According to the production process of 20g steel(120t BOF→ LF→ CC), some system analysis are introduced to research on the content of T[O] and [N] and the type, source, composition and quantity of micro inclusions in refining process, pouring process and casting billet. The results of the study show: in billet, the main type of large inclusions is CaO-SiO2-Al2O3-MgO complex inclusion of sulfur contained. The content of large inclusions is 14.5mg/10kg in normal billet. The content of large inclusions is 33.14mg/10kg in compound casting billet which is 1.29 time than normal billet.The content of large inclusions whose particle size is more than 300μm in billet is 8.39mg/10kg, and make up 87% of the total. The content of large inclusions whose particle size is 140-300μm in billet is 2.29mg/10kg, and make up 15.79% of the total. The content of large inclusions whose particle size is 80-140μm in billet is 3.82mg/10kg, and make up 26.35% of the total. Unsteady casting plays an important role in the steel cleanliness.
In order to reduce the production cost, In one factory product the SPHC steel of general requirements using slag washing process (BOF→Slag washing oxygen alloying→Ladle argon-blown→CC), the system study was analyzed about deoxidization and desulphurization behavior of slag washing process. The results of the study show that, when the content of Als 300~500ppm, dissolved oxygen 3~6ppm, the steel desulfurization rate remains stable at 35% to 48%, the average desulfurization rate is 42%. The process of the [N] content, increasing [S] are lower than the LF refining, the operation is simple and can meet the metallurgical requirements.
Influence on the transient casting of large inclusions in steel were studied by means of tracer method, kinds of steel large inclusions content in transient casting is 1.5 times ~8 times to the steady casting, large inclusions principal from crystallizer mold powder entrapment, then the tundish slag and the ladle slag. Slag and refractory has a certain influence on high quality steel. Reducing fluctuations caused by transient casting is the key to improve the quality of the steel.
Aimed at the Q195 steel production process in a steel mill, using tracer analysis make system analysis to the process of production and microscopic inclusions content. In the steady casting average T[O] is 117.22ppm, [N] is 22.6ppm, micro inclusions average content is 11.96/mm2, while the average T[O] and [N] in transient casting billet is 161.93ppm and 30.49ppm, micro inclusions averaged content is 16.068/mm2. The total oxygen content in steel on the high side, should strengthen deoxidization. Argon stirring strength is too large, inclusions in casting slab containing tracer element, illustrate the ladle slag, tundish slag, mould protection slag are forming pollution on billet, should reduce the influence of transient casting on the steel quality.
Aimed at the Q195 steel strip inclusion defects in a steel mill, using tracer analysis make system analysis to casting of large inclusions content. Large inclusions in casting containing ladle slag accounted for about 39% of the total number of test, containing tundish covering agent accounts for about 42.2%, while containing protection slag accounted for 45%. Shows that large inclusions in the billet is mainly comes from the crystallizer mold powder entrapment, secondly is the tundish slag and the ladle slag powder entrapment. When transient casting large inclusions content is steady casting several times, increasing the stability of operation on transient casting, controlling the stability of cast-on and ladle changing, stabilizing the liquid level of tundish and mould can improve the quality of the steel.
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