at primary stage of tundish casting is comparatively high, Ca/Al reached 0.15, and Al2O3 in molten steel is fully denatured. In continuous casting process, only carbonized rice husk is used to ensure the heat preservation of tundish liquid level, tundish alkalinity protective covering is not used. The air-isolation ability of carbonized rice husk is bad, this leads to the twice oxidation of tundish molten steel, the large quantity of Al2O3 is thus made. At the time, Al2O3 can't be fully denatured, with the going of pouring; it continuously aggregates on tundish and finally leads to clogging.In continuous casting billet, inclusion distribution rule of silicon -killed-cold-heading steel 35K and aluminum-killed-cold-heading steel 22A are same on the whole. In the positive camber direction of the casting billet, accumulation phenomenon of inclusions obviously appears at the 1/4 thickness of negative camber side which threats the cold heading process. The inclusion in 35K steel is silicate, the content is very high. The inclusions of the 22A steel are mainly calcium-aluminate, the content are comparatively low. And the calcium-aluminum inclusions shows spheric shape, the content of calcium obviously increases, indicating that the effect of calcium treatment is better, Al2O3 inclusions fully denature into liquid inclusions, and the tundish nozzle clogging is prevented.The metellographical structure of wire rod is ferrites and pearlites, the ferrite assumes massive, the ferrite accounts for 37%~50%. Widmanstatten and Bainitic tissues have not been found. The grain size of rod is generally higher, results the improvement of tensile strength, and cold upsetting performance decreased.